| JesseG |
Hi all...
Has anyone ever come across the 6159 in a power amp design? I understand the 6146 is simmilar except for the heater voltage.
Tube library says they were used as AF amps, but I an find no hits on the web.
I have 5 of these tubes - very pretty to look at. Anyone have schematics, suggestions?
Jess |
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| tubelab.com |
The 6146 was used in the original Ampeg SVT bass guitar amplifier which used 6 of them to produce 300 watts. That amp had a reputation for blowing up, so they switched to 6550's in the later models. The schematic is in the book "A desktop reference of hip vintage guitar amps" by Gerald Weber. It may be on the web somewhere.
There is very little literature showing the use of this tube in HiFi applications especially SE. The tube was used in the modulator section of transmitters back in the 1950's, that is where the AF amp reference comes from. You could probably get them to work in a circuit that was designed for an 807, although the tubes are not that similar. Some resistor values would need tweaking, and the bias would need adjustment. |
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| Giaime |
| Hey Tubelab, here's the schematics you're referring to: |
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| Giaime |
| And here's the other one: |
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| JesseG |
Hey, thanks guys! I was hoping someone would know something about them.
And, thanks so much for posting the schematics - really helps.
Like I said before - tehy are reallp pretty things. I am going to study the schems and see if I can come up with a monoblok design using these - maybe SE, maybe PP.
Do either of you fellows think an OTL design would work here?
Cheers
Jess |
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| tubelab.com |
The maximum cathode current rating is 125mA per tube. If you were trying to drive a conventional 8 ohm speaker you would need a box full of these to build an OTL.
I think that you could get 5 watts per tube in triode connected SE but the low screen grid voltage points to pentode connection where 10 Watts per tube could be attained in SE.
These tubes would not work great in ultralinear due again to the low screen grid voltage rating. In push pull pentode mode the spec sheet claims 55 to 120 watts per pair, depending on how hard you push them.
I guess that your decision really depends on how much power you need (or want).
http://www.mif.pg.gda.pl/homepages/...049/6/6146W.pdf |
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| JesseG |
Tubelab
"I think that you could get 5 watts per tube in triode connected SE but the low screen grid voltage points to pentode connection where 10 Watts per tube could be attained in SE.
These tubes would not work great in ultralinear due again to the low screen grid voltage rating. In push pull pentode mode the spec sheet claims 55 to 120 watts per pair, depending on how hard you push them.
I guess that your decision really depends on how much power you need (or want)."
OK - clearly, you have far more knowledge in this area that I do - would you be up to helping me through this?
I would like to build a pair of the best-sounding monoblocks these tubes can make. Huge power is not the target - best sound and bandwidth is... 25 wpc is plenty.
One of your earlier posts mentioned that an amp based on these tubes had a rep for blowing up - we don't want that! I like the Rolls-Royce approach: 734 CuIn motor making only 235 HP, but it will run for 40 years!
If P-P pentode is its best configuration, so be it. There are lots of good-sounding P-P pentode amps out there.
How much can I extrapolate from the SVT schems, and how muct will have to be designed from scratch?
Jess |
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| Giaime |
Hello Jess
If you need only 25W, and you have 8 of them, you could triode-connect a push pull parallel and run them very conservatively I think. Or if you have only 5, use 4 of them and make a single push pull in pentode connection. Take care of regulating the screen voltage and you're there. These are ideas, the actual schematics is to be determined. IMHO you can't use much from SVT schematics, they're quite a bit pushed.
But in pentode mode they will require some NFB to work well: if I was you, I'd sell those at some ham fest and get some EL509/PL509, still ham tubes but much easier to work with, and more powerful. Maybe a bit less pretty... :smash: |
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| JesseG |
Thanks for the comments, Giaime
I guess I might be able to dump them on ebay. I live at the northern end of Vancouver Island - not many ham fests (or any other kind of fest) here abouts :xeye:
I liked your previous comment about building with previously unused tubes - exploring new ground, so to speak.
I think I will stick with them at least until I have a plausable schematic, then decide.
BTW: I just noticed that the Ampeg schematics you posted have been downloaded 19 times - someone out there must be interested
;)
Cheers
Jess |
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| Giaime |
| quote: | Originally posted by JesseG
BTW: I just noticed that the Ampeg schematics you posted have been downloaded 19 times - someone out there must be interested
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No, that was just me to check if I uploaded the right file and not something that could hurt my reputation ;)
If you meet some ham guys, try to trade them in for iron or EL509 family tubes. Ham guys use to have many of those at least here in Europe... and they're easier to work with. Maybe you'll find 807s too... :) |
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| isaacc7 |
If you're interested in making the most of the 6146 family of tubes (and the 6159 is one of them) check out Dennis Grimwood's ideas on what he calls "Optimized Ultralinear" operation. He claims that the 6146 tube family is a great one for audio when used the way he describes. Unfortunately it requires a custom output transformer and you must regulate the screen supplies. I'm very tempted to order some transformers to make use of my 6159 and 2e26 tubes...
