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In the Forum: Audio Discussions
In the Thread: Initial thoughts about new/old Lamm ML2s
Post Subject: Symptoms of a V1 tube dying?Posted by Lx_ on: 12/5/2009
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 Paul S wrote:
A year (and a pair of V2s) goes by like nothing.

I just changed V2 tubes again, and this time I dialed the current way down before I fired up the amps, per instructions.

After a few minutes, I checked the amps with a (Fluke 189) DMM, just for drill.

Voltage was set down to 175, but current was about 450 mA.  Dialing down the pots, I could not get  the current below 390 mA, even though the pots still turn freely.

How good are these pots?  Do they actually have "stops", where they won't turn any further?  Again, I ask because it seems like I've come to the end of their electrical adjustment (current will not drop any lower with further turning), even though it is still quite easy to turn the pots with a tiny screwdriver.  FWIW, I am pretty good with tools and I have a pretty sensitive touch, so it's not like I roughed them up, or anything.

This is the third pair of V2s I've put in these amps.  This is the first time I've encountered this situation; but then, I've never taken measurements so soon after start-up, either.


Paul S

Paul,

Thank you for this feedback. I do kind of have the reverse problem: I cannot get the plate voltage higher than 169V, no matter how up I dial the pot (BTW, mine does not seem to have stops, though it is on a ML2.1). Then the amp failed, I suspect the internal fuse blew as it did a few days ago. I replaced it today, the amp then worked for around 10 minutes before this failure. Except this time I kept an eye on the Fluke and noticed I was unable to set plate voltage as should be. Is this a sign of the V1 tube dying (might as well say dead)?

For info, I bought those amps used almost a year ago. I have changed the 6N6Ps twice already (every 6 months), but other tubes are probably the original ones. I have just realized that they date as far back as January 2005! It would be no surprise that a 6C33C failed. In that case, from what I have been reading here, V2s are probably sonically dead as well (note to self: do yourself a favor and change V2s once a year at least).

I would love to be able to buy 6C33Cs in bulk and match them by gain as required for the ML2(.1), though I lack the methodology to do so, which is too bad as it surely is quite easy to do. Are you still getting your V2s from Ken Chait?

Regards,
Laurent

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