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6159 for SE Power amp

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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
 
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.
 
Here are some datasheets: the philosophy of using never-used-before tubes in audio is really intriguing me this period. I am searching for cheap powerful NOS tubes too, to build an SE amp.

http://www.wps.com/archives/tube-datasheets/Datasheets/Amperex-CC-363/4.JPG
http://www.wps.com/archives/tube-datasheets/Datasheets/Amperex-CC-363/5.JPG

http://www.nj7p.org/Tube1.php?tube=6146
Here at least you can find graphs of the 6146.

I think that you could try with 6L6/807 circuits in SE, some 400V on the plate, 200 regulated volts on the screens, and 6K OT... of course cathode resistor will need to be calculated.
 
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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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/frank/sheets/049/6/6146W.pdf
 
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
 
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:
 
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
 
JesseG said:

BTW: I just noticed that the Ampeg schematics you posted have been downloaded 19 times - someone out there must be interested

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... :)
 
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
 
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

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!
 
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
 
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.
 
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:

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.

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
 
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
 
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/showthread.php?s=&threadid=70399

In that thread there is reference to another thread about the connection of G3 in an EL34:
http://www.diyaudio.com/forums/showthread.php?s=&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.

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.
 
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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