Fisher Console Pulls Finished

FlaCharlie

Super Member
Finished restoring the Fisher 100T Pre/Tuner and the SA-16 amp. These were pulled from a console that I found on CL several years ago. Here are a few before and after pics.

As you can see the SA-16 had two dead output tubes that had to be removed in pieces. One was caused by a leaky coupling cap. Not sure what happened to the other. Unfortunately, most of the tubes were long past being useful. You can also see that the resistors in the heater circuit had gotten a little . . . uh . . . toasty. I'm guessing that the failed output tubes might have shorted their heaters and burned them up.

I decided to replace only the first PS cap since it deals with most all the current. I went with a 35uF Panasonic 500v poly. The other sections measured fine with ESR that was just as low as the new caps I would have used to replace them. So I decided to just leave them in, for now anyway. Replaced the .022 ceramic coupling caps with some nice .033 PIOs. I added a CL-80 thermistor and replaced the 100 ohm 10w PS resistor with a 150 ohm 20w to bring down the B+ a bit. The voltages before this were actually very close to those on the schematics but at those voltages the output tubes were being run at more than their 12 watt dissipation spec. Now they're just under the spec. Added some 10 ohm resistors to the cathodes and was able to identify four matched quads of NOS outputs.

The 100T was in better shape. Mostly I just made some changes to bring the voltages down to spec and replaced all the lytics. A few tubes were replaced. Despite not having the knowledge or equipment to align tuners, the FM sounds great and I didn't notice any problems when I A-Bed the new tubes with the old ones. I don't listen to radio much anyway. It's mono, of course, since it isn't equipped with the multiplex. I have a Sherwood S-3000 mono tuner too so I'm used to mono. The phono section sounds really nice too, although I don't have much recent experience with vinyl either.

 
nice, how did you clean the chassis?

With lots of patience. Fortunately, it was mostly just a thick coating of dust on these pieces.

I use a mix of 1 part rubbing alcohol and 3 parts water which is sprayed on pieces of paper towel to get most of it off. Once the larger areas are done I go over it all again using the same mixture applied with lots of Q-Tips which allows access to tight spots. Sometimes there will also be some yellowish oxidation too. I believe this is cadmium, which is toxic, so be sure not to inhale it. If I encounter that, and there was some on this piece, I use Arm & Hammer with Oxy spray bathroom cleaner applied with paper towels and Q-Tips. Then I go over it again with the alcohol mix. Sometimes I'll also use straight 91% rubbing alcohol in some spots too. The bathroom cleaner also works well on RCA connectors and tube sockets - followed by either the 91% alcohol or a spray of contact cleaner. I think I also used a wire brush on the tube shields.

These cleaned up real nice.

I've been working on another Fisher, a 440A amp, the past few days. Unfortunately, it's a bit of an ugly duckling. Lots of corrosion on the top of the chassis. I may try some Never Dull on it but I don't expect it will help too much. Funky doesn't really bother me that much if it sounds good.
 
Looks good.

Not sure if those resistors are tied into a bias circuit, but I know Fisher did sometimes use tubes as cathode resistors on their 7189 amps, and it had some resistors to feed some positive voltage back into the grid. A roasted tube and/or coupling cap would dump too much voltage in there, which could certainly make them go toasty.
 
Looks good.

Not sure if those resistors are tied into a bias circuit, but I know Fisher did sometimes use tubes as cathode resistors on their 7189 amps, and it had some resistors to feed some positive voltage back into the grid. A roasted tube and/or coupling cap would dump too much voltage in there, which could certainly make them go toasty.

The SA-16 has a single cathode resistor for all the output tubes. The burned resistors were in the filament supply. They create an artificial center tap for the heater winding and serve as a kind of non-adjustable hum pot, I guess. I'm not sure why they burned up. I've speculated that when the output tubes died it may have created a short in the heater circuit.

One of the dead output tubes was due to a leaky coupling cap. That surprised me because they were ceramic caps and I was under the impression that they rarely go bad. Not sure what happened to the other output tube, maybe it was just drawing so much current that it "blew up real good".

