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Here is a photo of the underside of my rehabilitated 30-A mono amplifier after recapping, etc


This and the FM-50 mono FM tuner will power a 1950s cabinet for which I've built custom crossovers, etc




Some vintage NOS GE EL84 tubes provide the amplification, with vintage 12ax7 and rectifier tubes.



Is it ok to discuss "reforming" & or replacing caps on this topic ? 


For sure ! While I know what "caps" (capacitors) are, how to do anything with them is beyond me. I noticed my amp *sizzling* a little from time to time. Is that something with the caps or was that this rectifier going bad?


A couple more questions on the rectifier, if you please:


  1)  If I press it really hard or rock it toward one side it come on. It looks to have a "retainer,  but the tube won't stay plugged in. Is this just a connectivity problem with the chassis?


  2) I've heard that these amps should not just be left on, but I'm guilty of that more lately without using the "standby."  Has this contributed to my rectifier problem?





Reforming capacitors refers to electrolytic capacitors that have "dried out" due to lack of use, say sitting unpowered for a decade or three.   In some cases one may be able to reform the electrolytic paste by slowing introducing current and slowly raising the voltage versus just plugging the equipment into full 110V/220V AC main current which in a worst case can expose you to an electrical shock hazard or minor explosion/fire if the capacitor fails dramatically.


To reform the capacitors one uses a variac, which is a big variable resistor like one may have used in high school or college physics lab.  You plug the variac into the main, then the tube equipment into the variac, then over hours or days you slowly increase the voltage.  This may restore the electrolytic capacitors to spec, but honestly this is really only useful if one wants to the keep the equipment in some museum original state or just for some initial testing before a complete rebuild.  For safety and reliability, the electrolytic capacitors throughout most electronics should be checked and considered for replacement after 20-30 years, especially if they have sat unused for a decade.


The good news is that with the resurgence of hobby interest in restoring old audio gear, there is a lot of information available online for the DIY amateur and parts too.  For a long time the main electrolytic filter capacitors (the ones in the shiny cans) were unavailable as the original manufacturers stopped making them in the 1980s when solid state finally killed most tube equipment in the consumer space.  But in the 2000s these and other tube specific parts have begun to be made again.


I remember in the 1980s having to give away boxes of tubes to a TV repair guy, versus throwing them out.  My grandfather had repaired TVs and radios as a side job, and we had tons of old tubes.  The TV repair guy said he wouldn't buy them from us as he had a whole room full of old tubes, and no one wanted them, but he'd take them if we wanted to get rid of them.  



Regarding your questions:


1)  That does sound like you have a connectivity problem with the chassis, not the tube.  It is possible that you have a broken/cracked pin on the tube, but I suspect you have a loose socket or other intermittent electrical connection.  It's likely that the socket just needs to be replaced.  To be honest, you might consider taking it to someone.  I bet they can diagnose and replace a socket for a lot less than your time & worry are worth in this case.  As far as how the tube is secured, I don't know about this amplifier but some tube amplifiers with inverted (hanging) tubes do have a little metal hook, spring or ring to secure the tube from vibrating out.



2)  Actually it's good to leave most amplifiers, whether tube or SS, in an "idle" state so that some electrical current is trickling through the power supply; see the comments about electrolytic capacitors.  Some higher end SS equipment do this by default and will often indicate it with a "standby" LED, and many tube amplifiers will have a "standby" switch that keeps the tubes and power supply warmed up and ready to go.  But if you play your amplifier regularly, every month or so, I don't know that it is helpful to keep it in a standby mode and you are exercising it enough to keep it healthy.


Keep in mind that with most tube amplifiers it can be destructive to the output transformers to run the amplifier without a speaker connected.  For an integrated/combo guitar amp with a speaker built-in, this isn't an issue.  For standalone heads it can be.   The amplifier won't "fry" instantly, so I don't mean to frighten anyone, but it's best just to avoid it entirely by keeping a circuit closed on the output side by having a speaker attached and giving the induced current somewhere to go.

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We have been discussing cap reforming at work for about 6 mos. (at first  I thought this was a bunch of ____) . If a Freq ( Variable Frequency Drive )drive sits for more than 3 mos. , this procedure needs to be performed or you can have LOUD firecrackers in the Freq Drive . If you have ever seen a exploded cap it is ugly . I'm not sure what types , style or size this is limited to .   

Google or YouTube this procedure for more info .   

p.s. you can check them w/a meter and they can test good but when you put them in service , POW !

