Tube Amp Service Time - Pot Removal From Chassis Anyone?

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User211

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My Bill Beard needs a service - tube sockets need replacing, potentiometers need cleaning etc etc.

But I have a problem - how do you remove the potentiometers used as balance controls? See the pictures below. The first shows what looks to be a clip.

The second shot shows the back. There is a nut underneath the pot but it is pretty inaccessible - I have no tool that can get behind it, and if I did, I couldn't move it much.

There are two such pots. They can't be cleaned as far as I can see, but the wipers are in a bad state.

Question - how do I get them off the chassis? Remove the clip? If so, how? Are there special tools for it? A screwdriver is risky (I have tried) and I don't want to damage the chassis finish.

The blue Alps pot I have disassembled and can just prise open to get at the wipers with some Deoxit.
 

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Difficult to tell with the flash and reflections, but the brass nut(?) appears to be knurled. If it is the nut, I should think you simply unscrew it from the body of the pot, allowing the stem of the pot to pass thru the chassis. The circlip is more likely used in the assembly of the pot, itself.
 
The brass-coloured ring is actually a nut. Put a couple of layers of masking tape on the jaws of a pair of pliers, and try to hold it as you gently rotate the pot. Remove the wires first. That'll get the pot loose. For your ALPS pot, after cleaning I recommend Caig's Moving Contact Lube applied to the wiper. It's designed for such an application, and for switch contacts, etc.
HTH!:D
 
Thanks for the quick response. Will give it a try later.

It does beg the statement "what a ridiculous thing to use". Is there any logic behind this circular nut? The Alps didn't use one, just had a normal nut for easy removal.
 
Justin, don't replace the ALPS pot with another ALPS. Use a DACT stepped attenuator instead. You will be astounded at the improvement in sound. It is expensive ($200 here), but well worth it.
 
It's not worth it, Bernard. It's just for a lowish res 2nd system. Going cheap on this one. If it was still connected to my old Aerius, as it used to be, it probably would be.
 
Said pot removed. However, they are completely sealed - no way in for a cleaner...

It's a 500K mono pot, made by the Violet Electric Co, Japan. A web search reveals nothing. The amp is 18 years old, so it may be this component no longer exists.

I found this, but dimension wise, it's a bit too small: http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5220524#header

I've spent quite a time looking, but come up with nothing better so far.

The dimensions of the casing on the Violet are 3cm diameter by about 1.5 cm depth. But the critical bit is the rod - the thread part has a 0.9cm diameter, and the non-threaded part - the bit the knob fixes onto, is about 0.6mm. It's 2cm long.

Any recommendations on a suitable part would be fantastic... and if it's a plastic type, like my Mod Squad Line Drive used to use, I'd be over the moon - they just don't go noisy.

Whole underside shown with faulty sockets removed. Apparently, smoking kills!:D

Check my system pages if you want to see why the amp is worth saving. Not only does it sound very nice, it's a beauty too!
 

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Well, in the end I ordered 2 500K Alps pots - though they are stereo, they will fit in all respects. Obviously, each pot will be wired for one channel only.

Also, all 220uF 25V caps - 12 in all, will be upgraded to Elna Silmics. These are in the signal path, and the effect on sound is profound. I know this because the Rubycons were once replaced with a non-audio grade cap, because one went wrong, and I soldered all 11 original Rubycons back in, leaving the cheapie in place for the broken one. The amp simply sounded terrible with the replacements.

Additionally, I will probably hook it up to some Mark & Daniel Maximus Topaz & stands for a modest stereo lounge system - TV sound, mainly.

One advantage of buying garage built electronics - you can fix/upgrade yourself, and very, very easily. This old amp will live forever...:)
 
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Let's qualify that - I can fix a lot of problems as long as they are relatively simple. There are problems that can occur that I would not be able to detect with the test gear I have. However, it is easy for me to get the use of extremely advanced kit, and far more electrical knowledge than I will ever posses!

Also, there's the obvious danger of messing around with high voltages...:devil:

So really, it's just something that works for me, I suppose!
 
Whilst I appreciate this isn't the best DIY site, maybe Tube60 can help. Worth a shot, anyway.

Basically, today I replaced 2 tube sockets, all the 220uF caps with the Elna Silmics and all three volume pots. Hooked the sucker up to some speakers, and hey presto - the amps sounds fine, an odd noise that came on and off in one channel has gone, and all pots make no noise when used. Great!

Not so fast - the heaters on the replaced sockets don't come on. According to the manual, the amp will work fine with just one operational tube per channel (there are six per channel). Obviously there is power loss and an aesthetic problem. Power loss no problem for the speakers concerned.

