LM350T failure - counterfeit component or fundamental construction problem? Opinions requested.

[chilidawg]

You will have to use a tripler instead of a doubler. A doubler would deliver about 50V unregulated, which leaves almost nothing for teh regulator. A tripler would easily deliver 70V, which leaves plenty of room for a CRC filter and a regulator.

Or use a DC boost converter module

 

[Gold]

I'm having a problem with the Heater Supply. I'm getting maximum voltage at the output and am unable to adjust it. AFAIK I have checked every component and every connection, more than once... I have a board that works in the same chassis as the one that doesn't to check against. Each board has a separate power transformer.

The input voltage to the LM350T is 9.73VDC the voltage at the output is 8.46VDC. The target is 6.3V. This is with the tubes in place. When I measure at the adjustment pin I am able to adjust the voltage. I can adjust to 6.3V at the adjustment pin but it makes no difference to the output voltage. The only difference to the circuit as drawn is that I am using a 1K trimmer because I don't have a 2K trimmer. I measured the trimmer resistance on the other board and it was approximately 200Ω with about the same voltage at the regulator input.

Any ideas? The circuit seems so simple I can't believe I'm stumped.

The "broken" one passes signal and compresses as expected. The regulator doesn't get any hotter than the other one and the tubes don't seem like they are hotter than the other ones. I'm assuming it's not good to run 6.3V heaters at 8.45V.

 

[Brian Roth]

D13 bad or installed backwards?

Bri

 

[Gold]

Nevermind. Fixed. It was a bad connection inside the terminal block I used to connect the LM350 to the PCB. I’m using the cheap Chinese ones. Not genuine Phoenix. They aren’t quite as good…It’s mounted on a heatsink attached to the rear of the chassis.

 

[MidnightArrakis]

Nevermind. Fixed. It was a bad connection inside the terminal block I used to connect the LM350 to the PCB. I’m using the cheap Chinese ones. Not genuine Phoenix. They aren’t quite as good…It’s mounted on a heatsink attached to the rear of the chassis.

[I’m using the cheap Chinese ones] -- "Live & Learn".....as they say!!!

/

 

[Gold]

[I’m using the cheap Chinese ones] -- "Live & Learn".....as they say!!!

/

At 1/4 the price of the genuine article I will live and learn the quirks of the cheaper ones.