fisher 800-b ...tubes/tricks/mods

sansuigirl

Active Member
hi guys

does anyone want to list THEIR input on all the modifications that they would perform on an 800b....if they were going for the best of the best - and i mean ALL the modifications and things to replace and add to it ... all that stuff.

the one i read and dont see always suggested isthe electronic thing that slowly puts power to the machine - so it doesnt get a burst of energy when powering it on - but i want all of you r input information - compile it - and make a master-list...and i am going to have it all done...by whom? not sure yet - you can give references for that too.

but lets talk tubes for a moment - should i just test the tubes and use the ones that test OK? or if you had bottomless pockets - tell me what tubes i should use instead of whats in there right now - maybe you could give me a choice #1 or #2 or #3 according to price/sound/availability. i do not have bottomless pockets - but i want this thing in a techs hands once...and with luck...never again.

so build me your "dream machine" and i will see how much or to what degree i can do to the thing. this is for a gift for my husband - but i dont feel its going to make it by Christmas - but our anniversary is valentines day - maybe i can have it worked out by then.:smsex:

here is another post i started - you guys have been a ton of help so far - Fisher Fans Unite!

http://www.audiokarma.org/forums/showthread.php?t=328775

kisses:smlove:
sansuigirl
 
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Other than the output tubes and the 1st IF tube (usually a 6BA6 or 6AU6) the tubes on an 800b are exercised fairly lightly. TEST ALL THE TUBES FIRST. Replace any that are WEAK or Bad. Sometimes even a weak tube will perform in a non stressful slot. If the tubes in it are Marked FISHER, more than likely all the small tubes are Telefunken, Mullards, and the outputs are Westinghouse. If so then you've got it all. If not then don't fret, put good tubes in and enjoy. Unless you really know what the voicing is on each brand tube, it's a Cluster #*$# trying to figure out whats best. There are as many answers as there are tubes.

Matching Output tubes put less of a strain on the output transformers and the rest of the circuit. So these should match. Jim McShane is one of the best for matching tubes. And he's got most all of the tubes for it. But in any event keep the old tubes.

Replace the selenium rectifier 1st. Bring the bias Circuit into spec voltage wise. Then work on the Power supply sections, with emphasis on the Heater filaments for the 12AX7's.

Replace ALL Electrolytics.

Replace coupling caps. ALL 600-630V caps.

Replace any ceramic disc caps in the signal path with poly's.

Jim McShane can probably make a cap kit for it. It will include most everything above. And the parts are VERY GOOD. He'll even make recommendations for circuit mods if needed or requested.

Strip the chassis and have it reconditioned(cadmium or chrome) with all new silkscreening. (You asked for a dream machine!!!!).

Send it to Punker X for an RF/IF Alignment unless your tech can do them.



Larry
 
Congrats on your 800-B!

As far as recommendations for doing a thorough restoration, there are things that are done pretty much as standard, and then there are things that are more a matter of opinion or personal desires. If you take it to a good, experienced tech, he should already know all of these recommendations. Here's my take on what really should be done if you want a solid, reliable unit.

1. The unit should be cleaned of all dust, debris, and any layers of oily film on the chassis that might be present.

2. All of the switches, controls, and tube sockets should be cleaned with a good contact cleaner, and potentiometers lubricated with something like DeOxit Faderlube.

3. All of the tubes should be checked on a tube tester known to be in good working order. Weak tubes should be replaced. If any of the output tubes need to be replaced, ideally all four should be replaced with a matched set.

4. The selenium rectifier should be replaced. The bias supply capacitors should be replaced. The coupling capacitors should be replaced. The bias should be adjusted to approximately -20 to -22 volts by replacing resistor r-132 with a 2.7k. Install 10 ohm 1/4w 1% resistors on pin 5 of the output tubes to make it easy to measure the current.

5. The 330k resistors should be replaced with 220k.

6. There is no general consensus on replacing any ceramic disk capacitors. My personal recommendation is to leave them alone.

7. Replace all small electryolytics.

8. There is no general consensus on replacing the power supply filter capacitors. Many experienced techs recommend that if there is no audible hum, and the filter capacitors are not warm to the touch, there is no need to replace them. If you wish to have them replaced as a safety factor, that is perfectly ok.

9. If you wish to have a showpiece, then you certainly could strip the chassis, have it replated and re-silkscreened. The disassembly, replating, re-silkscreening, reassembly, and rewiring would undoubtedly cost you at least $1,000 and would only be cosmetic. I know Larry wasn't really serious!:D

10. If you like to listen to FM, then a realignment is a must, especially if you replaced any tubes in the tuner section.

There are literally dozens of great threads on restoring Fisher tube receivers, posted by several very knowledgeable AK members. If you do some searching, or have the tech you choose do some searching, you'll find plenty of reading. Just for an example, here are a pair of fairly recent threads on the restoration of a 500C. While not exactly the same as an 800B, the basic concepts are identical. They also include some additional modifications that, while nice to do, are not necessary and may add some complexity.

http://www.audiokarma.org/forums/showthread.php?t=288198
http://audiokarma.org/forums/showthread.php?p=3543025#post3543025

Have fun!
 
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