"Phil Allison" wrote in message
...
"Arfa Daily is a ****wit "

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.


** Does nothing.

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.

** Ruins the amp.

The cathode voltage now rises up with increasing drive level and at full
drive biases the tubes almost completely off.

This result is gross waveform distortion of the crossover kind - same
as severely under biasing the amp.

Very bad mod.


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.

** So ****ing what.

That is only the idle current.


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.

** Utter bull****.

As anyone with a functioning scope, dummy load and eyes can see.


I have a functioning scope, and a functioning generator, and a
functioning dummy load, and a functioning power meter, and functioning
eyes,

** Do you have a functioning DC volt meter?

Bother to measure the cathode voltage ??

Obviously you did NOT !!!

The cathode voltage rises dramatically under increasing drive with the
circuit you have installed.

No brand name guitar amp has a similar mis-behaving bias circuit.


And far from "ruining the amp", the owner is actually delighted with it.


** Yaaaawnnnnnnnnnnnnnnnnnnnnnnn.....

Guitarists are congenital ****wits - especially those who come asking for
wacho mods to be done.

Sounds like you and this guitar playing fool are a match made in heaven.


.... Phil



So, like I said. Just goes to show the **** all that you know. Let's take a
look for a moment, at the Vox AC30, shall we ? One of the most famous amps
using 4 x EL84 ever made. And guess what ? Cathode bias. What was it you
said ? Oh yes. " No brand name guitar amp has a similar mis-behaving bias
circuit." Dopey ****.


Now shut your stupid mouth, Philip, and **** off.

Arfa