Fender Princeton

[Big chief]

Have low voltage from PT to 5u4 tube
Pin 6 313
Pin 4 312
Pin 8 257

tube 6v6 pin 3 309
              Pin 4 239

Replaced rectifier socket
Any help would be great

[Willabe]

You need to list AC or DC voltage.

What's the acv coming from the PT's high voltage wind going to the rectifier tube. Need red to red, 1 red to CT, then the other red to CT.

Edit; Added the words 'then the other'. Willabe

[Big chief]

Red to red 642 ac
Red to ct 318 ac
Red to ct 315

[Big chief]

Rectifier tube pin 3 313 ac schematic shows 340 ac
                    Pin 4 312 ac.                          340 ac
                    Pin 8 257 dc schematic shows 420 dc
6v6 tube pin 3 309 dc schematic shows 410 dc

              Pin 4 239 dc schematic shows +400dc
Have tried 2 5y3. 5u4 tube that are new  and replaced the tube socket
Thanks for any help

[mresistor]

Why are you using a 5U4?   If this is an AA964 the rectifier should be a GZ34. Is this amp a Princeton Reverb or a Princeton?

I assume it's a Blackface AA1164 or AB1270 and you just conviently left this information out of your title.


Were the red to red and red to ct AC voltages checked without a rectifier installed?  Empty socket?


Has the cap can been replaced?   
 

[Willabe]

And how much current are the 2 x 6V6's pulling?

The more current, the lower the B+ dcv will drop.

Is this a real Fender or a clone? And what PT is in this amp?

[AlNewman]

Try pulling all tubes and measure ac voltage to center tap.
330ish?

Plug in the rectifier only and measure dc voltage at the top of the reservoir cap.  Should be over 450V.  If not, you likely have a bad rectifier or filter cap, (could be any filter cap).
Measure DC voltage at pin 5 of both power tubes.  Should be somewhere in the range of 20-30V maybe?.  If not, you might have a bad component in your bias supply.

If still good, try plugging in your power tubes, test again.

You're losing voltage because something is drawing too much current.

[Willabe]

AlNewman, we know nothing about this amp, a real Fender, is it a clone, what PT he's got? I've asked him this and am waiting to see what he say's.

There's too many guys starting a new thread with very little information to go by.

 

[AlNewman]

Same rules still apply though, right?
Unplug all the tubes and see what the ac voltage is.

Pictures might help.

[Willabe]

Rectifier tube pin 3 313 ac schematic shows 340 ac
                    Pin 4 312 ac.                          340 ac
                    Pin 8 257 dc schematic shows 420 dc
6v6 tube pin 3 309 dc schematic shows 410 dc

              Pin 4 239 dc schematic shows +400dc
Have tried 2 5y3. 5u4 tube that are new  and replaced the tube socket
Thanks for any help

[Willabe]

Same rules still apply though, right?

Yes, but your guess numbers could be way off because of the PT he has.

[AlNewman]

A guess based on a princeton PT.  Except if we plug it in and take data, then it won't be a guess anymore.

[Willabe]

A guess based on a princeton PT.  Except if we plug it in and take data, then it won't be a guess anymore.

Yeah, I get that.

And what did I say?

Yes, but your guess numbers could be way off because of the PT he has.

Which we still don't know. I'd just like to know what it is and that's more than fair.

[AlNewman]

A guess based on a princeton PT.  Except if we plug it in and take data, then it won't be a guess anymore.

Yeah, I get that.

And what did I say?

Yes, but your guess numbers could be way off because of the PT he has.

Which we still don't know. I'd just like to know what it is and that's more than fair.

I agree.  So how would you suggest finding the voltage on the PT secondary?

[Willabe]

I agree.  So how would you suggest finding the voltage on the PT secondary?

If you agree, then why are you asking me this? I told you already, I'd like more information about this amp and I want to know what PT he is using.

And I already said until we know more, what PT, then any numbers he posts might not mean very much.

And my 1st reply;

You need to list AC or DC voltage.

What's the acv coming from the PT's high voltage wind going to the rectifier tube. Need red to red, 1 red to CT, then the other red to CT.

Are you even reading this thread? Or just parts of it?

