TWEAKING A SILVERTONE 1484 BY JEFF BOBER
Hi Jeff,
The first decent amp I owned was a Silvertone
Twin-Twelve 1484 I bought from my guitar teacher in 1967 for $100. At some point I traded it, but
I’ve missed it. Now I’m in my second childhood,
so I just got one that appears to have been made in
1965. It has all the original components and needs
a cap job and general maintenance. The reverb and
tremolo work fairly well, but could be stronger. Do
you have any suggestions for making this amp all it
can be? I just want the amp to be as robust as I can
make it, so I can crank it up and enjoy the sound.
I know the 1965 Jensens won’t take a lot of abuse,
so I would play through another cabinet with relatively new speakers when cranking it up.
Are there any different values you’d suggest
for the 100 µF 150 VDC filter caps or any of
the other components? In addition to the filter
caps, there is a 5-10-20 µF 450 VDC can cap.
I can’t find a source anywhere that has those
values. Do you know of one? Or if not, what
available can cap would you suggest? Also, are
there any mods you’d suggest?
I’ve been working on amps for about three
years now, and I’m at the point where I can
do basic amp troubleshooting, cap jobs, etc. If
I’m not comfortable attempting anything you
suggest, I’ll take it to an experienced amp tech.
Thanks!
—Dave Ellis
Hi Dave,
Thanks for writing. I actually
owned a 1484 head years ago
and wish I still had it. Just the
fact that you could turn the
volume control off and turn the
reverb control up to get nothing but cavernous, sci-fi reverb
made it cooler than most other
amps. Another cool fact: The
1484 is almost identical to the
higher-powered 1485 favored
by Jack White. The 1485 has
four 6L6 output tubes, double
the power, and four more speakers! Yes, the 1485 had six 10"
speakers. But hey, those two
vintage 12" Jensens in your
amp are pretty sweet, too.
You mentioned the amp
needs a cap job. In 1484s, the
filter capacitors in the initial
section of the power supply
are crucial. This power supply
employs a very nontraditional
voltage-doubler type of circuit.
In fact, it employs two voltage-
doubler circuits running off
two separate secondary taps of
the mains transformer. These
circuits are placed in series and
the voltages add to develop
the 480 VDC plate voltage
stated on the schematic. If these
capacitors are dried out and
underperforming, the proper
voltages will not develop,
resulting in low plate voltage
and low output. Replacing the
four 100 µF 150V caps in the
voltage-doubler circuit generally
improves performance.
Back in the day, if the Silvertone
1484 wasn’t enough, you could
crank up its big brother—the
mighty 1485. This beast sported
six Jensen 10" speakers and
pumped out 120 watts of vintage tube tone. Photo courtesy
of Fargen Amplification
Hopefully, the capacitor mod
will give you more gain in the
front end so you don’t have to
push the output stage so hard.
That said, there’s nothing like
the sound of output tubes distorting, so if you need to crank
it, go ahead. Luckily Mercury
Magnetics makes replacement
transformers for these amps, too.
There you go. I’ll bet Jack
White doesn’t have these mods!
JEFF BOBER, one of the
godfathers of the low-wattage amp revolution, co-founded and was the principal designer for Budda
Amplification. Jeff launched
EAST Amplification in
2010, and he can be reached at pgamp-man@gmail.com.
