Silvertone 1448 guitar case amp

[jim]

A guy want me to "restore" this.  It lights up fine on the limiter but there is no sound at all.  I cannot get any click from the speaker by using a battery.  I'll try a 4 ohm speaker later.  Obviously I'll need to install a polarized AC plug with safety ground.  I have never worked with an isolation transformer and I know I'll need one.  What is appropriate and how do I wire it?  Can it fit inside the box or
perhaps externally on the box? BTW, the "chassis" is press board.....

[PRR]

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[jim]

Thanks, PRR.  The amp works fine with a known good speaker and actually has decent low volume tone.  I'll make it safe to play.
Jim

[HotBluePlates]

Should he yank C3 (cap from filament string to chassis) after installing the iso transformer?

[sluckey]

I would. In fact, I'd replace it with a piece of wire.

[jim]

got it! thanks.   Jim

[PRR]

> Should he yank C3 (cap from filament string to chassis) after installing the iso transformer?

It needs "something" there to return V1 DC current and pass signal from V1 to V2.

What do we want?? To make it "good"? Or leave it sadly-stock (except no-shock)?

You could quickly make a very-good case-amp with a heater transfo and an LM386 or LM383 chip-amp. Get new pressboard, transfer the trim, all reversible for eventual collector value.

If you like tubes, Epi Jr, stock or mod, is a much "better" tube amp at bargain price.

IMHO, if you are gonna futz with this, it is for "original flavor". Not hot-rod potential.

R5||C3 limit shock-current but also affect operation of V1 so that it must strain more to drive the 50C5. "Fix" it, less flavor.

But WTH. You can instantly jumper R5||C3 and try both ways.

[CraigB]

Just want to make sure I am following the diagram PRR posted above correctly for wiring one of these up with the triad isolation transformer.  Does the green line represent U-ground on a three-prong power cord?  Also, apparently there is no advantage to having a separate 12.6v filament supply for the 12AU6?  Thanks!

[DummyLoad]

...Also, apparently there is no advantage to having a separate 12.6v filament supply for the 12AU6?

no - it is not needed.

Does the green line represent U-ground on a three-prong power cord?

yes. power source ground to chassis.

--pete

[PRR]

> no advantage to having a separate 12.6v filament supply for the 12AU6?

The original 12AU6-only heater transformer was a halfway measure to decrease shock around the input jack (12AU6).

Now that you have the WHOLE amp on a proper power transformer, that cheater transformer is redundant.

It is like putting a muzzle on a vicious dog, or putting the whole vicious dog inside a cage. With a proper cage you don't need the muzzle.

Obviously in context of a $9.98 amplifier the kid would out-grow in a year (if he lived), the halfway measure was preferred. Now 60 years later, if you are still messing with these things it is justified to make them safe-safe-safe, and incidentally clean-up halfway safety measures.

[CraigB]

Many thanks Gentlemen!