Isaac |
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| JesseG |
| quote: | | If you're interested in making the most of the 6146 family of tubes (and the 6159 is one of them) check out Dennis Grimwood's ideas on what he calls "Optimized Ultralinear" operation. He claims that the 6146 tube family is a great one for audio when used the way he describes |
That sounds GOOD! Just looking at these tubes, and beam power tubes in general, I had a feeling they could make good tunes.
Unfortunately, I don't have enough background in tubes to be able to work up a suitable cct myself.
So, THANKS for the suggestion
| quote: | | Unfortunately it requires a custom output transformer and you must regulate the screen supplies. |
Hey, what's the fun of this nutty hobby without a few challenges
:D
Thanks Isaacc7! |
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| isaacc7 |
I don't mind challenges too much, but the hit on the wallet can be painful. I'm hoping that I can make use of all the 2e26 and 6146 tubes I have collected over the years, but having a transformer custom made for me sounds expensive. It would need a tertiary winding that is "in synch" with the tube in order for it to work in his circuits. Wanna talk crazy? How about a SE custom transformer with tertiary windings, I'm not even sure that can be made...
Isaac |
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| tubelab.com |
It would be possible to build a SE version of this transformer. I believe that this is one of his ideas that might actually work. But some of his other ideas sound pretty bogus.
If you are looking for a first amp design, I wouldn't use such a unique design. I would do a conventional pentode push pull design, with screen voltage regulation. Use a reasonably priced off the shelf transformer, about 6000 ohms. |
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| JesseG |
| quote: | | having a transformer custom made for me sounds expensive. |
I read Grimwood's entire site - interesting stuff. I think that he is suggesting that if possible, one should find trafos from one of the designs he uses as examples, if not wind our own. Not sure if I am up to that :xeye:
| quote: | | It would be possible to build a SE version of this transformer. I believe that this is one of his ideas that might actually work. |
Tubelab: I can follow the PP designs - they make sense to me (sort of!). How would a SE config work using this class of tube? Do you have a schem / sketch/ desc? I am not interested in high power - 10-15w is lots for me.
| quote: | | If you are looking for a first amp design, I wouldn't use such a unique design. I would do a conventional pentode push pull design, with screen voltage regulation. Use a reasonably priced off the shelf transformer, about 6000 ohms. |
I'm with you here - again, can you suggest a design? Is seems that Grimwood's main point in his 'Optimized Ultralinear' is screen regulation with lower screen DC.
Jess |
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| isaacc7 |
I wouldn't do anything that "unique" as a first project either, but I gotta say that it's refreshing to read someone putting it out there instead of going by the same old "rules". I don't know enough to be able to know what parts of his website is bogus, but I do like some of the ideas. I really liked his thing on screen grids, I feel as though I actually learned something! His optimized ultralinear page was really interesting too. I do wonder how much of the same effect that he claims happens with the unique output transformer could be accomplished with screen voltages based on his ideas and the judicious use of feed back. I do know that not all feedback is created equal, but I would think that the effect could be tried out before shelling out the bucks for the transformer. Just out of curiosity, what did you think was "bogus"?
Isaac |
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| tubelab.com |
| quote: | | Just out of curiosity, what did you think was "bogus"? |
The concept of "OPTIMISED ELECTRON STREAM © TECHNOLOGY" calls for operating the suppressor grid (G3) at a higher potential than the screen grid (G2). The reason that the suppressor grid was invented in the first place is to SUPRESS secondary emission. It is a third grid operated at a potential negative with respect to the plate and screen grid to repell electrons that were emitted by the plate to to bombardment by high speed electrons from the cathode (secondary emission). This whole concept was discussed in another thread:
http://www.diyaudio.com/forums/show...&threadid=70399
In that thread there is reference to another thread about the connection of G3 in an EL34:
http://www.diyaudio.com/forums/show...&threadid=67422
In the course of investigating the concepts presented in that (often heated) discussion I performed testing on 2 different EL-34's the result is that the curves become distorted when G3 is operated at a potential equal to or above G2.
The concept of SILICON DIODE FEED © implies that inserting an ordinary silicon diode in series with the screen grid will cure distortion just smells funny, but I must admit that I have not actually tried it.
The concept of SCREEN GRID (GRID #2) - AC CIRCUIT BYPASS CAPACITOR © tells us that electrolytic capacitors are not the best types of bypass caps. OK, we know that!
The fact that all of these concepts have been copyrighted even though some are general public knowledge leads me to dismiss all of it even though there may be some good ideas here. If there really are some unique concepts back them up with some supporting data and less hype. OK that is the engineer in me talking.
| quote: | | Is seems that Grimwood's main point in his 'Optimized Ultralinear' is screen regulation with lower screen DC. |
The OPTIMISED ULTRA-LINEAR © technology that he refers to implies both ultralinear operation and seperate regulated screen supplies. Ultralinear operation is where the screen grids are connected to a tap on the primary of the output transformer. This affords most of the benefits of triode mode with most of the power of pentode mode. Many pentode mode amplifiers have a seperate regulated supply for the screen grid. Some amplifiers simply tie the screen grid to the plate supply. Since the plate supply voltage changes somewhat with varying load it influences the screen grid voltage causing some distortion. The OPTIMISED ULTRA-LINEAR © technology allows both, but requires a speciallized output transformer. On his web site there is a schematic of a 100 watt amplifier using 6146's and Acrosound transformers. These transformers would be hard to find today.
