Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bakerlite on April 07, 2011, 06:55:13 pm

Title: oh no - another power supply gone.
Post by: bakerlite on April 07, 2011, 06:55:13 pm

i recently swapped out a power supply for a friends marshall jcm 2000 tsl 122
he played for 2 hours and the amp died went over to the amp and felt real hot over the power supply.
i feel awful - all voltages checked out when i put in the last one for him.
other than bad power suply filter caps or tubes anything else that would kill a PT?

Title: Re: oh no - another power supply gone.
Post by: navdave on April 07, 2011, 09:31:03 pm

Hmm you sure the PT is dead? A dead short would do it something that would bypass the mains fuse.

Title: Re: oh no - another power supply gone.
Post by: bakerlite on April 08, 2011, 04:06:33 am

pretty sure
blows the fuse with the tubes out
exactly the same as before

Title: Re: oh no - another power supply gone.
Post by: darryl on April 08, 2011, 05:38:52 am

This may be relevant:

http://www.lynx.bc.ca/~jc/TSL122.html

 :sad2:

Title: Re: oh no - another power supply gone.
Post by: VMS on April 08, 2011, 05:40:29 am

Do you know what killed the first PT?

Title: Re: oh no - another power supply gone.
Post by: HotBluePlates on April 08, 2011, 02:43:46 pm

You'll find a short with much less frustration if you use a light-bulb limiter.

Title: Re: oh no - another power supply gone.
Post by: phsyconoodler on April 08, 2011, 04:33:09 pm

That site has one guy's interpretation of TSL problems.I have been fixing TSL's for quite a while now and never had bias problems.I do however,have a problem setting bias on this amp to 45ma per tube with a 470+v plate!!!

  I set the bias to 35ma per tube and all future problems are usually avoided.
The problems I see are poor push-connectors on a power transformer,bad rectifier diodes and burnt tube sockets 'between' the PC board.You can't see it from the outside or inside until you remove the board.Then the usual sprung 16 ohm speaker jack scenario.
  The odd burnt PC board from the little 500pf cap on one of the power tubes next to the PT.
45ma per tube! Alarmingly high current for EL34's.

Title: Re: oh no - another power supply gone.
Post by: bakerlite on April 11, 2011, 05:07:16 pm

Quote from: phsyconoodler on April 08, 2011, 04:33:09 pm

  The odd burnt PC board from the little 500pf cap on one of the power tubes next to the PT.

how much resistance should that cap show if any?
if i use the shortcut and stick my meter in pin sockets 3 and 4 i get about 1200 ohms?
should there be any reading at all there?

other than that there doesnt seemt to be sign of much else wrong -

Title: Re: oh no - another power supply gone.
Post by: sluckey on April 11, 2011, 07:02:50 pm

Quote

how much resistance should that cap show if any?

Infinity. If measured in circuit, resistance would depend on the circuit.

Quote

if i use the shortcut and stick my meter in pin sockets 3 and 4 i get about 1200 ohms?
should there be any reading at all there?

That sounds typical if using 1KΩ screen resistors.