Least invasive cap job for VC?

[Rick1114]

I know some guys just say replace ALL the caps but I feel this amp should stay as original as possible, because the sound is very sweet. First off - all the controls are weak and have a very "watered down" effect. I can't even hear the amp before "3" on the volume. The amp is not noisy at all, but it may sound a bit on thin side - which may or may not be attributed to the speaker (the cone seems paper-thin on the original Jenson, great highs but that's it) - I've already ordered a Weber 8A100 speaker to experiment with.

Regarding the cap job - If I wanted to keep as many original parts as I could, what should be tested/replaced and with what? (I would only want to use parts worthy of a vintage amp)

Here are some pics of the inside so you know what I'm dealing with!





Thanks!

Rick

[Garydean]

Hi Rick,
That thought always runs thru my mind when I acquire a vintage piece. Probably the parts most changed in older tube amps would be the AC line cord, the tubes and the filter caps...the silver can in your case. Fresh tubes or some NOS tubes can do wonders. Changing to a 3 prong cord would make sense for safety reasons and the electrolytic capacitors would be compared to replacing bald tires on a vintage car. You'll get plenty of opinions here and all are valid. How often do you plan on using the amp? Are you gigging with it or are you simply using it for home enjoyment and recording? If it's going to be a steady amp for gigging, I would consider the fact that in today's world, the AC line voltage is a bit higher than when your amp was built. With 122+VAC and more at the wall, the amps original components are going to feel it. There are many old amps being used on a regular basis with no problems and still running strong. I replaced a multi can in an old PA head a few months ago and the amp seemed to come back to life. The interior of your amp looks clean and well taken care of. Keeping it original for investment purposes? is that what you're after? or do you want to replace some parts and adjust some values to change the sound? Anything you take out should be kept in case you want to restore back to original condition. Perhaps fire it up and take some voltage reading to see if your platform is at least on spec and then decide. Will you have this amp long enough to realize a sizable investment gain? Most people wont. I know I haven't answered all your questions directly but perhaps you now have some other ideas to consider before messing with it.

[R.G.]

If you're serious about keeping anything original that can be used, then you need to buy an ESR meter. This is a meter that measures the Equivalent Series Resistance of a capacitor. When an electro starts to go bad, its ESR goes up.

For most electros, ESR starts low, only increases slightly over life, then rises fast at end of life.

This is the ONLY tool that will tell you on the spot whether an electro cap is still good.

However, even with the ESR reading there is no guarantee that it won't start going bad tomorrow with old caps. For longevity, they need to be replaced.

True vintage nuts will insist that you drill out the old housing of the old caps and put the new cap inside the old housing with hot glue. That looks very, very vintage indeed, but gets new caps into the amp.

[Rick1114]

Gary,
I'm going to playing it mostly at home as a practice amp. I'm not a "keep it locked away for re-sale value" kind of guy. I just want to give it a tune up and get it running optimally while retaining as much of its original tone as possible. So I will start with the cap can. Are there any other essential caps that may need replacing (I remember reading that the paper foil caps dry up in these as well?)

Thanks for your help,

Rick

[Rob Mercure]

Unless, due to a weak design, a model amp is known to "fry" a particular part/cap the only parts that are routinely changed - besides the tubes - are the electrolytic filter caps. As part of the composition of these E-caps a paste of aluminum oxide and water is used as the electrolyte. Eventually the water will dry out turning this paste into a resistor which will pass current, get hot and then either spew out the safety relief valve in the end of the cap or ocassionally blow up (confetti mess). Back during the 1950s and early 1960s these parts were designed for a service life of around 15 years - as we all know in reality they vastly exceed their service life but they will fail eventually and it seems that the older they are the more catastrophic they fail (at least IMHO I see more really old electros that have exploded).

As to the VibroChamp the big silver can is the only filter electrolytic cap. But the white cylinders with the blue ink (with a + on one end - sure sigh of an e-cap) connected between the tubes cathodes and ground (get out your tube manual kiddies) are also electrolytic caps - cathode bypass caps - and while they rarely explode as they fail the amp's performance will greately deteriorate as they go down so replace 'em while you're in there.


Rob

[R.G.]

Gary,
I'm going to playing it mostly at home as a practice amp. I'm not a "keep it locked away for re-sale value" kind of guy. I just want to give it a tune up and get it running optimally while retaining as much of its original tone as possible. So I will start with the cap can. Are there any other essential caps that may need replacing (I remember reading that the paper foil caps dry up in these as well?)

