1965 Fisher 200-T one channel not working

[gui_tarzan]

I got bored and a bit distracted with the guitar amps I was working on so I put them aside for now and dug this out. It has a beautiful sound - out of one channel. When I put it on Mono it obviously works on both sides but the sound quality plummets and I can't stand it. So I put it on the shelf many years ago and it has just sat since. I figured it was time to either fix it to use or sell, so my task is to try to figure out why only one channel works. What I don't understand from the service notes that I pasted into the one pic is how to test the transistor without using a multimeter??? How else would you do it?

The insides look like it's never been touched. I have some 1000/50 caps to replace those two cans, is there a reason they would have used two big cans instead of the smaller axials like you get today? Availability?

I take that back, the bottom circuit board looks like crap around the rectifier. There is either solder flux schmutz or something else in several areas. The filter cap doesn't look like it's leaking but the solder work on those diodes is horrid.

So since the output in mono comes out both sides I can assume the problem is likely in the pre-amp or switch areas, correct? Time to see if the Simpson scope will tell me anything.

[Leo_Gnardo]

I have some 1000/50 caps to replace those two cans, is there a reason they would have used two big cans instead of the smaller axials like you get today? Availability?

Yeh that would explain it . . . smaller axials and even smaller radials are now available. The filter caps, bypasses etc have all shrunk over the decades. AND if you feel daring you might double or even triple values on the initial filter caps. Then as now, "build to a price" was a factor, so barely adequate parts were often chosen. "Gotta keep the price low, there's competition you know!" = song of the accountants.

So since the output in mono comes out both sides I can assume the problem is likely in the pre-amp or switch areas, correct?

I wouldn't ASSUME, but there is a fair chance switch contacts have corroded over the last 57 years. Deoxit is your friend. Apply the smallest squirt you can, and work all the switches & pots back & forth, dozens of times, and you may be able to clear the missing channel problem

FWIW I spent way too much time last October reviving a mid 60's Lafayette receiver. Wound up replacing ALL electrolytic caps. On the preamp, EQ and RF boards maybe one out of ten measured bad on the capacitance meter. Bad as in, lost most of its capacitance. When you have a 10 uF cap that's supposed to pass signal, and it measures 173 pF, you can't expect much signal to come through. (A problem like this could also explain one of your preamp channels not passing signal.) Plenty of way out of tolerance & noisy carbon comp resistors too. Surprisingly NONE of the germanium transistors were defective! Let's hope none of your silicon or germanium transistors have gone bad.

By coincidence your Fisher looks mighty similar like the Laffalot 900T I worked on. (900T had an AM section plus a couple more switches.) Could well be that Fisher was building 'em for Lafayette. I've heard a story that Sansui had a hand in building "house brand" hifi gear, then eventually started selling under their own brand name early 70's.

My advice is to also maintain the power amps. After you replace dodgy old electrolytics and drifted noisy resistors you'll have a much better chance of having your prize continue to sound terrific through upcoming decades.

Fisher was a quality marque back in those days. It may take many hours of PITA component changes but in the end you will have equipment that sounds primo. Looking forward to reading as you do the maintenance and restore your venerable Fisher.

[gui_tarzan]

What brand and where are you getting your caps? I've been looking all weekend at the usual suspects (Mouse, Newark, etc.) and it's been a difficult search for some of them.

[Enzo]

Well, what caps are you having trouble finding? If you are trying to match the old ones, a lot of standard values have changed 50uf would now be 47uf. 75v would now be 83v.

[gui_tarzan]

I was trying to find close to the original values (470 vs 500, 220 vs 200, etc.) at a step or two higher voltage and temp rating but not the low-end cheapies. This will likely be with me for the duration and be passed down to my son after so I want it to be as top-notch as it can be without breaking the bank.

[Jazz P Bass]

A little advise.
If the caps are doing there job (filetering the Vdc) with minimum Vac across them, fix the amp first.
After verifying that the supplies work, I would test the output transistor base voltages to see if they the circuit is trying to work.

[Leo_Gnardo]

What brand and where are you getting your caps? I've been looking all weekend at the usual suspects (Mouse, Newark, etc.) and it's been a difficult search for some of them.

Smaller ones I got from Antique/Tubesandmore.com, larger filter caps from Mouser. Just generic parts, no fancy schmantzy booteek "name brands." As Enzo states, don't sweat about exact values, "close enough for rock n roll" will do fine here. But in that Laffalot, so many were leaky I didn't want to take a chance on misbiasing now rare & expensive germanium transistors, so I shotgunned almost the whole thing. I know that's not popular with our professional highly experienced techs & I'm not much in favor of it either, but the sound quality when completed was vastly better than when I started so that sorta justified the effort.

One more thing real quick, the Laffer's power supply was around 49V, single ended. I reckoned the 50V rated main filter cap in there was marginal and lucky to survive 55+ years so replaced with a higher voltage rated part.

[gui_tarzan]

I have trouble buying into the "this cap sounds better than that cap on the 500-1500hz range" audiophile stuff too, but I also know from experience that some brands are more reliable than others, those are what I want to use. My son is a rigging tech and sometimes monitor tech for Eighth Day/Clair Sound. His ear is trained moreso than mine and he can tell the difference in sound quality that I used to be able to before my eardrums ruptured. Tinnitus prevents me from hearing the crystal-clear highs but I also have to take into consideration that this is a hi-fi, not a guitar amp. It's expected to sound better.

