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Vacuum Tubes for Amps
Is Tube Matching Needed
Doug Ahern (dou--(at)--osmic.uga.edu) wrote:
: I was talking to a guy who has been working on tube equipment since
: the forties, although it has been primarily Jukeboxes, pinball games,
: and PA's (some Guitar amps). He insisted that that selling tubes
: in a matched pair is a joke. As he put it, if 2 tubes are not matched,
: you can put them in an amplifier, and leave it on over night, and
: when you get back in the morning, they will be matched. any truth to
: this??
I'm sorry, but that's total bullshit. The military started matching
tubes as far back as the '20s, so the concept of tube matching is
not some recently-conceived marketing scheme. When you use tubes
as pairs or quartets in push-pull (like in most guitar amps),
the tubes won't be working together very efficiently unless
they spec out about the same for transconductance and current draw.
Plus, if one tube is drawing more current than the other, that causes an
imbalance in the output transformer, resulting in hum.
You can't cause unmatched tubes to match up simply by running them
together in an amp overnight. It just doesn't work that way.
Since the oldtimer you talked to cut his teeth back in the '40s, he's
probably used to cathode-biased output stages, where the match
between the tubes is not quite as critical as in fixed-bias
setups.In his day, I doubt most servicemen worried much about
installing matched tubes, especially when working on "consumer"
equipment. Tube manufacturers adhered to stricter tolerances back
then; and like I said, most equipment used cathode-biased outputs.
So, in conclusion: yes, tube matching makes a difference.
--Dr.Distortion, New York
: He also has some RCA 12ax7's made by National in Chicago, but they say
: "RCA National, made in Yugoslavia", I'm probably going to pick up 3
: to plug them in to my amps. Anyone know who made these??
: The guy had a lot of interesting stories about working with Wurlitzer
: and RCA (he's got a picture of himself at the Wurlitzer factory in
: the fifties, and picture of himself with Hank Snow, and a VP from
: RCA, all three with wifes too).
: By the way. I'm playing the "find some new power tubes and not lose
: my ass" game right now. A local tech who sells only Groove tubes
: quoted me some prices: $300 for a quartet of US 6550's or $250 for
: a quartet of kt-88's, $70 for a duet of 6L6GT's !!! Groove Tubes
: is making a bundle!!! I called Antique electronics (Thanks for the
: pointers here on the net) and orders a matched pair of Sovtek 6L6's
: for $11.20/pair, and a matched pair of Sovtek 5881's for $17.50/pair.
: 12AX7's were $4.90-$5.35 depending on soviet or yugoslav original.
: and the folks were super nice.
: doug, the systems guy, high-tech custodian.
: COSMIC~Nasa's software technology transfer center. Athens, Georgia.
: got a problem with my driving? dial 1-800/dev/null
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