Vintage Fender Princeton reverb too splashy

[bohema79]

Hi guys,
Can you please tell me what components should I check for value if the reverb on my 1966 Princeton Reverb is too sensitive and sprashy.
Everything pass 2,5 is useless. :(

Just so you know. The reverb tank is fine and the tube works great as I have checked both in my other vintage princeton reverb.
Please narrow it down to the pot, resistors or caps.
Which ones should I check that might be responsible for the problem. Can a pot be the problem?

Thanks,
Piotr

[sluckey]

Replace the reverb pot with a 100K audio taper pot.

[tubenit]

Replace the reverb pot with a 100K audio taper pot.

+1   Great suggestion by Sluckey!

You could also add a dwell pot if you wanted.

With respect, Tubenit

[bohema79]

Replace the reverb pot with a 100K audio taper pot.

Hi,
Thanks for the tip. I want the amp to be stock.

The other princeton Reverb is stock and the reverb is great. It has a stock pot and I ve connected my reverb tank to it and used my tube and it sounds just the way I want it so the difference must be in the value of the components. I would like to know what resistors or caps are responssible for the amout of reverb in the signal?

Thanks,
Piotr

[tubenit]

 

I want the amp to be stock.

I am not sure what that means?  Are you saying that replacing the 100kl reverb pot with a 100ka reverb pot would make the amp "not stock" & so you won't try that suggestion?   
 

Maybe you should give us the parameters of what you are willing to change and still view the reverb to be "stock"?

I would like to know what resistors or caps are responssible for the amout of reverb in the signal?

All the reverb components effect the "amount' of reverb.  Increasing or lowering the values of resistors or caps change the amount
of reverb.

With respect, Tubenit

[sluckey]

Thanks for the tip. I want the amp to be stock.

Well, you already made the amp non stock when you put that 50µF/100V cap in the bias circuit.

I think it's typical for a PR or other tube Fender amp to have strong reverb at 2.5 on the dial. Perhaps your 'other' PR has a weak reverb circuit. Anyhow, I've attached a drawing and circled the components that will affect the level of reverb.

[Willabe]

I think it's typical for a PR or other tube Fender amp to have over-the-top reverb  at 2.5 on the dial. Perhaps your 'other' PR has a weak reverb circuit.

Yep. Had a BF SR for years I gigged with and rarely went past 2 1/2 or so on the verb knob. Plenty of verb on that setting. Most guys in the blues clubs set theirs the same. I still have a BF PR and it's the same, very wet at low settings.

Your other 1's probably weak like Sluckey says.

You could try using a 12AU7 for the verb driver tube and see if you like that better. That way the circuit says stock except for the tube and that can be easily swapped out for a 12AT7 again.


                  Brad     

[bohema79]

I want the amp to be stock.

I am not sure what that means?  Are you saying that replacing the 100kl reverb pot with a 100ka reverb pot would make the amp "not stock" & so you won't try that suggestion?   
 

Maybe you should give us the parameters of what you are willing to change and still view the reverb to be "stock"?

I would like to know what resistors or caps are responssible for the amout of reverb in the signal?

All the reverb components effect the "amount' of reverb.  Increasing or lowering the values of resistors or caps change the amount
of reverb.

With respect, Tubenit

Hi,
What I meant was that maybe some parts are off tolerance and changing them out would make the reverb play better. Changing the original '66 pot that works good is the last mod I would like to do. The other princeton also has a 100kl pot and it works great.

I just wanted to know what resistors and their value are the most crucial for the amount of reverb in the signal and make one amp different from the other.

Thanks,
Piotr

[John]

I know very little about reverb, so take this with a (big) grain of salt. But, I think the first thing I'd try (if you don't want to change the pot) is to clip in maybe a 1Meg resistor across that 3.3M in the little red circle Sluckey drew for you, or even a 500K. I *think* that would send more signal straight to the next valve stage, and less signal through the reverb tank.

And if I'm wrong, Sluckey'll come slap me around a little. 

[sluckey]

clip in maybe a 1Meg resistor across that 3.3M in the little red circle Sluckey drew for you, or even a 500K. I *think* that would send more signal straight to the next valve stage, and less signal through the reverb tank.

