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
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
Connect (triode connected) pentode halve in parallel with the triode halve of 6F12P. Then you get almost D3A equivalent combination.6F12p can?
How are you planning to drive 811A? With cathode follower or transformer coupled common cathode stage?
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
May be 6E6p-dr might be possible. I have low budget
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811a tube are discount for Christmas so I just bought 2 and my friend 4 total of 6 for my future amp
45 tube is too expensive 6 time more than 811a
45 tube is too expensive 6 time more than 811a
EL12n is a useful tube - mu=18 in triode. It's my regular output tube driven by type 26. That combination could work. EL12n are sold new in Europe quite cheap.
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).try to use as mr bartola but skip source follower using ordinary negative fixed bias as my 45
So 811A require some sort of low impedance driver stage DC-coupled to grid of 811A.
What about something like 6P3S (if I have recalled the number correctly) the Soviet 6L6, of you don't like EL34?
Or maybe a regulator type tube, provided it can supply the necessary voltage swing to the output stage?
Or maybe a regulator type tube, provided it can supply the necessary voltage swing to the output stage?
Look at the values on that schematic. The grid (bias) voltage of 811A is 18,5 V positive and 18 mA grid current is flowing without any signal, i.e. at standby.
811A has high mu (>100), so the needed (drive) voltage swing is not very big, but as already stated, significant current is needed.Or maybe a regulator type tube, provided it can supply the necessary voltage swing to the output stage?
For my humble knowledge MR bartola use Regulate to get 28vdc and send through source follow to get final of 22.5v then pads 330R might get some value may be 20v need ohm law cal 22.5v R 330R 18ma
I want to skip source follower due to need 2 sections to get + and - 100V
I want to skip source follower due to need 2 sections to get + and - 100V
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
I'm glad I was no mistaken, as I am incorrect often!811A has high mu (>100), so the needed (drive) voltage swing is not very big, but as already stated, significant current is needed.
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.
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