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We have been discussing cap reforming at work for about 6 mos. (at first  I thought this was a bunch of ____) . If a Freq ( Variable Frequency Drive )drive sits for more than 3 mos. , this procedure needs to be performed or you can have LOUD firecrackers in the Freq Drive . If you have ever seen a exploded cap it is ugly . I'm not sure what types , style or size this is limited to .   

Google or YouTube this procedure for more info .   

p.s. you can check them w/a meter and they can test good but when you put them in service , POW !



...which is why I don't even bother anymore.


The old can multi-capacitor electrolytics in the power supply filter circuit are what we're primarily talking about, and there was a time where one really only had two options to replace them:


1)  Find a NOS can capacitor, but those are almost certainly "dried out" too

2)  Replace the can with a board and individual capacitors, or gut the can and pack it with individual capacitors.


Option 2 is still very popular to retain the vintage look and use discrete individual high quality capacitors.  


But one can also now buy reproduction can multi-capacitors that are made on the same tooling as the originals.


So to me there really isn't much point in trying to reform these old capacitors, and as you mention that are more likely than not to "pop" later even so.


And for the other smaller electrolytic caps throughout a chassis, some/many might be candidates for non-electrolytics as a replacement, and even if you have to keep some electrolytic capacitors (usually due to rating, electrolytics can handle much more power) there are lots on the market of very high quality like Panasonic and Silmic.




Oh, and on the topic of popping electrolytic capacitors, many (I'd venture to say MOST) failures in cheapo electronics these days such as in computers and LCD TVs are due to very cheap electrolytic capacitors leaking(popping).


If one is handy with a soldering iron, you can probably fix these for a few dollars with better quality capacitors (105C rated is best) that will likely never leak again.


Here are photos and descriptions of a popped and leaking junk capacitors:  http://www.capacitorlab.com/visible-failures/

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  • 9 months later...

It seems that I am just beginning to scratch the surface of the deep shit that you guys are into!

’68 drip edge Fender Twin Reverb here. I love twins, be it motorcycles, guitar amps, or ladies. I played this amp along with a Magnatone M15 for years with a ‘65 Emmons D-10 pedal steel in local bar bands, until I got too busy with my business and had to sell off a bunch of gear to raise cash for the biz. I still have the ‘68 Twin and my homemade Strat. Now I mostly do saxophone yoga (anyone into tenor sax?), but break out the Strat and the Twin when I feel the call to play blues real loud so I can hear the texture of the tubes. I feel what someone said earlier about Guzzis and old tube gear having soul and demanding attention but returning love....something like that. I’m analog all the way. Except for on-line forums and email I write with an Olympia manual typewriter and a few nice ink pens. I have a tenuous relationship with my phone and see it going onto a skeet trap soon. 

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11 hours ago, Kane said:

Yes, a little old lady from Pasadena.

Not quite, but it would have been interesting to have come of age in the late ‘50’s / early ‘60’s.

An old Chinese curse is "May you live in interesting times."  I've done that in the 60s, now doing it again. :angry2:

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  • 1 month later...

My recent mistress at "The Memphis Room" I am fortunate to be invited to sit in . . .


What a rich, sultry sound she has! :wub:

(Don't tell my Fender Bassman at home . . .) :huh:

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  • 1 year later...
On 10/15/2015 at 12:50 AM, Trevini said:

Now we're talking! 


Here are some of my efforts...


Trevinitone TT15. This is my main gigging and recording amp




Prototype build pics.  It's a tight fit in the chassis, but sounds superb.




Another Trevinitone...This one is the TT18




Internal shot...



I am trying to find a way to restore @Trevini's images of his amazing work . . .

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I just inherited my late uncle's 1965 Fender Pro Reverb and Gibson Melody Maker.  They are both 100% original and unmolested, he had both since he had been a teenager, and my father bought the amplifier (and other equipment) as the manager for the band.


I really haven't gotten around to doing anything with them yet other than to purchase a nice cover for the amplifier to protect it from pets and kids.


I still have a few Fisher and RCA tube amplifiers and console stereos around, and a really nice 1971 Fisher solid state console that I'm slowly renovating.

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  • 3 months later...

Just sharing a couple pics of my recent audio projects

Original Large Advents fully recapped, refoamed, reupholstered, and rebadged.  In here you can see the Marantz 2270 which is currently on my bench for a full restoration.



Heathkit W5-M monoblock amps fully recapped and restored.  Before pic. 



The after pic of the W5-Ms with my Bozak 302a Urbans, which also have been fully recapped and upgraded crossover


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