Pot Questions (St. Louis Music Company Vintage 30 help)

GuitarsBuicks

Tele-Afflicted
Joined
Jul 16, 2020
Posts
1,065
Age
26
Location
Somewhere between here and there
Okay, so Its been a while since I have been active here. In the time that I have been busy and away, I acquired an epic sounding Vintage 30 tube amp. However the drive potentiometer needs to be replaced desperately, as I' m pretty sure the pot basically melted down. Anybody out there in amp repair land know what kind of potentiometer goes in an amp like that? Personally I'd rather replace it myself than pay $200 to get it fixed by a shop that may not have it done in time for my next gig on the Aug. 11th. So I guess my questions are this...

1. Is it a printed Circuit board that can be worked on if you are not a tech?

2. What would be the correct rating of pot to replace it with? I have replaced pots before on various amps I have owned but the have all been cheap practice amps, never a great tube amp.

3. What would be considered an "upgrade" in quality over the original potentiometer that is in there?

Thanks,

Guitars Buicks
 

RetiredUnit1

Tele-Holic
Joined
Jun 18, 2022
Posts
893
Age
66
Location
SoCal
Most of the time pots just get dirty and you can clean them with DeOxit 5. Works miracles on all electrical connections. Just follow the directions on the can.

I've never heard of this amp you speak of, any pics?

 

Dacious

Doctor of Teleocity
Joined
Mar 16, 2003
Posts
10,713
Location
Godzone
Be careful if the pot has a plastic body. These sort you must use a special spray grease and not the sort with evaporating thinners. They can melt the body which holds the track.

You can replace most PCB pots with metal ones and short leads. It's not a job for newbies. That's a good way to screw up the PCB. Find a tech. Even a general technician can do that. You need to find out what value pot. It's a Vintage 30?
 

Wally

Telefied
Ad Free Member
Joined
Mar 17, 2003
Posts
42,181
Location
Lubbock, TX
Crate vintage 30????
PCB amp. +1 with Dacious. Got a tech? The amp needs to be assessed by a tube amp tech so that you what it is that you have acquired...and what condition it is in.
 

GuitarsBuicks

Tele-Afflicted
Joined
Jul 16, 2020
Posts
1,065
Age
26
Location
Somewhere between here and there
Most of the time pots just get dirty and you can clean them with DeOxit 5. Works miracles on all electrical connections. Just follow the directions on the can.

I've never heard of this amp you speak of, any pics?

Its basically a Crate vintage 30, but instead of Crate it says St. Louis Music Company on the back. Its all the same but has nothing to indicate that its a Crate. It was the last hoorah for the company before it was sold to LOUD. At least that's what I have been able to find.

As far as the pot is concerned, it is most definitely broken or melted apart. The shaft moves around inside the pot for one, and it is completely non-functional since the incident that made me think that it needs to be replaced. DeOxit 5 is not going to work with that level of damage or whatever.
 
Last edited:

GuitarsBuicks

Tele-Afflicted
Joined
Jul 16, 2020
Posts
1,065
Age
26
Location
Somewhere between here and there
Be careful if the pot has a plastic body. These sort you must use a special spray grease and not the sort with evaporating thinners. They can melt the body which holds the track.

You can replace most PCB pots with metal ones and short leads. It's not a job for newbies. That's a good way to screw up the PCB. Find a tech. Even a general technician can do that. You need to find out what value pot. It's a Vintage 30?
I have replaced them before. I'm not worried about the board, like I said I have done it before. The big problem for me is a $20 fix is going to cost me more than $180, which is more than half of what I paid for this amp.

Is there any reason I can't or shouldn't do it myself? Its not like I'm actually re-wiring the whole thing or anything.
 

RetiredUnit1

Tele-Holic
Joined
Jun 18, 2022
Posts
893
Age
66
Location
SoCal
I have replaced them before. I'm not worried about the board, like I said I have done it before. The big problem for me is a $20 fix is going to cost me more than $180, which is more than half of what I paid for this amp.

Is there any reason I can't or shouldn't do it myself? Its not like I'm actually re-wiring the whole thing or anything.

The biggest problem is draining the capacitors so you don't get shocked, and using a meter to verify the charge is gone.

If it's modern construction the pot will be soldered directly to a circuit board. Sometimes these have been charred and become fragile. Then you may also need to completely disconnect the face board from the circuit board and remove all the faceplate connections just to access it.

Older construction, you just desolder the old wires, take out the pot, put the new one in and solder it back up.
 

dan40

Friend of Leo's
Joined
Aug 19, 2015
Posts
2,845
Location
Richmond Va
It's very easy to permanently damage a pcb, especially a cheaper board. If you do decide to try it yourself, be sure to have the correct tools such as solder wick and a solder sucker to help with the desoldering of the potentiometer lugs from the board.
 

