Other Amps

What happens to an amp that isn’t used for years?

1

I have a couple of vintage tube amps that I've not used for a number of years, maybe around 7 or 8. I've had them stored in an outhouse, each under its own padded vinyl cover. The outhouse is dry (and has had a dehumidifier running for the last year or two), but they will have got cold - maybe down to freezing or even a little below.

Is there anything I need to bear in mind before firing them up?

2

Find a local amp tech who can slowly bring them up to working voltage and check for any problems.

Many will do that for free if the amp doesn't need any other work.

3

It does depend on how old, you know? If critters have gotten into them, they can do some real damage. I have an amp waiting for some love and kisses, where the mice ate the insulation off every wire in the chassis. If I plugged it in without knowing, sparks everywhere!

4

Ya know, across the pond THIS is an outhouse.

Remove the rear panels, vacuum out the spiders and rat turds. Look for signs of corrosion, rust or damage, especially the caps/resistor leads and tube sockets. If all looks clean and dry plug them in. 7 years wouldn’t worry me. 40 would.

If in doubt or not feeling confident, take em to a tech.

6

Thanks all so far. Nothing so intrusive as vermin, but maybe a spider or two. The temperature is a bigger concern than water or wildlife (although damp air may be a consideration).

7

Condensation can cause problems, even when the amp is kept indoors. The white fluffy stuff on the resistors, wire and sockets is mold or mildew. I spent a few hours using electronic solvent and a box of q-tips to get this old Premier 71 spick and span.

8

I would suspect blowing them out and cleaning they would probably work ok to start out. Non use and broad temp changes tend to be bad news for filter capacitors, and I would not be surprised if after a couple of months of use some problems in this area didn't start showing up......pops, crackles, hum, ect.

9

Deke, I'd just go for it. Switch 'em on and if nothing nasty happens for about ten minutes then plug in and turn it up. I appreciate this isn't exactly a scientific method so maybe a domestic fire extinguisher could come in handy!

10

I bought a 1963 Fender Tremolux off eBay a number of years ago from a guy in Altantic City. After a year the volume started to cut out or fade when playing it. I took it to my local amp tech to check out. The seller said it had a cap job and grounded plug done which my tech confirmed. The only issue was it had an insect infestation at some point. The inhabitants had left. It took him hours (and cost me $300) to clean it up. Works perfectly after the cleaning. Still don't know what critters lived in it.

11

Deke, I have a 40 year old Fender tube amp, that set unused for about 10 years. When I resently plugged it back in, it had a wicked hum. The power supply electrolytic capacitors had dried out, and I had to replace them.

If you plug the amps back in, and everything is fine, vacuum out the dust (don't blow), and drive on. Sometimes the pots might need to be sprayed out, with a cleaner/lubricant, if they are scratchy sounding. It's also a good idea to spray out all of the input and output Jacks, with an electronic cleaner as well.

12

The worst possible thing you can do is to plug them in and turn them on without servicing them first.

13

Billy, I suspected that would be the case. I have to confess I was in the plug-it-in-and-see-what-happens brigade, but there's a lotta volts in there and I'm not ready to go just yet. I found a good guy locally who fixed my Music Man last year so I'll give them to him to make sure everything's OK before flying solo. Thanks to all for the input.

Just for the record the amps in question are a '64 Fender Showman that I completely rewired about 25 years ago, and a 1966 Vox AC50 that's in an AC30 combo cabinet. Both great amps. Oh, and there's a '59 Gretsch 6161 in there too...

14

Deke, I suggest you do it the right way (IMHO) if you decide to do it yourself.

Put a 100W or so bulb in series with one of the amp mains 120v input wires if you dont have a variac. (I use a variac.) If you feel comfortable doing that then you should have all you need to bring it out of its dormancy.

Then switch on. The supply voltages will be quite low and will help the supply capacitors to slowly get back to life. One of the biggest problems occur when you ramp up old electrolytics after extended time standing to full B+. Most times you can save all capacitors by just ramping up the voltage slowly as I describe using bulbs in series if you dont have a variac. They will generally not fail this way.

