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Post subject: Update on my SR
Posted: Fri Jan 14, 2011 2:39 pm
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I just finished adjusting the bias on my SR. This I how I did it . Please let me know what you think. I removed the existing 15K resister on the balance pot and in its place put a 5k resister and a 10k .5 watt trim pot. I set it @ 40ma with 6l6gc =c=. It is sounding great at low volumes with a TS-808 pushing the front end. I have another question though. I noticed what looked like a capacitor running from power tube pine 5 to pin 8. On both power tubes,It looks like a brown M&M with wires? It is not shown on the schematic layout.


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Post subject: Re: Update on my SR
Posted: Sat Jan 15, 2011 6:08 am
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From what I can find out it looks like it was used to prevent the output transformer from going into oscolation. Also I hear alot about the dreaded death cap. What is that all about?


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Post subject: Re: Update on my SR
Posted: Sat Jan 15, 2011 6:38 am
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So the mod i told you about worked? Why did you only use a 10k pot


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Post subject: Re: Update on my SR
Posted: Sat Jan 15, 2011 8:58 am
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joncarr1979 wrote:
So the mod i told you about worked? Why did you only use a 10k pot

It was sujjested by someone. It had plenty of range. I don't fully understand it, but I am trying. I also had someone helping me that has some experence. What would a different k pot have affected?


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Post subject: Re: Update on my SR
Posted: Sat Jan 15, 2011 8:13 pm
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Blues, I would have chosen the 10K myself. Those 2000pf caps are indeed there to suppress parasitic oscillation, due to errant lead dress of the wiring in the amp. Sometimes these can be removed, but if a high pitched squeal is heard, or if the amp shuts off intermittently, they will have to stay. The "Death Cap" is a bypass cap, off the standby switch to ground, for noise suppression. Usually this is removed, when the amp power cable is rewired to modern specs. Art

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Post subject: Re: Update on my SR
Posted: Sun Jan 16, 2011 3:15 am
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aclempoppi wrote:
Blues, I would have chosen the 10K myself. Those 2000pf caps are indeed there to suppress parasitic oscillation, due to errant lead dress of the wiring in the amp. Sometimes these can be removed, but if a high pitched squeal is heard, or if the amp shuts off intermittently, they will have to stay. The "Death Cap" is a bypass cap, off the standby switch to ground, for noise suppression. Usually this is removed, when the amp power cable is rewired to modern specs. Art

Thanks Art, I replaced the 3 prong power cord yesterday. I always plug the amp into a surge protector. I plan on leaving the switch as is for now. I feel confident it will trip the breaker if it grounds out. I was thinking it was an issue with the polarity switch.


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Post subject: Re: Update on my SR
Posted: Tue Jan 18, 2011 10:24 am
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Blues you're right ! That bypass cap is off the polarity switch. Here's a link for it's removal, if you like. http://www.unclespot.com/3prongconversion.JPG . Art

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