apt holman problems

1st culprit I would be checking is the cartridge/cartridge wiring. You did not mention if you replaced it or not or what it was. And any of the other info in the 2 posts above should put you on solid ground, no pun intended till I had the thought.

I have owned an Apt Holman preamp for the past 16 years. It has been used primarily as a back-up preamp for whatever I am using as a main preamp. About five or six years ago the preamp developed a similar problem to the one you are describing regarding the right channel intermittantly cutting out. I spoke with a tech from Tomlinson Holman's current company (can't remember exact name) and was told that this was a fairly common development. I was asked to gently tap on the back corners of the preamp and see if the right channel would come back. It usually would. They offered to service the preamp, replace any defective parts, and ship it back for a fee of $250.00. They also offered to sell me a copy (xerox) of the original manual. I took them up on the manual offer, but declined the service/rebuild, opting instead to take the preamp to a local electronics service center. They replaced an inexpensive part (capacitor possibly, but I don't have the paperwork to verify this) and the preamp has worked fine since. I made a copy of the manual that they sent, and had both bound. I will send you one of the bound copies if you are interested. If you like the preamp, I would suggest having it tested by an electronics service center that you trust. The problem may be an easy fix. Best regards, Chuck.

Wow thanks for the quick response. The table is new with the wiring upgrade. I always do the reconnect dance and usually it has solved the problem. It seems I might need to find a preamp doctor in Alaska to take a look, or try tapping the thing to deal with the humming. I wonder about just leaving it on when I finally get it working properly--it can't cost anything compared to the 2 adcoms sitting there sucking up juice 24/7. I almost sounds like an internal ground is unhooked. I thought I would try to run a wire from the unit's ground post to see if that would work.

Manual is at https://www.hifiengine.com/manual_library/apt-corporation.shtml
Does hum only come when channel cuts out? That sounds like cable.
If hum in both channels, the turntable to pre-amp separate ground wire is suspect as others wrote. This ground is a separate wire, not the shield of the RCA interconnects. Post on back of pre-amp to ground on turntable.

What is Holman's current company?

Also, even on pre-amps that are encased in solid metal on all six sides, do not have a pre-amp too close to a power amp. Even if the power amp is off, some keep the power supply on standby, generating an electromagnetic field that can cause hum. I had this problem, and ended up moving the pre-amp a foot from any amp, and the problem went away. Especially true if your pre-amp has an MC input, and is the kind where there is just a phono input select, meaning it picks up signal from both the MC and MM inputs all the time! For that, put an all metal shorting plug in to the unused phono inputs. This advice is for all pre-amps.