[Big chief]

The amp is a Princeton reverb silverface Sorry for not saying what it was I was just frustrated from checking all the voltages Bias was -50 on both Power tubes had 2.5 ac at heaters the pt was very hot  caps were with in specs checked for loose ground pulled all tube cleaned all sockets all tubes checked good
Am at a loss possible bad pt

[Willabe]

Ok, take out all the tubes, including the rectifier tube.

Now set your meter to acv and use alligator clips, 1 on each leg of the 6.3 heaters. Do not measure from 1 leg to the heater CT. Post what you get.

 

[Big chief]

With all tubes out 6.9 ac volts to heaters

[Willabe]

Ok, good.

If you stick around for a little while I'll help you get some answers.

[Big chief]

Ok thanks

[Willabe]

For all these measurements, use your alligator clips.

Now with all the tubes out, set meter for acv, measure the across the 5acv heater for the rectifier tube. Pins 2 and 8 on the rectifier tube socket.

Then measure across the B+, with rectifier tube still out, meter set to acv, red to red legs, then red to CT, then other red to CT.

Now put the rectifier tube in, should be a 5U4, don't use a 5Y3, measure for dcv at pin 8.   

And last, measure the -bias dcv at pin 5 of both power tubes, with the rectifier tube still in. (All other tubes still out.) 

 

[Willabe]

And when taking all the above measurements, plug straight into the wall outlet, NO light bulb limiter. 

And what is your wall acv?

[Willabe]

Where'd ya go?

I thought you were going to stick around?      

[Willabe]

And what's the model number on the paper tube chart in side the amp cabinet? 

[Big chief]

Rectifier pin 2-8 53 ac
Red to red 780 ac
Red to ct 385
Red to ct 390
Pin 8 22.4 dc
Pin 5 bias .5dc
Pin 5 bias .5 dc

Again thanks for all your help

[Big chief]

Wall current 124.2
No markings on paper tag except tube chart

[Willabe]

Rectifier pin 2-8 53 ac

If you meant 5.3acv (not 53acv) then this is good.

Red to red 780 acRed to ct 385
Red to ct 390

This is fine for being unloaded.

Pin 8 22.4 dc

This is wrong. Measure this again, positive meter prob to pin 8, negative meter prob to ground.   

Pin 5 bias .5dcPin 5 bias .5 dc

This is very bad. Please measure this again.

If this measurement is correct, then the output tubes would have been red plating (over heating) pulling massive current and that would have been the problem. Pulling massive current pulls down the B+. The more the power tubes pull, the more the B+ drops. 

[Big chief]

With rectifier in pin 8 384 dc

[Big chief]

Thank you guys very much my wife needs attention at time have to take care of her then go back to work on amp

[Willabe]

   Yes, I said now put the rectifier tube in.

With rectifier in pin 8 384 dc

Is this with the 5U4 or the 5Y3?

If this is with the 5U4 something's off. Either the 5U4's bad or you have a bad filter cap leaking to ground.

[Big chief]

Yes 5u4
I’ll replace the main filter caps and let you know thanks

[Willabe]

Wait, the tube could be bad.

The 5U4 is a dual rectifier, has 2 rectifier sections in it. Sometimes only 1 side goes out.

 

[Willabe]

You can test without changing all the filter caps, if you have 1 filter cap, say 20uF @ 450v.

Just disconnect the red wire on pin 8 going to the 1st filter cap. Now take a couple alligator clip leads and clip in that cap.

Now with your meter gator clips measure the dcv at pin 8/1st cap positive lead.

If the dcv is up over ~420dcv, then it's at least 1 of the B+ filter caps. If the B+ didn't come up then the rectifier tubes bad.     

[Willabe]

Still need this;

Pin 5 bias .5dc Pin 5 bias .5 dc

This is very bad. Please measure this again.

If this measurement is correct, then the output tubes would have been red plating (over heating) pulling massive current and that would have been the problem. Pulling massive current pulls down the B+. The more the power tubes pull, the more the B+ drops.

Your looking for a negative dcv of at least -30dcv to -35dcv.

Be sure to discharge all the filter caps, including the test cap (after you use it) before you mess with them.

[Big chief]

Thank you sir it will be later today that I can work again
I really appreciate your patience

[Willabe]

What patience, your not a problem. 

You take care of your wife. She's more important than an amp.

When you get time guys will still be here to help. 

