Courtesy of DREWBOLCE (It's his drawing!);
IBAM (Individual BIAS ADJUSTMENT MODIFICATION) PARTS LIST AND SCHEMATIC. Mainly for the 400-500C-800C. I don't see any reason it won't work with slight modifications for other 7591/7868 based FIXED BIAS units. Matter of fact i modified this for my Sansui 1000A (changed resistor value) and it works just fine. R117-R120 are the Grid resistors that are changed( were originally 330K) for use with primarily the EH and JJ variant's. Make sure the coupling caps are changed to .1uf when the resistors are changed.
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ON THE 400.
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On the 800
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And now we have Dave Gillespies Balance/BIAS board. It's basically a universal variation (my words not his) of what FISHER did in in their higher ended amps/integrated. You balance the pairs with 2 of the pots (one per side), then set the BIAS. You get the BIAS improvements of Drews board, with a null when balancing out the pair (null meaning 0.00v) to equalize the loads. I've used both, and with an UNMATCHED QUAD, Dave's board works better to equalize the tubes. With new matched tubes from McShane, it's 6 of 1, 1/2 dozen the other. In any event BOTH WORK WELL, and I'll leave it up to you as to which one you use.
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The long wires may be an inductance issue. I'd leave them where they are but that's just me.
On the 400's you can replace the 2 terminal strip shown circled with 3 terminal strips, and connect the resistors individually so no flying leads. You can do the same thing on the 500/800's. Might be a tight squeeze, but do-able!
This is a 400. You can do the same thing on a 500/800.
Sometimes a Brick Flies, sometimes it doesn't.
11.) 12v 3A C.T. Transformer to make a bucking transformer. This one is a good performer and you can have 2 different voltages (6V and 12V) on the output side. Model: 273-1511 | Catalog #: 273-1511 12.6V CT 3.0A Chassis-Mount Transformer with Leads
Larry,It lowers today's higher wall voltag that may be higher than what a piece of gear is designed for. Usually used for amps, but tuners, receivers, consoles also benefit. Say your wall voltage is 125vac. ad for example, Your gear says on the back it's designed for 115VAC. The wall voltage is almost 10% higher than spec. In tube gear that means higher voltages in the tubes, and the heaters or filaments are overloaded and will burn out faster, and may cause a H-K short (heater to Cathode) which is very bad.
Click on this link to google which has all audiokarma threads pertaining to Buck/boost transformers. These will answer your questions better than I can.
https://www.google.com/search?q=buck+transformer+:+audiokarma.org&ie=utf-8&oe=utf-8#q=buck+transformer+:+audiokarma.org+site:audiokarma.org