This tube has a 250 volt maximum screen voltage rating. The Grimwood page states that this tube will not work in conventional ultralinear or triode mode because of this. I am inclined to believe him on this point. I might be tempted to try it for myself if I had a bunch of these tubes to blow up, but I gave the box of them that I had to a ham radio friend.
That leaves conventional pentode mode, either Push Pull or SE. I searched the web and there aren't many schematics out there for this tube. This one can put out 100 watts, but it is a conventional circuit. You could scale down the voltages to get lower power and longer life.
http://www.bonavolta.ch/hobby/en/audio/6146.htm
If I find more I will put them here. I don't have the time to cook up one of my own right now. |
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| isaacc7 |
Many thanks Tubelab! I stumbled across this site because of your experiments with the 6av5, I think I'm going to attempt a PP 12av5 triode amp since I have the tubes and you say they have potential:-) I'm going to keep ideas in mind for 6146 tubes though, nothing like a good challenge.
Isaac |
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| tubelab.com |
I was so impressed with the sound of the 6AV5 that I am going to explore it further in the near future. Keep in mind that some of my experiments were operating the tube far in excess of its ratings. Especially the screen grid voltage rating. In this case nothing bad happened.
It may be possible to do the same thing with a 6159, but I haven't experimented with those. If you decide to operate any tube in excess of its published ratings, do so with tubes that you can afford to loose. Install a fast acting fuse between your last filter cap and the output transformer. I use 1/8 amp but 100mA fuses can often be found. This is to protect your OPT and power supply in case a tube arcs over.
A P-P with 12AV5's should work well and provide ample power without severly exceeding the tubes ratings. The 12AV5 has a maximum screen voltage rating of 175 volts, that implies that you can only use a B+ voltage of 175 in triode mode. I would stay below 250 - 300 depending upon the amount of risk you want to take. |
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| isaacc7 |
Well I had heard that in triode the 6av5 mimics (to a large degree) our good friend the 2A3, so I figured it would sound decent enough. Your experiments are pretty exciting considering how cheap these things are, I don't mind screwing up a 2 dollar tube in the name of good sound! As far as the 6146 family goes, I have always heard that the screen voltage limits were hard and fast, that's why I was excited to read Grimwood's ideas about using them to their full potential for audio without exceeding those limits. I may try something with them in the future sice they do have a lot of power potential.
Isaac |
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| tubelab.com |
I have heard the 2A3 rumor but I didn't buy it since the two tubes are so different. Then there was another rumor that Sylvania had actually built some triode wired 6AV5's and sold them as 6B4's to fulfill a military contract. I didn't buy that one either.
Well go to Angela Instruments web page:
http://www.angela.com
Click on Tubes, then click on The Tube Gallery, Scroll down to the very last tube and see it for yourself. It is marked 6B4G and it clearly has multiple grids and an indirectly heated cathode. Looks like a 6AV5 to me. A 6B4 is an octal 6A3 which is a 6 volt 2A3. Now the rumors begin to make sense. It also explains that even Sylvania beleives that these tubes can take 275 volts. |
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| JesseG |
Hey guys...
I just came across the attached schem. Simple 6146 pp from 1951. It looks like just what I had in mind when we started this thread.
Have a scan and let me know what you think, please.
Do either of you think that the trafos will be hard to get, or will std Hammonds work here?
It is far higher power than I was after but I have never been sorry for having more power :cool:
Cheers
Jess
BTW: I had to resize (shrink) the original schem to attach. If you would like the full sized one, email me and I will send it along |
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| tubelab.com |
This should work well with modern transformers, if you can find a combination of off the shelf transformers that can provide the necessary voltages. I can't quite read the details, but do you have the impedance specs on the output transformer?
In any case DO NOT install the capacitor shown that connects one side of the power line to chassis ground. That used to be common in the past, but 55 years of shocking experiences have told us that it doesn't work. Use a 3 wire cord and ground the chassis. |
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| JesseG |
| quote: | | This should work well with modern transformers, if you can find a combination of off the shelf transformers that can provide the necessary voltages. I can't quite read the details, but do you have the impedance specs on the output transformer? |
Doesn't seem to be any trafo specs that I can make out. OPT seem to be ct primary, 3-tap sec - pretty normal. The plate DC on the schematic is 750V, with B+ at 375v
As said, I have the detailed hi(er)-res pix if you want it.
| quote: | | In any case DO NOT install the capacitor shown that connects one side of the power line to chassis ground. That used to be common in the past, but 55 years of shocking experiences have told us that it doesn't work. Use a 3 wire cord and ground the chassis. |
:cannotbe: Got it! Actually, I have a lot of listening to experienced fellows like you before I begin to build something like this.
