RE: Amp question

["adams, john" <adams_john@xxxxxxx>]

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

- -----Original Message-----
From: The Bernadettes [mailto:mdestefano@xxxxxxxx]
Sent: Thursday, March 13, 2003 6:38 AM
To: Priest, Jim
Cc: harp-l@xxxxxxxxxx
Subject: Re: Amp question





"Priest, Jim" wrote:

> Don,
>
> Thanks for the advice. I'll definitely entrust this to a tech. I also
found this on Harmony Central:

Be careful about performing mods intended for guitar that you read on
Harmony Central, they'll have different requirements...though what is
written here is kinda like I would suggest:

>
>
> "A summary of my mods described in the previous two reviews: My
recommendations are to change the speaker to a Vintage 30 (or better),

better speaker choices for harp, I'd look at the C12N clone made by Weber
with a harp dust cap

> bypass the 68K input resistor and 0.0047 cap, change the 470K input grid
resistor to 1 Meg,

Don't bypass the 68K resistor.  Two kinds of inputs to consider, cathode
biased or grid leak biased.  For a cathode biased input, dump the .0047 cap,
I'd go with the 68K resistors and a 5 meg gridleak resistor if you're using
an Astatic mic.  For a grid leak biased input: 68 K resistors, change the
cap to a .047mfd, 5 to 10 meg grid leak resistor, cathode direct to ground
(you should be familiar with how to implement grid leak biased schemes if
doing this one.

> change the 100K plate resistor to 200K,

220K, possibly bypassed with a 1000 to 2000pf ceramic disc cap of a 500 volt
rating or better, also up the cathode bypass caps to 25 mfd. or maybe even
higher to 100mfd.

> change the 0.01 coupling cap to 0.022,

go to either a .047 mfd. or .1 mfd. cap

> change the 250K volume pot to 1 meg,

yup, but reconfigure the the volume/tone control as is done with a tweed
Harvard or Princeton, (check out one of their schematics/layouts to see how
it's done.

> and finally change the power supply stacked 20/20/300V cap to 50/50/500V.
Now that last one I'm not convinced you need to do. It will give you more
bottome end, maybe more than you want.

I'd probably do this.  Don't know if you need to go as high on the
microfarad value but would use a higher rated voltage on the filter caps.
The original voltage rating is too low for the kind of voltages you'll find
in that amp.  While you're at it, I'd go to a higher voltage rating on the
power tube cathode bypass cap and go with a higher wattage rating on the
cathode resistor, 2 watts is too low, use a 5 watt resistor.

>
>
> The end result is tone! Grinding 6V6 crunch at a reasonable low volume.
Still loud enough to play in a small room with a drummer."
>
> Is this along the same sort of lines you were thinking ? Would you think
it would be worth doing ? Any alternative suggestions ?

Read what I suggested.  The Musicmaster is basically a single channel tweed
Deluxe (or cathode biased tweed Harvard) with a transformer coupled phase
inverter.  Doing these changes will get it closer to a tweed Deluxe/Harvard
type amp which BTW are great harp amps.

Good luck, contact me offlist for more info if needed

Don D.

>
>
> Regards
> Jim
>
> -----Original Message-----
> From: The Bernadettes [mailto:mdestefano@xxxxxxxx]
> Sent: 13 March 2003 01:56
> To: Priest, Jim
> Cc: harp-l@xxxxxxxxxx
> Subject: Re: Amp question
>
> "Priest, Jim" wrote:
>
> > Amp wizards,
> >
> > I just acquired a 1970's Fender Musicmaster amp, from the look of it in
pretty much original condition: 2 x 6V6GTA and 1 x 12AX7 tubes, Fender 12"
speaker, volume and tone controls, on/off switch, two inputs - that's it.
Playing through my Astatic JT-30 it sounds OK-ish - plenty of bite though
maybe not as much depth as I was expecting (but see below). I'd appreciate
some advice on:
> > 1. Is there anything to be gained in replacing any of the basic
components: tubes and/or speaker ?
>
> There's some to be gained, especially if the tubes are worn.
>
> >
> > 2. The tone control appears to have no effect, other than switching the
volume off completely when I turn it down below 2.
>
> This could be several things, the tone control pot is bad (grounding out)
or the tone capacitors in the tone stack circuit or shorting out...or just
the design of the circuit.  I have a schematic of a Musicmaster Bass Amp,
pretty strange tone stack, don't know why Fender went with that type.  The
older tweed style single tone control I think would have worked better and
is a proven design.  Also a lot of the component values I
> see would make this amp pretty thin sounding.  I could think of some nice
mods to do with this amp, basically convert it to a tweed Princeton type
circuit with larger coupling/bypass caps to increase low end response.
Pretty interesting on this amp is the use of a transformer coupled phase
inverter, rarely ever see this in a instrument amplifier, usually see this
design in tube hi-fi gear...I did this past summer work on a
> Gibson Explorer amp that had this same kind of phase inverter.
>
> > Is this likely to be something I could fix myself, or should I entrust
it to an amp tech ? I'm moderately competent with a soldering iron and have
worked on hi-fi amps (solid state) in the past, but am wary of the words of
warning frequently issued here about the voltages hanging around inside
valve amps.
>
> Unless you're hip to reading schematics and know how not to electrocute
yourself, this is better left to a good amp tech who's knowledgeable of
vintage tube amp designs.  If you need the schematic, lemme know, I have it
as a PDF file.
>
> Regards,
> Don D.
>
> >
> >
> > Any advice welcome.
> >
> > Jim
> >
> > --
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