As others said, spider sh* is usually everywhere, and it is usually quite conductive and arcs at high voltages especially inbetween tag board terminals that can cause a plasma fire. Dried Rodent urine is one of the main reasons for arcover. on sockets and tagstrips. Rats ate my 1964 Vox TB Choke and removed most of the insulation to nest elsewhere and p'd all over the sockets. Since I worked on amps my entire life I restored the Choke to new condition, but I now plug the openings in my vox with fine mesh wire. They can now go gnaw on my wifes Gucchi bags, I now keep electronic rat traps with my amps permanently. Dont think I live dirty, most people have no clue they have mice in the house. They are always there.

Running the amp for an extended period with a 20 then 60W ultimately 100W bulb in series will heat things up enough to get rid of immediate mold/dampness arcovers if it stood a long time.

I wouldnt advise you just switch it on if you have reservations, trust your reservations and try using bulbs in series with mains and let everything reform slowly before you go full B+.

If there are no problems with tubes plugged in with a 100W bulb in series you can see, you can try full power. It is not a guarantee you wont have a plasma fire, or a firecracker capacitor, but it takes care of 90% of the cases of trouble I found.

Some of the amps you mention are 500V plate voltage, so it absolutely necessary to bring it up slowly after such a long downtime.

Shame on you for storing such nice amps in the outhouse. If your outhouse looks like PowDogs, then you will have mold and rat urine all over it. Hopefully you dont jam there. Would make a nice Jazz club I guess.

15

Don't stick your tongue in anything. Wear rubber

16

Don't stick your tongue in anything. Wear rubber

That's good advice right there, yessir.

17

Don't stick your tongue in anything. Wear rubber

– Vince_Ray

I think I was at that party...

Thank again for all the help. Retnev, your post is encouraging, The bulb idea sounded pretty easy, but I ordered a variac today so will proceed over the weekend to follow your advice. Can you go into a bit more detail though:

  • How many steps should I take to get up to full power?
  • How long should I leave it in each step before stepping up a notch, seconds, minutes, hours...?
  • Do I power down in-between?

Also, I'm in the UK so our power is a nominal 240v, but is usually a bit less than that, especially out in the sticks where we are.

Yeah, shame on me, I know. In my defence it's not an outhouse, it's an outbuilding. It's a timber-frame, timber-clad shed I build in 2013/14. It has double-glazed window and door, and is also lined with a breathable DPM in between the framework and the cladding. It doesn't leak and has had a dehumidifier running for the last year or so to cope with any damp air that comes in. There's no evidence of rodents anywhere that I can see. My biggest concerns are the possible damp, temperature drops (again, I'm in the UK so our low temperatures are pretty mild compared to some; maybe -5C is about as low as it goes generally, although it did get into minus double figures a few years ago), and length of time out of service.

The Showman was last used July 2012. The Vox was serviced in around 2007 and after a few years dormancy was fired up in 2016. It popped and crackled a bit, but no more than it ever did in my ownership. The Gretsch was probably fired up within the last 4 or 5 years (as a side note, the Gretsch is 110v and I run it on a 240/110 step-down).

18

Variac is the way to go. Great that you made the right choice.

I will write up the method I suggest. I havent answered yet as I cannot upload images for some reason to gretschpages and have to use external links to my photos.

Give me a bit of time.

20

BTW, when do you expect to get the variac ?

21

I’m away on business, but I got word from home it arrived yesterday. I’ll be home later today and plan to start on it tomorrow am UK time.

22

Here is the written information: I might make a video later putting a fault I fixed back in an amplifier so you can see what to expect, but I have upload problems with Gretschpages.

Legalese: Please note I supply this information how to do this, and do not tell anybody to actually must do it. I bare no responsibility for anyone's actions performing these steps. I know legalese is annoying, but it has to be said.

It is a howto based on my experience working on amps and I by no means take responsibility for anyone performing this and doing something stupid. Safety is paramount

That said, these steps can be performed without taking the chassis out of the amp enclosure so it is certainly as safe as playing through an amp.

I understand that you already wired tube amps in one of your previous posts, so you should know all that is needed for basic work such as this.

How many steps should I take to get up to full power?

See below.

How long should I leave it in each step before stepping up a notch, seconds, minutes, hours...?

See below

Do I power down in-between?

No, only if you have a problem

1) I work with 120VAC here so I will adjust the required voltages as read on my variac for your 220-240V mains.

Since amplifiers do not have the same standby switch location in circuits it is senseless to rely on standby. So standby will be on when the amp is switched on in below tests. Standby is left on when amp mains switch is switched off, so that capacitors can discharge.

