RE: [Harp-L] EL84s



"EL84" is the British nomenclature for the American "6BQ5". Any amp
which uses 6BQ5 tubes, uses EL84 tubes. They are identical, and can be
swapped at will. EL34 tubes are slightly different than their 6L6
cousins on the other hand, and may require circuit mods such as bias
adjustments and power supply changes. Not always, but sometimes. 
Gibson, Kalamazoo (Gibson), and Silvertone (Danelectro) all made a huge
array of amps incorporating the 6BQ5/EL84 tubes, including some
harp-standards like the Gibson GA-5, Kalamazoo Model 1 and the
Silvertone 1482.

For the money, the best value in an EL84 amp these days is the Epiphone
Valve Junior combo. $139 brand new, and comes with a 5-year warranty!
You can't beat that, period. Even the acclaimed reissue Gibson GA-5 uses
the same circuit, also without a tube rectifier, but sells for $500! The
Valve Junior, in my opinion, is a great way to "tap into" EL84 tone
without the headache of finding, repairing and caring for a vintage amp.
It's got all the tone, none of the problems, AND a warranty.

A triode is a basic tube design which incorporates a cathode, a grid and
a plate. Tri=three components. All power tubes (6L6, EL34, 6V6, etc.)
are triodes. Older preamp tubes were also triodes. 

In the mid-to-late 50s, amp manufacturers started switching to the
pentode PREAMP tube design. (power tubes have remained triodes).
Pentodes incorporated "two tubes in one glass bottle". Each pentode has
essentially two 6-Volt tubes residing within. (In the name 12AX7, for
example, the "12" represents "12 volts", meaning that there are two
6-volt tubes in the glass. In the power tubes (6L6, 6V6, 6BQ5, etc.) The
"6" means a single 6-volt tube. The older preamp tubes such as the 6SJ7,
and 6SN7 were, as the name implies, 6-volt triodes.

The 12-volt pentodes were favored by manufacturers for a few reasons:
they had more gain, one tube could do the work of two, less tubes and
sockets meant less cost to the manufacturer and the 12AX7, with its
"two-sided" configuration, eliminated hum with its inherent "humbucking"
design. Each side of the tube worked out of phase with the other,
thereby cancelling hum in the preamp section. Everybody wins!

Hope this helps answer your question,

John Balding
Tallahassee, FL



-----Original Message-----
From: harp-l-bounces@xxxxxxxxxx [mailto:harp-l-bounces@xxxxxxxxxx] On
Behalf Of Jim Alciere
Sent: Sunday, January 21, 2007 3:53 PM
To: harp-l@xxxxxxxxxx
Subject: [Harp-L] EL84s

Did any of the old 50s amps use EL 84s? Did any of the old amps run in
triode mode? I still say my hybrid EL 84 amp is the best harp amp I've
had a
chance to play. I like the 2X12 cabinet as well. Just curious because
I've
never heard of any harp players using anything like this.

As a side note, the mad scientist guitarist in the band is building what
he
describes as a Vox Marshall Champ frankenstein amp. Marshall preamp,
something Champ, and EL 84 tubes with ancient 8 inch speakers taken from
an
old 5& 10 store. When Sonny talks about how much time is involved in
designing an amp, never mind an amp that's economical to build--he's not
kidding.

-- 
Rainbow Jimmy
http://www.spaceanimals.com
http://www.myspace.com/theelectricstarlightspaceanimals
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