Dynaco VTA-inspired KT88 PP AMP project

[AnatolyAA]

Are you still working from the schematic you initially posted? Sorry, if I missed an update. I remember you said B+ was 509V. Could you post you revised schematic with the higher supply voltage?

The Lundahl LL1679 transformer is really good and 4.5k impedance will be perfect for two PP KT88. Or are you now leaning to KT120? The LL1679 AM with amourphous core is even better, if you can afford it.

the output transformer I made is designed for 360 V AC, which should give around 504 V DC. Taking into account the chocke resistance we should end up around 490 V B+.

6A3sUMMER, thank you for noticing. It seems that I made a mistake when copying the schematics.

 

[multi]

I had a Jadis amp for repair had 1 meg grid resistors on the 6550 and was driven by 12AX7's
The inside was covered in Soot. from burnt up resistors. 12AX7's certainly can't drive 6550's with 50K.

Sovtek; KT 88 and 6550 50 k is max grid resistors

 

[AnatolyAA]

ok, we have started moving. I have finally purchased the OT, so no turning back.
After correcting the mistake with R29, 31 - now they are set to 100 kOhm, I have noticed that the C5, C7 are 0,33 in my schematics, which is bigger than on the ST70 driver board (0.22 was used).
Does it make any sence? I have ordered the Jantzen Superior Z-Caps 0.33. I may still change the order. What do you think?

 

[AnatolyAA]

Ok. So I have got the Llundahl OT, the Russian local made chokes and Jantzen Superior Z-Caps. The Nichicon caps will follow.
What resistors do you prefer in PP amps? Anything special to consider?

 

[gerrittube]

Hi Anatoly, on hificollective.co.uk you can find many high class brands of resistors. Just ordered some Takman resistors today, but they have other fine brands too. Looking at this website may help you to discover what’s available. Good luck!

Regards, Gerrit