Dacious

Doctor of Teleocity
Joined
Mar 16, 2003
Posts
10,713
Location
Godzone
Here's the Crate preamp. Hopefully you can work out what pot you need.

To drain caps power on amp, plug in guitar. While strumming strings pull power cord out of wall or back of amp. As soon as amp stops making noise and pilot light is out, you're good.

Check the large filter caps +ve with Dmm set to DC to ensure they are holding no charge. Don't plug in the amp again until it's buttoned back up.

Watch out for ribbon cable connectors, they're very fragile.
 

Attachments

  • crate_vc3112_preamp (1).pdf
    122.4 KB · Views: 37

telepuller

TDPRI Member
Joined
Apr 11, 2022
Posts
19
Age
71
Location
Mojave Desert
Let me start with apologies to GuitarsBuicks for the slight off-topic nature of this comment. I'm not trying to pirate the thread here.
This isn't directly connected but I hope close enough to the comments of the electronic nature I've seen here:
How long can a vintage tube amp ('70s PR) sit unused (not powered up) before it is not safe to plug it in? It's probably been five years now. I have looked at all the resources I can find, but none of them specifically speak to this question.
 

Mr Mojo 54

TDPRI Member
Joined
Jun 10, 2018
Posts
28
Age
68
Location
Fullerton, California
Let me start with apologies to GuitarsBuicks for the slight off-topic nature of this comment. I'm not trying to pirate the thread here.
This isn't directly connected but I hope close enough to the comments of the electronic nature I've seen here:
How long can a vintage tube amp ('70s PR) sit unused (not powered up) before it is not safe to plug it in? It's probably been five years now. I have looked at all the resources I can find, but none of them specifically speak to this question.
50 years, maybe. It varies. The electrolytic caps are the only thing that goes bad with age/lack of use. Probably safe to plug in but could be noisy and hum a lot. More realistically, I'd estimate about 10 years before the caps should be checked or replaced. A visual inspection would disclose their physical condition, i.e., leakage or swelling. Obviously a swollen or leaky cap indicates it's unwise to plug it in. Otherwise you can plug it in and hear how it's sounding. You can usually hear when they need replaced. It would be "safe" and sound like crap.

P.S. Unless some dumbazz has been messing around with it. In that case, nothing is safe to plug in until it's been opened up and examined.
 

Wally

Telefied
Ad Free Member
Joined
Mar 17, 2003
Posts
42,181
Location
Lubbock, TX
Let me start with apologies to GuitarsBuicks for the slight off-topic nature of this comment. I'm not trying to pirate the thread here.
This isn't directly connected but I hope close enough to the comments of the electronic nature I've seen here:
How long can a vintage tube amp ('70s PR) sit unused (not powered up) before it is not safe to plug it in? It's probably been five years now. I have looked at all the resources I can find, but none of them specifically speak to this question.

Due to the age of those electrolytics…maybe 50 years??? coupled with maybe 5 years of inactivity, I would err on the side of safety and bring that amp up on a Variac. That would be done starting at 20VAC, and one would increase the voltage each hour by 10 VAC.
If full AC voltage is applied without doing this, there is a chance that an electrolytic could catastrophically fail. IF an e-caps shorts, voltage cane be misapplied and take out a transformer. The chance of this happening may be small; but IF that happens, one loses an expensive component and the originality of the amp is compromised. That lack of originality of a major component detracts 50% of the value of the amp in my world. My thought is that this amp has been unused for 5 years, so what is the hurry. It has value in the market, and it is time for a tech to properly assess the amp.
or….sell the amp as is with the condition stated…’has not been turned on in 5 years’. However, if offered to me in that state; it is not worth as much as it is if it had been brought into operation.
 
Last edited:

telepuller

TDPRI Member
Joined
Apr 11, 2022
Posts
19
Age
71
Location
Mojave Desert
Due to the age of those electrolytics…maybe 50 years??? coupled with maybe 5 years of inactivity, I would err on the side of safety and bring that amp up on a Variac. That would be done starting at 20VAC, and one would increase the voltage each hour by 10 VAC.
If full AC voltage is applied without doing this, there is a chance that an electrolytic could catastrophically fail. IF an e-caps shorts, voltage cane be misapplied and take out a transformer. The change of this may be small; but IF that happens, one loses an expensive component and the originality of the amp is compromised. That lack of originality of a major component detracts 50% of the value of the amp in my world. My thought is that this amp has been unused for 5 years, so what is the hurry. It has value in the market, and it is time for a tech to properly assess the amp.
or….sell the amp as is with the condition stated…’has not been turned on in 5 years’. However, if offered to me in that state; it is not worth as much as it is if it had been brought into operation.
Thanks, that was a useful answer.
 




Top