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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

D3a Russian equivalent recommendation

I plan to use D3a. To drive RCA 811 fixed bias. Due to low budget can anyone suggest Russian tube that fully interchange pin with D3A?

Thank you very much

Or if I omit d3A to drive 811a.

Any inexpensive pretube suggest?

My friend use el34 to drive 811a but i dislike EL34 sorry for my opinion may be i am wrong

Thank you very much for help in advance.

PS. My VT-231 45 SE2 watts is difficult to drive 85 db SB acoustic brommo.

That is why 811a might suitable
 
6F12p can?
3510DAC1-E7FF-471B-934B-454ACAD9B909.jpeg
 
I try to use as mr bartola but skip source follower using ordinary negative fixed bias as my 45

May be 6E6p-dr might be possible. I have low budget
 

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Many chinese design use 6J5 and EL34 to drive 811a.

But to save cost I plan to use 6e6p-dr to drive. I want this amp to optimal budget. I don't expect as good as 45 SE.

But more watts might drive my other speakers better
 

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try to use as mr bartola but skip source follower using ordinary negative fixed bias as my 45
811A is a zero bias tube and needs "power", i.e. grid current to be driven properly. 45 is ordinary tube and can be properly driven with voltage (only).
So 811A require some sort of low impedance driver stage DC-coupled to grid of 811A.
 
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811A has high mu (>100), so the needed (drive) voltage swing is not very big, but as already stated, significant current is needed.

In addition the grid current will be not linear so will be mandatory to check carefully the bias point and plot a good load line.
With a strong driver ( hopefully not with sand ) :)
The use of tube were the grid current is necessary is a point that I can't still understand.

Walter
 
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811A has high mu (>100), so the needed (drive) voltage swing is not very big, but as already stated, significant current is needed.
I'm glad I was no mistaken, as I am incorrect often!

Perhaps then it would be simpler to use something like a regulator, since nice low mu, maybe 2-5, high voltage is not required for the 811 input swing.

Then the PSU does become....interesting
 
For 811a i have 2 decision to use 6l6GC which i can buy at shop nearby. Or contact Mr bartola to buy 2 source follower boards. Then i can add 80-0-80V small transformer to get +|-100v. Due to long distance if anyone can share schematic of source follower. I can save cost of 6L6GC.