I've been lurking in the tube area for a while, and I've started a project loosely based on this http://headwize.com/projects/showfile.php?file=ahammer2_prj.htm
But I've changed the output tubes to 2-5687 med mu dual triodes to increase output current for my 64 ohm HD 570's. I've also added pots to adjust output bias and neg feedback to the grounded grid in the LTP (I can't help it, I cut my teeth on SS. I can turn it down to zero if I don't like it)
The question is.... How conservative are the plate dissapation ratings. If I'm running class A, do I need to derate things 50% like with transistors or can I safely run a tube that's rated 4.2w each section, 7.5W total for both sections at 3.5W per sec, 7W total in class A continuous and expect 5000 hrs out of a tube, or what would you say is a safe continuous dissapation. I'de rather not learn by burning up $50 worth of tubes 3 or 4 times.
I've also bought a couple of 833 's I hope to make a big *** SET out of, but I thought I should try something a little more forgiving and less costly for my first glass amp.
I'll take some pics of the board I etched last night and post after I hear some music. The tubes should be on the front porch when I get home this evening, and I may get to fire it up tonight.
But I've changed the output tubes to 2-5687 med mu dual triodes to increase output current for my 64 ohm HD 570's. I've also added pots to adjust output bias and neg feedback to the grounded grid in the LTP (I can't help it, I cut my teeth on SS. I can turn it down to zero if I don't like it)
The question is.... How conservative are the plate dissapation ratings. If I'm running class A, do I need to derate things 50% like with transistors or can I safely run a tube that's rated 4.2w each section, 7.5W total for both sections at 3.5W per sec, 7W total in class A continuous and expect 5000 hrs out of a tube, or what would you say is a safe continuous dissapation. I'de rather not learn by burning up $50 worth of tubes 3 or 4 times.
I've also bought a couple of 833 's I hope to make a big *** SET out of, but I thought I should try something a little more forgiving and less costly for my first glass amp.
I'll take some pics of the board I etched last night and post after I hear some music. The tubes should be on the front porch when I get home this evening, and I may get to fire it up tonight.
If you don't exceeed other maximums, you can indeed run the tubes full throttle. But that means not exceeding maximum current, voltage, or (very important!) bulb temperature. The last is often a problem in tight constructions with no forced air cooling.
Thanks SY That's the answer I was hoping for. It's going to be in the open proudly displaying itself, so temp shouldn't be a problem.
Brian/ at it again with the extra output devices
Brian/ at it again with the extra output devices
You can generally run tubes at their maximum ratings with no adverse effects. They will usually live longer if operated below their maximums. Many of the guitar amp makers used to run the tubes well above their published ratings, that is why the guitar players are always changing tubes.
I have been collecting the parts for my big *** SET amp using 833A's. I put together a prototype for the purpose of testing some transformers. Pictures are on my web site. I would definitely NOT recommend this kind of stuff for a first amp. The power supply has enough juice to kill you and then cook you to a crisp. Hopefully I will have this done well before you get to building yours. I will post the schematics and construction details when it is finished. There will be two amps, a HiFi amp with about 100 watts per channel. The output transformer is the limiting factor here. There will be a bad to the bone guitar amp that can put out over 200 watts (it only has to go down to 80Hz).
http://www.tubelab.com/833SE.htm
I have been collecting the parts for my big *** SET amp using 833A's. I put together a prototype for the purpose of testing some transformers. Pictures are on my web site. I would definitely NOT recommend this kind of stuff for a first amp. The power supply has enough juice to kill you and then cook you to a crisp. Hopefully I will have this done well before you get to building yours. I will post the schematics and construction details when it is finished. There will be two amps, a HiFi amp with about 100 watts per channel. The output transformer is the limiting factor here. There will be a bad to the bone guitar amp that can put out over 200 watts (it only has to go down to 80Hz).
http://www.tubelab.com/833SE.htm
Good to hear you made it through the huricane OK. I've checked out your site a while back.
I've came up empty handed on a SE output transformer (except for one that a guy wants $4000 for ) and was thinking parafeed may make it workable with cheaper iron. I decided I need to learn a little more before I go throwing around big bucks on the parts.
I've came up empty handed on a SE output transformer (except for one that a guy wants $4000 for ) and was thinking parafeed may make it workable with cheaper iron. I decided I need to learn a little more before I go throwing around big bucks on the parts.
After spending considerable money to have the prototype transformer made that prompted that web page, and finding out that it wasn't suitable for HiFi, I realize that there are only two reasonable alternatives. Hammond 1642SE for about $250 USD each, or Electra-Print CU5KB for about $350 each. I haven't decided which to use yet. I would like to hear from someone who actually tried the Hammonds in a high power amp. They are the largest (28lbs) of the big SE transformers, so they should have some impressive bass. The prototype transformer that I had made was 20 lbs and it was capable of serious bass, it just couldn't go past 15KHz.
