From detritu–(at)–x.netcom.com Sun Nov 22 11:19:40 CST 1998
Article: 140490 of alt.guitar.amps
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From: detritu–(at)–x.netcom.com(Lord Valve)
Newsgroups: alt.guitar.amps
Subject: Re: 6L6 in Champ
Date: 22 Nov 1998 08:26:48 GMT
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In <19981122023515.01216.0000125--(at)--g-fa1.aol.com> risehig–(at)–ol.com
(Risehigh) writes:
>
>cpdriver–(at)–ol.com wrote:
><
>
>caramba!!
>i’m no expert (see my o-scope leads help post)
>but my understanding is that you’ll fry the 6V6’s
>if you put them in a 6L6 amp!
>gurus??
>risehigh
Lord Valve Speaketh:
Depends on the plate voltage. You’d need to change the
screen resistors to 1K/5W, too. Chinese or Russian 6V6s
don’t stand a chance in this application, but if you use
some good NOS and the plate voltage is less than 450, you
might get away with it. I don’t do it, though. (Rumor
has it that this mod only works well above the 49th
parallel…) As for putting 6L6s where a 6V6 goes, I do
*that* all the time, in Fenders. This question pops up
like clockwork about every two months; on the one hand,
you usually have the spec-book jockeys raving about the
filament current being twice as much as the winding is
rated at (it ain’t; a little logical analysis makes this
crystal clear, but few of ’em are willing to take the time
to do so) and so on, while on the other hand we have cats
like me (and trem, timtube, etc.) who’ve been doing it for
years with no tranny failures. The rated filament current
for a 6V6 is 450 mA; the rating on the 6L6 is 900 mA. When
you first look at those figures, you think “uh-oh, twice
as much, don’t do it…” but you need to take into account
the fact that the filament winding feeds *all* the tubes in
the amp, as well as the pilot light. For a Deluxe Reverb,
for instance, we have 4-12AX7s, 2-12AT7s, and 1-#47 lamp,
besides the power tubes. At 300 mA per preamp tube, 150
mA for the pilot lamp, and 450 mA for each 6V6, this gives
a total burden on the filament winding of 2.85 amps. (The
rectifier tube has its own winding; more on that in a moment.)
Using a pair of 6L6s increases this to 3.75 amps, which is
only a 32% increase…not anywhere near twice, see? The
filament winding can easily deal with the increase, but if
you’re worried about it, you can pull the #1 (Normal channel)
preamp tube. You could also pull the #5 tube if you don’t
use the tremelo. This knocks the current back to 3.15 amps,
a measly 11% over the stock value. You could even pull the
pilot lamp, and get down to 3 amps…only 5% over. If you
go to a solid-state rectifier, you remove the load from the
5V recto heater winding, and this lowers the PT’s core temp,
which is beneficial. Using the SS recto will increase the
plate voltage too, which goes nicely with the 6L6s. I’ve
set up a lot of Deluxe reverbs this way over the years, and
I can’t recall even one of them frying a power tranny.
Other amps may not be quite as robust, but Fenders can do
this with ease.
Lord Valve
Visit my website: http://www.freeyellow.com/members2/lord-valve/
Good tube FAQ for newbies. Click the e-mail link and request a
tube catalog. I specialize in top quality HAND-SELECTED NOS and
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