Tracking down a hum.

Today when I powered up my system, I noticed a hum from my tube pre amplifier, a Rogue Audio Model 99 (line stage only). It is worse when first powering up. It is absent through my headphones, (using an external headphone amp and the record button on the pre-amplifier)  Listening to speakers the noise is present but diminishes and eventually goes away as the system warms up.
I'm using the Rogue to send a signal to a Musical Fidelity X-P200.
I don't think the issue is the tubes as I'm using Tung-Sol 6sn7 tubes with less than 300 hours on them.
I bought this Rogue used and had to take it back to get it fixed as one channel kept cutting out because of a bad solder in the out put jack. Maybe something else failed?


It would be something else in the room or also some DC on the line causing the transformer to hum.

@ jond I don't think its the line. I swapped out the amp with an old NAD C 340 using the preamp outputs and everything is fine, nice and quiet. No noise in any other components using the same outlet.

This time the noise doesn't dissipate. The noise pulses. get louder then softer louder then softer. I have no idea what the cause is now. I'm thinking a faulty rectifier.

Noise presented on both channel?

For a tube preamp, the power supply seems very complicated! Curious what's inside the external power supply and did you send it in for repair along with the preamp?

This is frustrating and starting to get expensive.

Send it back! Rogue Audio should not charge for a failed repair. 


Oh yeah I sent it back to Rogue this morning. Power supply and all. There isn’t much in the external power supply, a transformer, some wires and a fuse. I don’t remember much else.
Hum is present in both channels and pulses. Failing rectifier maybe?
People are trying to tell me its an issue with my power outlet or a compatibility issue with my power amp. I’m starting to think it’s a ground loop issue. I know it’s not my power amp or my local utility that’s causing the problem.
We’ll find out soon enough. I’m about ready to call in a Priest to do an exorcism!

Hum is present in both channels and pulses. Failing rectifier maybe?

Sounds like low frequency oscillations associated with humming! There could be many things causing this problem, faulty rectifier, diode, regulator IC, capacitor or bad solder joint... Hopefully Rogue will be able to fix it this time. Keep your fingers crossed!