BTW: is that a REGULATED ps? |
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| tubelab.com |
The plate voltage is not regulated, but the screen voltage is. This is exactly what you need with these tubes.
Lacking impedance data on the transformer in the original design, you are going to need an educated guess. The plate voltage of 750 is the max for this tube with this voltage you would need an 8K ohm transformer and get about 100 to 120 watts. Hammond does not make this transformer, although it could be found. If you don't need this kind of power I would use a lower plate voltage, and get a lower power output. Your tubes will last longer.
At 600 volts you would get over 90 watts with a 6K ohm transformer and 80 watts with a 7K ohm transformer. The higher impedance transformer offers slightly lower distortion to go with the lower power.
At 450 volts you will get 60+ watts with a 4K ohm transformer, and 50 or so with a 6K transformer. Same story with the distortion.
So you need to pick a desired wattage, or a close guess. The higher power requires more money in transformers, and power supply parts. Then you can pick an output transformer.
Hammond lists 3 transformers for use with a pair of 6146's. To squeeze the most power from a modest power supply, use the 1650N (4300 ohms) run it at 500 volts or less. The 1650P (6600 ohms) would offer less power in the same amp at lower distortion. It could also operate at up to 600 volts to get more power. If you have the space and the money the 1650R (5000 ohms) would provide the most power and could provide 75 watts at 500 volts.
If this was my choice, and a first amp. I would use the 1650P and set up the power supply for something between 425 and 465 volts using 500 volt capacitors. Any higher voltages get more complicated quickly. You could expect 50 watts or more from this combination.
Hammond only makes one transformer that has the power capability to adequately support both channels drivem to full power. That is the 278CX. It does not have 5 volt windings. You could use a SS rectifier, or extra transformers. The voltage might be over 500 with SS, you would need HV caps.
If you don't plan to run the amp at full volume a lot (I don't think so) you could use a smaller transformer. The other possibility is a seperate power supply for each channel. |
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| JesseG |
| quote: | | At 600 volts you would get over 90 watts with a 6K ohm transformer and 80 watts with a 7K ohm transformer. The higher impedance transformer offers slightly lower distortion to go with the lower power. |
As stated, raw power is not a priority. 50-60w is PLENTY! But, I am not clera on the relationship between trafo impedance and distortion. Do you know of a reference on the subject - or a reading list? This interests me.
| quote: | | If you don't plan to run the amp at full volume a lot (I don't think so) you could use a smaller transformer. The other possibility is a seperate power supply for each channel. |
For a while now I have been thinking about a pair of monobloks rather than a stereo pwr amp.
Hey, thanks TubeLab, this is very informative...
Jess |
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| Giaime |
George is great, isn't he? ;)
Btw George you did many "over-the-specs" tube tests some time ago, tests that can be found in various threads here (I remember some 6B4G under test), I can't find them on your site. Are you planning to put them online? They're quite useful I think :D Thank you! |
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| tubelab.com |
I have not done a major update to the web site in a long time because I was running near the bandwidth limit for my web hosting plan. When you go over your limit it is like using too many minutes on your cell phone, it cost money. Sometimes a lot of money. I noticed a long time ago that NEW content on the site causes a lot of interest, which gets a lot of hits, I get charged for this. I was limiting the addition of new content to the site to eliminate these overage costs. The hurricane pictures were bandwidth hogs. They generated far more interest than I expected.
As of the first of this year I have a new web hosting plan with more room than I can use (for now) so I will be adding new content as fast as I can get it prepared. Since many of my older experiments were not well documented (if at all) I will need to recreate many of them. Most of the experimenting that I have done in the past 2 years is documented on paper at least, and many were photographed. The experiments that were chronicled in this forum will be posted on the site when I get the time. The older stuff will follow. I have photographed many of my old paper schematics, and will be adding them also.
I have had zillions of e-mails asking for the construction manual for my SE amp board, and for a cookbook approach to PowerDrive, so those will be posted first. |
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| stepitup |
G'day Jess .... did u ever get ur 6146 based amps up n running? Despite all the conjecture and speculation in a lot of the threads I don't remember anyone ever actually saying they had built or heard a 6146 based amplifier.
It may interest you to know that DGC Haire built a lot of Theatre amps for the Cinerama group - (do a google and u'll get an idea of this wide screen 6 channel discrete audio theatre process) ... now these power amps used a pair of 6146 in PP and used the 6146 optimally. They had a choke input HT supply, seperate regulated screen supply with adjustable 180vdc-240vdc from a 6BL7+12AX7 reg. and used 6072+5814 for input & phase splitter.
