Where to insert preamp bias-vary tremolo?

[funkgang49]

Built a single-ended amp with a modified 5E5-A preamp using 6SL7's and was unsure where in the preamp to tap into for a bias-vary tremolo circuit.
Any suggestions would be greatly appreciated.

Here's the preamp circuit:

https://ampgarage.com/forum/download/fi ... dbe02d4391

[sluckey]

Connect the INT pot to V2 pin 3.

[bal704]

I'm trying Eagle to view this, and getting an error. What program do I need to view this schematic?

[sluckey]

ExpressSCH. It's free

[bal704]

Got it...thanks.

[funkgang49]

Yo sluckey, tapped in at V2 pin3 (cathode) and... DISCO! Movin' and a groovin', I have tremolo!

Now I would like to increase the intensity of the effect, if possible. The 6SL7, even though 'similar' in gain to a 12AX7, has slightly less gain. Is there a component/s that I can adjust in this circuit to help increase the intensity?

[sluckey]

Replace the 4.7K/25µf cathode RC on V3A with a red LED. Cathode of LED connects to ground.

[funkgang49]

Diffuse red or waterbright clear red? Does it matter if it's 5mm or 3mm? 'Cause in some instances size matters.

[sluckey]

Just a common diffused red 5mm LED. Yellow works well too. The important thing is to use a LED with a forward voltage of 1.7V to 2V. Green, blue, and white are not good choices.

I used a yellow LED in a 6SL7 trem circuit... http://sluckeyamps.com/RCA/Ampeg_J12B.pdf

[funkgang49]

Tried a diffuse red 5mm (1.74v):
Slightly more output but when I slow the speed down oscillation stops. I have to crank up the speed then turn it back down to get it to oscillate at slower speeds - not ideal.

Yellow diffuse 3mm (1.85v):
A hair better than the red as far as output but still same problem with oscillation stopping at slower speed settings.

Note - all results are with the Intensity knob cranked.

Also anything I can do, in this preamp circuit, to mitigate volume drop when tremolo is engaged?

[sluckey]

I'm surprised that the oscillator drops out at slow speeds. Maybe the way the buffer is connected to V3A is a factor? Disconnect the INT pot from V3A. Does the LED drop out at slow speeds now?

Have you considered connecting the trem into the grid of the output tube? This would require a slight mod to your trem driver.

[funkgang49]

Do you mean V3b, middle lug of Intensity Pot to V3b cathode via 68K resistor?

Can't use output tube, this amp is cathode biased.

[sluckey]

Do you mean V3b, middle lug of Intensity Pot to V3b cathode via 68K resistor?

Sorry. I mean V2A.

Can't use output tube, this amp is cathode biased.

Doesn't matter. You can still modulate the grid. Post a schematic of your power amp.

[funkgang49]

Disconnect the INT pot from V3A. Does the LED drop out at slow speeds now?

I mean V2A.

Isn't that where the audio signal comes into the trem circuit from the preamp?

[funkgang49]

Isn't that where the audio signal comes into the trem circuit from the preamp?

Disregard that question.

Disconnecting the intensity pot from V2a pin 3 would shut off the tremolo completely, no?


Would changing the values of the Intensity pot (50K) and/or the 68K resistor that connects the Intensity control to V3b cathode effect the Tremolo output level?