TSE smokin' R16

[tcrane]

Going through the checkout on my TSE build and all is well until I get to the 5842 portion. While adjusting the plate voltage the R16 332 ohm resister started smoking. I am thinking U2 has failed, the 10M45, how can I test this, not being hip to solid state devices. And what else should I be looking at?

I am going to add to my array of cheap meters today, so I can test more things at once and maybe I can figure it out that way.

tc

 

[rknize]

Check for solder issues on U2 and R17. Measure the voltage across U2 and R16 and verify the value of R16. If U2 is shorted, it would definitely smoke R16, but there could be an issue with the tube that caused U2 to go.

 

[tcrane]

Thanks for the reply.

R16 was of the correct value- now testing higher now that its cooked- have replaced it. Also checked solder issues- not easy with U2 as it's mounted under the board- may just replace it. Testing voltages across R16 and U2 I am assuming must be done with a 5842 installed?

You may be right about the tube though, I now have one 5842 that won't light up. I am being extra cautious now not knowing where the fault lies. More tubes are on the way.

Without 5842 installed my filament voltage at that socket is over 7 volts, which I reckon I'd see a higher voltage with no load since that's not regulated, still seems on the high side.

Got some disposable meters from Harbor Freight for $3 each, so now can test more things at once. I shelved this project- literally- in a cardboard box and did nothing on audio for over a year, so I'm just now getting my chops back- such as they were.

tc

 

[rknize]

It will float a bit without a load. What transformer are you using?

 

[tcrane]

I'm using a nameless surplus transformer- too large for the application actually. I'm having to bring it up on a variac to around 100 volts AC to be in the range I'm shooting for. (My line voltage is at 125 today.) Thinking about buying an Edcor.

Went through a complete testing session on the board today and determined that U2 is indeed dead, will replace that with spares on hand. I went ahead with the testing routine on my good channel and found that the filament voltage starts dropping rapidly after about 2 minutes. It did this with several different 45s and a 300B. No other voltages changed. I intend to use 45s so had the B+ at 320 and set the current at 25 milliamps. Is this the regulator dropping out?

tc

 

[rknize]

Yes, it sounds like thermal overload of the filament regulator.