Voltage Check off on side B with very high voltage on T26 & T35

[gort]

Hi Everyone,

Just completed my SEX 4 and started testing. Resistance was all within spec. Voltage was good on the "A" side. The "B" side is off outside of the 10-15% wiggle room. Some values are low by over 15% where other values are too high by a lot. Also the Resistor 1.5k/5w between 32U/35U got toasted. Stopped testing after I noticed the toasted resistor, clearly there is some voltage where there shouldnt be but cant seem to find it. Here are some readings and pics, any guidance would be appreciated.

T24: 214v
T26: 61v (!)
T27: 290v
T35: 96v (!)

 

[Paul Birkeland]

The 1M resistor at 26 may not be well connected by solder at terminal 26. The presence of any voltage at T26 is the only problem you need to focus on, and this is bled through that 1M resistor connecting to T26 and back to the ground bus at the front of the amp. Be sure the bare wires running to and from the feedback switch don't touch the metal bits of the switch, as that will make another problem.

 

[gort]

Thanks @Paul Birkeland. I’ll take a look at the solder job on T26 tomorrow, will reflow and make sure it’s a good joint. If the 1m resistor connection is the problem do you think that would resolve my other voltage issues? Also do you think the resistor at T35 should be junked and replaced given it looks a bit roasted?

 

[Paul Birkeland]

If the resistors at T35 still gives the proper DC resistance, I would leave it alone.

Also keep in mind that it could be either end of the 1M resistor going to T26 or and of the ground solder joints that lead up to it.

 

[gort]

Hi @Paul Birkeland. I was able to do some work on the amp this morning and I believe I found the problem.

First I reflowed T26, the 1m connection at the red switch and all the ground points. Also confirmed that no bare metal wire was touching the metal on the red switch. Readings were more or less the same.

Then I reflowed T24, T35, double checked all other solder points on the B side. Readings where more or less the same.

Then I had a thought, what if its the valve? So I flip flopped the tubes, powered on the amp and low and behold, T6 was now receiving voltage and T26 was reading 0V.

So I think I have received a dud tube with the kit. Visually the pins/wiring inside look intact but the "bad" valve has some crusty dirt/powder on the outside of the glass.

 

[Paul Birkeland]

It's also somewhat possible that the tube may have a slightly crusty pin. I'd have a close look at pin 3 on the suspect tube to see if it needs a little scrape with a hobby knife perhaps.

 

[gort]

Hi @Paul Birkeland. Gave the pins a light scraping. Still having voltage issues on T6/26 and T15/35 with the suspect tube. Any other things to look at or do I need a fresh valve?

Thanks!

 

[Paul Birkeland]

You'll likely need a replacement for that one.

-PB