Tremolo ????

[C Moore]

As I look at this again, I am wondering if there is another way to "do" the Intensity pot.? Does that 470K resistor have to be there. Would it be possible, in this circuit, for me to just use a 50k RA pot that you see in a lot of trem circuits.?
That is to say.....Do I need to keep the "voltage divider, or can I abandon the resistor/potentiometer set for just a 50k RA pot.?
Thank You

http://www.webphix.com/schematic%20heav ... 12_6v6.pdf

[jjman]

A friend has that amp and the trem is strong. I would start per the scheme and reduce the 470k only of needed. I'm not understanding your reference to a 50k pot since that part of the circuit is 1470K all together.

[C Moore]

With the stock circuit, the Trem is real weak until you are at about 7-8 on the pot. It comes on late and fast. I thought maybe if I switched to a RA pot, it would relieve that. Playing around with the voltage divider gets nowhere with that 1M audio pot. The sweep is almost inactive until very late in its travel.
Anyway......I have the pot and I will just see what happens.
Thanks

[tubeswell]

My experience with bias vary trem on cathode biased output stages is exactly what yours is hired hand. And my explanation for it is that the auto-bias characteristic of cathode-biased stages tends to 'fight' the bias vary trem voltage swing until you have a really strong trem swing.

But removing the 470k would make the trem voltage swing weaker (because it would be swinging across 1M instead of 1M5). You could however try putting the 470k on the ground side of the 1M pot. JM2CW

[C Moore]

My experience with bias vary trem on cathode biased output stages is exactly what yours is hired hand. And my explanation for it is that the auto-bias characteristic of cathode-biased stages tends to 'fight' the bias vary trem voltage swing until you have a really strong trem swing.

But removing the 470k would make the trem voltage swing weaker (because it would be swinging across 1M instead of 1M5). You could however try putting the 470k on the ground side of the 1M pot. JM2CW

OK....something else to try, and I will.

Thanks

[C Moore]

My experience with bias vary trem on cathode biased output stages is exactly what yours is hired hand. And my explanation for it is that the auto-bias characteristic of cathode-biased stages tends to 'fight' the bias vary trem voltage swing until you have a really strong trem swing.

But removing the 470k would make the trem voltage swing weaker (because it would be swinging across 1M instead of 1M5). You could however try putting the 470k on the ground side of the 1M pot. JM2CW

This is just not quite working the way I would like it to. It almost sounds better to do away with the Intensity Pot, and use the foot switch to turn the trem on and off and have adjustment for speed only. The "intensity is full on, which is not the best, but the speed adjust works well.
What do you think about making this amp fixed bias, like a Fender Princeton, and adjust the trem circuit accordingly. It uses octals instead of 12AXX dual triodes, but maybe the trem would work better. I just cannot seem to find a happy compromise with the Intensity control.
Well....just for sake of discussion, would it be reasonably possible for me to grab part of the rectifier HV Secondary, and use that to get negative bias voltage for the power tubes.? That would be my first hurdle. Do you guys think that would be more trouble/work than it is worth....??? I am perfectly willing to spend as much time as it would take.
Thank You

[tubeswell]

bias vary trem always works better with a fixed bias stage. With cathode bias the cathode resistor has an auto bias function in that if current increases through the (fixed resistance) resistor, then the voltage dropped across the resistor will increase - changing the bias point. When you apply a different bias voltage to the grid you alter the tube current - hence the cathode resistor adjusts the bias voltage which prevents the effect of the grid voltage change from having effect, unless you force a lot of current through the grid with a bigger trem voltage swing at the grid.

That's my take on it anyhow

Now if the output tube is fixed bias, then there is no cathode resistor to stuff up the change in tube current provided by the trem voltage swing at the grid, so you need less trem grid voltage swing to produce a change in bias - and the depth pot works more effectively.

[d95err]

50k pots are used in Fenders optically coupled tremolos. This is a completely different circuit.

[C Moore]

Yeah.....you are both correct. Or at least my recent experience corresponds with what you are telling me. So that is what I am wondering. To get some kind of usable control from the Intensity Pot, do you think I should try a fixed bias set-up for the power tubes.?
I was thinking to use the Fender Princeton as the model and see if that gets me in a "better" place.
Thanks Again

[tubeswell]

Yeah for 6V6s, either a 5E11/6G2/5F11 using a single stage LFO, or a 5G9 (with the CF after the LFO stage) for a more hypnotic slam.

[C Moore]

Yeah for 6V6s, either a 5E11/6G2/5F11 using a single stage LFO, or a 5G9 (with the CF after the LFO stage) for a more hypnotic slam.

So are you saying it would be better to change the Trem circuit, rather than the bias circuit.? This Ampeg circuit uses Octal preamp tubes.
Thanks

[C Moore]

http://www.webphix.com/schematic%20heav ... 2b_jet.pdf

Perhaps I should just try something like this. Inadvertently I already did. I can play around with the value and see what works best, but if I replace the Intensity Pot with a fixed resistor, the Trem does function better. The Intensity is pretty full, but the speed works well and this may be a happy compromise. Then I just use the foot switch to either have the Trem On or Off, but with no Intensity adjustment.
I am willing to do whatever it takes, I have the time. But maybe this is one situation where I would not be able to bail water as fast as it is coming into the boat. Maybe I should just find something that "works", get it all ship-shape and put her up for sale......
Thank You So Much for helping me. I wish I had the knowledge to reciprocate, but that just is not going to happen. You guys will just have to settle for a bunch of honest and heart felt "Thank You's" from me.
Just the price you guys pay for being smart/well educated I guess.......

[tubeswell]

Yeah for 6V6s, either a 5E11/6G2/5F11 using a single stage LFO, or a 5G9 (with the CF after the LFO stage) for a more hypnotic slam.

So are you saying it would be better to change the Trem circuit, rather than the bias circuit.? This Ampeg circuit uses Octal preamp tubes.
Thanks

Nah I'm just saying that the 5G9 circuit produces a more hypnotic trem than the tweed vibrolux or brown princeton. But all of these use fixed bias output stages (which works better overall with bias-vary trem)