The Fisher 440A amp that I'm working on now (almost done) does use voltage from tubes in the separate pre/tuner section to bias the output tubes. Since I'm rebuilding it as a stand-alone amp I added a 270 ohm 20w cathode resistor in place of the original bias scheme.
 
heater-cathode short could certainly torch one of those.

If its a common cathode resistor, having one dead tube in the mix can cause the others to try and carry the load, which eventually kills them. Ceramics can go bad as you found, its just a lot less common than other types.
 
Very nice 100T and SA-16. They are an exceptional combo :music:

Must be common for damaged or broken output tubes in these. I bought a SA-16 recently and these 4 Telefunken output tubes were included...

After a recap it's working well and it is surprisingly a very nice sounding amplifier.

sa16 tubes.jpg
 
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Vendo; I find in all my amps that use 6bq5 types, the tubes are top heavy and the tubes move around excessively. In my TA-600, I installed tube retainers, and didnt have any more problems. So any amp i have with 6BQ5 type tubes get retainers. Since then I have had no Leaning Towers of Fisher, expanding sockets, or tubes with boken bottoms. The retainers hold the tube tightly in the socket.

https://www.tubesandmore.com/products/retainer-el84-tubes

el-84 retainer.jpg
 
Vendo; I find in all my amps that use 6bq5 types, the tubes are top heavy and the tubes move around excessively. In my TA-600, I installed tube retainers, and didnt have any more problems. So any amp i have with 6BQ5 type tubes get retainers. Since then I have had no Leaning Towers of Fisher, expanding sockets, or tubes with boken bottoms. The retainers hold the tube tightly in the socket.
https://www.tubesandmore.com/products/retainer-el84-tubes

View attachment 809465


Great solution Larry!

I'll order a handful of them. I constantly find 6BQ5's leaning in amplifiers.

What do you use to attach the retainers to the chassis?
 
Vendo; I find in all my amps that use 6bq5 types, the tubes are top heavy and the tubes move around excessively. In my TA-600, I installed tube retainers, and didnt have any more problems. So any amp i have with 6BQ5 type tubes get retainers. Since then I have had no Leaning Towers of Fisher, expanding sockets, or tubes with boken bottoms. The retainers hold the tube tightly in the socket.
https://www.tubesandmore.com/products/retainer-el84-tubes
https://www.tubesandmore.com/products/retainer-el84-tubes

View attachment 809465

In my SA-16 the tubes were in the sockets quite snugly. I had to pry the bases out. I think the heat, or the combination of factors that caused their death, caused the tubes to crack. The two that were broken on mine looked exactly like those pictured. Unfortunately, the two that survived intact were extremely weak, as were the 12AX7s. The rectifiers were still usable.
 
Drill out the rivetsfor the sockets, and install over the socket, and connect it to the chassis with 4-40 x3/8 machine screws. I get them in the little packs at Home Depot or Lowes.
 
In my SA-16 the tubes were in the sockets quite snugly. I had to pry the bases out. I think the heat, or the combination of factors that caused their death, caused the tubes to crack. The two that were broken on mine looked exactly like those pictured. Unfortunately, the two that survived intact were extremely weak, as were the 12AX7s. The rectifiers were still usable.
Yes, these 4 were cracked at the base and I had to pry them out. Other tubes were weak as well. These consoles got a lot of use!
 
Drill out the rivetsfor the sockets, and install over the socket, and connect it to the chassis with 4-40 x3/8 machine screws. I get them in the little packs at Home Depot or Lowes.

Thanks Larry. I've seen the retainers used in several 6BQ5 and 6973 amplifiers and have wondered why they were used when the tubes were vertical.
 
The Custom Electra's from 65/66 hung their amps on their sides. The 6HU8 tubes would sag and lose contact. same for the 6BQ5's, so any amp / radio I get with 6BQ5 types get the retainers while in overhaul.
 
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