SE amp with tranny hum, only thru speakers with tube phono preamp

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Do It Yourself (DIY) paradise for tube and SET project builders.

Hi, tube gurus:
I have been listening to, and enjoying, a little console pull SE amp, that uses only two 6BQ5 tubes (does anyone have any idea who made it?).
There is a hum/buzz (120Hz?) that can be heard coming from the transformers - all 3 are very close together, so I can't tell which one or ones are humming/buzzing. I thought it was the PT, but now I am not sure.
I am running a Garrard SL-72B into the phono input of an old Vector Research VXR-7100 receiver and Tape Out from there into a cheap little FX-Audio Tube-01 tube buffer as a preamp, and into the SET amp.
Lovely sound! The trans hum is not coming through the speakers in this set up.
I thought I would see how my EAR 834 clone would be, as the system could use a bit more gain, and I like vinyl through an entirely tube-amplified signal chain.
With the EAR clone put in, the hum now comes through the speakers, loud and clear. I placed the phono preamp as far away from the SE amp as cables and furniture allowed (roughly 3 feet). The EAR plays silently in my main system.
The main table uses a Rega arm which grounds through one of the RCA plugs (R?). The Garrard has the classic green ground wire. I tried it plugged into both the tube preamp, and the Vector receiver's phono ground plug. Loud buzz.
Any idea why it hums through the speakers only with the tube preamp?

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Topic - SE amp with tranny hum, only thru speakers with tube phono preamp - Dr. Fuse 09:46:16 05/20/21 (5)

RE: SE amp with tranny hum, only thru speakers with tube phono preamp - cellailuca 09:55:03 05/20/21 (4)

RE: SE amp with tranny hum, only thru speakers with tube phono preamp - Dr. Fuse 10:29:13 05/20/21 (3)

RE: SE amp with tranny hum, only thru speakers with tube phono preamp - sony6060 10:54:55 05/20/21 (2)

RE: SE amp with tranny hum, only thru speakers with tube phono preamp - Tom Bavis 18:04:01 05/20/21 (1)

RE: SE amp with tranny hum, only thru speakers with tube phono preamp - Dr. Fuse 11:56:16 05/24/21 (0)

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