[Big chief]

Possible bad 5u4 tube new JJ  caps did not help ordered new EH 5u4  should be here the 19th
Down till then  Thanks

[Willabe]

Were the caps old, original? 

[AlNewman]

780V ct seems pretty high for a princeton. 
I wonder if the transformer has been replaced, or maybe it was an international transformer which was wired differently.

Pics would definitely help.

[Big chief]

Can cap appeared to be original 20- 20-20-20 I used f&t 22uf 500vdc
I can’t send pics from my phone
As soon as my tube comes in I’ll be back to work on it I just do this for my friends that don’t have much money

[Willabe]

780V ct seems pretty high for a princeton.

That's totally un-loaded, no tubes.

With a wall acv of 124.2.

[Willabe]

As soon as my tube comes in I’ll be back to work on it I just do this for my friends that don’t have much money.

Kind thing to do for your friends. 

[Willabe]

After you get the new rectifier tube in and if it was the problem, before you put the 6V6's back in;

Pin 5 bias .5dc Pin 5 bias .5 dc

This is very bad. Please measure this again.

If this measurement is correct, then the output tubes would have been red plating (over heating) pulling massive current and that would have been the problem. Pulling massive current pulls down the B+. The more the power tubes pull, the more the B+ drops.

Your looking for a negative dcv of at least -30dcv to -35dcv.

[AlNewman]

When I look at princeton schematics, either there's a tap off the HT for the bias voltage, or the bias is pulled directly off the HT.  Would it matter if there's a rectifier tube or not to get negative bias at pin 5?

[Willabe]

Would it matter if there's a rectifier tube or not to get negative bias at pin 5?

No, doesn't matter. That tap is before the rectifier tube.

But the -dcv will be high because the PT will be un-loaded.

[AlNewman]

Would it matter if there's a rectifier tube or not to get negative bias at pin 5?

No, doesn't matter. That tap is before the rectifier tube.

But the -dcv will be high because the PT will be un-loaded.

Unless there's no path to ground.
The PT seems fine unloaded.

[Willabe]

I don't understand what your saying half the time.

Unless there's no path to ground.

What are you talking about? The -bias circuit has a path to ground. The PT CT is hooked up to ground.

The PT seems fine unloaded.

You said the unloaded PT B+ dcv looked high. Now you say ^^^

[AlNewman]

The PT seems to be working fine at AC voltage.
780V CT, fairly balanced, 6.9 at heaters.
Looks good for that transformer, correct transformer or not.

The Op is not available, but with a rectifier or not, there should be a negative voltage at pin 5 of the power tubes.  If the bias supply was shorting through the capacitor, there would be a draw on the PT with nothing plugged in, which there doesn't seem to be.

If one of the resistors at the bias circuit was open, that would mean the PT would test ok without any tubes.

With the rectifier plugged in, it could be drawing from any parts of the circuit.  So say for instance a higher voltage transformer was added, the 450V caps which are stock in the schematics that I see, may not handle the voltages well in excess of 500V when the amp's in standby.

[Willabe]

The PT seems to be working fine at AC voltage. 780V CT, fairly balanced, 6.9 at heaters.
Looks good for that transformer, correct transformer or not.

We all ready know that.

The Op is not available, but with a rectifier or not, there should be a negative voltage at pin 5 of the power tubes.  If the bias supply was shorting through the capacitor, there would be a draw on the PT with nothing plugged in, which there doesn't seem to be.

We already know that.

If one of the resistors at the bias circuit was open, that would mean the PT would test ok without any tubes.

He hasn't got that far yet. The last thing I reminded him to do was check for a -dcv of ~ -30dcv to -35dcv, because the dcv's he posted where wrong. If your reading the whole thread then you saw them.

With the rectifier plugged in, it could be drawing from any parts of the circuit.  So say for instance a higher voltage transformer was added, the 450V caps which are stock in the schematics that I see, may not handle the voltages well in excess of 500V when the amp's in standby.

Cross that bridge when we get to it. He has made no mention of a changed PT.

When he gets the new 5U4 and puts it in, we'll see where the amp's at. If good, then he'll check the -bias circuit.

[Big chief]

Just put in new 5u4 E H tube
Voltages reciter pin 8 397 vdc

v6 pin4=396vdc pin3=362
V5 pin4=363vdc pin3=365
Bias v5 -30.4 v6 -30.5

Amp sounds pretty good to me

What do you think?