TSE-II high voltage on plate of 5842, cathode pots have no effect.

[tubularfluxus]

I have two TubeLab TSE-II board presenting the same exact issue when installed.

With 80v AC using a variac, the plate / pin 1 of both 5842 tubes read exactly the same high voltage of 260v. Turning either R9 or R20 potentiometer has no effect on the plate voltage.

Anyone has run into this issue before or has any suggestion on what to look for?

Thanks!

 

[Tubelab_com]

The 5842 tubes are not conducting. Verify the heater voltage at the tube pins. It is possible that 80 volts on the line input doesn't get them hot enough to conduct. I have never tested a TSE or TSE-II on a voltage that low.

 

[tubularfluxus]

I found out I had connected wrongly the filament jumpers. I had Pad 1 connected to Pad 3 🤯

It is possible that 80 volts on the line input doesn't get them hot enough to conduct. I have never tested a TSE or TSE-II on a voltage that low.

True! When the volts on AC line input are high enough the 5842 gets enough to finally conduct.

All good now! It is working.

Thank you for pointing me in the right direction!

 

[boywonder]

After many years of trouble-free performance I have the same issue....

Original TSE board 300B's

A few months ago I had one channel acting up similarly..now both channels.

Plates of both 5842's are at B+ (370VDC) voltage.......and plate voltage pots do nothing.

300B heater voltage 4.5VDC both channels

Pin 3 of 5842's 3.8V (both channels)

What next? Check the pins of the heater regulator? I have a few extra Sharp regulators.

 

[boywonder]

..a few more test points...

T1-7 2.63 Vac

T1-8 4.1 Vac

Assuming these should be the same......

Getting these same voltages on A1/A2 of the Schottky diode STPS30L30 and 5VDC on K (the middle leg)

The board is black around the 1N5401's (D4/D5) so I'm suspecting one of these may be the issue.....

 

[boywonder]

Fixed......

the 1N5401 solder joints were crispy..........so removed them, tested them, cleaned everything up and re-soldered.

Everything biased up as expected and 5842 plate voltages adjusted no problem.