DR Bias and Bypass Caps?

[Rick1114]

I want to do complete cap job and I'd like to start by ordering the parts without having to open the amp up again. I can find the filter caps/values but I'm not familiar with where the bias and bypass caps are just by looking at the schematic. The circut for the DRRI is the same as the original, so the Cap numbers should be the same, and then I could look up the value from there...

Any help would be appreciated!

Rick

[EETStudent]

If you are looking at a schematic, locate the power transformer in the bottom right corner, and in between two lines/wires that read 330VAC you will see that one wire goes straight to ground, where as the other feeds into the bias circuit. If you follow that line, you'll bump into a 470/1W resistor, and then you'll see a diode, and then a 25uf/50v cap and 10k adjustable resistor/pot that allows for adjusting the bias. This is your bias circuit. As for the bypass caps, mainly the cathode bypass caps, locate the tube section that reads
'7025' in the top left corner. Not sure if you are familiar with schematic symbols, but the half circle with the rectangle and the squiggly and the solid line is your symbol for that tube section. Locate the solid line at the bottom of that circle, and that is your cathode. Connected to it is a 1500 ohm resistor and a 25uF/25V bypass cap. You'll notice each preamp tube has this similar arrangement. you can tweak your sound by slightly adjusting these values. Hope this helps!

[ajeffcote]

I want to do complete cap job and I'd like to start by ordering the parts without having to open the amp up again. I can find the filter caps/values but I'm not familiar with where the bias and bypass caps are just by looking at the schematic. The circut for the DRRI is the same as the original, so the Cap numbers should be the same, and then I could look up the value from there...

Any help would be appreciated!

Rick

Rick,acouple of those caps are radial mount,so an axial cap won't fit in the allotted space.I ordered the filter caps and the bypass caps.2 100uf 350/V's for the main filter,1 40uf 500/V for the screen supply,2 20uf 500/V's for the pre-amp supplies.25uf 50/V's for the bypass caps.I haven't had time to install them yet.That's why I haven't responded.The radial caps are both in the bias circuit.I didn't buy replacements for those because I don't think that they will directly affect the tone.Another consideration is the physical size of the caps.I don't think the Sprague Atom's that I bought will fit under the cap cover,so I may be in for some custom saw work.
Aubrey

[ajeffcote]

The bias caps are at C29,a 22uf 63/V and at C36,a 100uf 100/V.Both are radial mount.
Aubrey

[Rick1114]

Anyone know if there are there any good filter caps that are smaller in size than the Sprague? I seem to remember that there were, but I can't remember the brand....