They were in service at many theatres from mid 50's when they were designed and built ... till late 70's in some cases(I'm only talking about Australia here as I have no info on other countries - Altec & RCA I'm told also built amps for the Cinerama system in the US). From all reports they were extremely reliable and excellent sounding. Many ended up in audiophile systems with the original input transformer(to interface with the projectors) and tone control stage disconnected... allen wright modified a pair minimally for a guy who was driving the big accustats and the owner told me it was the best sound he had ever heard in his audio room. When I met him he was driving the accoustats with electrocompaniet amps and the set-up sounded very good. Unfortunately the cineramas went underwater in a flood in late 80's and a dumb tech turned them on b4 the iron was fully dried out !! poof!! however I inherited one full set of the original unpoofed iron and have been looking for another to complete a stereo pair ever since. Obviously I never found another set so I utilised the great chassis to build an updated version as I said. My iron is all dble C core and uses 2 x 350v windings summed through a differential choke to give around 600v on the plates of the 6146. This yields a very stiff HT supply. Just about everything else is the same as the originals including the input and screen regs, although I did not utilise tube rectification like the originals. If I had the room I would have utilised 6AU4 TV damper diodes, but for 2 x 350v windings thats 8 x octals per chassis!!
The 6146 is an "excellent bottle" as the Maestro article says, and does not appear to have a sonic flavor of its own if done correctly in the right circuit to optimise its potential.
Acrosound wouldn't have used it if it wasn't and neither would the DGC Haire people. These amps were designed by professionals to excel in their applications ... not by DIYers. But as they say for every expert there is an equal and opposite expert!!
Also there was a schematic of The Maestro cutter-head amplifier from the AES journal early 50's ... I'm told this was what sparked interest amongst audio design engineers for use of the 6146 in audio applications.
I have a copy of the original article and the original DGC Haire (they used Kenyon Transformer Coy NY iron in the amps) schematic if you are interested .. tropicalblayney@optusnet.com.au ... I also have 2 x modified original mono-block dgc haire chassis - they are now rigged for 4 x 6146 per chassis ... and I have 3 pairs of different output Tx to play with ... 2 x pairs include tertiary windings. The thing with tertiary windings is that you get decreased distortion and the ability to utilise the optimised UL concept dennis talks about.
So if the project is still going email me and I will send the schematics to you. I don't have them scanned - too large and messy and don;t have the time to engage in discussions about the pros & cons of the 6146 ... I've heard them and built amps with them. As for ampegs problems with them ... They were used in australia in audio and guitar amps by Lennard for quite a few years with no reliability probs ... but I think its fair to say that a lot of design considerations for guitar amps are at odds with how you would design for high quality audio. Seems to me that guitar amp manufacturers will push to the limit and under-design rather than over design for both economic and distortion reasons ... look at the output & mains Tx on some guitar amps!!
cheers .... cb;) ;) |
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| JesseG |
| quote: | | did u ever get ur 6146 based amps up n running? |
Nope!
Some wonderful info, Stepitup. I had sort of given up hope that anyone knew of any audio uses for these very pretty and seemingly well-made VTs.
I will email you off-line about a schematic, but you might want to post it - who knows, we might spark some interest and soon every NOS 6146 bottle in every nook and cranny of the planet will be snapped up by over-wealthy DIYers and soon they will go for $75 ea and... :xeye: On second thought, don't post anything - we'll keep it our secret ;)
Actually, it would be very interesting to get some enthusiasm going for a new and 'undiscovered' VT - maybe someething fresh for all of the experts out there.
Thanks for all the info.
Jess |
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| w5jag |
If you really want to play with the 6159 family of tubes, you could probably make your life easier by going to a Hamfest or on Ebay and picking up a Heathkit HP-23 or later series power supply.
It will supply the needed high voltage, the screen voltage, an adjustable negative bias, and filament power. They are ugly, but cheap and widely available. A good hosing down at a car wash and some new caps and they would probably be like new. You could also just rob the parts and build them into a better looking supply with some screen voltage regulation.
Mike Bryce sells a drop in update board for the HP23 that has all new components and screen regulation built in (http://www.theheathkitshop.com/hp23r.html).
If you just want a transformer and / or choke(s), Peter Dahl Co. (www.pwdahl.com) has all types of high voltage transformers and equipment in their ham catalog, but this is much more expensive than just using a beater power supply.
Let us know how it works for you. I have a bunch of this family of tubes, and power supplies at hand, so I am definitely interested in your results.
edit: Oops, I see you have decided not to pursue the project. Maybe the above source of easy, cheap power will get you reinterested!
Win W5JAG |
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| JesseG |
| quote: | | picking up a Heathkit HP-23 or later series power supply. |
Good tip.
My solution was to watch the test equipment section on eBay - I bought a Scientific Instruments 0-1000V / 0-200ma regulated lab bench ps for $80. I still have to provide filament, but the big HT supply makes it so easy to provide regulated B+ with current-limited o/p that I could not now do without it.
| quote: | | Oops, I see you have decided not to pursue the project. |
I do intend to pursue the project - this bottle has me mightly intrigued. :D
| quote: | | Let us know how it works for you. |
You can count on it! This project marks my departure from building OPD (other people's designs). This one will be me working out the math, poring over data sheets and reading reams of stuff about transformers - very likely without understanding it any better :xeye:
If I do succeed in getting any tunes out of this project, you can bet that I will want to blab it all over this forum. :)
Jess |
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| Ado |
Hi All,
I also planned to make a SET with this 6146, Does anyone have the schematic ? if so pls send me one at : unoselecta@yahoo.com (no need PP circuit, already have it) . Many Thanks.
