Starting up a probable dormant vintage amp

[Gtr0]

Hi Everyone!

Sometime between Friday and Tuesday I will (should) receive my first ever, real vintage amp via UPS - a ’69 Laney LA60BL (later named the Supergroup). I’m rather excited about this - currently my favourite amp that I own is a JTM45, the reissue - so having something substantially older… well, I’m looking forward to getting it fired up.

It appears, and was advertised as, all original. As far as I can tell looking at the photos that were sent to me, it literally looks all original. Perhaps others that either have had or worked on one of these amps could verify.

Of course this makes me a bit nervous that the amplifier has been lying dormant for some years, or decades! The seller said he last fired it up in December, so four to five months ago. And with all of this, I can only assume this will be more involved than the usual startup precautions.

I have no ability issues in replacing parts, other than the fact that I’d love to keep it as original as possible. I’ve got the usual tools - oscilloscope, variac, tone generator, ESR meter, DMM etc etc.

Can anyone offer any pointers on how I should properly handle this? I’d very much appreciate it!!!

STAY SAFE!!!!

[Chuck H]

Well it would surely take away from the interior decoration, but you see all those blue cans? Yeah, you know what I'm thinking. 41 year old electrolytics in an amp that clearly hasn't been used much are likely to be faulty. Failures in those caps can cause damage to other, more expensive and less replaceable components. And testing those caps for relative goodness has little to offer since the caps can test fine on bench gear and still under perform or fail in the higher voltage environment of the amp circuit.

JM2C

[Leo_Gnardo]

41 year old electrolytics

51 years Chuck. How time flies... and that makes their long term prognosis even scarier. I'd swap in new ones without a second thought. Also bias supply filter(s) & cathode bypass caps - all the electrolytics. Cheap insurance.

[Chuck H]

Haha! Yep. Ooops. I'm missing a finger you see and I didn't trouble to stand up and pull down my pants

[galaxiex]

Haha! Yep. Ooops. I'm missing a finger you see and I didn't trouble to stand up and pull down my pants

Pics or it didn't happen... wait... what...

Ya the only way to test old electro's (and I'm not sayin' you should use 'em, even if they test ok)...

Is to test 'em at rated voltage...

I use this...



Capable of putting 450 V to the cap under test.

[Enzo]

I had the Eico version of that cap tester, it is a great tool.


Ah Chuck, you beat me to it. I was going to say I can't count past 21.

[g1]

If you really want to start it up without changing any parts, bring it up slow on a variac while monitoring current.
If you don't have a variac, you could use a limiter lamp with a low wattage bulb.

[Chuck H]

If you really want to start it up without changing any parts, bring it up slow on a variac while monitoring current.
If you don't have a variac, you could use a limiter lamp with a low wattage bulb.

I did exactly that with a lamp limiter. In 2008 Dean Markley was all exited about a couple of still boxed CD60's from about 1985 that he wanted to try out. I told him the electrolytics were probably failed and that went right over his head. He didn't understand that something electronics related that hadn't been touched in 23 years could "go bad". So he unboxed one and plugged it in. It hummed and hissed and then started smoking. He looked at me like I should know what the hell just happened. I re-explained what I'd told him before that he didn't listen to and I asked him if he had an old lamp he didn't care about. Then I made a lamp limiter out one. We fired up the next one on the limiter and let it cook for about six hours. That kept the amp alive, but it was still noisy. I went to the local Fry's and got the bias caps I needed and the UltraSound factory over nighted the PS caps. I cleaned up the first one (which had been painted with goo on it's innards) and replaced the all the electrolytic caps in both amps. Now, these were those crappy gray and black IC caps. The caps in that Laney are surely better quality. But 51 years? Possibly mostly unused and so allowed to lose the oxide layer. I wouldn't trust them based on personal experience. But if one were anxious to fire it up I suppose a four to six hour cook on a bulb limiter might allow the amp to "function". If the caps were ordered now you could replace them in less time.

[g1]

I hope this is not too heretical but this is how I see it (trigger alert )
It depends on whether it's been used or not. If it's a known recently running unit, I'd plug it right in and use it. If it's been sitting a long time, then yes, I'd want to slow start to prevent any damage should a cap be bad or fail during start up.
Half my amps have 50yr. old caps in them with no issues. I don't worry about them, they don't hum or cause any other issues. When they go bad, I'll replace them. In my experience, caps of that vintage almost always fail open, shorted filter caps is a more modern phenomenon. I could probably count on one one hand the amount of real old caps I've encountered having caused damage to the amp. They usually dry up and hum. Often only visual clues that they are dried out unless you take them out and test them.

He did say he wants to keep as original as possible.

[eschertron]

And regardless of what's done as restoration, take enough hi-def pics when you receive it to ensure that you can show off its 'original vintage-ness'. I don't expect you to crack open the chassis every time someone stops by to "see what you got there".