Procedure:

Preparing the Variac.

First check with a multimeter if your variac passes ground wire through to the output ground. Some variacs ship without ground pass through (fully isolating variacs) . This is dangerous and means the amp will be ungrounded ! Please check the variac.!

1) Turn the Variac to Zero. With the amp unplugged connect the multimeter (set to AC Volts) to the variac output. Check that the variac measured output corresponds to the Voltages printed on the top of the variac. You will find that the marked scale on the variacs are usually quite off. 2) IMPORTANT: You need to set your variac so that the multimeter reads 240V (if your mains is 240V) or 220V (if your mains is 220V) etc, I assume you have 240V. 3) Now use a piece of two way sticker or something that you can stick on the top of the variac so that it can never pass this 240V setting. (Better variacs has a hard stop set screw for this purpose to constrain maximum voltage) Remember variacs can upconvert by aboout 50% ! (If you accidentally pass 240V you most definitely can damage capacitors as the B+ varies by at least 2x your overshoot and you can easily pass the capacitors voltage limit)

4) So now your variac is set to never be able to pass 240V and is safe to use. Set the variac back top zero volt.

5) Preparing the amplifier. 5.1) Make absolutely sure that you have the correct fuse in the amp, else the OT can blow in fault condition if you have a plasma fire. We will try to avoid any plasma fire by selecting the following voltage steps on the variac. 5.2) Connect the amp to a speaker at all times, I usually use a dummy load rather than a speaker but I will assume you dont have dummy loads. 5.3) Make sure speaker is at the correct impedance w.r.t the transformer.

6) Now you can plug the amplifier into the variac.

Performing the slow ramp up. 6.1) Variac at 0V, amp plugged into variac. 6.2) Switch on both mains switch on the amp and the standby if it has that. 6.3) Since you have 240V you need to select the voltage in the following steps. 30V 60V 90V 120V 150V on the variac 6.4) 150V is important as that is where there will be enough emission for the amplifier to just barely work and it will be just just operational as an amplifier and is our safe operational voltage. More later. 6.5) With the amplifier switched on (both mains and standby switches on) and the variac at zero volt, increase the variac to 30V. Check if the pilot light on the amp starts glowing, usually it doesnt yet. Leave it at this voltage for about 2 minutes. 6.6) Now increase variac to 60V (the pilot usually starts glowing dimly at this stage) At this stage you usually have about 120V B+ This one is quite crucial. Keep at 60V for about 5 minutes 6.7) If all is OK adjust variac to 90V for 5 minutes. At this point in old amps you might start seeing little arcs appearing if there are bad quality tag strip substrate that absorbs moisture. (I had that problem last week). If so obviously shut down if not continue. 6.8) Set variac to 120V, at this stage there will be serious arcing if there is a fault due to rodent urine or mold or dustbunnies or moisture absorbsion. At least it wont be able to blow your output transformer at this low B+, but enough arcing for you to see you have a problem. If just switched it on it will blow the OT if the fuse were no quick acting enough or wrong type. Again leave it at 120V for 5 minutes 6.9) If you made it at 120V you are almost in the clear. If no problems encountered during previous step, set variac slowly to 150V and see if you dont see any arcing or noise or ozone smells etc. The tubes should all glow at this point. Again leave it at 150V for 5 minutes. At this stage after 5 minutes you plug a guitar cable into the input, you should hear weak signal noise if you touch the guitar cable tip as the amp should be just just in emission. Without a guitar cable in the input you should not have a lot of mains hum at this point. If there is a lot of 50HZ (in your case) hum (or more than you could remember) , then supply capacitors failed. If normal hum and you get signal in the speaker when you touch the guitar cable tip, the amp should be ok to use normally.

7) Doing the last stage. 7.1) Keep the guitar cable in the input. 7.2) Now slowly take the variac voltage up from 150V to 180V and leave for a minute, Then 200V until you reach 220v. 7.3) Stay at 220V for 10 minutes. The amp should be well usable at this stage. During this 10 minutes the amp will warm up nicely. 7.4) If all goes well after 10 minutes you can go to 240V. If all still goes well at 240V after say 5 minutes, you can set a time aside that amp will be in the same room as you and leave it on for an hour or so to heat up properly and drive all moisture out. At this stage dont just switch the amp hard on and off, still use variac to ramp up slowly, but at this stage you can just just ramp it up from 0-240V in 10 seconds or so. 7.5) After an hour all the moisture should be gone and it should be fine for use. Unless a rat urinated on it which can cause all kinds of circuits created, but you should see such trouble clearly around the 150V stage.

