BC21 preamp problem

just purchased used preamp and last nite i hooked it up;
a hum was coming from the speakers that could be heard 8-10 feet away when no music was being played. i thought it might
be a problem with the ground, do tonite i used a cheater
plug; the hum was still there and now a loud pop comes from the speakers each time i turn it on/off. in addition, my amp goes in and out of a "sleep" mode with the preamp on

i'm afraid to turn this preamp on as it might blow the speakers. this is my first experience with tubes and felt the BC 21 would be a good starting point.

i hooked up my old SS preamp and no problems.

any help would be appreciated.

my amp is McCormack DNA.5(A revision), speakers proac 1.5
cables MIT/Magnan

Make sure the cables are plugged in all of the way.
If you are up to it, open the chassis and examine it for poor connections. The BC-21 is wired point-to-point and, if the unit has been mishandled or grossly jostled, it's possible that connections have been opened. I had a sample direct from the manufacturer that encumbered such a problem in shipment. A quick application of the solder gun fixed it.
Is it both channels? If just one channel you could also have a poor or bad tube; or maybe just a loose tube.

Don't be afraid to also ask the friendly folks at Blue Circle.

E-Mail Angela at bcircle@bluecircle.com

You can tell her I sent you, if you feel funny asking about a used product. (She knows who I am)
You made a wise decision buying Blue Circle. Now you can reap the benefits of your choice. Call Gilbert, the deginer, and he will troubleshoot your problem for you. I suspect if anything is wrong he'll have you send it up to him and repair it for minimal to no charge depending on he age of the unit.
i put the preamp back in my system today and the hum has dropped dramatically. i hear it in one speaker but i have to get about two feet from the speaker to hear it . i e-mailed angela at BC and she was helpful as well as all of you that responded were. part of my problem was due to using a cheater plug on the preamp. also for the last 40 years, i've turned on my preamp before the power amp (and if my memory is still decent) I 've not had a problem. today, i turned on the power amp first and voila, no pop in the speaker.

i'm going to order additional tubes and try those. i guess i'll order a pair of the 6SN7. if anyone has suggestion for
other tubes i might try, please post your recommendations

again thanks to all who responded

You can try for Gilbert, but Angela usually responds to inquiries even if directed to Gilbert. It is probably a lot quicker starting with her. She is an electrical engineer by training, and will definitely discuss your problem with Gilbert. It is a small shop. I think they only have 5 full time employees including Gilbert.
I have this problem similar to you as i turn on my power amp. The humming noise was dissappeared once i disconnect the earth for the pre source, but there is a high pitch appearing from the left speaker and i tried replacing the BC21 tubes but still can't help.
As for tube, KEN RAD VT231 is good in mid, RCA VT231 and Brimar 6SN7GTY will sounds warm and rich, Sylviania GTW gives laid back soundstage. Good luck for searching.