I had an idea to use a PP transformer in a SE amp by using one half of the primary with the triode like any SET amp, and a current source feeding the same curent into the other end of the tansformer. My thoughts were that I could use a much smaller and cheaper ungapped PP transformer, but wanted to ask if anyone has done this and how did it sound. (actually, I could use a much bigger triode as I can't find a SE transformer over 50W)
I wanted to avoid parafeed because of the big cap needed.
I wanted to avoid parafeed because of the big cap needed.
On Plitron's site under special designs I found this:
PAT HQ5090 Application: Svetlana SV572 Triode 90 Watts
This Single Ended output transformer is intended for paralleled Svetlana SV572 triode tubes, with a primary impedance of 2.5 or 5 kOhm, depending on secondary loading. Secondary impedances are 2, 4 and 8 Ohms. The -3dB bandwidth is from 8 Hz to 43 kHz with a high frequency Q-factor close to 0.5 (critical damping). The insertion loss is an extremely low 0.15 dB ensuring no loss of audio power and creating excellent damping at the low frequency end of the power spectrum. The DC current capability is 400 mA maximum. This transformer is designed for no overall negative feedback applications, completely relying on the tube characteristics for the purest sound quality.
I couldnt find any further information though.
PAT HQ5090 Application: Svetlana SV572 Triode 90 Watts
This Single Ended output transformer is intended for paralleled Svetlana SV572 triode tubes, with a primary impedance of 2.5 or 5 kOhm, depending on secondary loading. Secondary impedances are 2, 4 and 8 Ohms. The -3dB bandwidth is from 8 Hz to 43 kHz with a high frequency Q-factor close to 0.5 (critical damping). The insertion loss is an extremely low 0.15 dB ensuring no loss of audio power and creating excellent damping at the low frequency end of the power spectrum. The DC current capability is 400 mA maximum. This transformer is designed for no overall negative feedback applications, completely relying on the tube characteristics for the purest sound quality.
I couldnt find any further information though.
Thanks
$611 each for the Plitron...ouch
I was looking for 200watts worth for an 833A, but if I can't find the iron at a reasonable cost, I may just do an OTL 6C33C x6 amp.
I was thinking maybe the 280W they sell for PP. Any comment on counter-biasing a PP tranny
I need 1800 ohm or so 400 to 500 ma.
$611 each for the Plitron...ouch
I was looking for 200watts worth for an 833A, but if I can't find the iron at a reasonable cost, I may just do an OTL 6C33C x6 amp.
I was thinking maybe the 280W they sell for PP. Any comment on counter-biasing a PP tranny
I need 1800 ohm or so 400 to 500 ma.
Now that's my kind of amp. I have just about decided to use the Hammond 1642SE. I might go for custom Electra-Prints if I have the bucks. This amp will have to wait till early next year though.
I tried the custom transformer route, through a transformer winder who builds good 300B transformers, but the 200 watt SE transformer didn't quite work as good as his computer program said it would. It is good enough for a 200 watt SE guitar amp, which is currently being breadboarded.
The CCS load on the other half of the transformer trick does work. I tried it at the 8 watt level using a 300B on one leg of the transformer, and an IXYS 10M45 on the other leg. To get 200 watts out of an 833A, I had to run 1500 volts. That voltage tends to turn silicon back to sand if you are not careful. I have been experimenting with hybrid CCS's. There is a thread discussing the results of a few peoples experiments along these lines.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=67437
Just a CCS countering DC offset will have a lousy overall efficiency, and its safe to say that in Texas it wont be offset in your heating bill either. Rather the opposite. For 2 channels its an extra ~700 watts + whatever the CCS eats making it. 
At ~8 cents a kilowatt hour, how long does it take to pay for a single ended transformer over a push-pull one? I dont know but its a question worth asking.
Am I misunderstanding something here, looking at wrong circuit?
At ~8 cents a kilowatt hour, how long does it take to pay for a single ended transformer over a push-pull one? I dont know but its a question worth asking.
Am I misunderstanding something here, looking at wrong circuit?
Tube amps are not known for efficiency, and SE tube amps are among the worst. I have been experimenting with "chokeless parafeed" which operates at less than 10% not counting big hungry filaments. I am planning one that uses 845's for the output triode, and 813's for the CCS. That ought to waste a few watts.
Hey here in South Florida, I had to add a room air conditioner just to make up for the heat added to the room from my 845SE amp. Now what is my efficiency? The 833A SE amp will use a dryer vent to port the tube heat outside the house.