[Chuck H]

I hope this is not too heretical but this is how I see it (trigger alert )
It depends on whether it's been used or not. If it's a known recently running unit, I'd plug it right in and use it. If it's been sitting a long time, then yes, I'd want to slow start to prevent any damage should a cap be bad or fail during start up.
Half my amps have 50yr. old caps in them with no issues. I don't worry about them, they don't hum or cause any other issues. When they go bad, I'll replace them. In my experience, caps of that vintage almost always fail open, shorted filter caps is a more modern phenomenon. I could probably count on one one hand the amount of real old caps I've encountered having caused damage to the amp. They usually dry up and hum. Often only visual clues that they are dried out unless you take them out and test them.

He did say he wants to keep as original as possible.

I did have an old Traynor (a brand you might be familiar with) with the original big tannish/orange cardboard Mallory caps in it (about 33 YO at the time I think) that never exhibited any trouble for it's age. And I've seen a couple of SF Fenders that had original caps and sounded fine. So it does happen. In that light I agree, but with the caveat you outlined. Has the amp been operating without problems recently? That, unfortunately, is not the kind of question you can expect a sincere and educated answer to. You can hope for it. Maybe the seller owned the amp for the last fifty years. More likely the seller would have turned it on and maybe played a few notes through it. Sound came out and it didn't blow up. "Amp works great" is the only response you could expect.

[Gtr0]

[sigh] - a very long one.

As much as it saddens me, I tend to think the way Chuck H does. I was hoping that there would be a way that I didn't know of - like reforming caps for example (which I have never done) - but from what I think I understand, properly reforming caps is something I don't think I am prepared to take on.

There's no way I can trust that a 51 year old amp was run enough that it parts were kept in operating order. The seller was a vintage gear dealer on Reverb, so regardless what he says, or how nice he is, I expect that the amp has set for a few decades, was dealt him through whatever means at which time he turned it on, maybe struck a chord, and posted it to Reverb. In other words, I have no real choice but to expect worst case scenario.

I think before turning it on I will replace the caps - I should have hoarded enough F&T's to do the job. Assuming the cathode bypass are of a typical value (which I think is 22 or 25 uF in this amp), I should be good to go there as well.

Unfortunately I do not have a proper current meter built into my variac. But I do have a lightbulb limiter. In some extreme cases in the past I ran the lightbulb limiter out of the variac to bring voltage up somewhat slowly (as in over the course of 30 seconds or so) - but it just occurred to me that the smallest bulb I have is 150 watts. I really need a proper current meter... I just keep forgetting that.

Thank all for the suggestions! I DO want to keep it as original as possible, but not at the expense of more "exotic" items like the trannies, choke etc - otherwise I would just save a little money building my own

[Chuck H]

You surely could bring it up on a current limiter for a few hours. You'll be able to tell pretty quick if it's not going to work at all because the amp will be in play mode while your doing this. Just turn up the volume a bit and listen. If it's NOT making noises just leave it there anyway for a few hours. If it IS making noises then monitor it. If the noise diminishes or goes away then the caps may reform for you. Just leave it there a few hours. If noises don't reduce substantially after about an hour you can bet they aren't going to reform sufficiently so quit the effort and resign yourself to recapping it.

[Mick Bailey]

I've worked on a few old Laneys and there's always a feeling of regret as I remove those original UK-made Erie electrolytics, but it has to be done for the safety of the amp and reliability. I have tried re-forming them but the effects are fairly short-lived. In the absence of a dedicated cap tester like the one galaxiex has I've use a DC-DC HT converter and DMM for leakage testing and re-forming on the bench for experimental/observational purposes.

These old electrolytics have an excessively high leakage current when removed from an old amp that hasn't been used for many years. With careful and prolonged re-forming they can be rehabilitated to the point where the leakage appears to perfectly fine. In my experience this is short-lived and after even a few hours of non-use the leakage starts to climb. After a few days without power the initial leakage (and inrush current) is too high, though not as high as before the cap was re-formed and this quickly drops again in use. A characteristic of a re-formed cap is the tendency to revert, and this results in a high inrush current and hum upon powering up an amp until it stabilises after a few seconds or minutes. During that time though the PT and caps are heavily stressed and with an old amp a failed HT winding can be an expensive and unwanted fix.

[HaroldBrooks]

If you really want to start it up without changing any parts, bring it up slow on a variac while monitoring current.
If you don't have a variac, you could use a limiter lamp with a low wattage bulb.

Very Good Advice.

A limiter lamp saved a zenith amp I bought that was blowing fuses. Allowed me to locate a shorted filter cap without much carnage (only toasted one big resistor just off the rectifier). Lamp limiters are absolutely great and essential if you are working on old stuff !