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Old 26th February 2016, 12:20 AM   #1
AJT is offline AJT  Philippines
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Default Pioneer SA-81 integrated tube amp

Pioneer SA-81 for conversion to 230v mains and restoration, uses the 7868 tube, contemplating on using the 6L6GC tubes instead...
i am chasing down schematics, pm me please if you have, that will make my work much easier...

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Old 26th February 2016, 02:26 AM   #2
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The power O/P of 6L6GCs will overwhelm the O/P "iron". Use 7591s to convert to Octal based O/P tubes, as the 7868 and 7591 are electrically equivalent.

The 7591 family is as easy to drive as 6BQ5/EL84s. That fact was/is exploited by Fisher, Scott, Sherwood, and (at a minimum) me.

BTW, the 6L6GC draws 100 mA. more heater current than the 7591 family.
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Old 26th February 2016, 03:02 AM   #3
anatech is online now anatech  Canada
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Hi AJT,
Eli is right on the money, exactly on the money. The output iron isn't set up for 6L6 type tubes either.

I have an Eico ST-70 that I'll be restoring sometime. I waited until I found some real 7591A tubes. The 7591XYZ thing did not fill me with confidence. I ended up with 7581EH tubes. See, going the same way you were thinking of going. It wasn't a good path to take. The only reason I didn't use other tubes was that I couldn't find any for reasonable money.

-Chris
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Old 26th February 2016, 04:41 AM   #4
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yes, i have convinced the owner not to do that, we were talking about it on the phone
and when he brought the amp to me, the first thing i noticed right away is the wimpy opt...

but you may be surprised, the same size opt i saw in one of the KT88 offerings from Cayin,
the opt is housed in a box so it is not noticeable until you open up the box...

the 7868 is no slouch either, i remember while in high school, this was the amp we would use during, a diy amp based on the 7868....

i was hoping some one would lead me to schematics so that i will not have to reverse engineer this amp...
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Old 26th February 2016, 09:43 AM   #5
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From memory, some years ago as a Pioneer main repair agent, the SA-83 is similar.
Pioneer SM-83 Manual - Stereo Integrated Amplifier - HiFi Engine
Hope that helps but is is a very simple amplifier. 6L6 or EL34 will draw too much heater current.
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Old 26th February 2016, 10:33 AM   #6
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Quote:
Originally Posted by JonSnell Electronic View Post
From memory, some years ago as a Pioneer main repair agent, the SA-83 is similar.
Pioneer SM-83 Manual - Stereo Integrated Amplifier - HiFi Engine
Hope that helps but is is a very simple amplifier. 6L6 or EL34 will draw too much heater current.
thanks, the unit that i have is a tad more powerful but the topology could be the same...
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Old 26th February 2016, 02:46 PM   #7
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Hi AJT,
The 6L6 won't perform as well as it could in that amplifier, but it would work. Your bias currents might be lower, closer to what is used with the original tubes. Otherwise the HT supply may have trouble with the increased current draw for the 6L6 types.

In a more perfect world, you would use the 7591A as it is the same tube that was in there from the factory with a different pin out.

For the customer to go to 230 VAC, it would be the least expensive to use a step-up transformer. I would look at going with one that went from 115 VAC to 220 VAC since the mains voltages seem to be higher these days. 120 VAC to 220 VAC would also give more safety room if the voltages are higher in the future.

-Chris
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Old 26th February 2016, 04:41 PM   #8
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Quote:
Quote:
Originally Posted by JonSnell Electronic
From memory, some years ago as a Pioneer main repair agent, the SA-83 is similar.
Pioneer SM-83 Manual - Stereo Integrated Amplifier - HiFi Engine
Hope that helps but is is a very simple amplifier. 6L6 or EL34 will draw too much heater current.
thanks, the unit that i have is a tad more powerful but the topology could be the same...
Remember what I said about the same small signal circuitry being used with "12" W. tubes and the 7591 family. Adjust the B+ rail of the SM-83 and you're looking at the SA-81. Compare Sherwood's S5000 and S5000 II.

I agree with the step up autotransformer idea. However, if a suitable model will fit, a low cost AnTek toroid power trafo could be a reasonable alternative.
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Old 26th February 2016, 06:06 PM   #9
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You mean step down transformer....... I would use a variac but that's just me.....
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Old 26th February 2016, 07:08 PM   #10
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Hi lexx21,
Quote:
Pioneer SA-81 for conversion to 230v mains and restoration, uses the 7868 tube, contemplating on using the 6L6GC tubes instead...
That's post #1.

-Chris
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