Many of my experiments are done just to see if something will work. They may not be practical, but they are cool. How practical is a 200 watt SE guitar amp that weighs over 100 pounds. But it will be the baddest amp on the block, and you won't be able to buy one at Sam Ash Music.
Back to the point, I have performed many experiments that use a P-P style transformer in a SE amp. They have worked and measured well, but some of the SE magic has been lost. On the other hand I have made some true SE amps using some really cheap transformers that measured lousy and sounded really good. I once ran a 300B through a $15 "Fender Champ replacement transformer" that sounded sweet. I listened to it for a few days, and had friends listen to it, no one could believe that it was a $15 transformer.
Hey here in South Florida, I had to add a room air conditioner just to make up for the heat added to the room from my 845SE amp. Now what is my efficiency? The 833A SE amp will use a dryer vent to port the tube heat outside the house.
Many of my experiments are done just to see if something will work. They may not be practical, but they are cool. How practical is a 200 watt SE guitar amp that weighs over 100 pounds. But it will be the baddest amp on the block, and you won't be able to buy one at Sam Ash Music.
Back to the point, I have performed many experiments that use a P-P style transformer in a SE amp. They have worked and measured well, but some of the SE magic has been lost. On the other hand I have made some true SE amps using some really cheap transformers that measured lousy and sounded really good. I once ran a 300B through a $15 "Fender Champ replacement transformer" that sounded sweet. I listened to it for a few days, and had friends listen to it, no one could believe that it was a $15 transformer.
Its being eaten in a resistive ballast, talk about some gross inefficiency. The Jakob's ladder is basically just a big transformer shorted across an air gap. Heres another pic, taken after the ballast heated up, but blurry. The pink looking thingy in front of me are 14 oven boiler elements in parallel. Each element switched in adds 5 amps. Its hard to find reactive ballast of this power cheap. Using surplus pfc caps atm now.
Your right though, I doubt real power on the secondary is more than a couple kW.
Each element switched in adds 5 amps. Its hard to find reactive ballast of this power cheap. Using surplus pfc caps atm now. Your right though, I doubt real power on the secondary is more than a couple kW.
"Just a CCS countering DC offset will have a lousy overall efficiency,
If I understand correctly, The DC resistance of a tranny primary is much less than the "advertized" AC resistance, si it would only take a percent of the voltage at the same current. Then again, maybe I could load it with a constant voltage.
I need to read and think before I post more.
If I understand correctly, The DC resistance of a tranny primary is much less than the "advertized" AC resistance, si it would only take a percent of the voltage at the same current. Then again, maybe I could load it with a constant voltage.
I need to read and think before I post more.
Hi Brian,
You are trying to cancel the dc flux in the pp transformer core created by the quiescent current flowing through one leg of the primary and through the output tube, given that the turns ratio is the same for both halves of the primary the amount of current through the winding will need to be the same, and hence the dissipation in your ccs will need to be the same as well.
A voltage source incidentally would result in an ac short across that half of the winding and cannot be used - you need a ccs.
There are lots of reasons for not taking this approach at these power levels, but amongst them high leakage inductance would be my reason.
You may very well get better results with a PP amplifier design.
You are trying to cancel the dc flux in the pp transformer core created by the quiescent current flowing through one leg of the primary and through the output tube, given that the turns ratio is the same for both halves of the primary the amount of current through the winding will need to be the same, and hence the dissipation in your ccs will need to be the same as well.
A voltage source incidentally would result in an ac short across that half of the winding and cannot be used - you need a ccs.
There are lots of reasons for not taking this approach at these power levels, but amongst them high leakage inductance would be my reason.
You may very well get better results with a PP amplifier design.
I went to bed after my last post and realized a voltage source would be the same magnetically as a shorted coil. Until then I hadn't considered the dynamic AC conditions of this biasing scheme. My first thought was to make my own huge SE transformer, then I was thinking 3,4 or 5 in a tri, quad, or pentafilar primary for paralleled smaller triodes, Then I thought to add a extra few turns of heavyer wier for a DC biasing to reduce the magnetic bias in the coil, but I never thought of the AC.
Now I see. If you go through the bother of CCS, why not modulate the CCS, then you have PP.
Or I could put a plate choke in series with dc voltage source sized to provide the bias to the other leg, but That would be as big and costly as a propper SE OPT.
I knew there was a reason noboby thought of this in the last 50 yrs of triode amp design.
Now I see. If you go through the bother of CCS, why not modulate the CCS, then you have PP.
Or I could put a plate choke in series with dc voltage source sized to provide the bias to the other leg, but That would be as big and costly as a propper SE OPT.
I knew there was a reason noboby thought of this in the last 50 yrs of triode amp design.
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