Yamaha / Soldanop T100

[Valvehead]

Ive got an old T100 Yamaha / soldano here , and the owner wants the reverb circuit put back to the Mike Soldano original design...but i can only find the yamaha scem...anyone know exactly what needs to change between the 2 circuits ? I cant find anything on it and Soldanos email is full !!




Quote from Mike =

"My last complaint with those amps is a change that was made to the reverb circuits after the amp went into production. They really screwed things up on that, and to this day I still don't know what the hell they were trying to do. All I know is that it made the reverb very weak and lifeless. I opposed the revision, but they went ahead and did it anyway. The early amps had my original design, and the late amps can be modified to get them back to that design."

[glebert]

Does this help?

http://music-electronics-forum.com/t14851/

[Valvehead]

hmm.....so the scem with the hand drawing is Soldanos ?? or the yamaha version?? trying to zoom in..i cant tell the values scribbled for the stuff on far right ??? Hard to see

[Enzo]

MAybe this is what was meant? Scroll down near the end of the manual there is a multipage REverb modification. It shows before and after circuits and how to do it. WHich means you could undo it too.

[Valvehead]

ok--thanks guys !

[Valvehead]

Well...the new rev tank is in and i have no verb . I have not done any mods yet. So far ive checked the wiring / shielded cables / resistors at V6 (rev tube) . Cant find anything wrong yet.

How do I test the Vactrol Ldr's ? Could it be one of those? Do i test the + and - like a diode ? Is there a voltage I should be looking for at the reverb transformer ?

If i bump the amp i can hear the reverb wayyyyy in the background ... if that helps

I have swapped the V6 tube .

EDIT-- i see that someone did most of the mods........so i verified that and found they didnt add the jumper and the 2 resistors as shown .

Got that all done and still no verb......and a lovely loud hum when the reverb controls are turned up...

[Enzo]

You shake the amp and you can barely hear it. it ought to be LOUD. That means the return side has a problem, not the drive side. Forget the transformer.

You have two LDRs you wonder about. All either one does is complete a circuit from the reverb controls to pin 7 of V4. SO with the amp running, measure resistance to ground from pin 7 of V4. If the LDRs are not on, you will get an open or very high reading. If one is on, then you will read the resistance of the reverb control setting.

V4 is the mixing tube, did you replace it? Does touching pin 7 of V4 make a hum/noise out the speaker?

[Enzo]

You shake the amp and you can barely hear it. it ought to be LOUD. That means the return side has a problem, not the drive side. Forget the transformer.

You have two LDRs you wonder about. All either one does is complete a circuit from the reverb controls to pin 7 of V4. SO with the amp running, measure resistance to ground from pin 7 of V4. If the LDRs are not on, you will get an open or very high reading. If one is on, then you will read the resistance of the reverb control setting.

V4 is the mixing tube, did you replace it? Does touching pin 7 of V4 make a hum/noise out the speaker?

[Valvehead]

You shake the amp and you can barely hear it. it ought to be LOUD. That means the return side has a problem, not the drive side. Forget the transformer.

You have two LDRs you wonder about. All either one does is complete a circuit from the reverb controls to pin 7 of V4. SO with the amp running, measure resistance to ground from pin 7 of V4. If the LDRs are not on, you will get an open or very high reading. If one is on, then you will read the resistance of the reverb control setting.

V4 is the mixing tube, did you replace it? Does touching pin 7 of V4 make a hum/noise out the speaker?

swapped V4

pin 7 to ground is open

there is no noise or pop when i touch pin 7

[Enzo]

Then ther can be no reverb either.

Is V4 conducting on both sides? Do both heaters glow?

[Valvehead]

Then ther can be no reverb either.

Is V4 conducting on both sides? Do both heaters glow?

yes sir

[Enzo]

Wait, loud hum when reverbs are turned up?

So you can control the volume of this hum with the reverb controls? Both or just one?

If the reverb control turns hum up and down, that tells me the optos must be on of the hum would never reach V4.

You swapped out V6, fine, but is it conducting? What voltages are on pins 6 and 8?

[Valvehead]

No hum when reverb pots are off. Both affect it .


V6 -

pin 6 = 217 v

pin 8 = 1.7 v

[Enzo]

Does the hum remain if you pull V6?

Is pin 7 already shorted to ground? What resistance do you get there?

If you look at V6-8 ther is the 1k resistor to ground. Find that resistor and its ground end. Then tack a wire from pin 7 to that ground point. With tube back in place. Does that kill the hum?

V6 appears to be conducting, And unless the grid is grounded it ought to amplify whatever is coming in the grid. I am concerned both reverb controls seem to be working at once.

[Valvehead]

pull V6 ---- no hum


pin 7 to ground is 200 ohms with tube removed

wire pin 7 to the ground = yes hum is gone with V6 in .