That's half right. You will have more dry signal straight to the next stage, but the signal through the tank will remain the same. In fact, if you mistakenly put a 3.3K in place of that 3.3M you'll get no reverb. And if you put a 1K in place of the 1M on the grid of the driver tube you will also get no reverb. I've seen both of those mistakes right here on the forum.

The problem with all this is now it ain't stock. 

I still don't think there is anything wrong with the amp. At least anything wrong that can be fixed to Piotr's way of thinking AND keep the circuit stock. I think the amp he is comparing to has weak reverb. That Fender reverb circuit is really strong straight outta the factory.

There are lots of things that can be done to tame the reverb. Using an audio taper reverb pot is the dead nuts simplest thing to do to satisfy his complaint.

[tubenit]

Using an audio taper reverb pot is the dead nuts simplest thing to do to satisfy his complaint.

Yes, I agree.  Pretty simple and straight forward.  Original pot can be kept and put back in  so it could be "stock" if it's ever sold.  

I guess what I can't figure out is IF you replace or change anything then it's not stock & yet he wants it all stock?  I personally don't see replacing a reverb pot as a greater deviation from stock then changing a resistor or cap.  Not sure where that rule book is?

If you don't want to change anything from stock then why ask what to change?  I don't mean that as a criticism, I just simply don't understand what exactly he is wanting to do?   

With respect, Tubenit

[bohema79]

Using an audio taper reverb pot is the dead nuts simplest thing to do to satisfy his complaint.

Yes, I agree.  Pretty simple and straight forward.  Original pot can be kept and put back in  so it could be "stock" if it's ever sold.  

I guess what I can't figure out is IF you replace or change anything then it's not stock & yet he wants it all stock?  I personally don't see replacing a reverb pot as a greater deviation from stock then changing a resistor or cap.  Not sure where that rule book is?

If you don't want to change anything from stock then why ask what to change?  I don't mean that as a criticism, I just simply don't understand what exactly he is wanting to do?   

With respect, Tubenit

Thanks for the input.
You guys dont seem to understand what I mean by stock. By "stock" i mostly mean component value. I just dont see a reason for replacing the original pot (when the guality of modern CTS pots is not even close) for a different value when I have another '66 Princeton reverb with the same pot and sounding great. Maybe the other Princeton has a "weak reverb" I dont know, but it sounds stunning. I just want to know what parts make a weak reverb (great sounding) and a strong reverb (crap).
I've conected my tank to the other princton and it sounds great.
I've used my AT7 tube in the other princeton and it sounds great.

So what parts should I compare and test to get them close?!

If thats so hard to do and not possible than it must be magic...

Regards,
Piotr

[sluckey]

So what parts should I compare and test to get them close?!

The ones I circled in red.

[punkykatt]

Pull both chassis and put them side by side and compare the resistors and caps in the reverb circuit(circled in red in the post above) to see if they have the same values. You may want to use a meter  to check their values for drift too.  Discharge the filter caps first.

[tubenit]

Do you know the difference between linear and audio taper pots and why Sluckey suggested the 100ka pot?

Can you name specifically what parts in your original Princeton Reverb that you would be willing to replace in order to accomplish your goal?

Are you able to read schematics?  Honest question & no disrespect intended.

With respect, Tubenit

[eleventeen]

Of all the ideas presented, I like the swap-in of a 12AU7. At least try it. 

[HotBluePlates]

You guys dont seem to understand what I mean by stock. By "stock" i mostly mean component value. I just dont see a reason for replacing the original pot (when the guality of modern CTS pots is not even close) for a different value when I have another '66 Princeton reverb with the same pot and sounding great. ...

Respectfully, maybe you're not familiar with how these amps sound stock. Measure all resistor values, but I'll bet money you won't find any much beyond 10% from the marked value (which is exactly what those resistors should be).

Most blackface Fenders have a lot of reverb, and more than most people want. I've owned a lot of Princeton Reverb amps, and never needed to turn the reverb above 4 on any of them. Most of them did not give exactly the same amount of reverb (or even the same reverb tone/brightness) at the same setting.

Measure the parts Sluckey circled. Also measure the supply voltages in that area. If the resistors measure within tolerance, and you want the amp "stock" then you'll have to accept the difference in reverb between the amps. If the supply voltage is very different, that could account for some difference in reverb strength, even though both amps might be as they left the factory.