paraphase bias wiggle again

[andrew]

Hi, I'm having trouble getting the bias wiggle to work in a Gibson GA-20 clone.http://home.comcast.net/~psymonds/GA20.htm I have used the following tremolo layout with no problems on a Rocket and (after adjusting the plate and grid resistors) a KT66 Rocket. http://theinside.net/FLR/TremoloLayout.jpg
I unsoldered the 270k/6.8k junction that goes to ground and attached the junction to the 250k pot. I got 360v on the plate of the triode using the power tube screens as a source. I rigged up a new node and now I get 300v on the plate of the triode. It just doesn't work. Should I try a different tremolo design? Thanks for any help.

[tubeswell]

A 6V6 PP amp with a paraphase inverter and trem = 5E9A so why not copy that trem circuit? JM2CW

[d95err]

I unsoldered the 270k/6.8k junction that goes to ground and attached the junction to the 250k pot.

That resistor divider sets the input level to the second PI triode. Lifting it and attaching a pot to it might yield wierd results.

Like tubeswell says - go for the 5e9a type tremolo; wiggling the PI triodes instead of the power tubes.

[andrew]

Thanks , I will give it a try.

[andrew]

http://www.prowessamplifiers.com/schema ... layout.pdf The 5E9A layout has 370v on the screen node going to the plate of the 12ax7. Is that too much voltage for a newer 12ax7? Thanks

[jjman]

I have 340 on my oscillator which is similar. I think 400 is the alleged max spec?

[tubeswell]

http://www.prowessamplifiers.com/schema ... layout.pdf The 5E9A layout has 370v on the screen node going to the plate of the 12ax7. Is that too much voltage for a newer 12ax7? Thanks

Nah - it should work fine. I would build it first and see. Don't try to troubleshoot too many issues before you have started, otherwise it could be a case of paralysis by analysis

[andrew]

It's all wired up but I need a 10M resistor.Shucks. Maybe tomorrow. Thanks guys.

[andrew]

I put the 10M resistor in, the tremolo works but the tremolo makes a "beating" sound which is louder than the guitar signal. The speed control changes the speed but the noise stays the same loudness. Any help please.Thanks

[andrew]

Te 6.8k resistor divider is causing the problem. With it taken out it works fine although I would like it a little stronger. With it in I get the "beating".

[tubeswell]

6k8 in the paraphase grid supply? You need that voltage divider to get an appropriate level of inversion in the PI. And you need that 6k8 to complete the grid leak circuit of that 6V6.

Have you built the whole circuit using the 5E9A circuit values? (Just to check)

'Helicoptering' trem is usually a sign of too much trem voltage. When you turn the depth pot down does the beating go away?

[andrew]

Hi Tubeswell, the helicoptering gets less intense as the depth is lowered but it never goes away. I can still hear it with the amp volume turned fully down.
pin 1 380vts voltage taken from the screen supply
pin 6 207vt

280vts going to the 10M ohm resistor.
28vts on the tremolo jack

[tubeswell]

the helicoptering gets less intense as the depth is lowered but it never goes away. I can still hear it with the amp volume turned fully down.

You shouldn't get any trem with the depth turned down. Are you using a 250k pot for the depth control? Did you use 10M for the feedback resistor?

[andrew]

With the depth turned fully down the tremolo guitar signal is off but the helicoptering is still there. I used a 10M for the feedback and the depth pot is 250k. Thanks.

[tubeswell]

With the depth turned fully down the tremolo guitar signal is off but the helicoptering is still there. I used a 10M for the feedback and the depth pot is 250k. Thanks.

Did you measure the resistor as 10M before you put it in?