Sano 50wr tremolo

[pontiacpete]

The tremolo on this amp isn't working, of course, but I think it has something to do with how it is activated. The reverb works through 'guitar' and 'instrument' channels pretty well, although, it creates a high pitch ringing feedback'. I think that's the tank.
Changed all tubes, and caps, black one's in the pre amp and checked all the resistors for tolerance and changed a few that were out, but still have no tremolo.
This particular Sano is an older version, I believe, than the one's that have been discussed here earlier. It doesn't have a stereo 1/4" jack for the so called stereo channel, which is what I am now thinking will turn on the tremolo. Instead, it has a Cannon style input similar to an XLR but there are 4 prongs on the inside.

Does anyone here have any experience with this amp or this kind of input jack?

Is there a way I can bypass it and set the amp up to have reverb and tremolo on the guitar or instrument channel?

thanks in advance for any input.

pete

[pontiacpete]

maybe a schematic?

[Gtr_tech]

8417s with no grid stoppers? Brave.....

[52 Bill]

Very interesting design. The tremolo only works on what I assume is the accordian channel.

The schematic shows that the gain of the first tube stage of one of the stereo channels is modulated by an FET. There is a 1/4" stereo jack for a foot switch and there appears to be a remote tremolo switch that connects to the 4 pin XLR, probably mounted on the accordian.

Rewiring to access the tremolo from the other channels is possible, but quite involved.

[pontiacpete]

The problem I'm having with this schematic is that there is no FET in the amp nor a 6U10 compactron tube.
I've search around quite a bit for the right schematic and this seems to be the only one available.
Here's a picture of the tube layout.

[52 Bill]

Sorry, I thought that you were showing us the correct schematic.

There aren't that many ways to create a tremolo effect in a tube amp. You have to have an oscillator and then some sort of interface to the signal path. 99% of all guitar amp tremolo oscillators are very basic phase shift circuits.

If you look at your amp can you find the tremolo section? Can you identify the oscillator circuit? Is it at all similar to the one in the wrong schematic?

If you measure the output of the oscillator can you tell if it is running? If it is running, how does the output of the oscillator connect to the signal circuit? Optical lamp and photocell? Bias circuit?

If it isn't running, are there any wires from the circuit that go to a footswitch jack?

[pontiacpete]

"If you look at your amp can you find the tremolo section? Can you identify the oscillator circuit? Is it at all similar to the one in the wrong schematic?"

This is what I'm having trouble with. Would you be willing help me identify how this works?
So far the only way I've been able to identify some of the components of the oscillator is by following the wires off of the trem depth and speed pots.
From the speed pot the wiper has a 100k resistor to ground and on the other used lug has a lead that goes to where two .05 caps meet(similar to the wrong schematic). On the other side of the one of the .05s is a .02 to 100K and the .... should I go further?
The depth pot wiper has a wire that goes across the board to , what I'm calling V1, a 12AX7 , the first in line where the input jacks a located, and is connected to pin 7, the grid. Also, at pin 7 of V1 is a wire to a small transformer which I was assuming is for the reverb, but maybe I'm wrong.??

"If you measure the output of the oscillator can you tell if it is running? If it is running, how does the output of the oscillator connect to the signal circuit? Optical lamp and photocell? Bias circuit?"

So far I have not seen any signs of it running, like a fluctuating voltage or moving sine wave when probing around the pre amp. It doesn't have an optical lamp or photocell. It probably is suppose to oscillate like a princeton would or similar amps...but I can't seem to activate it.
There is a 1/4" jack just above the speed pot. I've tried triggering it there with no results.
Here are some more pictures , I don't think they will help much but here they are anyway.

[52 Bill]

So far the only way I've been able to identify some of the components of the oscillator is by following the wires off of the trem depth and speed pots.

Yes OK, you've found the oscillator circuit and it sounds like it comes close to the circuit in the wrong schematic. I'd take a copy of the wrong schematic and mark it up where your circuit differs.

If you look at the schematic you will see the basics of the oscillator circuit. It uses one triode section. Notice that there is a feedback loop from the grid to the plate that consists of three caps and three resistors. There is a resistor from the grid to ground, and between the caps there are two resistors to ground, one of which is the speed pot with a series resistor. The cathode of the tube is grounded through a resistor which is bypassed with a 2uF cap. If the oscillator is running, you will find a fluctuating voltage at the plate.

If the oscillator isn't running, check to see where the footswitch wire connects to the circuit. Some designs will unground one resistor leg of the feedback loop, while others will disrupt the circuit in some way to stop the oscillator. The wrong schematic design seems to ground the cathode of the tube. What you need to find out is, does the footswitch enable the circuit or disable it?

The depth pot wiper has a wire that goes across the board to , what I'm calling V1, a 12AX7 , the first in line where the input jacks a located, and is connected to pin 7, the grid. Also, at pin 7 of V1 is a wire to a small transformer which I was assuming is for the reverb, but maybe I'm wrong.??

I don't think that there is any reason for a transformer going to the grid of an input tube that would relate to the reverb. Where do the other wires on the depth pot go to?

There is a 1/4" jack just above the speed pot. I've tried triggering it there with no results.

Where does the wire from this jack lead to?

Start by getting the oscillator to run. Trace out your circuit and check all of the related caps and resistors. Another question, did you check the tube?

[pontiacpete]

52 Bill, thanks, I really appreciate the help.

I drew out the V1, by hand. IN the lower corner the 100K goes off to the .02 cap that is part of the series of caps .02 , .05 and .05 (the latter 2 joining the wiper of the speed pot. Does this make any sense?
To me this seems to be the accordian channel. V2 shows a wave on the grids when plugged into the guitar input. Perhaps I should try clipping into the accordian plug somehow and inject a signal.

I have tried changing all the tubes , right now the are 4 new ones in the pre amp.