If you're not going to use it on stage, so it dying on you at any time is not an issue, you can stand to replace one at a time.

In that case, replace the main filter cap. That's the one that, if it blows, can kill the power transformer too.

I very much recommend some reliability mods for preserving the power and output transformers. These are the biggies:
- put a silicon rectifier (1N4007 is good) in series with the transformer leads going to the rectifier tube. This will protect your power transformer if the rectifier tube shorts
- put a fuse in series with the B+ to the output transformer to keep it from burning out if a power tube shorts
- put a fuse in the heater winding(s) so that if a tube heater shorts, it will not burn out the power transformer.

The power and output transformers are the two most expensive parts in the amp, and the OT is a huge contributer to the sound.

[Rick1114]

Okay - Thanks to everyone here, I think I basically have it. A basic cap job would consist of:

Cap Can (AES has one: CAPACITOR, ELECTROLYTIC, 20/20/20/20 µF @ 475 VDC). This probably should be replaced either way if it original sine the amps 45 years old!.

Cathode Bypas Caps - These are the WHITE mallories. I see there are widely varying opinions on these. For this reason I might consider an experienced tech who can measure them (or see if I can borrow an ESR meter somehow), but it may cost too much here in NY. What's the latest consensus on these?

6V6 Bypass - This is a 25mf/25VDC cap that is a likely candiate for replacement. Most say upgrade this to 25/50. I'll be playing this at home mostly so I'd keep it stock if possible, not sure if that value is still available.

Thanks again everyone for you help. Even if I go to a tech I will know exactly what to talk about.

Thanks,

Rick

[Rick Erickson]

Okay - Thanks to everyone here, I think I basically have it. A basic cap job would consist of:

[Cap Can (AES has one: CAPACITOR, ELECTROLYTIC, 20/20/20/20 µF @ 475 VDC).[

Reliability of these new manufacture multi-section caps is questionable at best. I refuse to install them anymore. You would be better off to leave the original cap in place but disconnected, and install (3) single 20 or 22uF caps inside the chassis.


[Cathode Bypas Caps - These are the WHITE mallories.]

These are almost always bad, especially after 45 years - Replace them.

6V6 Bypass - This is a 25mf/25VDC cap that is a likely candiate for replacement. Most say upgrade this to 25/50. I'll be playing this at home mostly so I'd keep it stock if possible, not sure if that value is still available.

The voltage rating is not going to change your tone. Put a 22uF/100V in there and it will work just as well. btw - is the original 470 Ohm cathode resistor still in one piece, or even in tolerance? I replace these with 5W wire-wound types.


[Thanks again everyone for you help.]

You're welcome

[Even if I go to a tech I will know exactly what to talk about.]

Any tech worth going to would want to examine your amp and then tell you what he recommends, not deal with a bunch of opinions from the internet. Ask me how I know this...

[dai h.]

even though it's another internet opinion (as well as this one), listen to Rick!

[Rick1114]

Okay - Thanks to everyone here, I think I basically have it. A basic cap job would consist of:

[Cap Can (AES has one: CAPACITOR, ELECTROLYTIC, 20/20/20/20 µF @ 475 VDC).[

Reliability of these new manufacture multi-section caps is questionable at best. I refuse to install them anymore. You would be better off to leave the original cap in place but disconnected, and install (3) single 20 or 22uF caps inside the chassis.


[Cathode Bypas Caps - These are the WHITE mallories.]

These are almost always bad, especially after 45 years - Replace them.

6V6 Bypass - This is a 25mf/25VDC cap that is a likely candiate for replacement. Most say upgrade this to 25/50. I'll be playing this at home mostly so I'd keep it stock if possible, not sure if that value is still available.

The voltage rating is not going to change your tone. Put a 22uF/100V in there and it will work just as well. btw - is the original 470 Ohm cathode resistor still in one piece, or even in tolerance? I replace these with 5W wire-wound types.


[Thanks again everyone for you help.]

You're welcome

[Even if I go to a tech I will know exactly what to talk about.]

Any tech worth going to would want to examine your amp and then tell you what he recommends, not deal with a bunch of opinions from the internet. Ask me how I know this...

Rick, thanks for your opinion - it sounds the most sensible to me, let me know if there is anything else you recommend. I have decided to look for an experienced tech in NYC/Long Island area. Let me know if anyone knows someone...

At this point, IMO there is no reason to keep 45 year old electroylics in the amp other than for re-sale value, and that means I wouldn't be enjoying it. If I can find someone in my area who can do the job right, I'll just pay him and call it a day and enjoy the amp!

Rick