Re: Amp question

[The Bernadettes <mdestefano@xxxxxxxx>]

Hi John,
    I took a look at the schematic.  The 1482 is very similar to a tweed Deluxe
circuit with tremelo.  Obviously you know your way around amps so I won't warn
you about the dangers involved.

First: tube swaps, get those 12AU7's outta there, you're sucking all the balls
out of that amp.  Here's a great tube swap that works good for all amps that
have a cathodyne phase inverter (which the 1482 has.)  Use a 12DW7 in the phase
inverter slot.  The cathodyne inverter is a proprietary name by Fender (I think)
for what is know generically as a split load inverter, with the addition of
another triode in front of it for an additional gain stage.  The 12DW7 works
great for harp on cathodyne inverters by lowering the gain on the input side of
the inverter but keeping a high gain triode on the output side providing a
strong signal to the power tubes.  This allows you to raise the gain (or volume)
on the first gain stage of the amp before feedback.  You can then experiment
with a 12AX7, 5751, or 12AY7 on the first gain stage tube position.  I do this
with my tweed Harvard which uses a cathodyne inverter and it works great.  I
suggested this swap some time ago on the Weber board and I received quite a few
replies from other harp players who loved it.  For any of you interested in this
swap on-list, the following amps also use this cathodyne phase inverter circuit:
the following Fender narrow panel tweeds: Harvard, Deluxe, Super, Pro, and early
2 hole Bassman.  The popular later 4 hole Bassman uses the more modern long tail
inverter, using a 12DW7 in the phase inverter will have a different effect.

    Internal mods: coupling caps, all those .01 mfd. coupling caps are rolling
off all the bass out of that amp.  Try replacing all or some with either .1 mfd.
or .047 mfd. caps or a combination of.  Power supply resistor: see that 27K
power supply resistor (the one with 260V circled over it), find and try
replacing that with a larger resistor to get the plate voltage on the pre-amp
tube down to around 85V (presuming it's a 12AX7), and see how it sounds, the
lower the voltage (larger the resistor), the more breakup you'll get.  Since
you'll be disipating quite a bit of voltage and current, use a minimum of a 3
watt resistor.  Rolling off high end gain: try some plate resistor bypass caps;
see those 330K plate resistors, try soldering some ceramic disc capacitors
parallel to those resistors.  Start with a 1000pf, if you won't more high end
rolled off, try larger, maybe 1500pf or 2000pf, use at least a 500 volt rating.
    You may also want to consider converting one of the channels to a grid leak
biased input, these sound great with Astatic crystal mics.  It would entail
removing the 2.2K cathode resistor on that particular channel and tying the
cathode directly to ground, then placing a .02 or .047 or .1 mfd. cap between
the input and the grid, then a 5meg to 10 meg resistor from the grid to ground.
Check our some early wide panel Fender tweed schematics to see how this done.

Let us know how ya made out and what worked.  Work safe.
Regards,
Don D.

"adams, john" wrote:

> While we are on the subject of amp mods, I have a Silvertone 1482.  I have
> experimented with several tube swaps on the preamps, replaced all the
> electrolytic caps and installed a 3 prong plug. I know the dangers of tube
> amps from experience.  I nearly killed myself in high school when I was
> building a tube amp ( ooops, I'm dating myself ) and had one hand on the
> chassis, and the other got the 450VDC.  DC hurts a lot more than AC.  I was
> knocked to the floor.
>
> Anyways, I would like maybe a bit more breakup before feedback.  I have
> tried 12au7s in both of the pre-amp stages, and it mellows it out a bit, but
> still not quite what I'm looking for.  I usually mic the amp on the PA, so
> mega volume is not what I'm looking for. I'm not sure if they copied some of
> the fender schematics or not.  I have pasted a link to the schematic.
>
> http://www1.korksoft.com/~schem/bargainbin/silvertone1482.pdf
>
> John Adams
> www.deludedblues.com
>
> -