MATT GILBERT'S GUITAR PROJECTS AND MODS PAGE
this page includes:
AB switch project
Silvertone 1484 add bias pot mod
Silvertone 1484 standby switch mod 1 (Good)
Silvertone 1484 standby switch mod 2 (Better)
Silvertone 1484 standby switch mod 3 (Recommended!)
3 tube guitar amp like harmony H400
SIMPLE A/B CHANNEL SWITCHING PROJECT
SILVERTONE MODEL 1484 BIAS MODIFICATION
SILVERTONE 1484 STANDBY SWITCH MOD #1 (Good)
(SWITCHES OFF HIGH VOLTAGE TO SAVE YOUR TUBES)
Some notes on this circuit:
This diagram (above) shows the heart of the silvertone's 1484 power supply. The complete 1484 diagram can be rather confusing to look at, but everything you see above is exactly what's in it, simply add the two 100K / 5W resistors and the SPST switch, shown in gray. By simplifying the diagram in such a manner you can better understand it's design. D1, D2, C26, C27, with it's associated transformer winding create a classic voltage doubler circuit, as does the identical section comprised of C28, D3, C29, D4, and it's associated transformer winding. Each voltage doubling section takes the (approx) 120 volts a/c from a transformer winding and converts it to (approx) 240 Volts DC. The two sections are *stacked* for a resulting voltage of (approx) 480 volts DC. The transformer has two other secondary windings, not shown, one which provides the grid bias for the 6L6's, and another winding which provides 6.3 VAC for the tube filaments and pilot light.
This mod will allow you to power up the 1484 in standby mode to allow the tube filaments to warm up instead of *slamming* high voltage on the plates. You can also put the amp in standby mode during breaks. This makes life a lot easier on your tubes.
SILVERTONE 1484 STANDBY SWITCH MOD #2 - ALTERNATE SWITCH PLACEMENT (BETTER)
SILVERTONE 1484 STANDBY SWITCH MOD #3 - ALTERNATE SWITCH PLACEMENT (BEST!)
THIS METHOD USES A DPST (DOUBLE POLE SINGLE THROW) SWITCH AND IS THE PREFERRED METHOD
3 TUBE GUITAR AMP SIMILAR TO VINTAGE AMPS LIKE THE HARMONY H400
THE MAIN DIFFERENCE IS THE WAY I HAVE THE FILAMENTS WIRED (NO TRANSFORMER) AND I ADDED A 3 PRONG GROUNDED CORD FOR SAFETY!
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