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...
i am chasing down schematics, pm me please if you have, that will make my work much easier...
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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.
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.
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
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
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...
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...
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.
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...
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
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
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.
i can do the conversion myself, in my case since i make my own traffos myself, this is not a problem.....and external step down will not guarantee murphy staying out....😉
Hi AJT,
Did you rewind the primaries on that? Did you dip it, and if so, what did you dip it in?
You went way further than I would. I haven't any experience rewinding transformers at all.
-Chris
Did you rewind the primaries on that? Did you dip it, and if so, what did you dip it in?
You went way further than I would. I haven't any experience rewinding transformers at all.
-Chris
yes i did, i dipped it in a tub full of air drying clear polyurethane varnish...
figuring out the primary turns was easy, count the 6.3 volt winding turns and
you can get the required number of turns pro the new primary..
i waited more than two months for the varnish to fully dry up....
testing this amp, it had a power draw of around 45 watts without B+....
with the B+ on., and the output tubes all warmed up, power draw is about doubled...
with the B+ on., and the output tubes all warmed up, power draw is about doubled...
thanks Chris, there is another SA-81 on deck, but this time, the power traffo
is already 230 volts....
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