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811a Push Pull need help

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I have a lot of 6SN7 to utilized.

Can anyone help me to replace 5U8 to 6SN7 for this diagram? 811a 26 watts Push Pull.

Thank you.
 

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> a lot of 6SN7

Pair of 811 can deliver 200 Watts (but only 26W this way). Pair of EL34 is close to 20W (to 70W). Sure is a lot of big bottles. Don't see why you would choke at a little 5U8. Many other pentode-triode tubes will work as well. Check pinout. Adjust cathode bias to get the pentode plate voltage as designed.

Pentode has voltage gain of near 100. 6SN7 has voltage gain of 16. That's a major change in the amplifier, lost NFB. You "can" cascode two sections of 6SN7, but do you know how? Or anybody who will work-out the design cheaper than finding a little pentode-triode tube?

The attached shows the concept but the values are absolutely un-checked. It is a 10-minute thought but only worth 5 minutes because I am very tired.
 

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Surely is best to use the original circuit I have built lots of 811a amps in my opinion they sound the best of any amp I have tried the circuit I use give over 100 watts; I have yet to find a speaker they won't drive; The first amp I biult I used 6sn7 instead of 12BH7 and max output was 30 watts; {No 12BH7 available;} I get over 100 watts with 12BH7. 5U8 are a dime a dozen; you would be lucky to get 6SN7 that are not highly micro-phonic.
 
If i cant find 811a pp schematic I have back up plan to cope with KT88 PP using 12ax7 6sn7 and kt88

But i will try go find 6sn7 kt77 811a pp first due to cost and easily to find a lot of 811a near my house

Look for the Altec 1570B for a good example of a PP 811A amplifier. The 1570B does 165Watts with some headroom.
You could do 100 watts if you want to be somewhat to class AB instead. Perfect amplifier if you are looking for 100 watts or a bit more.

Also, the 811a can do about 15 watts class A. Plate resistance is a bit high but there are ways around that.
 
811A makes a good audio tube in push pull. Look up the Gotham PFB150WA disk recording amplifier (used to drive a Grampian mono disk cutting head).... 150 watts of clean audio from a pair of 811's.... or the McIntosh MI-200.... 200 watts from a pair of 8005's in push pull....811A's are much less expensive than 8005's....
 
811A amps

The Grampian record cutting amp uses 12BH7 or 6GU7 and two 6BL7 they are listed On the circuit; the output transformer is 2.2k,P-P But I have used 5K as well.
The original power supply used mercury vapor rectifiers, but I use a Normal capacitor in put using a solid state bridge, or choke input. You need very good regulation so A toriod is very good. I recently ordered toroid out put transformers from Poland sound excellent but have not had time to do tests. One good thing about Russian or USA made 811A's they last so long at 600volts.
Phil
 

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811s are class B amplifiers, they need grid current to provide drive. At 500 volts they need about +20 volts on the control grid and about 20ma. So the EL34s will be running at about 20ma. I made his 811a se using a 6DB5GT to drive the 811s.
 
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