Rgds,
Ado |
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| kevinkr |
The low screen voltage rating of the 6146 makes it a lousy triode and UL is only practical with a separate winding. In most instances you will need to run it as a pentode with lots of feedback. One thing that may not be clear from the spec is that you may be really sorry if you put much more than 200V on the screen grid. :hot: It's not particularly popular with audio designers for a reason.
IMHO You would be far better off with a triode connected KT88/6550 - better linearity, better sound, and far easier to design with.
The AMPEG SVT used the 6146 in its first incarnation which was quickly replaced with a version using 6550 due to serious reliability problems.
Just my two cents worth. |
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| Wavebourn |
| quote: | Originally posted by tubelab.com
The 6146 was used in the original Ampeg SVT bass guitar amplifier which used 6 of them to produce 300 watts. That amp had a reputation for blowing up, so they switched to 6550's in the later models. |
...but they still blew up because of directly connected cathode followers ... Cold solder, dead tube, or just bad contact in the socket between grid and resistor... strong pulse on grids of output tubes... spark between 2 and 3 legs... blown anti-hum symmetry resistors in filaments, probably output tranny...
It is a myth about bad output tubes (urban legend). The problem was in some overlooked details (the Devil is in details!)
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| Ado |
| With that's all "unsave parameter" 6146 ,make me more desire to built it on SE line due to High power posibly deliver rather than use other popular tube with very high cent & Low power. Two weeks ago I just succeded to built SE using rare EC360 with myown Circuits design(No body have SE schematic for this Tube) and My boss love its sound, He asked me to give him a price. Base on it I think I can do the same to this small giant 6146 even nobody give me the Schematic(hope someone do, to make me easier)...just waiting for the tube shipping |
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| Ado |
Hi All,
Finally last nigth just finished my 6146 SE(after I broken 1 Tube for the expariment), The sound much better than my previous EC360 SE maybe caused by the bigger Power Out from 6146 ... Too bad (or too good for me :-) my friend asked this new SET for him, so I will built the new High Power SET using 6012 Tube ... again Nobody have the SE schematic for this Cute Giant Tube....but no big deal for me, I think it's easier than 6146...can't wait to hear the sound...It would be my Serious SET coz I'll used my Topgrade component & won't "give it" to anyone ....
Rgds,
Ado |
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| JesseG |
| quote: | | Finally last nigth just finished my 6146 SE |
Ado - could you please post a schematic - I would love to see how you have done this...
What O/P trafos did you use?
Jess |
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| Ado |
Hi Jess,
Sure, I attached the 6146 Schematic for you.
Thanks.
Ado |
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| JesseG |
Ado: Thanks REALLY VERY much :D
Now that I have a viable design for the 6146, I will be building it in the early autumn. This is just what I have been looking for.
Thanks again!
Jess |
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| kevinkr |
| quote: | Originally posted by Colt45
SEP, not SET ;) |
Aka pentode connected. Screen regulation is a good thing here.
Note that the output impedance will be pretty high and this should be taken into consideration in pairing with loudspeakers. (Damping factor less than 1?) This thing will probably look a lot like a current source to most loudspeakers. |
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| JesseG |
From Kevin| quote: | | Aka pentode connected. Screen regulation is a good thing here. |
Not sure what you mean by screen regulation - a voltage regulator on the cct that feeds the screen of the tube?
| quote: | | Note that the output impedance will be pretty high and this should be taken into consideration in pairing with loudspeakers. (Damping factor less than 1?) |
Isn't the output impedance (as seen by the speakers) determined by the secondaries of the O/P trafo?
| quote: | | This thing will probably look a lot like a current source to most loudspeakers. |
I thought that speakers wanted current rather than voltage - ala Krell amp design philosophy...
Jess |
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| kevinkr |
Originally posted by JesseG
Not sure what you mean by screen regulation - a voltage regulator on the cct that feeds the screen of the tube?
There is a 200V zener diode connected to the screen - so the screen supply is regulated as a result.
Isn't the output impedance (as seen by the speakers) determined by the secondaries of the O/P trafo?
Not completely, the transformer just transforms the source impedance of the tube driving it by the 1/ turns ratio^2. The individual taps just change the reflected ratio. So lets say that your transformer has a 20:1 step down ratio then this squared is 400 on say the 16 ohm tap (Primary Z 6.4K). Lets say your tube has an RP of 10K then the reflected source impedance is just 10K/400 or 25 ohms, not neglecting the dcr of the secondary winding say 4 ohms (and ignoring the dcr of the primary) this is a source Z of 29 ohms from the 16 ohm tap.. Damping factor will be about 0.55 - no longer much point to looking at it this way as the amp is providing very little damping to the driver.
I thought that speakers wanted current rather than voltage - ala Krell amp design philosophy...
