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Post subject: Amp guru's please help me.
Posted: Fri Jan 02, 2009 4:14 pm
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My 59 watkins clubman has developed a hum. I've replaced the el84 and ecc83 valves but not the ez80 rectifier as i dont have a spare one. The new valves made no difference. I stuck my head into the back of the amp to hear if it was the power transformer of the speaker. The hum is coming from the speaker but does not increase when the volume is raised or lowered, it just stays at a constant volume.

Anybody got any idea's on what it could be?

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Posted: Sat Jan 03, 2009 1:48 pm
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Last edited by tinker tech on Wed Jul 29, 2009 10:36 am, edited 1 time in total.

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Posted: Sat Jan 03, 2009 4:33 pm
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Thanks Tinkertech. Its nothing to do with the guitar as it happens without a guitar plugged in. When the volume of the amp is on zero the hum is the same volume as when its on full and definately coming from the speaker. Also the hum seems to be kind of behind any amp noise from the circuitry, (crackles slightly when the tone pot is adjusted).

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Posted: Sun Jan 04, 2009 6:41 pm
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Nikininja,

I believe your valves are not the issue at all. This amplifier is 49 years old, and this is a common problem among the point-to-point wired amplifiers: your filter capacitors probably need to be changed. These dry out and begin to leak sometimes. A word of caution, DO NOT try to change these unless you are a qualified electronics technician! These capacitors in your amplifier are going to be charged with 400-600 volts, and if you touch the lead and the chassis by accident, you WILL get a nasty shock.
If you want to, take the chassis of your amp out of the case to look at the circutry. Near the large transformer, and where the rectifier valve is, you will see these large cylindrical capacitors. They will most likely be wrapped in coloured cardboard casings, these are the ones. Without touching them, look at the ends of them where the leads come out of them to see if you can spot anything that looks like a yellowish crystalline substance that might be oozing out. If you see anything like that, or close to it, then that is your problem. I'm pretty certain that is the problem you are experiencing regardless if you can see the leak or not.
Once again, be careful not to ground the leads with yourself. A technician will discharge these before replacing them. New ones will have to be powered up with a Rheostat before they will be ready to operate normally.
-Harley 8)

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Posted: Sun Jan 04, 2009 6:43 pm
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Sounds like it just needs to go on the bench to be checked. Perhaps a heat sensitive resistor or a capacitor that's bleeding. The Watkins is a glitchy little amp, and has some British gremlins, I swear. But it's a great sounding amplifier and worth going and getting checked rather than worry about it by not knowing what's wrong. Don't be cheap, get it fixed!


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Posted: Mon Jan 05, 2009 7:30 pm
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Thanks guys it looks like the cap's going. Now for the insurmountable task of finding a replacement. :(

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Posted: Mon Jan 05, 2009 8:21 pm
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Antique Electronics Supply carries them, it won't be so hard to find.

With all the old amps I have, I HAVE to know where to find parts :lol:

-Harley 8)

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Post subject: Re: Amp guru's please help me.
Posted: Fri Jan 16, 2009 6:17 am
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nikininja wrote:
My 59 watkins clubman has developed a hum. I've replaced the el84 and ecc83 valves but not the ez80 rectifier as i dont have a spare one. The new valves made no difference. I stuck my head into the back of the amp to hear if it was the power transformer of the speaker. The hum is coming from the speaker but does not increase when the volume is raised or lowered, it just stays at a constant volume.

Anybody got any idea's on what it could be?


Does that hum apears suddenly or it develops in time?


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Posted: Sun Jan 18, 2009 6:59 am
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Marius it develops as the amp warms up then stays constant. Power sources play a good part in the problem too. Use it in my house it hums wildly, in my mates studio its far less. I also noticed it has something to do with the metal speaker grille too. Press the grille at the bottom and the humm drops off further.

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Posted: Sun Jan 18, 2009 12:25 pm
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nikininja wrote:
Marius it develops as the amp warms up then stays constant. Power sources play a good part in the problem too. Use it in my house it hums wildly, in my mates studio its far less. I also noticed it has something to do with the metal speaker grille too. Press the grille at the bottom and the humm drops off further.


I think is a problem with some bad or"cold" soldering with a ground connection.You should check them! Try to see if the problem is in the power stage or preamp.Disconect the preamp tubes one by one and see how is the hum


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Posted: Sat Feb 21, 2009 5:17 am
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Its all but eliminated guys. Turns out the speaker had worked loose over time and was vibrating the metal grille covering.

Thankyou all.

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