Small temp voltage on phono input-problem?

[trombone]

This may seem like a stupid question. A long while ago, I fried a phono cartridge after one of my preamp mods because I left a short between the B+ and the cartridge input. Ever since, I've always checked for DC voltage between cartridge input and ground after doing a mod. Normally, I turn on the preamp, let it reach operating voltage, and check. Always 0 DC.

For some reason, this time I connected the meter to the input and ground before turning the preamp on. (The preamp is a MFA Luminesence with tube regulated DC. It takes about 20 seconds or so to reach 330 VDC. ) Watching the meter from turn on, I saw it go up to about .9 VDC for a few seconds before settling down to 0. I assume this is what it always does, but now feel compelled to check. Is this normal? Or is my cartridge in some danger?

 

[hagtech]

Could just be grid current as the tube warms up. Depending on the power up sequence, maybe the B+ is applied too early, before heaters are warm.

May also be a leakage path of some contamination like solder flux or dust.

jh

 

[trombone]

Thanks. I thought the delay in the regulator powering up would slow this down, but I guess not.

Do you know if this few seconds of .9 VDC is dangerous to my cartridge. As I said, for all I know, it's always been this way, but now that I know it's happening....

 

[hagtech]

Well, if it is 0.9V with the cartridge connected, it could be a problem. If it is 0.9V into 47k ohm only, then maybe not so bad.

jh

 

[trombone]

Hey, good point. I forgot. I measured it without the cartrige attached. Just into 47K.