STME58
1195 posts
Feb 25, 2015
6:59 PM
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I just ordered an Eminence 820H for my Electar tube 10. I already replaced the 3 22uf/450v caps with 22uf/500v caps and it still works. I am aware of the danger of circuits with large capacitance, even when unplugged.
I am considering making some minor mods I found in a web search. I thought I would start with the R5 an C2 change to improve the low end.
4 12V 5W zeners wired in series with PT CT (yellow) and ground, to drop B+ to around 390V, which is safer on the 450V rated caps.
- Black PT heater CT re-routed to V2 cathode
- C12 changed to 47uF 50V
- C10 changed to 100uF 50V to improve lo-end
- R10 changed to 22k 2W, reduces B+ to 290V
- R14 & C11 removed as the NFB doesn't work here
- C5 replaced with a wire link. It has no use!
- R7 changed to 820 ohm, to fatten distortion
- R5 removed. There's enough attntn without it
- C2 changed to .022uF to reduce lo-end mushiness
- C1 to 10uF, for same reason.
- R3 to 1k5 for warmer bias and less lo-end mush
Any helpful comments or warnings from would be appreciated.
I also have a kepco op-Ampsitting on my desk at work right now that I am using to step up the current from a 1mA output D/A converter and drive a motor.  it has a max output of 100A. I was wondering how it would work driving a speaker. I thought I would try it on the old speaker that comes out of my amp as the chances of blowing it out are probably pretty good. A little knowledge is a dangerous thing!
Last Edited by STME58 on Feb 25, 2015 7:02 PM
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markdc70
157 posts
Feb 27, 2015
8:40 AM
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My 2 cents: Remove R5, that's in an odd spot and I'm not quite sure what it's benefit is there. Change R10 to at least 22K to get your plate voltage in the preamp down to 150-200 volts. Remove C1 and C4. Change R3 and R7 to 2.2K. No need to change C2. Try this and let us know how it sounds!
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STME58
1201 posts
Feb 27, 2015
10:20 AM
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@markdc70,
Thanks for your input. It looks like you concur fairly closely with the mod list I found.
I am hoping to gain (pun intended) some understanding or how amps work as well as end up with a good sounding amp. I hope to get the speaker and give things a try next week.
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