Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: MadMax on March 21, 2015, 01:24:51 pm
-
On the Princeton Reverb I built, the tremolo is not as strong as I think it should be. The 'rate' control works fine, but I have to dime the intensity just to get okay trem happening. Maybe it's just the nature of this design, but if could be modified, where would I start? I notice on the Fender Deluxe 6G3 schematic, there's a .05 uF cap coming off of the wiper of the tremolo intensity pot, what does that affect? Also, the Princeton has a 1M series resistor to the plate of the trem tube, whereas the Deluxe has just 220k, is that where my intensity is being dampened? Thanks for any input.
Mad Max
-
The .05 on the wiper in the 6G3 smooths the tremolo signal but it also reduces the amplitude. You don't want that.
Decrease the 1M that you mentioned to increase the tremolo. Take it on down to 100K if you like.
If you really want to increase the tremolo then replace the oscillator tube cathode resistor/cap with a red or yellow LED (cathode to ground).
-
You're the man Sluckey. I'd be happy if I just knew the stuff you've forgotten. I'll play with the resistor (maybe put a 100k in line with a 500k pot). Can you seriously replace that RC pair with a LED? Thanks for the help.
Mad Max
-
Can you seriously replace that RC pair with a LED?
Yup, I used that on my Revibe and works great, I believe that was Sluckey's suggestion?
-
ARCHIVES has additional info about tremolo mods:
http://el34world.com/Forum/index.php?topic=604.0 (http://el34world.com/Forum/index.php?topic=604.0)
-
Count me as another satisfied convert. I just replaced the trem oscillator cathode resistor and bypass cap (3.3M and 25uf) in my Fender PRRI with a big red LED. I also replaced the 1M resistor with a 470K. Nice, rich tremolo (always the weak point in my amp in its stock format) and now I can warm up the bias a little more and still have great tremolo. Thanks to Steve and Merlin. Loving my Princeton Reverb even more now.
-
Not to be a pest .... :icon_biggrin:
But what's the value on the LEDs you're using for this?
I went to the electronics shop thinking I'd pick up an LED, but there was a gazillion of different shapes sizes colours and values!
So red or yellow, but what are the actual values?
thanks
-
Red or yellow, 5mm size. The 5mm size also fits a lot of panel mount bezels.
Different colored LEDs have a different voltage drop. This voltage drop will become the bias voltage for the tube. Red or yellow has a voltage drop that works well for the trem oscillator. Green or blue or white will have a voltage drop that is too high for good trem oscillator operation.
Just get a variety pack and do some experimenting.
-
Cool!
Thanks. Will do
-
OOOps I should've asked Does this work okay with the 6G11 one tube tremelo
I tried the red LED and the yellow. both seemed about the same as the cathode cap/resitor so Installed the red one...it flashes..whee..now I strangely have less tremelo
My probelm was a little bottom end whoop whoop in my speaker and also i seemed to be getting some distortion with the tremelo on
More tremelo + more distortion
I have the AB763 lite biased conventionally
-
So which is it? Less tremolo, or more tremolo + more distortion?
The LED should work fine in that circuit. The whoop whoop makes me think you have a stronger trem that can be controlled with the intensity control or maybe resetting the bias.
If your meter will read low frequency AC then measure the tremolo voltage at the input to the intensity pot. Do this with the stock resistor/cap, then do it again with the LED. You should have a significantly higher voltage with the LED.
-
Well
I hooked it up with the cathode cap again
With either the cap/resistor or the LEd my bias on my power tubes seem to vary betwenn -25 and -55
The tremelo I get is strong (it just was being weak for a short bit with the red LED, not sure what that was about)
but it introduces distortion into the guitar sound
My guess is that it's the extreme bias swings, Is it supposed to change that much. I do know that's how it works
My bias voltage is about -37 which gives me around 27ma on the cathodes and 425 B+ to the 6V6s
I have it at 27ms because I figure that minus the screen current it really is around 23-25
i would lower the bias but then my voltage shoots up and I['m already contemplating outting teh dropping resistor back into the SS rectifier
-
I put a red LED in the circuit and it made a noticeable improvement in the tremolo depth. Then I lowered the 1 meg resistor to 500k (actually put another 1 meg in parallel). I really like the amount of trem I can get now. Thank for the valuable input. Do I need to recheck the bias setting?
Max