Actually Krell builds excellent voltage sources, an "ideal" voltage source will source an infinite output current into any load impedance. In the real world voltage sources have current limitations that modify this behavior. A current source otoh produces a voltage that is proportional to the load impedance for a given current, whereas a voltage source produces an output voltage that is not a function of the impedance connected across it. (Like a Krell) This implies that the output voltage will vary substantially with the load impedance, most speakers are not designed to operate with such a driving source and will have an acoustical output that is a function of its source impedance and the output current rather than just the voltage applied across it.
A pentode connected amplifier output stage is usually used in conjunction with NFB to lower its source impedance to something useful with most speakers. Triodes incidentally have much lower plate resistances and so avoid this issue.
Hopefully I have not muddied the waters too much, and perhaps someone else can explain this better than I.. :D |
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| JesseG |
| quote: | | Hopefully I have not muddied the waters too much, and perhaps someone else can explain this better than I.. |
Thanks, Kevin. I still have a hard time grokking the impedance thing. And as for damping factor, well... :xeye:
I think I understand your explanation (if I didn't, it is because I am dense ;) )
Let me see if I have it... you are saying that because of the much higher output impedance of a pentode, it has a different set of operating conditions than a triode and must be configured to either a: a - much higher ratio OPT or b - use of specific NFB to lower the impedance inherent in the pentode (I would imagine that use of both of these in appropriate amounts could solve the problems)
Can you suggest modifications to Ado's schematic that would amend the design?
Jess |
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| Ado |
Hi Folks,
On my previous msg I planned to built 6012 SE but sadly this tube asking a verry big Current 230mA/ch on 250V since I don't have any stock of big current the Power Trafo, I decided to change the project to reBuild & Improve the EC360 SE due to this "Real triode" power tube is so cheap in my local shop(only $20 each) & Now already got the final schematic with choosen components to get the pleasure sound, my SE now ready for 4x EC360(2 tubes each Ch paralel config for higher POut) & Driving my dummy Jamo Bookshelf 86dB with easy.
For Jess, sorry on my Schematic I used 2.5k primary trafo actualy that's my test trafo ex.300B/2A3 it's not recomended, You should use the higher impedance for safe operation (4K at least, see the attached text from tubelab for detail). Also the Rk you better use 30W at least.
Thanks & regards,
Ado
6146 tubelab.com
The plate voltage is not regulated, but the screen voltage is. This is exactly what you need with these tubes.
Lacking impedance data on the transformer in the original design, you are going to need an educated guess. The plate voltage of 750 is the max for this tube with this voltage you would need an 8K ohm transformer and get about 100 to 120 watts. Hammond does not make this transformer, although it could be found. If you don't need this kind of power I would use a lower plate voltage, and get a lower power output. Your tubes will last longer.
At 600 volts you would get over 90 watts with a 6K ohm transformer and 80 watts with a 7K ohm transformer. The higher impedance transformer offers slightly lower distortion to go with the lower power.
At 450 volts you will get 60+ watts with a 4K ohm transformer, and 50 or so with a 6K transformer. Same story with the distortion.
So you need to pick a desired wattage, or a close guess. The higher power requires more money in transformers, and power supply parts. Then you can pick an output transformer.
Hammond lists 3 transformers for use with a pair of 6146's. To squeeze the most power from a modest power supply, use the 1650N (4300 ohms) run it at 500 volts or less. The 1650P (6600 ohms) would offer less power in the same amp at lower distortion. It could also operate at up to 600 volts to get more power. If you have the space and the money the 1650R (5000 ohms) would provide the most power and could provide 75 watts at 500 volts.
If this was my choice, and a first amp. I would use the 1650P and set up the power supply for something between 425 and 465 volts using 500 volt capacitors. Any higher voltages get more complicated quickly. You could expect 50 watts or more from this combination.
Hammond only makes one transformer that has the power capability to adequately support both channels drivem to full power. That is the 278CX. It does not have 5 volt windings. You could use a SS rectifier, or extra transformers. The voltage might be over 500 with SS, you would need HV caps.
If you don't plan to run the amp at full volume a lot (I don't think so) you could use a smaller transformer. The other possibility is a seperate power supply for each channel. |
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| gorgon53 |
Use it in PPP with a 3.2k opt, 600V on the anode, groundreferenced 345-350V regulated on g2 (50%Ultralinear) , around -80V on g1 (adjust to a Ia of 26mA) and you will get 35W of EXCEPTIONALLY CLEAN high efficience output!!!
Offcourse there is a downside, needs around 320Vp input on the grids, floating low capacitance powersupplies, heatertransformers a.s.o...
In this configuration really hard to beat in ANY RESPECT WITH ANY OTHER TUBE! |
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| JesseG |
| quote: | | Use it in PPP with a 3.2k opt, 600V on the anode, groundreferenced 345-350V regulated on g2 (50%Ultralinear) , around -80V on g1 (adjust to a Ia of 26mA) |
Thanks gordon53
This sounds like the one I was looking for. Do you have a schematic for this configuration?
