incorrect voltage reading for right channel.

supmate · 1696

0 Members and 1 Guest are viewing this topic.

Offline supmate

  • Newbie
  • *
    • Posts: 1
on: December 02, 2013, 02:23:54 PM
recently installed the speedball upgrade and did not get expected readings for voltage checks measurements for the right channel. when i measure terminals 5, I get around 57 volts instead of 75 volts. Looking at the circuit diagram i think the problem occurs at the node that the collector of the MJE-350 transistor is connected to. I think it maybe a problem with the MJE-350 transistor but I'm not sure. Unfortunately I shorted out the two red LEDs on the left (comparing voltage readings between both channels) in the process of trouble shooting. So I am going to have to order new parts.
« Last Edit: December 02, 2013, 02:45:23 PM by supmate »



Offline Grainger49

  • Hero Member
  • *****
    • Posts: 7175
Reply #1 on: December 02, 2013, 02:30:33 PM
An often problem with this upgrade is that the center pin of the MJE-350 is the back of the transistor and sinks a lot of heat.  IT takes longer on that pin to get a good solder joint.

Try reheating it.



Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19732
Reply #2 on: December 02, 2013, 05:41:27 PM
recently installed the speedball upgrade and did not get expected readings for voltage checks measurements for the right channel. when i measure terminals 5, I get around 57 volts instead of 75 volts.

Hmm, I would've tried swapping 12AU7's, or swapping the small green PC boards.  It's possible that you have a 12AU7 with high emission on one side.  If you did, swapping the boards would not move that voltage around.

I don't think you have any bad transistors (at least before your accident).

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man