Questions about cap job I had done

[Rick1114]

I had a cap job done on my Vibro-champ a few months back. I think the amp sounded much better after a few weeks of break in. I had peek in there today because I want to perform a cap on GA5 (a similar amp), and wanted to see what components this tech chose.

Anyway, I noticed the filter caps were three 47uf caps soldered inside the chasis (he unhooked the can). Does this sound right? I thought it was supposed to be 22uf. I couldn't tell the brand, they were black with a letter "u" and a circle around it. Anyone know what these are?

Also it seems he replaced the 22uf bypass caps with brown nichion radial caps.I was a little suprised by this too, and he used mallory 150's to replace the "brown turd" tone caps.

Anyway, the amps sounds great - I was just a little suprised but what he used - I think he's an old time amp tech, but not close enough to where I live to keep using him.

Rick

[stokes]

Although the stock circuit calls for 20uf caps in the entire B+ rail,I would be okay with the 47uf's on the main and screen supplies,but,in my opinion the 47uf is a bit much for the preamp supply.I would suspect he used the values he did because that was what he happened to have on hand,and saved a couple of bucks not having to order the right values.These changes wont "hurt" your amp,they will alter your tone,if that is for the better or worse is up to you.Did you ask him to change the coupling caps?If not,why did he?Unless there was a problem with the coupling or tone caps as you call them,I wouldnt be happy with him changing them.As for the nichion bypass caps,it was probably what he had on hand,but theres no problem using them in that application.

[loudthud]

It's hard to find a tech who makes a living repairing vintage amps that uses vintage correct parts and doesn't charge a fortune. The guy may have used parts he had in stock and knocked out the re-cap job in an hour or so. His experience may have dictated the increase in capacitance. Keep in mind that most of the filter caps that Leo Fender used had a tolerance of -10% +100% so 47uF is not totally unreasonable.

The U in a circle is probably a trademark. Perhaps United-Chem-Conn. You'll have to search the internet for more data. I know a 2 in a circle is Sprague. You sometimes see it on old orange drops.

[Rick1114]

Did you ask him to change the coupling caps?If not,why did he?Unless there was a problem with the coupling or tone caps as you call them,I wouldnt be happy with him changing them.

I didn't ask him to change the coupling caps, but he said something didn't "sound right", so he changed them to Mallory 150's. He said those are referred to as "brown turds". I have all the old caps in a bag but he's clipped most of the leads off them.

Also, I will have to take another look at those filtercaps, I know at least two were 47uf but one I coundn't see - it was the same size as the other two though so I assumed all were 47uf. I may bring that value down on the preamp supply.

ANyway, that's why I want to learn how service my amps - I can put the care into it and won't mind spending like $20 more on decent parts. FWIW - I guess he got the job done a the cheapest cost.

Thanks for your help!

Rick

[Robert M. Martinelli]

I may bring that value down on the preamp supply.

ANyway, that's why I want to learn how service my amps - I can put the care into it and won't mind spending like $20 more on decent parts. FWIW - I guess he got the job done a the cheapest cost.

Thanks for your help!

Rick

Hi Rick,
Increasing the filter caps' value is a rather common practice, it usually does not harm, unless you have a combination of too big a filter connected to a tube rectifier ( in this case the initial current demand peak is rather hard on the rectifier tube ), I would say 47 microfarad is still reasonable, it won't hurt the way your amp sounds, and the DC voltage you get out of the PS section is smoother, with a lower ripple.

As Loudthud wisely noted, keep in mind that tolerances in the early days were extremely large, resistors and coupling capacitors had a 10 to 20 percent tolerance, filter caps ( not critical sound-wise ) even higher.

If you take a look to most guitar amp schematics, you' ll notice that the "better filtered" DC goes to the amp' s input stages ( which are the most sensitive and likely to amplify hum and noise ) while the output stage gets a less filtered DC ( because push pulls are hum-canceling designs, so they don' t need the supply to be filtered that much ). I' m not trying to be anyone' s lawyer but you should also keep in mind that high voltage electrolytic capacitors are rather expensive components, a 47 microfarad cap is surely more expensive than a 22 microfarad ( with the same voltage rating ) so I would not say he did the job at the cheapest cost...

If the amp works properly, then the most important consideration is "do YOU like the way the amp sounds?"

Oh, BTW I think your will to learn how to service tube amps is a fantastic thing, so keep on learning as much as you can, this is what I' m still trying to do, and I have lots of fun in the process.....

Hope this helps

Best regards

Bob

[PRNDL]

I guess he got the job done a the cheapest cost.

I'd rethink your assessment of his work, which may not be accurate.

Mallory 150's are excellent quality caps preferred by many tube amp builders. (Some may prefer orange drops).

Electrolytics are somewhat controversial as to manufacturer / price / quality / durability. Some believe that no-name cheap caps are just as good, but an experienced tech will know which ones are.

Increasing the electrolytic cap values is more a sign that he used more expensive components, since the price increases dramatically as you increase capacitance.

The real question involves both price and speed of repair.

[Rick1114]

Okay - I'll admit, maybe I was being a bit rough on him because his web-site built up a lot of expectations for me. He did the job for $125, which is cheap for NY, & he needed a few days to get to it. I'm sure he up to his ears in work as he repairs a lot of stuff, but vintage amps is his favorite thing to work on. I wasn't expecting Mallories or F&T, but I wasn't expecting these tiny brown Nichion bypass caps either!

That being said the amp sounds great IMO - that little VC blew my friends away when I played it for them last week. I may upgrade some stuff just as learning experience for myself if I get really bored on day.

Rick

[PRNDL]

He did the job for $125, which is cheap for NY, & he needed a few days to get to it.

That being said the amp sounds great IMO - that little VC blew my friends away when I played it for them last week.

That is an amazing price!!!

Keep his number in your rollodex!!