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Music Reference RM9mkII Driver Tubes

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Posted on August 21, 2020 at 14:09:41
Berrell88
Audiophile

Posts: 90
Location: Southeast
Joined: September 23, 2004
Contributor
  Since:
March 12, 2014
If it ain't broke, don't fix it. The driver tubes, Sovtek 6922's from Ram Labs, have been in this amp for at least 10 years. Decided to experiment by inserting a matched pair of Teslas NOS from Tubemonger. This resulted in loss of the right channel. I reinserted and even flipped the four driver tubes in the amp and nothing changed. No fuses blown. Now I can't null out the balancing LED's for the two key drivers, the V1's. Wondering if I just simply need to replace those two critical tubes.

The RM9's obviously don't like input tubes other than Ram Labs but I've read about other owners using NOS, etc.

Any suggestions? Thanks!

 

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RE: Music Reference RM9mkII Driver Tubes, posted on August 21, 2020 at 14:51:06
Blackdog
Manufacturer

Posts: 1423
Location: Ontario
Joined: March 20, 2006
Put the old tubes back in and try again. Despite the mystique of NOS tubes, your chances of getting crap are pretty high. Even if they were tested on a tube tester, once in circuit, with the higher voltages and currents a lot of tubes don't run properly.
If it runs with the old tubes, you've bought some clunkers. Also make sure they are the right tubes.




Dan Santoni

 

RE: Music Reference RM9mkII Driver Tubes, posted on August 21, 2020 at 15:51:22
Berrell88
Audiophile

Posts: 90
Location: Southeast
Joined: September 23, 2004
Contributor
  Since:
March 12, 2014
Dan,

Thanks for getting back. Wasn't clear in my note. I did reinstall the original driver tubes from Ram Labs and flipped them to see if that would make a difference. Nada. You get tired of fooling with the trim pots after a while. Something happened to upset the amp by inserting those NOS tubes--but what?

 

If all else fails, check the circuit board traces for the 6922 tubes, posted on August 21, 2020 at 16:48:20
garymuffley
Dealer

Posts: 356
Location: Maryland
Joined: March 29, 2006
The RM-9 series of amps had a known problem with the circuit board traces breaking when the 6922 tubes were inserted and removed frequently. I fixed several RM-9 amps over the years that exhibited this issue. The tube sockets grip the 6922 very firmly and the stress on the circuit board will sometimes result in the traces breaking right at the tube socket on the board.

 

RE: Music Reference RM9mkII Driver Tubes, posted on August 21, 2020 at 16:57:38
Blackdog
Manufacturer

Posts: 1423
Location: Ontario
Joined: March 20, 2006
As mentioned above, those boards are a bit flimsy. Probably a broken board trace or two.
Dan Santoni

 

RE: Music Reference RM9mkII Driver Tubes, posted on August 21, 2020 at 23:20:04
Jonesy
Audiophile

Posts: 2201
Location: Winnipeg, Manitoba
Joined: September 1, 2005
Contributor
  Since:
March 1, 2018
If comfortable doing so, just use a soldering iron to reflow the existing socket pins where they contact the pcb board. Just smear a titch of flux using a toothpick on each contact should give you good results. Don't add more solder unless you really need to. Remove flux with flux remover if you have any on hand. Not too critical if you use it sparingly.

Doing a solder reflow should fix any broken connections.

Soldering done with amp off if course.

Clean and tighten the tube socket insert contacts too if you can.

Barring all the work above, you could always try wiggling the tubes in their sockets to see if the sound sputters back. But if it does, you'll end up doing the repair anyways. And sometimes wiggling isn't the best thing unless you've felt with situations like this before.

Cheers!

Jonesy


"I know just enough to get into trouble. But not enough to get out of it."




 

Time for the pencil test, posted on August 22, 2020 at 06:49:08
airtime
Audiophile

Posts: 10504
Location: Arizona
Joined: February 4, 2003
While it's working and you have it flipped on it's side with the bottom cover off and one hand in your pocket!!!!

Take a pencil and push on the solder contacts of the tube socket on the effected side. See if you can get it to work. This way you can pin down what socket and where the failing joint might be. Also visually look at all the solder pads under magnification.

Reflow the solder on all the sockets on that board. Also make sure no components have started to become intermittent.

 

RE: Time for the pencil test, posted on August 22, 2020 at 11:19:12
Jonesy
Audiophile

Posts: 2201
Location: Winnipeg, Manitoba
Joined: September 1, 2005
Contributor
  Since:
March 1, 2018
Great idea! I've used the eraser end of a pencil many times to trouble shoot not only audio, but other household or auto circuitry.

Totally forgot about that one!

Cheers!

Jonesy




"I know just enough to get into trouble. But not enough to get out of it."




 

RE: Time for the pencil test, posted on August 24, 2020 at 15:01:52
6bq5
Audiophile

Posts: 3224
Location: SF Bay
Joined: August 16, 2001
While the unit is open and off- check the electrolytic caps for age/leaks and resistors on the circuit board for heat or burn marks - you may wish to replace those components-
Happy Listening

 

RE: Music Reference RM9mkII Driver Tubes, posted on August 26, 2020 at 13:55:45
Berrell88
Audiophile

Posts: 90
Location: Southeast
Joined: September 23, 2004
Contributor
  Since:
March 12, 2014
Re the NOS or more correctly old stock in most application, I share your skepticism.A matched pair of Sylvania chrome top 6sn7's acquired from Tube guru Brent Jessee in 10/2016 and not overused in my Cary preamp, are now unpleasantly noisy with gobs of tube rush. And this is going through a Class D stereo amp which is nearly dead quiet.

 

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