Trouble with my Friedman tonight

T-Rex said:
I looked at a gut shot of a PT. They are cathode biased with a 120R / 10watt resistor (higher wattage bias resistor= burns up the tubes before the resistor). I think Vox biased with a 130R which was toasty, Marshalls were 150R. Probably the reputation to chew up tubes may be quite real. Cathode bias at idle can be 100%, but I usually stay down @95%. Supposed pic of a PT gut shot below.

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Yes mine is the old version and looks almost exactly like that.
 
Heard back from the tech - problem was a just loose terminal on the V1 socket.
Huge sigh of relief.
He's putting in a new socket; should get the amp back in a day or two.

Been using a friend's JMP 50 head in the meantime - a very very good one which sounds great.
Still, I'll be glad to have my PT20 back.
 
syscokid said:
Vewy intewesting! I wonder if the amp tech found the problem by "chopsticking"?
Good news... :cheers:
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That’s how I fixed my 97 Evil Twin a few months ago. Tapped on the tubes with a chop stick (trick learned here) and found V1 was flaky. Replaced it and now good as new.
 
eclecticsynergy said:
Heard back from the tech - problem was a just loose terminal on the V1 socket.
Huge sigh of relief.
He's putting in a new socket; should get the amp back in a day or two.

Been using a friend's JMP 50 head in the meantime - a very very good one which sounds great.
Still, I'll be glad to have my PT20 back.
Click to expand...
The sockets used by Fender lately...have the same problem.
Seems like a bunch of bunk sockets.
 
Years ago I had a case of 50 Belton octal tube sockets that were defective arcing between pins 6 and 7 only under load
after that will never use Belton products just pay extra for the Mil Spec ceramic tube sockets.
 
Glad you got it sorted!

My Silkyn Super 50 is blowing power tubes in V7 only, most recently biased around 60%.
I have not dug further into it yet and am re-evaluating my understanding and methods of measuring and setting bias.
Only Tung Sol 6L6GC-STR tubes have blown: 3 times, always V7. The other 2 times the bias was @70%.

I will start a thread and post the schematic during the Thanksgiving extended weekend, when I have time.
 
jtcnj said:
Glad you got it sorted!

My Silkyn Super 50 is blowing power tubes in V7 only, most recently biased around 60%.
I have not dug further into it yet and am re-evaluating my understanding and methods of measuring and setting bias.
Only Tung Sol 6L6GC-STR tubes have blown: 3 times, always V7. The other 2 times the bias was @70%.

I will start a thread and post the schematic during the Thanksgiving extended weekend, when I have time.
Click to expand...
You should go through tests before installing any tubes.
You need to take meter readings with the tubes removed.

The first thing you do is:
Turn the power on but leave the standby set to 'warm-up.'
Do not turn the standby to 'operate' position.
Set meter for DC volts.

Connect black meter probe to chassis.
Connect red meter probe to pin 5 of output tube socket.
Measure pin 5 of both output tube sockets...write down the DC voltage reading of pin 5 for each output tube socket.
Report the DC volt readings.

Do not put the tubes in.
Do not try to play the amp.
Not until we have taken all the readings and corrected the problem.

Correct problems first.
Put tubes in last.
 
I thought I had bad tubes at first.

After each of the prior 2 failures, I put the stock / original Sovtek 5881/6L6WGC pair back in, biased them - and it is fine, for several play sessions.

For each failure, I played at least 2 hours, mostly with the master pretty low, then on the 2nd or 3rd session, the tube failed within a half hour.

So, again, I thought bad tube, but then the most recent failure.
It has been sitting waiting for my attention.
 
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