Re: Badly matched valves

On Fri, 02 Nov 2007 18:12:14 -0700, Lord Valve
<detritus@xxxxxxxxxxxxx> wrote:

Nobody knows what GT's rating system means. Nor does
GT, as far as I can tell. I have seen "matched" pairs of GT
power tubes (brought in by customers for installation/bias)
which were 13 mA apart. I've seen quads that were all over
the map. I know they don't burn them in prior to matching
(and neither does Mesa) so even if they're matched when
you install them, they're not going to stay that way. Some
amps will hum with mismatched tubes. (Some won't. ;-)
In your case, if you keep them, install one tube from each
pair on either side of the output stage and trim the bias
on one of the "hot" ones. The others will run too cold, but
at least you'll have matching plate current draw in both
halves of the OPT primary, which is what you're shooting
for. If I were you, though, I'd ask for a replacement quad.

If you're buying one of GT's "proprietary" tubes, like the
"Mullard" reissue EL34, you'll have to stick with GT - but if
you're buying re-labeled Sovtek, EH, JJ, Shuguang
(etc.) they can be had from damn near every online
dealer who sells tubes, and cheaper. Sooner or later,
the GT "Mullard" EL34 will show up elsewhere. (The
Chinese will sell to anyone with money, regardless
of any agreement of "exclusivity" they may have with
GT.) Their original "Mullard" 12AX7 turned up on the
open market in less than three months. It was a damn
fine sounding tube - if you could find one that would last
longer than three or four weeks. I had all kinds of problems
with those, but I still have the occasional customer who asks
for them. GT finally shitcanned the design awhile back.
I don't know what they have now, since I'm not doing much
biz with them. The last batch of 100 (Chinese Mullard
12AX7s) I got from GT ran 43% rejects - and SIX of them
were WHITE. (White getter means the tube sucked air.)
Somebody please tell me how six tubes could suck air
between Sylmar and Denver. With that many rejects
(including the devacuated ones) there is NO WAY
those tubes were tested prior to shipment.

Next time, get 'em from me. ;-) There *is* a reason why
some rather well-known players on the "A" tours pay for
mine when they could have (famous rebrander's) for free.

Lord Valve

White Spirit wrote:

I put four matched Groove Tube EL34-Ms into my Marshall 6100. They were
bought as a matched quartet but going by the current reading, I have two
pairs that are individually matched with a marked difference between
each pair. I ended up setting the bias according to the pair that draw
more current. With one pair idling at around 17.5W, the other pair are
idling at around 11W.

Should I try and get a replacement set? I only had ten minutes to try
them out, but they seem to sound good. My concerns are that perhaps
there is crossover distortion and that 70% of max dissipation might be
too 'hot' for this amplifier given what a short in the valve can do to
the channel switching board.

Groove Tubes claim that their rating system means that if you buy
another set of the same type with the same rating, no rebias is necessary...

I bought a half dozen tubes from him (and some other stuff) and they
were fine...everything matched as stated. I did have one Tung Sol go
lightning bezerkly in the SF Champ after I played slide on it for an
hour or so but hell, I would expect some tubes to short out on
occassion for no aparent reason. And he's sending me a new one ( I
hope...found his RMA policy on the CD after I had already sent it back
of course) and he doesn't like bear trap tube holder scratches on the
bases so open the trap before you pull them out and he doesn't like
magic marker on them and of course, I write gm's and notes on the
glass with a felt pen -( like shorted)...since my memory is so good
but doesn't last very long, and I usually don't scratch the bases but
I didn't look for it..but we will see what happens. I do not expect
him to refund something I have damged and/or prevented his being able
to return to his distributor for credit ..maybe the magic marker on
the glass will wipe off easily with solvent or handcleaner...and I
hope my packing is good enough. He ships pretty fast if you really
need him to. I didn't. I called on thursday or friday and I got it the
next Wednesday in small town Texas.. Mine came USPS Priority. His
shipping starts at $6.50 with more for additional stuff so that's real
fair...if you are gonna call in an order and wanna bullshit, be sure
and ask him if he is busy before you expect him to stop and bs with
ya..and his phone manner is pro.... and just for reference, practicing
slide runs all halloweeners right