I have the power transformer for the HiFi amp, got it on Ebay from a fellow member of this forum, but no OPT's. I have the prototype OPT which is good enough for a guitar amp, but no power transformer yet. Whenever I find all of the parts for either amp, I will build it. The results will be posted on the web site.
I have the power transformer for the HiFi amp, got it on Ebay from a fellow member of this forum, but no OPT's. I have the prototype OPT which is good enough for a guitar amp, but no power transformer yet. Whenever I find all of the parts for either amp, I will build it. The results will be posted on the web site.
Perhaps plate chokes, high voltage PiO-caps and non-gapped OPT´s would be easier to find?
I´m thinking parafeed.
I´m thinking parafeed.
I have only limited experience with parafeed amps, but those experiences convinced me that getting a flat frequency response with generic chokes, caps, and transformers is almost impossible. I have had good luck on low power designs using a CCS instead of a choke. This takes one reactive element out of the circuit. Unfortunately the efficiency and voltage requirements preclude its use for a mega power SE amp.
***** WARNING *** AMATURE HACK IDEA *****
How about plate choke with a servo to control bias to avoid the cap. Calculate the voltage drop due to resistance at the bias point, put a 15 V or so (whatever it takes) above the B+ to feed the hot end of the choke, and run the OPT from plate/choke node to B+ and use a servo to regulate the bias and keep the DC off the OPT. Now the only problem is finding a big **** choke that won't arc over at 1500V or saturate on 400 ma.
I got the pattern size way off on my tube sockets, Now i'll have to cheeze one on with pigtails. I knew I should have waited for the sockets before I did the board. I considered soldering the tubes straight to the board, but that would really be bad form.
How about plate choke with a servo to control bias to avoid the cap. Calculate the voltage drop due to resistance at the bias point, put a 15 V or so (whatever it takes) above the B+ to feed the hot end of the choke, and run the OPT from plate/choke node to B+ and use a servo to regulate the bias and keep the DC off the OPT. Now the only problem is finding a big **** choke that won't arc over at 1500V or saturate on 400 ma.
I got the pattern size way off on my tube sockets, Now i'll have to cheeze one on with pigtails. I knew I should have waited for the sockets before I did the board. I considered soldering the tubes straight to the board, but that would really be bad form.
Pinche Mierda
I was about to put power to the thing, and I was looking it all over and noticed that my paralleled resistors that should add up to 500 ohms were 7 @ 75 ohms each. I devided 500 by 7 instead of x 7. Now Ace electronics is closed and I'm stuck reading instead of adjusting and listening. Don't you hate that.
I was about to put power to the thing, and I was looking it all over and noticed that my paralleled resistors that should add up to 500 ohms were 7 @ 75 ohms each. I devided 500 by 7 instead of x 7. Now Ace electronics is closed and I'm stuck reading instead of adjusting and listening. Don't you hate that.
If you need 500 ohms, and you have 7 75 ohm resistors, put them all in series. You will get 525 ohms, which is likely close enough.
You read my mind. That's what I did, but it took some riggin. Sine looks nice on the scope. I like to test XY with the probes on input and output and look at the line as i raise the frequency. You can see phase error as a opening of the line when you get near the upper bandwith, and I had a perfect line up to 200khz, so I can use the neg feedback to lower output imp if needed. I'm only getting 150 mW RMS due to current starving the neg swing, so I may go to a larger than 500 ohm resistor and bias to get a lot more voltage across it and balance the current swings more to the ground without getting too close to the edge of the plate dissapation limit.
Or maybe get the other channel up and listen for a while first.
But my first tube project lives.
Or maybe get the other channel up and listen for a while first.
But my first tube project lives.
My vote:
Listen now, scope later.
On my new amps, I will make enough measurements (usually voltage and current) to make sure that the amp won't blow up, then listen for a while, sometimes a long while. Often I have been surprised to find that some of my best sounding amps, don't measure that good, and some really good testing amps sound lifeless.
Listen now, scope later.
On my new amps, I will make enough measurements (usually voltage and current) to make sure that the amp won't blow up, then listen for a while, sometimes a long while. Often I have been surprised to find that some of my best sounding amps, don't measure that good, and some really good testing amps sound lifeless.
You seem to post suggestions as I'm doing them.
I got the second channel up, balanced the gains, dropped the bias to a safe level, and plugged in the CD player. The second channel only has 2.5x gain, so I had to put a 2 dB of NFB on the first.
The cymbals are a little harsh, but I presently have **** electrolytics bypassed with **** MKT from the surplus store untill my big Solens get here. But even that seems to be easing as I type. The CDP is also semi **** Yamaha DVDSACDHDCD. I'm quite impressed. This tube stuff is too easy. I've never had a sand project work well right out of the hole like this.
It's almost good enough to slap it in a box and call it done.
Here's a pic
I got the second channel up, balanced the gains, dropped the bias to a safe level, and plugged in the CD player. The second channel only has 2.5x gain, so I had to put a 2 dB of NFB on the first.
