Silvertone 1333 tube amp

[frankeg]

I'd think someone was tweaking the plate voltage (while disregarding the bias, which seems common ) as you mentioned.
If the pots are rated 1/2W or better, I suppose you could leave them as is.
Out of curiosity, how far off are the set values from the stock values shown on schematic?

Sorry this took so long (Summer activities). The blue pot was wired between pin 5 (plate) of the 6SC7 and hot rail and measured 13k ohms out of circuit. Pin 2 (2nd plate) of the 6SC7 had a 560k fixed resistor. The stock 390k resistors (R7 & R8) were removed. The red pot was wired between pin 2 of the 6SN7GT (plate of 2nd pre) and the hot rail and measured 7.31k ohms. The stock 68k resistor (R19) was removed. Keep in mind that I have no idea how it sounded because it had bad caps in it when I got it.

[frankeg]

Here is the schematic. The pots are wired to pin 5 of each preamp tube.

Could someone tell me the purpose of C20 tied to the primary winding & ground? Is this for the 2-prong pwr polarity like Fender early Fenders had?

[Chuck H]

Could someone tell me the purpose of C20 tied to the primary winding & ground? Is this for the 2-prong pwr polarity like Fender early Fenders had?

It's called a "death cap" in modern parlance. That's because if it shorts you have a hot chassis. It's purpose is to reduce noise in the power supply. If you're doing things right the amp should get a proper, chassis grounded three prong AC mains cable and that cap should be removed.

[frankeg]

Thanks Chuck! I thought so but it's arrangement looked different than what I've seen in Fenders. It will be removed and a proper 3-prong cord installed.

[Justin Thomas]

Off-Topic: glad I can always provide a sig line or two, Chuck!

Justin

[Chuck H]

Off-Topic: glad I can always provide a sig line or two, Chuck!

Justin

It was "computers masquerading as amplifiers" that got me For me that's like putting a ball hitch on your smart car and calling it a tow truck

[frankeg]

Well it's all back together and working except that the tremolo is weak. I was hoping on getting away without messing with those caps since they're really hard to get at. Do you think anyone would notice if I used .015 uf caps instead of the stock .02 uf? I have a few .015's handy.

[Enzo]

There aer two parts to any trem: the oscillator (LFO) and the interface.

The LFO is the part with the three 0.02uf feedback caps, and it makes the pulsing we use.

The interface is whatever circuit we use to couple that pulsing to the signal path in order to modulate the signal.

If your trem is working, as in making trem, then the oscillator is working. Changing the three caps won't change that, it already works. Changing them from 0.02 to 0.015 will in fact not make the trem stronger, but it will peed the trem up. In my experience, many if not most amps have a trem that is too fast already. I want to be able to turn the speed down to a sexy throb. Many of them have a slowest setting that is still too fast. SO I swap in larger feedback caps, not smaller.

But a weak trem is usually in th interface. or the design is for a weak trem effect in the first place.

[g1]

Agree with Enzo above, look at the second half of the trem tube, not the oscillator side.
Have you tried another 6SJ7 tube there? R30 & R31 are good?
C16 and C17 caps ?

[frankeg]

Thanks Enzo/g1. I listened to another 1333 on youtube and the tremolo was strong. I'll check the output side. I don't have another 6SJ7 to try. I did change out C16 because it was in bad physical shape. Keep in mind that with my old guitar ears, I may be imagining the trem effect, it's that subtle! So I may still change some caps on that side. I found two .22uf and one .33uf that I can use.

[Enzo]

C17 is the one that delivers the trem pulses to the intensity pot. I'd sub something in there if you have not already. Is there any DC sitting on the top end of R32?

Turn intensity pot all the way up. Now measure resistance to ground from the grid of either powr tube. You SHOULD sdee about 1.3M. If you see only 300k, then the trem switch is either ON or shorted.

[frankeg]

https://www.google.com/search?q=enzo...+sales&rlz=1CA
HPZS_enUS791US791&oq=enzo&aqs=chrome.4.69i57j0l5.6291j1j 1&sourceid=chrome&ie=UTF-8

For those interested, I finished the Silvertone 1333! I decided to replace all the caps and two resistors in the tremolo circuit mainly because once I started de-soldering it was easier and neater. Thanks to those who gave me advice along the way. She sounds really nice & the tremolo is awesome with full range adjustment. It's a cool little amp that is worth restoring in my opinion. Hey Enzo, I found your auto repair shop here in York, Pa but not the electronics repair shop. Lol. I drive by this place a lot.

[Enzo]

Others have been to my several Pizza joints around the country.

[eschertron]

Others have been to my several Pizza joints around the country.

What? I won't go If they don't serve your chili