as long as i have it torn apart....

[nyazzip]

i have the DiyTube rev D board; i have it apart to replace the el84 cathode resistors (r17, r20, r23, r26)which i smoked pretty good a long time ago trying 6n1p tubes.
the amp still functions but the crispy look has been bothering me. oddly enough, the worst looking one, which is black and swollen, is bang on(471r)....
while i'm at it i guess i'll do the neighbors too, r18, 21, 24, 27. the xicon caps c5 and c8 look a little bulged on top so i think i'll replace those too, and their adjacent brothers
question: what material should the resistors be? metal film? oxide...? also would different caps be worth playing with or should i stick with the xicons?
anything else i should replace whaile i'm in there? the parts were from the Triode Electronics kit from '08 and they are all pretty decent i think....
also anyone know where i could find another new Rev D board?
all input appreciated

[Ty_Bower]

As far as the resistors are concerned, metal oxide will tend to be more flame-proof than metal film. I would tend to use metal oxide for cathode resistor duty. Metal oxide is almost mandatory if your putting them on screen resistors, or anywhere in the power supply section. Precision metal film is a good choice for plate loads.

I've been using the Nichicon KW series caps for cathode bypasses and the like. They claim to be "special audio grade", which is probably BS, but they only cost a dime or so more than the standard grade counterparts.

I don't think much changed from Rev C to D. I think Shannon isolated the ground plane from the six mounting holes, and there might be an extra trace or two for some feature that never fully surfaced (some kind of CCS on the finals, or something?). He could better explain the differences. Mechanically, I think the C and D are identical. I expect a C board should mount just fine on a D chassis. Don't try that with a B!

[nyazzip]

ok, thanks, now i can place an order. so many choices!
i queried about the boards, and triode got back to me and said:

the only difference is C14 & C15, which are listed as jumpers using cut resistor lead scrap. Basically, the Rev C was originally AC-coupled like the original ST35 and the Rev D was DC-coupled for higher performance. So with the jumpers, the Rev C will also be DC-coupled and the parts lists are essentially identical.

[Ty_Bower]

the only difference is C14 & C15, which are listed as jumpers using cut resistor lead scrap. Basically, the Rev C was originally AC-coupled like the original ST35 and the Rev D was DC-coupled for higher performance. So with the jumpers, the Rev C will also be DC-coupled and the parts lists are essentially identical.

Ah yes, that piece. I don't think those caps were directly intended to function only as AC coupling for the input signal, but rather as part of a low pass filter. Think of it like a rumble filter at the input of the amp to remove the subsonics that aren't audible but might still affect the power handling and/or stability of the amp. It was a commonly recommended mod for the ST70 amps. Maybe Shannon got the inspiration there. Anyway, here's a little more reading on the subject:

http://www.diytube.com/phpBB2/viewtopic.php?t=2734