Using EL34 for allen wright's pp-2c

[Alarudin]

Hi Everyone,

I will be building Allen wright's pp-2c ordering parts at the moment. A question for fellow forumers who build the pp-2c or have experience in the design.

I have 2 pair of winged =c= el34 from previous amp, and wanted to use it till it die on me. But instead of building a pp-1c catered for el34 I would like to build a pp-2c which is for kt88 which I may use in the future. And from Allen wright's words in the forum pp-2c seem to be a better design.

Beside changing the value of cathode bias resistor to bias it according to el34 max dissipation rate. What are the other component values needs to be changed? Does the screen resistor value or 470ohm need to be change to 4.7k ohm as stated in pp-1c?

I will be using the same transformer spec as stated in pp-2c so around 450v plate. Not sure if I'm allowed to post the pp-2c schematic which I found on other forum.

Hope to hear some advice. And permission to upload the schematic for some further questions. Thank you.

-askae

 

[artosalo]

Attached is the schematic. It is in public domain

Compromised URL removed by Moderation

I don't see any other changes needed except the bias of output tubes.
Have you realized that this design has very low gain. Therefore you need several volts input signal to get full output power.

 

[Bas Horneman]

I deleted that forum on my site. Here is a new link:
Compromised URL removed by Moderation

 

[45]

Have you realized that this design has very low gain. Therefore you need several volts input signal to get full output power.

Several volts?

With the recommended cathode resistor choice the overall gain with KT88 (including the OT) will be 20 dB. The EL34 in triode mode has a bit more gain than the KT88 and will give less power which means higher sensitivity....

 

[Bas Horneman]

I thought that a cascode had massive gain?

 

[ArthurDK]

Hi Bas, where did the schematic go?

 

[Alex M]

Have you realized that this design has very low gain. Therefore you need several volts input signal to get full output power.

Allen's preamps have high gain, which would be consistent with this. The SVP2 has about 20dB, and the RTP3 something like 10dB in the default configuration.

Alex

 

[Bas Horneman]

Hi Bas, where did the schematic go?

That whole site is gone.
Attached it to this forum now.

 

[6A3sUMMER]

With the 470k DC balance pot centered, the 6550 g1 will see at least 77k DC to ground.
That is too high for their fixed bias 50k max rating.
Your Mileage May Vary.

KT88 are fine there, 100k is their max g1 rating.

Just sayin'