princeton reverb trem mod

[phsyconoodler]

I just finished a princeton reverb with a raw control and it sounds great clean or slightly overdriven.The trem is weak even though I did the trem mod on it with the diode across the volume control and switched a 1 meg resistor for a 220k.
  I tried all bias settings from 14 ma to 30ma and it doesn't seem to change much at all.
What can be the reason behind this?I have the correct voltages and triple checked resistor and cap values.Very odd indeed.
 also I have a maste volume that works but this amp gets raspy as you turn it up high.I added a 1 meg grid stopper on the PI grid and it helped a bit but not much at all.Funny I've never had this issue with any PR I've built before.
  This one is eluding me at present.At high clean volumes the amp sounds awesome.Even at volumes of about 6 or 7 on the dial it's great,however as you turn it higher it gets really ratty sounding.Seriously awful sounding indeed.I have built quite a few of these amps and they all sound great cranked to 10.Not this one.

[jjasilli]

princeton reverb with a raw control and it sounds great clean or slightly overdriven. . .gets raspy as you turn it up high. . .At high clean volumes the amp sounds awesome.Even at volumes of about 6 or 7 on the dial it's great,however as you turn it higher it gets really ratty sounding.
Pretty much my experience with my hot-rodded SF Princeton (non-reverb).  Schematic:  http://www.el34world.com/Forum/index.php?topic=576.0

The trem is weak even though I did the trem mod on it with the diode across the volume control and switched a 1 meg resistor for a 220k.  The diode is optional. Maybe remove it.  (Do you mean Intensity control). 

Dropping the value of the 1M series resistor solved my anemic trem problem.

[Fresh_Start]

6V6 or 6L6 power tubes?

If 6L6, change the .022uf to ground between your 220K and the Intensity pot to .047.  Change plate resistor to 470K & cathode resistor to 4.7K.  I assume the jiggler triode has a 25uf bypass cap.  This will make jiggler stage like Hoffman's 6L6 bias vary trem for AB763.

I recently had a "low gain" 12AX7 that simply wouldn't jiggle.  Try another tube.

I'm not familiar with the diode circuit you are referring to.

Hope this helps,

Chip

[tubeswell]

I re-did my recent PR cloney thing with an IRF820 source follower in the trem circuit - utilising 5G9 trem circuit values. The trem is very nice in that now.

[jjasilli]

Fresh_Start : I'm not familiar with the diode circuit you are referring to.
From the FDP Forum:

[Fresh_Start]

What's that diode supposed to do?  The "top" of the bias supply filter cap is AC ground.  Normally the Intensity pot is a voltage divider between the trem signal and that AC ground.  With that diode in place, it seems to me that the trem signal's "positive" wave form goes straight to AC ground.  However, I'm a hacker at electronics.

Please 'splain this to me.

Thanks,

Chip

[jjasilli]

http://www.fenderforum.com/printmessage.html?db=messages&db2=topics&topic_number=445645

"To increase depth, the 1M resistor in series with the intensity pot is changed to 220K. But now that the depth has increased, the circuit will cause more thumping from the speakers. The diode across the intensity pot cuts off the positive-going half of the oscillator signal sent to the power tubes. The negative-going half turns off the power tubes and creates the tremolo effect, but the positive-going half just increases current in the power tubes and causes the speakers to thump. Adding the diode does not affect the tremolo depth, it only reduces the thump from the speaker."

[phsyconoodler]

I'm leaning towards the tube because I did the mods and it still has a weak trem.
  The awful overdrive has me concerned now.It sounds crappy.I am using .047uf driveline caps and have not had this issue with other builds exactly the same.However,I am using the master volume that Sluckey suggested in this build.It works but it's not really that good.
   I'm kind of lost at this point,having tried lots of supposed 'fixes' like a 1 meg grid stopper on the PI grid.It made such a small difference that I'm wondering if the master volume has something to do with the bad tone?Guess I could lift it out and try it without it.
  Like I said,the cleans are fabulous,it's just not giving me any magic when it's cranked up.
 

[jjasilli]

You've got a lot of great builds.  The numbers are on your side!

[PRR]

> The "top" of the bias supply filter cap is AC ground.

Yes, but at negative 30V (whatever) DC.

If the trem is too hot, over 30V peak, the voltage to grids goes positive. This makes trouble. With the diode, it can't go much positive; long-term the trem wave and average DC grid bias is shifted more negative.

It catches over-strong tremolo. It's not a primary fix for "weak tremolo".

[Fresh_Start]

Thanks PRR.  Seems like that diode is a fix for too strong tremolo.  I'd rather dial in an appropriate amount of tremolo signal and move on.

The MOSFET buffer OTOH is something I'll try out soon - next time I open up the Prankster Reverb.

Cheers,

Chip

[phsyconoodler]

Anyway,the amp is getting gutted and converted to a 2204 circuit and I'm saving the princeton for another amp.Assuming I can iron out the problems.This one is odd at best.
  Thanks PRR for piping in about the trem diode across the pot.It really didn't do anything for me anyway,as the lower series resistor did basically nothing either.
  I don't see what I did wrong as of yet but it'll have to wait for the next one.