The cymbals are a little harsh, but I presently have **** electrolytics bypassed with **** MKT from the surplus store untill my big Solens get here. But even that seems to be easing as I type. The CDP is also semi **** Yamaha DVDSACDHDCD. I'm quite impressed. This tube stuff is too easy. I've never had a sand project work well right out of the hole like this.
It's almost good enough to slap it in a box and call it done.
Here's a pic
Attachments
I like it....cool.
These usually don't evaporate into a cloud of smoke, like a solid state power amp does when you mess it up.
These usually don't evaporate into a cloud of smoke, like a solid state power amp does when you mess it up.
The Solens came in, and I replaced the the MKT / electrolytic caps with a huge fat Solen 33uf 660V paralleled with a cheesCyRappy litic. It still sounded a little harch, so I threw the scope on it. I used one probe on each side of the caps, and set it to inverse and add. Funny looking wave form. (watching music, you can see what sounds bad sometimes) There was some low level stuff, but it stopped dead +- 2.5 mV. It looks like the bass could charge/discharge the 33uf cap to 2.5mV, but then the 500uf 'lytic cought it beyond that. removing the 'lytic really cleaned up the sound, but the response is down a db or 2 by 30 hz, but the sound is MUCH better.
I also made the mistake of NFB divider was hooked upstream of the out cap, and adding NFB to the channel with more gain caused an ugly imballance in the LTP. Now I need some top shelf ECC88/6DJ8 's.
I also want to add CL to the power supply. I'm still getting 5 mV ripple to the plates, but the effect is inaudible and unmeasureable with my 5 mV/div scope at the output.
Has anyone else had this problem.... I have a pair of flourescent lights over my bench that make hash at 25khz and a few mhz. I go crazy when I forget to turn them off when I'm looking for noise with the scope.
I'll have to draw up the scematic and share because it sounds great even with my 64 ohm cans. Makes me think how nice it would sound not so heavily loaded.
I also made the mistake of NFB divider was hooked upstream of the out cap, and adding NFB to the channel with more gain caused an ugly imballance in the LTP. Now I need some top shelf ECC88/6DJ8 's.
I also want to add CL to the power supply. I'm still getting 5 mV ripple to the plates, but the effect is inaudible and unmeasureable with my 5 mV/div scope at the output.
Has anyone else had this problem.... I have a pair of flourescent lights over my bench that make hash at 25khz and a few mhz. I go crazy when I forget to turn them off when I'm looking for noise with the scope.
I'll have to draw up the scematic and share because it sounds great even with my 64 ohm cans. Makes me think how nice it would sound not so heavily loaded.
Any suggestions where to get nice (not $50 each boutique) 6DJ8 or ECC88 tubes. I think the JJ's I have are questionalble. It really isn't founded, but I feel like USA NOS may be the best, Maybe JAN or Mil Spec.
Yea I've watched the other thread and I'll look again. I'm bidding on some on Ebay knowing I stand a good chance of getting ripped.
Yea I've watched the other thread and I'll look again. I'm bidding on some on Ebay knowing I stand a good chance of getting ripped.
Some of the newer flourescent light balasts run the lights at about 25KHz. This makes them brighter, but as you found out makes a good transmitter. I see the same effect using my sound card FFT analyzer. The light makes a spike at 26 KHz. The TV makes one at 16KHz and the computer monitor makes two around 30KHz.
An old but sometimes effective 6DJ8 source. Some of the old Tektronix scopes use them, lots of them. I don't remember the model number but it was one of the 5 series scopes. The original tubes were Amperex. These scopes can be found at ham-fests and flea markets for 5 or 10 bucks.
An old but sometimes effective 6DJ8 source. Some of the old Tektronix scopes use them, lots of them. I don't remember the model number but it was one of the 5 series scopes. The original tubes were Amperex. These scopes can be found at ham-fests and flea markets for 5 or 10 bucks.
I've always beenable to hear the TV one. Even if the picture was black and in the other room.
I'm currently bidding on some that were pulled from NOS tec plugins http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5830656731&rd=1&sspagename=STRK:MEBI:IT&rd=1 Kind of a shame to see a thousand dollar new piece of equipment gutted for $40 worth of tubes.
Maybe I need to put a bunch of candles around my bench. Then I cound get naked with some wine...Oh, wrong forum.
Thanks Tubelab.
This thing is really sounding great, but it seems to reveal more background noise in recordings. And it's not the amp, because the hiss isn't there between tracks. Maybe the source. I plan to by a TEAC Esoteric DV-50 after the first of the year.
I'm currently bidding on some that were pulled from NOS tec plugins http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5830656731&rd=1&sspagename=STRK:MEBI:IT&rd=1 Kind of a shame to see a thousand dollar new piece of equipment gutted for $40 worth of tubes.
Maybe I need to put a bunch of candles around my bench. Then I cound get naked with some wine...Oh, wrong forum.
Thanks Tubelab.
This thing is really sounding great, but it seems to reveal more background noise in recordings. And it's not the amp, because the hiss isn't there between tracks. Maybe the source. I plan to by a TEAC Esoteric DV-50 after the first of the year.
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