Princeton Reverb Trem Intensity response

[Govmnt_Lacky]

Working on a PR amp and noticing that the Tremolo seems to be VERY weak when the Intensity pot is set to 5 or less. Almost like it disappears. I have seen some mods to change the Depth of the Trem (increasing the Trem cap values) but will that get me more usable range from the Intensity pot or will it just make the current usable range more intense?

[Chuck H]

Increasing capacitor values will slow the trem down but should not increase intensity. Though I'm not sure that increased intensity is what you want.?. The read seems to indicate that what you want is a faster increase of intensity relative to the knob adjustment. If that's the case you could try a 250k reverse audio taper pot for the intensity control. The overall inensity range would be the same but will be higher within that range sooner on the knob. About 20% log would be best I think though I don't know that you'll ever find one. I would go with an Alpha pot which will have a 15% log. The CTS and Bourns pots will have a 10% log and probably come up too fast.

If what you want is actually more intensity you're probably out of luck. The PR uses the influence of a single triode oscillator design to modulate the bias and will not have the same influence as more elaborate two triode systems that reduce the impedance of the oscillator output.

[Govmnt_Lacky]

The read seems to indicate that what you want is a faster increase of intensity relative to the knob adjustment..

This is correct. I am not happy with the Intensity of the Trem/Vibe with the knob below 5. Between 5 and 10, I get great depth and a deep trem/vibe. Especially between 8-10. Below 5 it is anemic.
As for the caps, after reseach I see that they have more influence on Speed so that is not my concern.

So... the only recourse I see is to try different pot tapers for the Intensity pot huh?

[loudthud]

First step would be to verify that the pot you are using now is a linear pot. Disconnect any wires, measure the resistance from the wiper to each end to see if the resistance is equal when the pot is half way through it's rotation.

[Chuck H]

THIS^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If it IS a linear pot then the reverse audio taper is an option.

[Tom Phillips]

The issue you describe is a fairly common problem. In addition to the advice that has already been given, I suggest that you check the bias setting of your power tubes. Note that the "bias wiggle" tremolo circuit operation is dependent upon where the bias is initially set. Often, the bias is not re-adjusted when Princeton power tubes are changed because there is no bias adjustment pot. The bias can be optimized by changing resistor values in the bias supply or by modifying the circuit to add a bias adjustment pot.