What mystifies me more than the hype is how the way a cap is made can actually alter the sound quality. If you think about it from a financial aspect, why would a manufacturer have several different variations of the same cap - and - tell you what the audio differences are if it wasn't partially true? Having multiple lines is expensive. When I read the descriptions on the Nichicon and Panasonic data sheets, they point out many differences and applications for their products. Is it all hype? I'm not so sure.

[gui_tarzan]

Initial voltage readings are pretty close to the manual. In the past I removed all the socketed transistors and cleaned the sockets with Deoxit. I also cleaned and put new grease on the power transistors and put the mica back in each.

I did some more testing today using FM radio on a local station. I'll try an aux source tomorrow. Zero output from the right channel. Super-cleaned and tested the switch, no issues there. so it's between the switch and the power transistors. I'm going to order all the electrolytics anyway because they are fifty-seven years old and they're cheap enough to replace. I did end up finding most of them in Nichicon from Mouser. Still looking for a few with higher voltage rating than stock just to be safe. I'll find them, I've still got more testing to do before I start replacing them anyway.

[Leo_Gnardo]

What mystifies me more than the hype is how the way a cap is made can actually alter the sound quality. If you think about it from a financial aspect, why would a manufacturer have several different variations of the same cap - and - tell you what the audio differences are if it wasn't partially true? Having multiple lines is expensive. When I read the descriptions on the Nichicon and Panasonic data sheets, they point out many differences and applications for their products. Is it all hype? I'm not so sure.

Geeze if Stan was still here he'd give you a lecture on how it's impossible for one cap to sound different from another. And maybe Juan will step up to the plate for some of the same. I don't quite believe this is so OTOH I haven't really heard much difference unless a properly working cap was replacing one that was defective. Those who wish to "roll" caps, expensive ones too with metal foils made of aluminum copper silver even gold, dielectrics made of various materials including teflon - well that's a game way beyond my pockets, and also brings the old "emperor's new clothes" story into focus. "If I spent more, and imported the caps from some exotic country (often Russia) well then they MUST be better." Pete's sake let's stick with what works and is affordable.

Another thing to remember, audio is a very small portion of the uses to which capacitors can be put. And companies that make them don't much pay attention to the few that are sold for audio purposes, EXCEPT those who make caps aimed at audiophile use. For those last I have a feeling it's the marketing department that directs the company's attention, with half-qualified "engineers" that learned to cook the data to fit the theory way back in high school and college labs. Must admit though, I haven't perused NIchi nor Pana data sheets however I doubt they would bother to tout things like "sounds better in the some audio range" that's the stuff of snake oil dealers. FWIW for film caps I've been very satisfied with Mallory 150, and more recently Panasonic polypro and polyester (mylar) dielectric caps at rock bottom prices. They're cheap - therefore must suck - well some believe that and let 'em spend themselves silly on exotic hype, that's not our place to go.

Clair - I had the pleasure of working alongside Clair techs & mixers on tour 1981-2005. Good for your son, I expect he's on cloud nine working with a great company making excellent gear and using it to the max.

Now I'm in danger of spending more time typing when I should be fixing gear so I'll leave you to attend to your venerable Fisher and hope your son will love it too when you have it working up to snuff.

[gui_tarzan]

Peruse this site when you get a few minutes.

https://www.nichiconcapacitors.com/

[gui_tarzan]

I've been very satisfied with Mallory 150

I've been using those for years along with some Mojotones and I've never had a complaint from a customer.

Clair - I had the pleasure of working alongside Clair techs & mixers on tour 1981-2005. Good for your son, I expect he's on cloud nine working with a great company making excellent gear and using it to the max.

He's on tour right now with "New Kids on the Block" and has worked directly with Donny Wahlberg daily, as well as hanging out with Rick Astley who he says is a really cool guy. Unfortunately he tested positive for covid today so he's sequestered to his hotel room for the next five days. He said his symptoms are mild, he sounds like he just has a cold so hopefully it will go away soon.

[g1]

Peruse this site when you get a few minutes.

https://www.nichiconcapacitors.com/

OMG.
KZ series - "Ideally suited for first class audio equipment where qualitative and quantitative comfortableness is required."
Ok, well I'm not sure I'm ready for both kinds of comfortableness just yet.

[Enzo]

I am sitting here naked with a stiff drink watching election returns. That is my idea of comfortableness

[The Dude]

......I'm not sure I'm ready for both kinds of comfortableness just yet.

Both kinds of comfortableness are only for those who can afford first class audio equipment

I've always thought all this capacitor hype was snake oil. I've heard (paraphrasing), "I replaced all the caps in my amp with Orange Drops, and you can really hear the difference". IMO, two things come into play that have nothing to do with capacitor type or brand. The first is a need to justify the money spent. The second is that often the caps replaced were bad or at least no longer up to spec, so of course new caps will sound better (or at least different) regardless of type or brand. Current scientific knowledge says that electrons do not have a brain, so how could they possibly know what brand of capacitor they are passing through or whether they should stop for lunch on the way. 1uF = 1uF.