PV12L whine/ringing issue

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PV12L whine/ringing issue

Post by wes_in_va » Fri Dec 23, 2016 2:00 pm

A few weeks ago my PV12 (linestage only) developed an occasional and intermittent very high pitched whine through the speakers. It was really only audible when no music was playing.
I thought it may be the preamp tubes so I replaced them which only made it worse. (I had checked the tubes that I used as replacements and they tested good.) Yesterday I decided to try yet another set of tubes.
With no music playing I turned on the system (MC2100 amp) and all was fine for a couple of minutes. Then a very static like sound came from the right channel. Not constant, but fairly loud and unaffected by volume control. It sounded like the static you might get as you're trying to tune in a radio station.
Turned things off, tried installing the last set of tubes that had been in place and the same thing happened.

I had previously tried a different preamp to make sure the high pitched sounds were the preamp, and it seems that was the case since I had no problems with the other preamp in place.

I asked for some input over on Audiokarma and a member suggested seeing if moving the tubes a bit made a difference. I tried wiggling the tubes a bit.
The static sound had just been on the right channel as far as I could tell, and moving that tube around did seem to help. However, while I was doing that I started getting a whine out of the left channel. Wiggled that tube a bit and while it did seem to make a difference, I also noticed that both tubes were extremely microphonic.

Another member suggested cleaning he tube sockets so I cleaned the sockets (with the handy dandy Caig tube maintenance kit). Cleaned the pins of the original tubes that I first noticed the high pitched noise with.
Fired 'er up. Dead quiet for about 2 minutes, then the whine and some "whooshing" from the speakers (unaffected by the volume control or input choice). That lasts for about a minute and during that time it may subside a bit and then get louder, subside, get louder. Also during that time and tapping on the preamp at all can be heard through the speakers, as can any movement of the controls.
After a minute, maybe 2, that all goes away and things are back to normal.

Last night I went through several album sides with no further issues.

I'm concerned if I keep using it I'm going to cause a real problem. Any suggestions?

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Re: PV12L whine/ringing issue

Post by admin » Fri Dec 23, 2016 8:03 pm

If physically moving the tubes and "tapping" on the unit affects the sound I have to believe it's some kind of connection issue. Sounds like with the tubes/tube sockets (although unlikely to be the actual tubes if you tried it with a completely new set and had the same problem). I would go through and look for any cold solder points, make sure all the components have tight solder joints and haven't come loose. You can do this with the unit on. Try poking the different components with the eraser side of a pencil.

If the issue resolved it may have just been a bad connection to the tubes that you fixed with your cleaning and manipulation.
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Big Dog RJ
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Re: PV12L whine/ringing issue

Post by Big Dog RJ » Sat Dec 24, 2016 11:27 am

G'day mate,

That's about correct with the PV series preamps. Infact my previous PV12 never had tube issues but the PV10AL did, exactly the same as you have described, and it was the tube connections. Remember these amplifiers are older circuits therefore several areas of natural degradation can cause these issues with tubes. However, the great news is with tubes, these areas can be very easily fixed and even better sounding once the component or connections have been properly addressed. With my PV10AL, there was quite a bit of oxidation in the sockets, tried cleaning them to such an extent where I got high after breathing in the contact cleaner fumes... still to no avail. A similar problem also happened on my Manley monoblocks, cleaned again but to no luck or major improvement. So Eve Anna Manley (president of Manley Labs) and Ed head of Service for CJ back then, shipped across brand new tube sockets with ceramic bases, and gold pins that are used in the premier series amplifiers- problem solved!

Not only did all noises vanish but also sounded quite better than the original older connections. The cost was also just a small investment, and something that I would highly recommend on older tube gear.

Another fact is that you mentioned you did clean the sockets with a special kit, and the noises were literally gone... this is good since the tubes must be settling in with cleaner connections, therefore by all means keep running the amp in. By running in won't do no harm, rather it will generate a better synergy with the tubes and their sockets. I would try to get hold of ceramic bases with high quality gold plated pins and replace all existing tube sockets. Or you could check with a tech and ask them to double check all contact points in each socket, re-solder using high grade silver and fully clean all sockets before re-soldering. This should sort the problem out and give you better sound.

For a finer "quality" in sound, I found replacing the sockets with high quality ceramics and gold pins was wonderful to experience on the PV10!
Trust you find a suitable solution.
Cheers, RJ

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