Crusty Caps from the 50's / 60's

[sr1200]

I recently found a gibson made amp from the late 50's early 60's under my stairs in the studio (belonged to my father i believe)  I found a schematic for it, so i can get a handle on what I would need to replace cap wise.  I'm assuming i should recap the entire thing, not just the big cap which looks like a half stick of dynamite (i assume is for the PS haven't checked the schematic yet), but all the little caps like the ceramic and sprague caps.... should those be done too?  There are a pair of VERY long poly looking yellow caps that look like they've grown crystals or caught a bad case of chicken pox... any idea what thats about?

 

[ln76d]

Any photos would be helpful - especially of "VERY long poly looking yellow caps". For sure you should change all electrolytic caps. For the big one - new with similar size. If the foil capacitors are not overburnt and have no visible damages you should keep them. With ceramic caps you can look for newer types (better dielectrics) or change for the foil caps. It depends on their function in the circuit (schematic or amp model would be helpful too). In some places if the original ceramics have no visible damages (you can try to scrape it with the fingernail - some can delaminate with the age) probably you could keep them.

 

[sr1200]

heres the schematic  ill try and grab some close up pics tonight.

 

[Gus]

I would not change all the electrolytic caps with out testing them.  IMO you need a have a good Cap meter to test the caps.  I have tested old amp with what looked to be original caps that tested fine value, leakage at operating voltage etc.  Sometimes old caps last.

You might not want better dielectrics remember a guitar amp is a producer of distortion

Does the amp work? 

 

[sr1200]

No tubes, can't tell. 

 

[sr1200]

The big guy

 

[mjrippe]

I would not change all the electrolytic caps with out testing them.  IMO you need a have a good Cap meter to test the caps.  I have tested old amp with what looked to be original caps that tested fine value, leakage at operating voltage etc.  Sometimes old caps last.

You might not want better dielectrics remember a guitar amp is a producer of distortion

Does the amp work?

While they *might* be fine, it is much easier to replace the electrolytics if you don't have the proper test equipment.  "The big guy" is a multi-section cap for the power supply and would be the most likely to fail.  The other two are low voltage and not as critical, but easy enough to swap out.

 

[sr1200]

are teh ones in the first pic supposed to look and feel crusty like that? I've never seen a cap with that kind of texture... are they even caps? could they be resistors?  Sure wish something was labeled on the board as a starting point.  Im gonna have to take it apart and trace the circuit through the schematic and label the stuff as i go.

 

[usekgb]

I had an old Stromberg Carlson AU-58 on my bench today to replace a seized pot.  Before changing out any caps, I fired it up to see how it sounded.  No hum, no problems, and great tone!  This thing was made in the late 50's, and the caps are still functioning just fine.

The moral is, get tubes for your amp, and try it out before you just start replacing parts.

 

[ubxf]

bringing it up slowly to operating voltage with a variac  is probably necessary to avoid blowing up those caps. Also using a Lightbulb limiter might help in case something fails

 

[Gus]

The two parts are next to two caps one looks like 25 VDC at 20uf? I can't see the other value.  Look at the back side of the board for connections
Find where there are two caps of the marked values used and look for resistor values etc of what are close to them on the schematic.
Looks like 26 week of 1960 date code on one of the caps

Is the first picture from the power chassis or amp chassis?

I would put a set of used tubes in it and try it with a Variac.

What is the value of this amp?  You might want to keep it as stock as possible.

 

[panman]

The schematic shows five 20uF low-voltage electrolytics. I take the Spraque is 20uF too? The first pic shows the two yellow and the crusted ones must be the remaining two caps. For an old amp like this, I would first check out the condition of the filter-caps before powering up especially if you don`t have a variac. The caps should not be far away from the nominal value, when measured. And lacking more sophisticated equipment you can measure the DC-resistance and after few initial seconds there should be none. If there is even mega ohms remaining, you better replace it.

