Trem not working in Silvertone 1472

[Brianbicknell]

Hi Guys,

I responded to an old thread and got some help about general maintenance stuff from Chuck H. (Thanks! It's dead quiet and sounds killer!) The trem still isn't working.

I don't have the footswitch, so after reading around here, I've heard a couple different things. 1) The trem is always on and the footswitch shuts it "off" and 2) The trem can be activated with a 1/4'' cord plugged into the footswitch jack with nothing at the other end. Needless to say, I tried both of those options, and even tried shorting the end of the 1/4'' when plugged in to see if that would do anything. Nothing. No pulse, no extra noise, nothing. When speed and strength are cranked, still nothing.

So, I did two things I figured would probably fix the problem without having to do any real diagnostics. I replaced the 6au6 tube with a NOS RCA. Still the same--nada. Next, I replaced C10,11,12,14,15,16 with Mallory 150s. I assume that .022 at 630v was a suitable replacement for a .02 at 600v (original?) Same for .047 and .5, etc?

Still nothing. Did I fix the problem and then fry something by poking around? What would cause absolutely no pulse at all?

Thanks in advance!

[52 Bill]

I don't have the footswitch, so after reading around here, I've heard a couple different things. 1) The trem is always on and the footswitch shuts it "off" and 2) The trem can be activated with a 1/4'' cord plugged into the footswitch jack with nothing at the other end. Needless to say, I tried both of those options, and even tried shorting the end of the 1/4'' when plugged in to see if that would do anything. Nothing. No pulse, no extra noise, nothing. When speed and strength are cranked, still nothing.

Based on the schematic the trem oscillator is always on. The footswitch grounds out the signal that is sent to the output tubes. If the jack is just a plain open circuit one, then you don't need anything plugged into it to turn the trem on.

So, I did two things I figured would probably fix the problem without having to do any real diagnostics. I replaced the 6au6 tube with a NOS RCA. Still the same--nada. Next, I replaced C10,11,12,14,15,16 with Mallory 150s. I assume that .022 at 630v was a suitable replacement for a .02 at 600v (original?) Same for .047 and .5, etc?

Yes the .022 is the modern equivalent of the old .02 value, same as .047 for an .05, etc.

Replacing the oscillator caps is the usual thing that everybody does to get these working, but the resistors in the circuit should also be checked. Have you tested any of them, including the pots?

Are you sure the new tube is ok? Have you tried it with the old one back in the circuit? Have you taken any voltage readings on the tube? Are you sure that there is voltage getting to the tube? Is the heater lighting up?

And finally, have you double checked your work? Are you certain that the new caps are all installed correctly and solidly wired, etc.

[Brianbicknell]

Hi Bill,

Thanks for the reply. I haven't tested any of the resistors, my multimeter is at work. I'll grab that this week and check things out. I'm pretty new to this, so any advice on what to look for/techniques/etc would be great.

I am not 100% sure the tube is okay, although it is lighting up. I swapped the old tube out, nothing changed, although it lit up as well. I'll check the voltages when I get my multimeter back. Again, any tips on what to look for would be great.

What I can do now is check my work again, but it appeared pretty solid. The only thing I can think of that I may have screwed up was heating up some areas too much where there were resistors. Maybe I pushed them past their limit?

Thanks,
Brian

[52 Bill]

There are two ways that the trem will not work in this amp. One, the oscillator does not run and two, the varying voltage from the oscillator is not getting to the output tubes. You need to figure out which is true in your amp. I could be both.

If the tube lights up, then at least you know that the heaters are getting voltage, but if the B+ voltage doesn't get to the plate then the tube won't run. If any of the three legs of the phase shift loop is too far out of tolerance then the oscillator won't run.

If the oscillator runs then you need to be sure that the varying voltage from the oscillator is getting to the output tubes. Read the voltage at the top of the strength control.

[Brianbicknell]

Hey,

Sounds good! So I just need to measure the voltage (with the amp on) at the top nub of the strength control. What should I be looking for?

[52 Bill]

Hey,

Sounds good! So I just need to measure the voltage (with the amp on) at the top nub of the strength control. What should I be looking for?

If the oscillator is working there will be a small fluctuating voltage at the top of the strength control. This will only be true if the oscillator is working and the connections and components that connect the tube to the strength pot are working.

[Brianbicknell]

Great, thanks Bill. So if I get an appropriate reading, what will be the next step? If I don't?

I won't be able to try this until probably Thursday morning, so I'll respond with my findings then.

Thanks!

If the oscillator is working there will be a small fluctuating voltage at the top of the strength control. This will only be true if the oscillator is working and the connections and components that connect the tube to the strength pot are working.

[Brianbicknell]

If the oscillator is working there will be a small fluctuating voltage at the top of the strength control. This will only be true if the oscillator is working and the connections and components that connect the tube to the strength pot are working.

Hi Bill,

I got my multimeter, and it appears that some voltage is coming to the top of the speed pot, but it appears to be random. I could be measuring wrong. It will momentarily go to 2 or 8 volts, then back to 0, then to 17. Any ideas?

[52 Bill]

I got my multimeter, and it appears that some voltage is coming to the top of the speed pot, but it appears to be random. I could be measuring wrong. It will momentarily go to 2 or 8 volts, then back to 0, then to 17. Any ideas?

If the oscillator is running the voltage will fluctuate in a cyclic manner up and down at a rate that is set by the speed control. If the voltage you are reading is randomly changing, then the oscillator is not running or you are not reading the voltage correctly.

Set your meter to read dc volts. Connect the black lead securely to the metal chassis or to a grounded connection in the amp. Take the red lead and connect it to the top (CW) lug of the depth pot. Be sure that it is making good contact to the lug. Turn the amp on and see what readings you get. If there is a fluctuating voltage there, turn the speed control and see if it changes the rate of the fluctuation.