Friday, December 2, 2011
Resuscitating A Silvertone 1396 Twin Twelve
I'm a sucker for projects, so when a friend brought me a Silvertone 1396 combo that had been in a barn for twenty years or so after being stripped of its speakers and grillcloth I was on board.
The owner represented that it had worked at that time but I find that belief problematic. There was no discernible preamp action, which I later discovered was because the cathode resistor upon which all in the preamp department depends had gone open. It fell apart in my hands, actually.
A preliminary power up with some borrowed speakers showed that the audio section and power supply was functional although needing a complete suite of new tubes and a thorough going over.
Down below there are two separate output transformers, each of which feeds its own speaker. It thus satisfies the Daniel penchant for weirdness and complexity coupled with cheapness of build. But nevermind.
Not so the top chassis-and thereby hangs a tale.
The top chassis contains the controls, a smallish phenolic slab that mounts eight capacitors, four resistors, a tube socket, and a single 12AX7 tube.
Looking at the schematic you can see that the filaments are in series with the cathodes of the power tubes-a favorite Nat Daniel Red Bank era feature.
The upper chassis is a nice cozy place, and it looks as if a field mouse or two shacked up in there for a while, using the upper chassis as a latrine and a source for things to gnaw.
Another feature of this amp is the blue green Sangamo capacitors, all of which showed unacceptable leakage and got tossed. I didn't even need to fire up the capacitor tester I built a while ago, as my trusty IRT2 insulation tester showed enough leakage to make that irrelevant.
The upper board required a complete stripout of all the components, a thorough cleaning and a rebuild that included a new shielded Belton tube socket.
After a few fits and starts and a bit of rework, it's as good as it will ever be. The speaker chores are being taken care of by a pair of period vintage Quam Nichols alnico speakers that came out of a PA enclosure I forgot I owned. They looked almost new, and I doped the somewhat light duty cones for good measure.
Finishing up the upper chassis I bridged the channels for more volume.
How's it sound? Bright and articulate, but the vibrato is slow and dreamy and it will take you to Link Wray "Rumble" territory in a short time.
It's not as in your face as the current day run of cheap amps, but it definitely is one to put on Santa's list. They're not the most common amps in the world either, mostly because they weren't built to last fifty years as this one has.