"Meat Plow" wrote in message
news
On Wed, 02 Mar 2011 02:47:24 +0000, Arfa Daily wrote:

So, today, I did the mods that the customer was asking for. The value
and type of a coupling cap in the overdrive channel was changed. The
input circuitry was stripped and simplified to standard Fender style -
i.e. a 68k series resistor from input jack to the grid of the first
12AX7, and a 1M grid return to deck. The fixed negative bias to the
grids of the output tubes was disconnected, and the injection point
decked, and the cathodes were lifted from deck and returned instead via
a 100 ohm 4 watt resistor, bypassed by 100uF.

I also put an additional 1 ohm resistor in the cathode path, so that I
was able to measure the idle current of the output stage. This settled
at about 130mA, or just over 30mA per tube, which was exactly what the
author of the mod notes suggested it should be.

I have to say that after carrying out these mods, the amp did seem to
have a much 'smoother' more Fender-like sound, and was still capable of
producing pretty much its full normal output of around 30 watts. I do
not have a sufficiently 'musical' ear to know if the revised sound is
what the owner is looking for, but it did seem to have a very sweet
sound, to me. He is picking it up tomorrow morning, so I guess I should
know if he's happy with it, in fairly short order ...

Arfa

Tone, the sometimes elusive prey in a jungle of equipment. That's what it
all boils down to. My favorite of all time combo amps is the Ampeg VT-22
loaded with a pair of Altec-Lansing 12's. It was my first 100 watter
combo back in the late 70's. If you think a Twin loaded with a pair of
EV SRO's is heavy lift a VT-22 with the Altecs loaded. I ended up trading
it for a 1x15 PV Artist combo around 1982. Still have that old beast.

I'm currently restoring a 1960's Ampeg Jet12. Uses a PP pair of EL84's
for output so it's around 15 watts. Someone has replaced the original
12" Ampeg speaker with a Vox. It's not much to look at but it's one
of those amps that are known for their tone. I've owned it for a decade.
One of those projects you eventually get to.

Hope your customer likes the mods.



He does. See my other post

Arfa