Supro S6698 Tremolo

[Bombacaototal]

I build this tremolo on an amp and having a few issues. The main modifications on my amp are the 3 LFO caps replaced to .05uF for a slower range and the INT pot as 250K, and I also moved the footswitch to PIN 2 and removed the 6.8M before. My supply capacitor is 10uF similar to the original

Firstly I had the tremolo circuit grounded at the Buss bar, but on that set up it was very very slow. With Intensity and speed at maximum one could barely hear the effect.

I decided to lift the entire circuit from the ground and when I engage the effect, for about 10 to 20 seconds the tremolo circuit works perfectly, but then the oscillation fades and I cannot hear anything even with Intensity and Master at Maximum.

Am I missing anything?

[Stevem]

Put it back the way it was and remove 1 .05 lfo cap for starters.

[Phil_S]

A tremolo needs a good strong 12AX7 to oscillate. If the tube is weak, it won't work or it won't work very well. Other 12A?7 tubes generally won't work due to much, much lower internal plate resistance. It might work with a strong 5751.

The good news is there is no tone on the tremolo. You can use a cheap (inexpensive?) Sovtek or JJ or Chinese 12AX7 if you need to buy one.

[Tony Bones]

As Phil said, you need lots of gain in that 12AX7. This is one case where a really big cathode bypass cap can help. Try a 100uF or even 220uF if you happen to have one laying around.

Or try Sluckey's LED bias.

[Bombacaototal]

A tremolo needs a good strong 12AX7 to oscillate. If the tube is weak, it won't work or it won't work very well. Other 12A?7 tubes generally won't work due to much, much lower internal plate resistance. It might work with a strong 5751.

The good news is there is no tone on the tremolo. You can use a cheap (inexpensive?) Sovtek or JJ or Chinese 12AX7 if you need to buy one.

Thanks for the reply Phil. I am using a high gain shuguang 12AX7, so indeed a very strong tube. I tried a Tung-sol and a Groove Tubes today and the circuit got a weird hum, so back to the chinese.

[Bombacaototal]

As Phil said, you need lots of gain in that 12AX7. This is one case where a really big cathode bypass cap can help. Try a 100uF or even 220uF if you happen to have one laying around.

Or try Sluckey's LED bias.

Thanks Tony, I tried a 30uF instead and it made no difference, the circuit still starts as it should be and then It speeds up for the next 20 seconds and only in a couple setting you can hear a bit of the trem.

I haven’t tried as high as 100uF though

[Bombacaototal]

Put it back the way it was and remove 1 .05 lfo cap for starters.

Thanks stevem, I will bring it back to original spec, probably safest bet

[Bombacaototal]

A tremolo needs a good strong 12AX7 to oscillate. If the tube is weak, it won't work or it won't work very well. Other 12A?7 tubes generally won't work due to much, much lower internal plate resistance. It might work with a strong 5751.

The good news is there is no tone on the tremolo. You can use a cheap (inexpensive?) Sovtek or JJ or Chinese 12AX7 if you need to buy one.

Thanks for the reply Phil. I am using a high gain shuguang 12AX7, so indeed a very strong tube. I tried a Tung-sol and a Groove Tubes today and the circuit got a weird hum, so back to the chinese.

By the way, voltages are 285V and 292V for PIN 1 and 6.

The supplies are 290v / 292v