Silvertone 1330

[lowell]

got one yalls?

[Sweetfinger]

Never heard of that model number. I thought the 133X series started with the 1331 which was basically a Champ circuit. Can you describe the amp, tubes, controls, and speaker(s) ?

[lowell]

It has 3 pentode-looking tubes in it. All tube markings have rubbed off over time or were never there. It's a 6" speaker and the OT is mounted ON the speaker terminals - very odd. There is no PT. I don't have it here w/ me at home, but I swear it said model 1330 on it... I'll double check in the morning. I did look at the 1331 schem and it looks as though it could be that, although I've not found a schem that I can actually read. They're all blurry the ones I've found for the 1331.

[Sweetfinger]

It isn't unusual in older stuff to see the OP X-former mounted to the speaker frame. Pull a tube and look carefully at the socket. Some of those older sockets have the tube type printed on them. You might get lucky.

[JHow]

This may sound dumb, but it sometimes works:

If you clean the tube gently with damp rag (I am assuming they are dusty) and then fog the tube with your breath on the side (or top) where you expect the tube ID to be, you can sometimes read, very faintly, the tube markings. If you have luck with this, then mark the tube base or box so you remember what it was.

Some of the smaller silvertones were transformerless and you can expect designs with things like 50C5 power amp, 12AU6 or 6AU6 preamp and 35W4 rectifier. Also you may have only a filament transformer, not a full power transformer.

If you know what the tubes are, its pretty easy to make your own schemo for a three-tube circuit.

[lowell]

Yep says 1330 right on the plate of the chassis. There's a 12sj7, 50L6, and some rectifier. I see about 5 digits near the rectifier... the 3rd and 4th letters look like Z5 but not totally sure. Anyone have the 1331 schematic in good quality? That may help.

[tboy]

the 3rd and 4th letters look like Z5

35Z5 would be likely.

[JHow]

35Z5 makes sense, being the octal version.

You may have to draw schemo yourself. The usual free sources don't seem to have exactly 1330. Schematic heaven has a very fuzzy copy of 1331, that provides little info.

[Sweetfinger]

The question now may be - Why do you need a schematic of this? Is the amp dead? Works, but you want to mod it?

[lowell]

I'm getting this amp up and running for someone. Aside from not knowing what the tubes were, there are a couple questionable components inside. Namely a cement-looking resistor that is inside a screw mounted bracket - this resistor is cracked and I'm curious what value it was. It's not your typical rectangular cement power resistor, instead it is thin like a wafer or cracker. Never seen one of these in a tube amp. I've yet to take it out of the bracket but will start just going to work on this amp since a schem looks to be unobtainable. I'm going to replace that resistor if I can find some markings on it or see what its purpose is in this amp is and use my best judgement. Then I'll fire it up w/ the bulb limiter etc...

[J M Fahey]

This amp is a KILLER !!

1) This amp is a KILLER !!
No kidding.
It sure has no power transformer, meaning the chassis or ground is tied to one side of the power cord.
Keep it strictly as a collector's item (that means never plug it), or use an 1:1 isolating transformer. No kidding.
2) Those flat, wafer-like power resistors, often covered in sand or a similar product, are called fusistors, and meant to crack open when severely overloaded.
Trace the schematic by hand and compare it to similar ultra-cheap beginner amps such as Valco, Kay, Supro, etc.

[lowell]

JM,
Thanks for the warning. I talked w/ the owner and already mentioned that he should have a PT installed in this amp.. and he wants it. Don't know why I didn't mention that in ANY of my previous posts. Better to be alive. Thanks for adding a clear warning to working on/playing this amp though.

[Sweetfinger]

At this point, plan on installing an iso transformer, or new power X-former and reworking it into an early Champ circuit. That is essentially what a 1331 is with the difference being a 6X5 rectifier instead of a 5Y3. Most of the early 3 tube amps are really similar in topology. Yours is probably something like this:
http://www.schematicheaven.com/barga...rtone_1301.pdf

[lowell]

Ok so I drew a little schem of the power supply. I cannot figure out what this component is. It looks like a cement resistor but is flat and square and was mounted in a metal bracket. I has cracked into a bunch of pieces. It says 22-1680ae on it.

[J M Fahey]

Probably a "fusistor". The name explains it all (fuse+resistor), They are a rectangular flat ceramic power resistor, usually covered in sand or a lookalike material, designed to crumble when excessively overheated. They were quite popular in B/W TV sets of yesteryear.
Just for kicks , have a glimpse of the future:
The Predicta Page from Greg's Sandbox
Mind you, not much older than your Silvertone.