Jess |
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| gorgon53 |
Hi JesseG
Sorry I have no scanner, but it is simply a kind of "circlotron" with the opt in 50% ultra-linear connection by connecting g2 of the tubes to a regulated voltage-source with 340-350V. It also needs a regulated, seperately adjustable g1 "fixed bias" source of -78V +-20%. The driver I used was my "universal-driver" wich can swing almost +-400V with 1kV Ub. But used 4 tubes in cascade working into a kind of White cathode-follower with also 4 cascaded tubes to drive finally 8 paralelled 6146 per side working into a 420ohm autotransformer with a load-depending voltage stepdown of either 7:1 or 10:1 (6 layers in serial with 6x1.5 layer in serial with 6x1.5 layers in parlell for 8ohm load or 9 layers in serial with 9 layers in paralell for 4ohm. A rather expensive driver because it had a total of 4xE288CC and 4x6BX7.
This driver is certainly overkill if you use only a pair of tubes on the output and settle for higher distortion you can use a simple much simple cascade with anode-resistor loading, or even only a selfbiased 6BX7 running at about 400V on the anode and resistor loaded (but the distortion of the driver will be higher than that of the outputstage)
It all depends on the goals you set, mine was lozza power with good efficience at the lowest possible distortion, complexity or cost of the circuit where no object, neither was "easy building" or "safety" like there would in commercial projects. |
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| JesseG |
| quote: | | it is simply a kind of "circlotron" with the opt in 50% ultra-linear connection by connecting g2 of the tubes to a regulated voltage-source with 340-350V. |
I sure wish I knew enought about this to understand what you are saying. I think get the part about the g2 power supply.
I don't get the part about the 50% ultra-linear. I thought that ultra-linear was done with a 45% tap on the opt primary. I think I will need a diagram to understand this.
| quote: | | you can use a simple much simple cascade with anode-resistor loading, or even only a selfbiased 6BX7 running at about 400V on the anode and resistor loaded |
So, these tubes need a very high voltage driver stage to operate well?
Jess |
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| gorgon53 |
In a circlotron half (50%) of the load is in the anodecircuit and the other 50% in the cahode circuit. Look at g2 (g2 works really like a "quasi-triodes" anode) referenced to the cathode. Can you see that this "quasi-triode works as cathode follower? Thats why this
circuit needs high drive voltage.
But you also get a cathodefollowers low distortion and low output impedance + almost double power and almost doubled efficience because the high impedance anodecurrent is added to the low impedance cathode cicuit.
Further more, the "quasi-anode" g2 needs almost no power (at comparable lower voltage) and can be easely stabilized, giving you almost the same benefits than a fully stabilized power supply.
As to the sometimes stated 43 (or what ever) % connection for UL, this is always stated for a specific tube under specific conditions. In this amplifier, the g2 voltage and load impedance is choosen to give the best results with the naturally occuring 50% connection. Not all amplifiers have the freedom of choosing the g2 voltage and therfore they have to jiggle the tap on the opt. Anyway, in this amplfier the anode does NOT have to swing below the g2 voltage (like it often does in amplifiers with Ua=Ug2). A further advantage. Did I mention the opt?
1 quarter impedance, no cross-over distortion possible, dc loaded only by Ig2 (wich gets slightly LOWER at full load).
NO?
This is the to my knowledge the best topology for a beam-tetrode pp amplifier. Some migth think that a lower voltage version could be improved by turning it into a full CF by referencing the drive voltages to the anodes. I would have done that if it would bring anything worth the higher drive voltages, but it is not worth the effort. In a OTL things would be different, I wish I had a dozen of 13E1 at hand, lol
Well, some day IŽll try those E130L with a low impedance ratio autotransformer...who knows, migth be just as good and would not require 600V on the anodes, 300V should do... |
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| JesseG |
Ok, this is good learning for me.
I will try drawing this up, per your description, and post it when I am done and maybe you can tell me where I ha gotten it wrong :xeye:
Please don't hold your breath - I am very busy with paying work right now. But I WILL do this. I am really interested in building a 6146 amp. :D
ttfn
Jess |
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| isaacc7 |
| quote: | Originally posted by JesseG
I sure wish I knew enought about this to understand what you are saying. I think get the part about the g2 power supply.
I don't get the part about the 50% ultra-linear. I thought that ultra-linear was done with a 45% tap on the opt primary. I think I will need a diagram to understand this.
So, these tubes need a very high voltage driver stage to operate well?
Jess |
Wait a minute, how cn you have both ultralinear operation (screengrids being run off of a tap on the OT) AND a regulated supply to the screen grids? Just a word of warning, I have been flying around the world and I'm in a bit of a haze, so my apologies if I've made any really stupid comments:-)
Isaac |
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| gorgon53 |
| quote: | Originally posted by isaacc7
how cn you have both ultralinear operation (screengrids being run off of a tap on the OT) AND a regulated supply to the screen grids?
Isaac |
Because the cathodes are connected to 50% of the opt. There is no need for a xtra tap on the opt. The "tap" is the connection to ground (in the middle), same point where the powersupply of the screengrids has its "minus"-connection. |
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