Silvertone 1432

[mtlbasslad]

Okay folks, fresh off the success on the Marshall - here's the next problem...



This was given to me by a neighbor who pulled it out of an abandoned house just before the roof caved in - yep
It was in pretty bad shape - PT hanging on by 1 bolt, fuseholder flopping around loose inside chassis, wrong size & wrong ohmage for speaker, missing tubes etc...

I actually got it running - all except for the tremolo. I've been staring at the schematic & the chassis for so long I've gone cross-eyed

There seem to be about 13 components clustered around the 6AU6 tube (a new one) - makes me dizzy.
I've checked all the individual components, & all cables from preamp to power amp, all seem good...
EXCEPT I think someone has been in here & flopped some components around - that just don't seem fair...

Take a look at the clusterf*%k around the 6AU6...

Transformer must have been replaced in the past, I don't think they made them with a Hammond 260... I also see 2 diodes between pin 7 to pin 3 & 5 which aren't on the schematic - but I believe this is a common mod to mitigate damage should the rectifier (6X5GT) blow...
Factory seems to have used spare (unused) pins on some tubes as convenient terminals, which just makes everything harder to follow - arrgh

I've put in a grounded plug, new JJ 6V6's, NOS GE 6X5GT & GE 6AU6, replaced all electrolytics...

Your thoughts welcome. So would a real-life visit from the nearest guru - I buy lunch

Cheers, Lorne

[olddawg]

I hate to say "shotgun" things. But imhe non working tremolos are usually caused by stale caps. Especially if everything is else is working.

[Enzo]

I think so too. Unless one is open, resistors can be way off and not matter much, just changes the speed some. But leaky caps will stop the oscillator.

[Leo_Gnardo]

leaky caps will stop the oscillator.

I'm with Enzo & olddawg on this. Replacing the trio of caps in the oscillator bridge, plus the one that blocks DC at the oscillators output - if there is one of those. 3 or 4 caps, 15 minutes or so, you should be back to wobbulating good as new. Done it hundreds of times.

[mtlbasslad]

Good advice from you all - and I think this is the first time I've seen everyone agree so quickly LOL

Just one problem - there are 7 caps in there (by my count) & I've only got 6 - .00068 C6 is missing!
Also the .5 C7 on the schem goes from pin 6 to pin 7 (6AU6) - but in this amp it goes from pin 6 to ground...

Someone has been in here before, obviously - & as I mentioned in the original post, unused tube pins are used as convenient junctions - makes my head spin...

Would that missing C6 be enough to kill the trem? Or the possible miswiring?
I'll try to take some pics to show the confusion...

Lorne

[Enzo]

Missing C6 should not kill the oscillation.

Also the .5 C7 on the schem goes from pin 6 to pin 7 (6AU6) - but in this amp it goes from pin 6 to ground.

OK, please look at the schematic. In fact hold the schematic a little farther out and take in the entire circuit.

The drawing shows C7 wired from grid 2 to cathode of the tube. Cathode of the tube is wired to ground. The amp has C7 is wired from pin 6 to ground. Cathode IS ground, so does it matter whether we wire it to the socket pin or the ground the socket pin is wired to?

Remember, a schematic shows the electrical relationship between parts. A layout shows the physical relationship. The schematic shows C7 wired to ground, it doesn'really say that ground connection has to be on the tube socket.

So C7 is wired parallel to R12.

[Mick Bailey]

It would be worthwhile to study how the oscillator works. It's a simple circuit and is a fairly consistent design in tube amps. Just variations in capacitor and resistor values, but basically the same thing.

The Valve Wizard- Tremolo Oscillator

[mtlbasslad]

It would be worthwhile to study how the oscillator works. It's a simple circuit and is a fairly consistent design in tube amps. Just variations in capacitor and resistor values, but basically the same thing.

The Valve Wizard- Tremolo Oscillator

Now that link was interesting, although a little beyond me (OK, a lot)

Thanks Mick

[mtlbasslad]

progress - no progress

Update - changed caps C5 C7 C8 C9 C10 C11 no improvement

Noticed 6AU6 not glowing? Put 6AU6 in tube tester - it glows & reads good (on Knight 600)

Checked voltage on heater pins - 6.8V (line voltage here usually 120-125) approaching max for this tube, but the little bugger does not glow in circuit!

Also voltage on pin 5 is way over spec (220V) I'm getting over 350V

Over my head once again...

[mtlbasslad]

Missing C6 should not kill the oscillation.



OK, please look at the schematic. In fact hold the schematic a little farther out and take in the entire circuit.

The drawing shows C7 wired from grid 2 to cathode of the tube. Cathode of the tube is wired to ground. The amp has C7 is wired from pin 6 to ground. Cathode IS ground, so does it matter whether we wire it to the socket pin or the ground the socket pin is wired to?

Remember, a schematic shows the electrical relationship between parts. A layout shows the physical relationship. The schematic shows C7 wired to ground, it doesn'really say that ground connection has to be on the tube socket.

So C7 is wired parallel to R12.

You are, as usual Enzo so right

[g1]

So with your meter across pins 3 & 4 you have 6.8VAC, but heater does not light? And tube lights up in another circuit? Sounds like a socket problem, have you cleaned the pins?

[mtlbasslad]

So with your meter across pins 3 & 4 you have 6.8VAC, but heater does not light? And tube lights up in another circuit? Sounds like a socket problem, have you cleaned the pins?

Cleanest pins in town - I'm scratching my head so much I'm going bald (balder)

[Enzo]

Also inspect the pins from the top to see if one of those has a mangled or spread socket pin.


If pin 5 is a plate, and the tube is not glowing, then no current will flow, so it is normal to see high B+ there.

[mtlbasslad]

Also inspect the pins from the top to see if one of those has a mangled or spread socket pin.


If pin 5 is a plate, and the tube is not glowing, then no current will flow, so it is normal to see high B+ there.

I'll look at the socket pins again, but I thought I would see the heater glowing. Good to know high B+ is not a problem in this case.

Thanks Enzo

[Enzo]

but the little bugger does not glow in circuit!

but I thought I would see the heater glowing.

It can't be both, so the heater is glowing or not?