Cap designations for Hayseed caps are top to bottom. A,B,C,D Note the Square, triangle, 1/2 circle and no marker. These are correct. FISHER marked the schematics wrong for the units that have the power supplies on the right side of the schematic and then moving LEFT. The CAP SECTION of the multiples CLOSEST to the Transformer is marked "D". It should be "A". In this way it will follow the cap.
On the HAYSEED Caps the MARKERS onthe BOTTOM of the cap are NOT up against the terminals, but are partially hidden by the chassis now with the cap installed.
Take off the RED CAP TO 87D. It doesn't belong there. Ground the end of the cap you removed from 87D. Otherwise it's wired correctly.
STOP!
WALK AWAY FROM IT for a few days! You've gotten the "Jumping Bean Syndrome" which is highly prevalent in new audio hobbiest in Southern California, and is working it's way up the coast quickly. IT's like OCD and ADD mixed together, as you concentrate on the current piece of gear but jump all over the chassis chasing problems you caused by not finishing that area(for example you're working on the Phono section, and your ADD flips you to the bias circuit. Then you go chasing stuff back in the phono section when it doesn't work and you have a hell of a time figuring out where you left off.) We've all had it in one form or another but have overcome it for the most part. It's incidient and pops up at the most inoportune times (kind of like a part of the anatomy when we were young.)
Concentrate on the task at hand, and if there is the slightest inclination for asking a question,
STOP, GET ON THE Computer and ASK! DO NOT Work on it until you have an answer that you understand 100%!!! ASK QUESTIONS, ASK QUESTIONS, ASK QUESTIONS! And wait for the answers. Sitting on your hands may sound like a 3rd grade thing to do, it actually teaches you patience. Wait for the answers, while sitting on your hands. Just like your Father and too many Adults probably told you bwhen you were growing up, the only dumb question is the one you DON'T ASK! IT's True! Just look at all the guys sitting in the Unemployment lines because they thought they were too good to ask a stupid sounding question. It may seem like the rehab on the 800c is going slower than molasses in Alaska in the Winter, you'll find that the time goes by faster with you NOT getting ahead of yourself and having to redo the mistakes you made, after not asking the questions that were piling up inside your head. Also if you are not sure of something ASK!!!!! BTDT, got more than a few T-Shirts (although they are faded and thin, with a few holes).
This to be done AFTER EVERYTHING ELSE HAS BEEN FIXED!!!!!
The BIAS CIRCUIT pot is a 10K trimmer, not a volume pot. Different types and tracking. One is linear and the other isn't linear. Big difference. IF you want to go with a single adjustment, get a 10K Bournes trimmer (I'll give you the link to the part to make sure it's the right one for you)
http://www.mouser.com/ProductDetail/Bourns/3386P-1-103LF/?qs=sGAEpiMZZMvygUB3GLcD7rufck0TIBKy52IOA1%2bUkM8=.
You tie together the middle pin with either of the outer pins. Then connect it to the wires from the bias circuit. Pull ONE (1) TUBE. Put your Meter on OHMS and put one probe on the bias wire on the bias caps side of the pot. Then put the other probe to the bias wire at the tube connection and adjust the POT for the HIGHEST OHM (Resistance reading). Take off the meter and reinstall the tube.
TURN THE SETTINGS Knob on the DMM to DCV. Put the BLACK PROBE ON A CLEAN SHINY CHASSIS POINT (alligator clip it to the chassis) and your Red probe on PIN 5 of Each OUTPUT TUBE (Mini Grabber here). Turn on the unit and let it warm up 15 minutes while watching the reading on pin 5 Write down the Readings once they stabilize. They will be really low. Average the readings and pick the tube that is closest to the average. Put your red probe back on that tube and adjust the bias to 310mv. Then re-measure the remaining tubes and write down the results in mv. TURN OFF UNIT, and post measurements.
NOTE: The - voltage on the schematic for -17 was FISHER's ideal for a quad of perfectly matched 7591's. Obviously back then when you went to the drug store and bought 4 output tubes you didn't get a matched quad (plus there was no explanation for either the -17v or matching tubes, so noone knew better. Actually -17v, along with all the other stuff FISHER did to these units, in the all consuming race to better everyone else in Watts, was too much close to ZERO (0) volts in that th tubes were actually being overdriven past their maximum ratings. So a way had to be developed to measure the tubes and get consistent readings. The cathode load voltage readings are easy to read and convert to milliamps (move the decimal 1 place, using a 10ohm resistor). You can then calculate the percentage of max dissipation of the tube with basic 2nd grade math (back in my day it was 3rd or 4th grade math depending on whether you went to Catholic Schools or public schools). The 7591 tube has a maximum dissipation of 19W. You want to ideally set them to between 70% to 80% of maximum dissipation. We'll get into the math in a future post. This will cool down the tubes somewhat, put them into an ideal operating state, and even tho the total wattage of the unit is less by a few watts, the distortion levels are a bit better also.
The single adjuster is really used for a tightly matched quad as is the stock configuration. For long term adjustments with either slightly mismatched or wildly mismatched tubes you can build a IBAM or IBBM (Individual Bias Adjustment or Individual BIAS/Balance Modules.) The difference is one adjusts just the bias of the tubes to a set point that is the same. The other Balances a pair to 0.0v between them then biases the pair to the set point. They both get the job done but the IBBM board does it better. They are both interactive between tubes so you are constantly adjusting one then the other 3 (or 1) so they all match. But once you get them matched it's all good.
If your tubes are the original I highly suggest building either board. They will overcome most inconsistent bias readings in the tubes. If you get a set of new EH's or Tung-Sols, I would still suggest either board to get and keep them tightly balanced.
Larry