Kustom K150 noise in channel 4

[jessadr]

K150 metal face kustom. When it has been off for a while it makes a spew sound as it warms up for just a minute or so.
It doesn't do it while it is on. It increases with volume. It is only on channel 4. If it has been on a while it doesn't do it. Only does if it has been off a while.
If I turn it on while cool then right off it does it then too as it bleeds down.
Just thought one of you guy's might have run into this before. I don't have board numbers I haven't opened it up yet.

[Enzo]

Without board numbers there is little i can tell you.


But is this actually a problem? It makes a noise when you first turn it on but not after?


You have some noisy component in that channel.

[jessadr]

It makes a squeal that can be changed with the volume pot. It only lasts for a short time then stops.It also happens on shut down. Only when it has been off for a while. I guess a cap bleeds off. man you are up late. I have searched this site and the vintage kustom site found no one with same problem.

[Enzo]

And you likely won't find someone with this exact problem. And if you did, it might not be the same cause anyway. What matters is the circuit, not the parts. A bit of instability is causing the noise, and any number of things can cause instability. it would be like having a rattle in your car and expecting it to be the same loose bolt as the next guy with a rattle.


A transistor may need to warm up a second to stabilize a voltage drop. A cap may leak a bit at first then recover. Only way to tell is to track down the problem in the circuit while it runs.

A can of freeze spray MIGHT reveal the source. let it warm up and settle down, then freeze that channel board area by area and see if anything when chilled makes it do it again. That assumes it really is a thermal issue and not just a voltage breakdown.

[jessadr]

That is what I was thinking. Cool the caps and transtors on the preamp board and find the one that makes it squeal. Cos it will only do it after it has sat a while then turned on

[Enzo]

Get that board number.


You may find some part triggers this, but it may not be the part's fault. Typical for amps that old will be dried up small electrolytics that are leaky. This can upset the DC balance in the circuit, and it is that offset making the whole circuit unstable. Be ready for that.

[jessadr]

PC5031 b It has had the ic chip changed to a nte part

[Jazz P Bass]

It may be wise to simply check the +12 & -12Vdc supplies.

See if there is any ripple riding on them, especially as the noise occurs.

[jessadr]

I don't have a scope. I am just a tinker not a tech by any means. There are so few cap on that board I wonder if I should just replace them. The tanulam would be the first , you think ? It is the pc5031 b board

[jessadr]

side question Is the reverb tank a 4fb3d1b ?

[Jazz P Bass]

You do not need a scope to check the power supply.

A simple volt meter will do fine.

Set it to read volts ac to read the ripple.

Ideally, opamps require a very smooth & steady power supply.

[jessadr]

Right, just looking for right voltage , not ripple I think I need to invest in a signal injector and a scope and learn how to use them.

[nashvillebill]

Hey I'm up in Gallatin, if you want to come up here I can show you how a signal generator and scope operates.

I wouldn't worry about that tantalum cap, if it hasn't exploded it's probably still good.

[jessadr]

That would be great. I went to high school in gallatin class of 71

[nashvillebill]

I moved here in '97.

This weekend is going to be busy, but later next week I'll be around; drop me a PM.