Bias-Modulating "Tremolo" mods?

[Bernardduur]

Hey all!

I just installed one in my EL34 loaded amp and she sounds sweet! Here's the link to the multiple tremolo circuits

Is it possible to mod these babies to get faster tremolo sounds / deeper tremolo sounds out of it?

[tubeswell]

Yeah I built a 5G9 which has this type of trem. I found out by experimenting that one simple way you can alter the speed is by changing the tapering resistor on the speed pot. Similalry I also experimented with the depth by changing the tapering resistor on the depth pot. You can also or the resistor attached to the depth pot input. I would only make small value adjustments to the tapering resistors, but the resistor attached to the depth pot input in the 5G9 is 1M, and when I initially built it I left this resistor out by accident, and the trem was huge but it chirped and so on by the time the depth pot got up to about 4/5th, so I put the 1M in, but I think it could have handled 470k for real intense trem. Sure is nice trem tho'.

[Bernardduur]

Thanks!

I had great results with the depth pot; not yet with the speed pot.

Edit: I realised that I had the speed pot backwards in function. Now I have more then enough speed!

[Bernardduur]

Another question on this;

When I bypass the vibrato by the switch to ground I usually have a ticking sound, sometimes not. What could cause this? How can I cure this?

[tubeswell]

Where is your trem ground grounded?

I'm just thinking if you have the trem ground grounded near one of the other grounds -esp the pre-amp ground (or worse, if you have a common ground bus, which probably would not be a good idea in an amp with tremolo), the oscillations could play havoc in the ground return path.

In my 5G9, I have the trem grounded away from the pre-amp ground and away from the power amp ground - in fact I grounded the trem at the trem footswitch socket ground, and I don't have any problem.

[Bernardduur]

Hmmmm, that would sure be a good cause of the ticking as it is grounded at the prescence knob. I'll try to find another one

[Bernardduur]

Another question;

It has worked for a long time very very good. But lately I have been getting some oscillation with the tremolo. I also now notice a blue light in my power tubes that lights up and down on the tremolo speed.

The only thing I added to the unit was another power stage filter to get part of my amp to a lower voltage.

I "think" it is due to the fact that I get the power of the oscillation tube from the power tubes. Maybe add some resistor + cap?

Edit:
Found this:
Note 3 Using a Matched set of power tubes helps elliminate power supply feedthrough that can potentially turn into a form of LFO pumping in your speakers ... it starts from the Tremolo circuit, drives the power tubes vertically at first, manifests through the output circuit through widely varying Plate currents, loading the power supply on half-cycles, feeding back into the preamp through its supply feed, and with preamp bass control maxed then feds back to the output thus driving the power tubes into "Assymetric" LFO mode and pumping the speakers (if it starts to happen it will seem very weird at first) ... using reasonably matched power tubes and employing the same power supply feeds as noted in the above schematics typically guarantees problem-free operation following proper power tube biasing ...

I guess I need some new output tubes as these are
A. Not matched
B. Not the same brand
C. very very very old

[tubeswell]

The blue glow surrounding the plates is normal. Without trem on, that blue glow would be continuous. It indicates that the plates are drawing current from the cathode. In the part of the cycle when the trem oscillator makes the grid go positive w.r.t. the cathode, the current stops flowing to the plate and the blue glow disappears, so the tube stops amplifying, and vice versa

[Bernardduur]

Originally Posted by tubeswell

The blue glow surrounding the plates is normal. Without trem on, that blue glow would be continuous. It indicates that the plates are drawing current from the cathode. In the part of the cycle when the trem oscillator makes the grid go positive w.r.t. the cathode, the current stops flowing to the plate and the blue glow disappears, so the tube stops amplifying, and vice versa

Thanks! That helped a lot!