Afterthoughts I did it in more detail as I should, but you should get the method clearly. It is easy. Best is to have the amp chassis out when you do all this so you can watch the underside where the tagboards are for arcs and trouble, while not touching anything, but if you havent worked on amps before just leave it in the box and dont open up the amplifier.

If you are experienced and did take your amp chassis out, and you set the variac to zero, make sure that the standby switch remains on .. Dont switch it off as it helps to drain the capacitors and minimizes risk of shock if you do something silly.

That is basically it. Anything that happens sideways from the above can be dealt with separately.

I was about to make you a video to show you how to do it and I wanted to place an error I had on an amp last week back into fault to show what a fault condition look like, but I cannot upload anything to Gretschpages. I will still do it and post it from my ftp site later if you are interested. But it sure would have helped to see it first hand what you will encounter with a dormant amp with a typical problem.

Ask as many questions as you want before or during the procedure.

23

That is very detailed and exactly what I was looking for. Thanks for going into so much detail. The error would be useful to see, but I don’t want to put you to any trouble.

Yes, I did fully rewire the Showman about 25 years ago, but I’m not the most experienced when it comes to amps and have no intention of doing anything even remotely risky. I will likely pull the chassis so I can keep an eye on the tag strips, but I’m fully aware of the risks involved and will take the appropriate precautions.

Thanks once again for the info, I’ll let you know how it goes.

24

One further question; is there a safe way to discharge capacitors or will leaving the standby switched on at power-down be enough?

I’m all about safety and it was just dumb luck I came to no harm during the rewire (back then I just assumed if it wasn’t plugged it then I’d be safe). I’m better informed now of course, but if there was a way I could be SURE the caps were clear I’d be glad to hear of it.

25

The short answer to discharging capacitors is unfortunately a BIG NO in general. There is no safe way unless you know exactly what you are doing. Any capacitor i.m.o charged to a voltage above 150V becomes problematic.

Just keep the amp in the box unopened and consider to do the test as I described. At the first sign of trouble put the amp aside and consider plan B. Move on to your next amp after that.

Again, please make sure your variac passes ground (earth in your neck of the woods) to the amp. Luckily you have earth-leakage in europe so most accidents are prevented. Here in the US unfortunately there is no earth leakage (only for bath rooms) which I find laughable and the lack thereof causes a lot of deaths here. (Remember the bathroom cellphone charger guy ? He would be alive today if US electrical codes included earth leakage. )

At least you wont pay 5x$300 = $1500 for someone just to variac your amps. The ones that dont want to come to life will be at most 1/5 and you can only spend on that one if you really have to.

Standby switches are actually introducing dangers and should be removed from amplifiers or it should be implemented correctly . I am in that camp. By removing a standby switch capacitors would arguably in most designs discharge on their own through the passive components in the circuit. Some standby switches keep the capacitors charged as it only disconnects the capacitors from the load. Those are the dangerous standby switches. The safe standby would be placed just before the choke AND preferably after the capacitors with the second spdt and would be a dpdt, where the wiper is on the choke wire and the other two are wired to the HT and the other one a resistor to the ground. the other switch channle of the dpdt does the same after the capacitors. In this case when the standby is activated, the capacitors are discharged .. always. No manufactuirer does this of course and most standby switches in designs actually keeps the capacitors at lethal charge.

That is why I said in the method that you cannot rely on a standby switch. Safest is to keep the amp not at standby at all times so the amp switches fully on and off with the mains switch of the amp as if there is no standby switch. That way capacitors will almost always discharge after a couple of minutes through the circuit.

Standby is actually in my opinion just useful for diagnostics and is indispensable when youi have a plasma fire and try to track it down properly. But for general use I really dont like them and is sure they cause a lot of the preventable accidents.

So in short, keep the amps in the boxes and only make sure your variac passes ground(earth) through to the amp. Hopefully your variac already has an output socket on it? Mine, I always have to wire up and add sockets to make it safe. Also again, make sure you constrain your variac to output maximum 240V. I bet yours will go to 350V which will put about +700V accross supply capacitors! They will pop, quite loudly.

Mind sending me a photo of your variac ?


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