Monkeymatic Shasta Princeton Reverb pine combo

[JazzGuitarGimp]

I just scanned the whole thread for a schematic. Did you post one and
I missed it?

[xtian]

I replaced the old ceramics with new orange drops. No change. The only oscillations I see are the minor (0.1v) ripple of the bias supply. I rechecked the wiring, but I'll double-extra-recheck again.

I'm not sure what to look for, other than the bias voltage should be oscillating, this being a bias-wiggling tremolo.

[xtian]

Using Hoffman. Attached. But it's same as Fender AA1164.

[xtian]

Just tried a third, brand new 12ax7. No change.

[Milkmansound]

tried dropping the 1M coming off of V4A plate down to 220K?

[xtian]

Been over the circuit a third time, with continuity checker. Can't find any errors.

The only not-to-spec part I have is a 3M cathode resistor instead of a 3M3 resistor.

[xtian]

tried dropping the 1M coming off of V4A plate down to 220K?

Which one? The grid's ground ref? There are three 1Ms in that circuit.

[Milkmansound]

that should be either a 3K3 or 4K7 on the trem tube cathode, with a 25uF bypass cap

[Milkmansound]

tried dropping the 1M coming off of V4A plate down to 220K?

Which one? The grid's ground ref? There are three 1Ms in that circuit.

the one at the junction of the 220K plate load and .1 coupling cap

[JazzGuitarGimp]

Just tried a third, brand new 12ax7. No change.

Do you have 400V at point B?
Did you look at the clockwise terminal of the intensity pot? Change the speed control while looking at this point. You should see a low frequenct sign wave.

[xtian]

that should be either a 3K3 or 4K7 on the trem tube cathode, with a 25uF bypass cap

I think we have a winner. Mistakenly used 3M cathode resistor instead of 3K3.

Hang on.

[xtian]

Yup, that got the Trem working, but it's got a pronounced "beat" -- not at all quiet when at idle, and goes into runaway oscillation when Speed control is turned all the way up. "beat" stays even when Intensity control turned all the way down.

Intensity pot is spec'd at 250K. Do I need a bigger value?

I'll search for that "beat" problem next. Anyone know off hand?

[xtian]

I found it. Lead dress. Moved the wire to the speed control.

[Milkmansound]

Glad you got it! It's a great tremolo circuit - for only half a tube it's pretty close to vibrato

Also, if you lose oscillation at high speed try increasing the value of the 100k hanging off of the 3M speed pot.

[drew]

something else you can experiment with, if you're inclined: http://www.el34world.com/Forum/index.php?topic=15087.0