Question is, why? All 9 pins for each socket where nicely soldered - pretty sure no dry joints. But pins 4&5 (the heater pins) show continuity in all other sockets but the replaced ones when doing a simple multimeter tone test.

Is it possible both sides of the PCB need soldering for each socket - cos they are for all the others? I am thinking the PCB tracking is on both sides of the PCB. This is a pain if true, since removing the PCB is a real feat. I can do it, but I don't want to.

Shot of the job below with all other work done and about half the Elna's in.
 

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Yup - after some reading & reasoning, pretty sure it's a double sided PCB, and the lands for the other active pins are on the other side. What a b****r.

Oh well. PCB comes of next weekend.
 
Whilst I appreciate this isn't the best DIY site, maybe Tube60 can help. Worth a shot, anyway.
I hope so! It's very likely that the heater voltage is carried on the other traces, and the solder points visible with the pcb in place don't carry voltage. What you're going through is THE reason I don't do anything BUT point to point wiring on an amp. What I'd suggest, if you have the schematic, is trace out the heater supplies, and, brave moment, cut the traces leading to the sockets, and abandon them. Get some good quality wire and bypass the heater traces, going directly from the supply to the sockets.
HTH! Good luck on getting it going properly.
 
Hm - 18 tubes with cut tracks and heater supply wiring = bird's nest for sure!

For this design, a PCB isn't such a bad thing due to the tube count. You'd like the insides of my 211 monoblocks, though...

Actually, my Air Tight ATM2 was hardwired. I showed it to a DIYer and he hated it - too complicated and tightly packed. He was a member of a pack of insane tube DIYers, including WE 212 amp builders. I have a pic of the inside of the Air Tight on my laptop. Will post it later.

Here's Justin's rule book for what electrons like:

1) Full hardwiring.
2) Woosh! Getting heated up and pushed through outer space - er, make that a vacuum.
3) Proper sized components - non of yer surfaced mount rubbish. Do you like being in a straight jacket?
4) Amp runs hot - buzz buzz happy party time electrons.
5) An easy path to walk through - no mazes - they get lost:D!
6) No pushin' and pullin' - do you like that? Nor do electrons. Single file please:)
7) No (or not much) negative feedback. Even ebayers don't like that.
8) No rules. Distortion at 0.005%? What's that? Don't understand. I'm only a stupid electron.
9) Sssssssshhhhhhh - nice and quiet please.

Got to look after those little fellas. They have feelings.

This post is a little tongue in cheek, but some of it rings true for a certain type of sound i.e. the one I like!

You treat me right, sez Mr Electron, and I'll carve you a huge soundstage full of euphony and be really nice to your less than great recordings.
 
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Air Tight ATM2 inards pic. Most DIYers probably have a problem with the retail price versus the component cost with things like this. It's only using ALPs blue pots, Nichicons etc, but it was and is a good, well built, KT88 based amp.
 

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Didn't realise there were that many tubes in that amp!:eek:
Hopefully when you get that board out this coming weekend you'll find the problem!
 
The problem was the tube sockets I removed. Because they were soldered on both sides of the PCB, on the unexposed side, the solder ripped off a few millimetres of track on pin 5 (heater supply) for both sockets I removed.

Up and running, all tubes lit. Pic taken during quick test after the fix...

I've learnt a few things - always use solder with LEAD in it - the lead free stuff isn't as easy to work with. Also, I can inform you there is a very significant labour cost in hand made tube amps. These things must take hours to put together, even if you're really good at it. The labour cost must be beyond the parts, really.

Plugged into the Scandyna Drops via some temporary bell wire, it sounds very pleasant. However, compared to the Drops driven by my 211s, there's a big distance. Ridiculous, in fact. The Drops sound 3 times the size with way more bass extension via the 211s.

Anyway, very pleased - Bill is sounding much cleaner and the relief of replacing those noisy pots to return to "clean" volume control is very welcome. Now I'll wait a hundred or so hours for those Elna Silmics to burn in, and I'm sure ole Bill will be better still.

Provides better sound than the X series Sony TV, that's for sure, which was basically the idea.
 

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That's a good looking amp! Glad to know you've figured the thing out.
I've used silver solder but I don't like how it erodes the solder iron tips, so I've gone back to traditional 60/40 solder, which unfortunately will soon be banned. I'll be stocking up a lifetime supply when I can.
 
Yeah, I heard that about 60/40...

Point about the construction of this amp - just soldering in the tube sockets is 324 solder joints... hmmm:)

And yeah - I think is is one of the best looking tube amps I have ever seen... totally cool in my book.:cool: There's better... but hey.
 
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