|frankeg||6/14/2018 4:18 PM|
|Silvertone 1333 tube amp|
I have a 1956 Silvertone model 1333 to re-cap and I found 2 pots wired as variable resistors between the plates of the 6SC7 & 6SN7GT preamp tubes and their power supply source voltage. The schematic I have shows normal resistors there. Could this be someones mod?
|galaxiex||6/14/2018 5:14 PM|
|I would say that's a mod.|
Someone trying to tweak something, or didn't have the correct resistors on hand.
|olddawg||6/14/2018 10:57 PM|
|Those pots are not from 1956....|
|Enzo||6/15/2018 1:11 AM|
|Most pots have a date code on them.|
|frankeg||6/15/2018 5:04 AM|
|Thanks guys. The only thing these pots would tweek is the two preamp tubes plate voltage. I haven't worked with 6SC7 or 6SN7GT tubes but I'm guessing he was playing with their bias for whatever sound he wanted. It still seems a onnce and done thing since you have to take out the chassis to tweek.|
|frankeg||6/15/2018 5:11 AM|
|Here's the schematic|
Here is the schematic. The pots are wired to pin 5 of each preamp tube.
|g1||6/15/2018 12:58 PM|
|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?
|frankeg||6/15/2018 1:13 PM|
|You are correct they are CTS pots made in 76 & 77.|
|Chuck H||6/15/2018 1:20 PM|
|frankeg||6/15/2018 1:21 PM|
|I'm taking it back to stock. I don't care for his soldering either. He told my friend that he's had it since the 60's and it's completely stock. That doesn't jive with CTS pots from 76 & 77. I'll let you know the values once I desolder which will be a week or so when the new parts arrive. The more I see of these old amps the more I liken them to a box of chocolates, you never know what you're gonna get...|
|frankeg||6/15/2018 1:58 PM|
|mozz||6/15/2018 2:05 PM|
|Those pots are out of a color tv set.|
|frankeg||6/15/2018 7:09 PM|
|Chuck H||6/15/2018 7:31 PM|
|g1||6/16/2018 1:10 PM|
|frankeg||7/25/2018 6:33 AM|
|frankeg||7/25/2018 6:38 AM|
|Chuck H||7/25/2018 7:22 AM|
|frankeg||7/25/2018 7:26 AM|
|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||7/25/2018 7:29 AM|
|Off-Topic: glad I can always provide a sig line or two, Chuck!|
|Chuck H||7/25/2018 7:34 AM|
|frankeg||7/27/2018 9:34 AM|
|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||7/27/2018 9:44 AM|
|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||7/27/2018 11:47 AM|
|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||7/27/2018 1:42 PM|
|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||7/27/2018 1:49 PM|
|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.