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Pioneer SA-810 rebuild help
Pioneer SA-810 rebuild help
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Old 17th October 2018, 03:55 PM   #21
Alan4411 is online now Alan4411  Wales
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A really dumb question.
Have you adjusted the bias? Have you got -19 volts on test point C, if not adjust VR7 so you do.

The other thing is what AC voltage do you measure on the B+ secondary (brown to red) with no load? I would have thought you would see more than 414 volts with no load if you expect 425 volts 'loaded' as per the schematic?
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Old 18th October 2018, 02:18 AM   #22
AlwaysTinkerin is offline AlwaysTinkerin  Australia
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not a dumb question.. Yes Bias is set. I have it plugged into a Variac set at 240VAC with a Dimb bulb tester in series after that... it measures 414VDC after diodes then taps off into a circuit full of CC resistors that are mostly a little bit up and down. I am not looking for perfect measurements, just ball park would be nice.

Just to be sure i re shuffled 7868's again installing only one tube at a time with the same 30V voltage drop on the same socket.. i then tried a socket on the other channel with same result.
I also, even though they measured fine on my ESR meter, removed the new C50 and C49 and re installed the old caps.
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Old 18th October 2018, 03:09 AM   #23
TonyTecson is offline TonyTecson  Philippines
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Pioneer SA-810 rebuild help
with prices of caps and rectifiers on the really cheap these days,
it would be a no brainer to choose "fresh caps" in the voltage doubler psu,
and 3A, 5408 rectifiers....

these amps uses plate load resistors that look different from your typical carbon comps, they fail without giving a hint, just measure the plate voltages on the small tubes and when you find 0 plate volts, you know that the plate resistors have become open..

i repaired two of such amps, one i converted to ac 230 volts from a rating of ac 100 volt primary, and another one where one channel was not working..
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Old 18th October 2018, 09:09 AM   #24
Alan4411 is online now Alan4411  Wales
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Dumb question 2: You mention the bulb tester in circuit after the Variac a couple of times, Are you taking the B+ DC voltage measurements with the bulb in circuit or out?
Just that the idle current draw of the output valves (according to the circuit) is 144mA times the B+ volts, say 400, and therefore at least 57.6 Watts. So if the bulb is in circuit it will be sharing the 240 volts and dropping the effective AC input voltage.

Last edited by Alan4411; 18th October 2018 at 09:14 AM.
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Old 18th October 2018, 12:13 PM   #25
AlwaysTinkerin is offline AlwaysTinkerin  Australia
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Ha.. You're right! crikey.. I think I've done about 20 laps of the circuit
Well at least I have learnt a lot about tube circuits. Still a lot more to learn though and i still have that hiss...

I am going to order up a full set of resistors and rework some of what i have already done... making a clean job of point to point work is harder than it looks..
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Old 18th October 2018, 12:19 PM   #26
AlwaysTinkerin is offline AlwaysTinkerin  Australia
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Quote:
Originally Posted by TonyTecson View Post
with prices of caps and rectifiers on the really cheap these days,
it would be a no brainer to choose "fresh caps" in the voltage doubler psu,
and 3A, 5408 rectifiers....

these amps uses plate load resistors that look different from your typical carbon comps, they fail without giving a hint, just measure the plate voltages on the small tubes and when you find 0 plate volts, you know that the plate resistors have become open..

i repaired two of such amps, one i converted to ac 230 volts from a rating of ac 100 volt primary, and another one where one channel was not working..
I will replace all caps mate.. someone has already been in this amp and given it a tickle at some stage.. There where some odd caps, German PINEX around the preamp and lots of resistors replaced..all clean work though looks factory..nothing was open probably due to previous repair.. its like half the jobs been done..
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Old 9th November 2018, 09:23 AM   #27
AlwaysTinkerin is offline AlwaysTinkerin  Australia
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Just a bit of an update on this.. I managed to cure the hiss by replacing the CC grid stoppers with some carbon film resistors i had on hand.. I've been trying to make up an order of parts to finish the amp but also experimenting replacing resistors and swapping caps around. It would be nice to have ideal replacements for these Soshin silver mica caps just to make a complete restoration and i would like to replace with modern equivalents to be honest if anyone has suggestions.
The amp is running well now, but I am not satisfied with it. It is just too bright lacking bottom end.. I have re checked all my replacement capacitor values which are good. I know this amp should sound a lot better..so i guess i am just fishing for advice?
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Old 9th November 2018, 09:53 AM   #28
Eli Duttman is offline Eli Duttman  United States
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For mica caps., look at Soviet surplus. If you want to tweak the voicing, Soviet surplus K40 paper in oil (PIO) parts are a definitely possibility.
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