 

[ln76d]

While they *might* be fine, it is much easier to replace the electrolytics if you don't have the proper test equipment.  "The big guy" is a multi-section cap for the power supply and would be the most likely to fail.  The other two are low voltage and not as critical, but easy enough to swap out.

I agree! Even if the electrolytic caps keep the capacitance, they can have tendency to damage in the near future... With the new electrolytics there can be only benefits like preventing damages for example. Few 22uF capacitors will be cheap so why not?

 

[ln76d]

are teh ones in the first pic supposed to look and feel crusty like that? I've never seen a cap with that kind of texture... are they even caps? could they be resistors?  Sure wish something was labeled on the board as a starting point.  Im gonna have to take it apart and trace the circuit through the schematic and label the stuff as i go.

Check if they are connected to the 20uF.

 

[ln76d]

I had an old Stromberg Carlson AU-58 on my bench today to replace a seized pot.  Before changing out any caps, I fired it up to see how it sounded.  No hum, no problems, and great tone!  This thing was made in the late 50's, and the caps are still functioning just fine.

The moral is, get tubes for your amp, and try it out before you just start replacing parts.

Do you know how it sound in the 50's to compare?

In my heathkit hi-fi amp was only few electrolytics (same "paper" spragues and one mulltisection in psu). All keeps capacitance in nominal tolerance. Amp was sounding good, but there was a little hum. After change hum gone and the bass reproduction response was improved a lot.

 

[sr1200]

Im not one of those "keep it original for the sake of nostalgia" kind of guys.  I'm more of the "keep it safe so my house doesn't burn down" type lol.  The big electrolytic in the middle (the multi-cap) is disintegrating to the touch, so that HAS to get replaced.  I plan on breaking it down this weekend so i can get at the components a little easier.    Also the heater wires feel very brittle, im thinking i may have to replace those as well.  As far as the pics go, they are both pics of the amp chassis box (the power supply is in a different enclosure at the bottom of the amp with the diodes and transformers.  A cable runs up into the chassis from that box and the pic with the fuzzy components in question is where it comes in to meet the on/off switch, lamp etc.)  I also notice that there is an extra jack in the back of the unit that doesn't seem to be on the schematic at all.  As far as value goes, they only made a few hundred of these amps total, which surprisingly didn't bring the value up that much on them.  That being said i've seen a couple (one exact and one the more "deluxe" reverb version) both selling over $2k USD, so its definitely worth looking into.  Thanks for all the comments and suggestions.  I do have a variac and I plan on ordering tubes for it this week.  I'll post some updates as i start the "restoration".  Still debating if i should re-do the filthy tolex or not.

 

[walter]

are teh ones in the first pic supposed to look and feel crusty like that? I've never seen a cap with that kind of texture... are they even caps? could they be resistors?  Sure wish something was labeled on the board as a starting point.  Im gonna have to take it apart and trace the circuit through the schematic and label the stuff as i go.

Those crusty's may be resistors. That is one clean looking amp on the inside.

 

[CJ]

just replaced one of those multi caps in an Ampeg Gemini,

problem was not capacitance,

problem was when you put your hand near it, a ;arge increase in hum was heard,

replacement caps got rid of the hum,

probably having to do with the shielding aspects of the cap,

 

[PRR]

> a half stick of dynamite

I love this description.... but it tells me you have little experience around old tube gear.

The amp has been under the stairs for years. Take a few weeks or months, learn about old amps.

I think you should get on a guitar-amp forum and read-read-read-read. People post their old-amp problems, get lots of answers (often at cross-purposes, everybody has an opinion), you see pictures of old and restored amps, you get an idea of what problems are serious and what should be left alone.

Also: Lamp Limiter!!

 

[sr1200]

I thought my description was pretty accurate... lol  look at it!  But yes, I know nothing about tube amps (besides the LA2A).  I was planning on building on to learn over the summer, but the baby saw to that not happening.  And... Lamp limiter?  I got a lot to catch up on.