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Made in Canada Silvertone "100" Twin Twelve head

Started by galaxiex, October 23, 2017, 03:18:29 PM

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galaxiex

I picked this up about a year ago. Finally got to looking at it.

Made by Mirtone in Weston Ontario, Canada.
Info on these seems to be non-existent. No schematics, nada.
Only thing I found was some other person looking for info too.

The only date code I found so-far seems to be 1966, so mid 60's design.
All germanium negative supply. -46V rail.
It is quite loud tho I doubt 100 watts.

Does not seem to have anything in common with the USA made Silvertone 100.
Those have a printed circuit board, this one, not at all.

Has nice compression/crunch at full volume.
The reverb sounds like ass. Very artificial metallic clank noise.

Did the usual 3 wire cord and clipped death cap.
Added a fuse holder as there seemed to never have been one!

It's quite noisy (hissing/rushing noise) but I'm waiting for the 3 can caps to see it that helps.
Temp jumpered up a big cap to the main cap can and the noise got a little less, so we'll see.

Already replaced all other small electros, what a pain point to point terminal strip wiring is!
Very robust construction but a dog for repairs and making changes,
unless you just clip the part and tack on a new one. Not my idea of the right way to do it.

The Mirtone model # is hard to read, says GA-100.

Reverb tank held with failing double sticky tape so I bolted it in with some rubber grommets.
If it ain't broke I'll fix it until it is.

galaxiex

#1
The bad reverb sound was bothering me a bit,
so I visually traced the recovery circuit and added a 100nF cap from emitter to base on the recovery amp transistor.

HUGE improvement.  8)

The reverb control is bottom left in the pic.
Green cap is obviously the one I added.

Reverb is actually usable now.

Edit; In the first pic the transistor is hidden behind the cap.
If it ain't broke I'll fix it until it is.

galaxiex

The new caps came today.
I love DigiKey, stuff comes overnight.  :dbtu:

Old and new caps from left to right.
1600uf 64V   2200uf 100V
1250uf 40V   1500uf 200V
1250uf 25V  1500uf 200V

The noise I mentioned before is about half as much with the new caps.

To describe it again, its as if you were constantly quietly balling up a piece of paper.
Kind of a unsteady hissing rustling noise.

I suspect what I'm hearing is leaky germanium transistors.

Playing with the controls has no effect on the noise.
Inputs shorted to ground and all controls at "0" noise is still there,
so I further suspect it does not originate in any of the preamp circuits.

The amp seems to work fine otherwise.

Thoughts?
Thanks!
If it ain't broke I'll fix it until it is.

galaxiex

Well... I found the noise!  :)

One of the germanium transistors in the preamp was wired backwards.
Hidden behind the heat sink.

Swapped collector and emitter leads and now just normal junction hiss.

Disconnecting various parts of the circuit helped track it down.
Looked like it had been that way since day one.

This amp must have been noisy since new.

Did folks expect these to be noisy and just live with it?

Turning up and playing, the noise was not audible so....?

Forgot to take pics and now the heat sink is back in place, oh well.
If it ain't broke I'll fix it until it is.

galaxiex

Well, I'm calling this one a success.  :)

Here 'tis all back in its cabinet.

On to the next....
If it ain't broke I'll fix it until it is.