Starting up a probable dormant vintage amp

[Jon Snell]

That Laney amp was made when Laney used quality components, most were sourced through RS Components in the UK.
I wouldn't mind betting that is you have no signs of bulging at the positive end of the capacitors, you will only lose value by replacing them.
Bring the voltage up slowly, with no valves in place, leave it on whilst monitoring for issues, switch off after an hour, check the capacitors are discharged, replace the valves, plug in a speaker load and you will be amazed.
Nice amplifier.
I have known the 15u bias capacitor go open circuit, that causes hum.

[drewl]

I pull the output tubes, power up with limiter then check for proper voltages and signal to grids of output tube sockets.

Then if everything looks good install one output tube at a time with load attached and check bias, ripple etc.

[Helmholtz]

Filter cap leakage can be measured in the application/powered amp by inserting a low value resistor (e.g. 10R) between negative lead/terminal and ground. DCV across the resistor divided by resistance gives leakage current.
A good cap should measure below 1mA.

[Jon Snell]

Always fit the EL34s in pairs to avoid hum!

[Leo_Gnardo]

One more: Filter caps leaking badly will noticeably warm up. You can let 'em run for a while, say half an hour, then switch the amp off & let the charge drain for a minute so there's no shock hazard, then touch the cap body & you'll sense the heat. Or not. If you have one of those infrared/laser thermometers you can check temp while power's on.

[R.G.]

It's a question of objectives. What does the owner want the amp to do? Here are some possibilities.
1. Be original; this one is easy. Don't do anything to it. It stays original.
2. Work; in this case, you would power it up gently, looking for what may fail as you do it. Light bulb limiters work well here. Note that there is a chance that a component will fail as this happens, meaning you can never go back to 1.
Notice that you may not be able to have 1 and 2 at the same time. Mother Nature may already have set that up.
3. Work reliably; this one requires both preventive maintenance and some testing. The preventive maintenance is to go replace all the electro caps and then do the slow bring up from item 2 for testing.

I have faced this contretemps several times, and my personal situation is that I can't afford sculpture - that is, things which may be admired for their beauty and state of being, but don't necessarily serve any useful purpose otherwise. I consider item 1 to be maintaining a piece of sculpture. To me, an amp is a tool for making sound. If it doesn't work, and work reliably, it's sculpture. I accept that other people may feel differently about their amps. That is their perfect right.

It's a question of objectives.

[Chuck H]

Following what R.G. is saying,..

Some guys want an amp to be original as possible because they believe that will preserve the original sound. Which to them would be the "sculpture" as it were. The art of the sound as crafted originally. And of that I can only say that there are still many players and techs that take this too far all the time. Like leaving un grounded AC cords in gigging amplifiers. And it could more reasonably be argued that a new set of filters is sure to sound more like the amp was originally intended than the original filters will in failing condition. But good luck convincing the wrong sort of person on that matter.

Again, objectives.

[Justin Thomas]

But I think it's safe to surmise that NO builder ORIGINALLY intended their amp to be a hummy, buzzy, smelly, unpredictable, unreliable, and dangerous noise-aker! :P

When I do get an amp like this in, I make a point to check coupling caps as routine also. Especially if it's got some rare/unobtainium tubes in it, because I'd HATE to tell someone that they need a new 6C10 because I missed a bad $1 part, or that their Mullard EL34s are blown up while knowing it's my own fault.

Measure the value of the parts that could be destroyed by the really cheap stuff like electrolytic caps, coupling caps, resistors, etc. Go from there.

Justin

[eschertron]

But I think it's safe to surmise that NO builder ORIGINALLY intended their amp to be a hummy, buzzy, smelly, unpredictable...

I sense a niche market here

[Chuck H]

I sense a niche market here

Didn't Metasonix already fill that niche?

[Randall]

Here's a good example of wanting museum originality gone bad.

A guy bought a pristine early 60's Supro amp like what Jimmy Page used on record. It was advertised as "the cleanest Supro on the planet". It had hang tags and a spare fuse in a little envelope. It was as if it had never been used, and the guy paid a pretty penny for it. I told him, "don't you turn that amp on before bringing it to me". He complied.

I put it on my bulb limiter, and brought it up very slowly on my variac, monitoring plate voltage, when suddenly, BANG! BANG! BANG! thru the speaker. The guy actually ran out of my shop! I immediately shut it off and explained this pristine all original time piece he just paid for needs to be re-capped. He was horrified, but it is what it is, and agreed to the job. The amp sounded great with new caps, but in the end he paid a premium for an all original vintage amp, and then paid me another $150 or whatever it was to make it not all original so he could actually use it.

So there you go.

[Chuck H]

I told him, "don't you turn that amp on before bringing it to me". He complied.

Amazing! I wouldn't have expected that. I bet it felt like just a hopeful wish in your head when you said it out loud.

[Justin Thomas]

Well, that thing Rob Hull made (The $@#%ing $@#%er) was pretty buzzy & noisy but I'm not sure if that was a joke...

Jusrin

Edit: see post #25 by Chuck H.

[g1]

I'll just re-iterate one of the points R.G. made. Even after the re-cap it needs to be brought up slow.
New parts are not necessarily good parts, and the kind of damage that can be caused by a defective old cap can also be caused by a defective new one. The argument is in the likelihood.

So you need to be set up to bring it up slow. Now that you have that capability, do you bother to bring it up with old caps and go through standard troubleshooting procedure (locate and replace defective parts), or do you just go ahead and re-cap?
That's a choice for the individual, I can accept either position, but I think you should be capable of carrying out either scenario.

[Justin Thomas]

Didn't Metasonix already fill that niche?

I <do> actually make some of those kinds of noises and more, with my pedals. I think some of these could actually be useful in the soundtrack work I'd like to do.

Justin (not Jusrin so you know I'm serious)