Shotgun Re-cap jobs... should we?

[hermitcrab]

When i watch others on YT work on equipment , most will scoff at the idea of shotgun re-capping .... I generally have been in that boat as well, if it ain't broke don't fix it .... until the last couple weeks ... equipment I have worked on before will all of a sudden just stop working , My fisher stopped working and it turned out to be the coupling caps to the speakers died... last year they checked out just fine...a Sony R2R that I completely re-capped a few months ago started acting up with noise in one channel... it turned out to be a leaky transistor ..., the imperial magnavox played all day a few days ago ... today I turn it on to nothing not a sound out of any function ... Now I am in the boat of recap it all ... shango said it, replacing a few components with new parts just causes a cascade of failures on down the line stressing out older components ... may not be true on tube equipment , but solid state that is now 50 - 60 years old is sure seems to be the way to go , otherwise pulling out a chassis over and over again gets real old ...
what do you all think?

[electra225]

I will admit I shotgun caps. I even shotgun them in a TV chassis. I typically replace the power supply caps, then establish a baseline of performance. This way, if I have an issue after recapping, I'll know if it's a new issue or if it existed before restoration. About the only issues I've had after recapping is function switches and tube sockets. I don't work with solid state equipment much, but, with their myriad of electrolytic caps, I'd think recapping, shotgunning, whatever you want to call it, would be more important than even in the tube stuff. I tried replacing a caps one at a time, then checking performance. I found that boring and harder to concentrate on where I was. I replace the caps that are hardest to access first, if that makes any difference.

BTW, just for context, I have a 1928 Temple model 890 that is running its original filter caps. And they all still check perfectly good. They are in a tar-filled block and I reckon that moisture doesn't affect them. This radio has the primary of the power transformer and B+ both fused from the factory.

You mentioned watching online videos so this comment should be on-topic. I basically watch three YouTubers who work on electronics. Shango, bandersenTV and Uncle Doug. They each have a different approach to troubleshooting and repair. Shango is most opposed to recapping, but he does resurrection videos. He digs an old set out of a mine shaft has been under water for 40 years then gets it running. "Make working" and "make picture" are his forte'. He makes no effort in making something clean or like new. Bandersentv gets a set running, but he also fully restores it to like new condition. Uncle Doug concentrates primarily on guitar amps, but his technical explanations are helpful in understanding the different circuits in an audio amp. You have to consider what their end goal is before you can figure out what their opinion on recapping would be.

My belief is that one has to establish their own routine when it comes to restoration. You know how deep you want to get. We are running this stuff from 60 to 90 years past anything they were designed for. Like putting our old cars in the Indy 500. I expect my stuff to hiccup occasionally for that reason alone. It's old. But I also expect to do my best in giving it the best chance for long-term survival.

[19&41]

I see this subject brought up regularly in various forums. Most of the consideration of whether or not to replace seems to revolve around the Q factor of the capacitors. I collect many different types of antique items, among which are old documents. I don't know if you have ever handled newspaper of 60 to over 100 years old. It becomes brittle and can crackle and disintegrate easily. it's not too much different from the paper used in dry filter capacitors. One critical aspect of their function is their dielectric strength, that can fail as easily as having a fissure form in the paper separating the metal strips. One spark within the capacitor can cause a catastrophic failure of the assembly. I replace all caps of dry paper and electrolytics for safety's sake, though electrolytics will slowly fail to filter AC hum before breakdown.

[TC Chris]

Replace 'em. When I, and my old equipment, were much younger and my wallet much thinner, I'd replace as little as possible. Now I can afford caps, plus good ones are much cheaper, and the equipment is that much older. Bad caps can take out much more expensive or rare components--IF transformers, coils, etc. Replacements are cheap insurance and result in reliable completed restorations. If you object to the looks, restuff the old caps. I did that on one visible paper cap on my old GE phono this winter.

Chris Campbell

[19&41]

With the newer electrolytic capacitors being of smaller size, I can usually find room under the chassis to place them. I just disconnect the multi section caps and leave them in place.

[Motorola minion]

Depends on brand many times. I go for an original look on top, most repairs are under the chassis.

Motorola and Admiral used few paper caps compared to ceramic disc and usually Mallory electrolytics which can reform. I can usually improve bass response by adding an additional 47 uf @450V at the OPT center tap.

Magnavox and Zenith used Mallory (code 240) as well, but no paper cap will be left in if I work on it, and I usually replace all electrolytics. Magnavox rolled their own sometimes (code 232)
RCA and Philco used lousy paper caps that can never stay in. The electros are usually bad too.
German radios have really awful paper caps but electrolytics are rarely bad.

I will shotgun all caps in anything like a 50+ YO TV, multi-section caps with bad common grounds WILL feed some bad ju-ju to another stage (there are endless failure modes here) such as a horizontal pulse into the video section...you spend more time troubleshooting than replacing electrolytics. I have been fooled many times in bench days (at TV shops) when an obscure capacitor failure allows something to pass that it should not.

Always remember that after you replace all these parts, there still may be the "original issue" that caused the set to be retired in the first place.

[electra225]

I have found pre-war Philco caps always bad, power transformer-eating bad. Dead shorted. I don't even plug one in at all unless and until filter caps are replaced. I have had similar experience with GE filter caps, mainly in printed circuit board chassis. Again, I never plug one in until I replace the filter caps. I don't understand the recommendation by the TV restoration community of replacing caps one at a time, then testing. Discharging the high voltage each time would be a hassle in itself. I will shotgun caps until I get burned real good, then I'll probably adjust my thinking accordingly.

Would you be good enough to elaborate on the .47 cap to the center tap? Which center tap, power transformer or audio output transformer? Why would that increase the bass? Have you made that change on a Magnavox amp to advantage?

[William]

I would like to know that too, the how to, and the why. Maybe that would help my bass lacking Motorola portable. Dave did say that it was center tap of the output transformer.

Bill