Simms Watt 100w Head

[josegrad]

...It is often feasible to retension female socket contacts, eg using a dentist's pick tool; try a google search for more detail.

Yep I did check google.
In this amp the sockets are of this type:



Adjusting the grip of the terminals is a bit hard since they are quite deep inside.

I think if those were like in the next image that would be easier.

[pdf64]

With a suitable tool, and manipulation of the contacts from the solder terminal side, it's often feasible to bend the contact forks in a little.
Obviously , ensure that the amp is isolated from the mains and its power supply caps de-energised before attempting that

[J M Fahey]

Just thinking aloud:

Now the amp is very sensible (some clicks and pops) to any kicks, even hitting the wall in a nearby room causes some clicks. That's after the new valves.

You always had them, or at least lately (measure that in years), but you didn´t notice them because dead/almost_no_emission tubes act as a cheesy "noise gate" , as in you need to drive them hard for them toproduce any output at all.
And now they are sensitive as new.

FWIW this causes some friction between techs and uninformed users: "hey, now the amp is noisier than before / it feedbacks too much / etc."

[pdf64]

It's a prime example of mission creep; fixing the HT cap issue revealed that the power tubes were dead, replacing them revealed a noisy / bad connection somewhere.

[josegrad]

Hi all. Happy new year!

I have the impression I should replace all the pots. I've clean them with contact cleaner, but I think their effect in the sound is now what it should be.
Channel two it not completely ok either so I should check it again.

But. I've been thinking for a while if I should just sell it and get a small tube combo.
I don't play around anymore so the amp wont ever get the use it deserves again.
But I don't know if I will regret it later. Though it was stored for 15 years until few months ago.

[Chuck H]

I might pursue a completed repair before flipping it for another amp. For one thing, you're already way past getting compensation for your time back from any purchase price. For another, the amp was good to you. If you sell it "mostly" working it will continue to trouble the purchaser and possibly end up either coming back on you or worse, end up languishing on a shelf until age and disuse render your old amp a useless doorstop.

At best though I suppose it's possible the amp will eventually find a tech that'll fix her right up. But I think that's the least likely scenario statistically.

I have my own regrets about some of my old amps that correspond with my position.

JM2C

EDIT: Oh, Happy New Year to you too.

[josegrad]

...the amp was good to you...

Yes. I mean now it would be sitting around and eventually used, at low volumes of course. So it would be kind of having a beast in a Zoo.
I bet the amp wants to run free and scream loud :-)

Of course IF I'd sell it I would make clear it should be properly serviced.

[josegrad]

I've decided to change the pots.
Some do strange things, like operating then fading away, if I press them a bit then clicks and change in volume happens.

But in the schematics I can only locate 5 out of 8. Any hints?

https://music-electronics-forum.com/...7&d=1542389576
https://music-electronics-forum.com/...8&d=1542389601

Also there's no indication about linear or log variant of the ones I can see in the schematics.

CORRECTION: I can actually see some details written on the pots, but I can't see all of them before I take them out.

[pdf64]

Each channel looks to have treb, bass and vol controls; so with 4 channels that makes 12 total there, plus master vol and presence, 14 in all?
I suggest log aka audio taper for them all, apart from linear for the presence.

[Chuck H]

Your amp has an additional "channel" that is only implied in the schematic. It would be the same pots as the preamp schematic X2. I can't know the actual taper percentages, but odds are it's all log (audio taper) pots except for the presence control, which would be linear taper.

[josegrad]

I've located now all of them. Volume, treble and bass are replicated, so the same for both channels.
I'm now taking note of the specs of each one, which is written on them.

500V voltage rating is enough right?

[Chuck H]

You shouldn't need to worry about it for any standard size pots. The circuit design has them isolated from high voltages.

[josegrad]

Just to have them listed here's the set of pots.

CHANNEL ONE

Volume	1M Ω	LG A1 AB CTS
Treble	250K Ω	LN E0 AB CTS
Bass	250K Ω	LN M0 AB CTS

CHANNEL TWO

Volume	1M Ω	LG A1 AB CTS
Treble	250K Ω	LN M0 AB CTS
Bass	250K Ω	LN M0 AB CTS

COMMON POTS FOR BOTH CHANNELS

Master	500K Ω Log	This one is a different model, might have been replaced at some point
Presence	5K Ω	LN E0 AB

So all clear.
I just wonder what the A1 AB, M0 AB, E0 AB mean. I don't have access to such a selection variety, at least with easy access.

UPDATE: I guess the letters are related to some characteristics of the pots. Which might even be obsolete today.
I guess part of the ordering information like in this pdf: https://www.ctscorp.com/wp-content/uploads/026.pdf

[HTH]

Well... What I see is that somewhere along the line someone (probably on more than one occasion) kludged that amp with an odd assortment of filter caps (one of which is axial instead of radial) and added a series resistor to the B+ string after the standby switch putting exposed high voltage nodes within reach of the user from outside of the amp. All I can say is that this is a very bad thing that can result in death if such an accident were to happen. Soooooo...
.

That big wire-wound resistor on the top of the chassis is a stock arrangement - I have three of these amps (though they’re the earlier clear-panel ones). The resistor gets quite hot, so I’d imagine they put it there to dissipate the heat better, rather than keep it inside the chassis.

I put a choke in one of mine and I’d recommend anyone doing this - I just prefer the feel.

[Chuck H]

That big wire-wound resistor on the top of the chassis is a stock arrangement

Yes. That was revealed in post #4 on page one. And I acknowledged in post #6. Thank you.

The resistor gets quite hot, so I’d imagine they put it there to dissipate the heat better, rather than keep it inside the chassis.

Of course. But IMHumbleO that's not a good reason to have HV accessible outside the chassis. And I said as much in post #6.

I put a choke in one of mine and I’d recommend anyone doing this

Good call. Being as josegrad was using his as a bass amp (IIRC) a choke would seem like a better choice than a resistor.