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One of my clients brought in his 60 year old Selmer Zodizc Thirty 212 Combo amp that had issues with it's six-button Switch array. Very cool amp, great sounding British Amp from the mid-60's. No universal Primary on the power xfmr, so for domestic power in the US and other countries, you need a step-up transformer.
It was recently serviced prior to it coming to me, but the pushbutton switch bank was still had intermittent behavior. I hadn't seen it yet, but had visions of horror tackling that. Not far from wrong.
The rear view image is with the upper and lower panels removed. Lower panel has a gold-colored perforated metal screen with sharp edges at the back of it to inflict injury to those reaching inside to follow a cable. I added rubber grommet edging to cure that.
Now to the switch bank, after removing the upper preamp chassis and opening it up.
These linear actuated switch contacts are similar in nature to typical rotary switch wafers, though the paired upper/lower rotor contacts terminals are not riveted to the phenolic panel which is set up with the moving interactive push-push switch actuators. I first had to go in with very fine round scub brush to clean all the surfaces at each location. I found the terminal where that green wire connects was not very stable, and trying to get additional tension on the upper/lower halves of the wiper blades was like herding cats. Plus the folded upper half of the terminal had fractured where it bends upwards to form the solder terminal before continuing onto the contact. After cleaning all those contacts/terminals, I went back and carefully soldered the terminals to the rectangular 'anchor blades that serve to hold each terminal in place. It did take two attempts to cure that one terminal where the green wire attaches. After that, I had reliable and repeatable results and the pushbutton array now works as intended. And a heavy sigh of relief from yours truly.
The owner of this also had a friend who reproduced an excellent set of schematics for this amp, which I've attached below.
There's physical damage from age on the side cleats behind the upper right rear panel so that lower panel screw presently is missing it's anchor point. There's a Magic Eye circuit that displays the Tremolo speed that's very cool. Preamp tubes are EF-86 pentodes. Power tubes are EL34's & cathode-biased. The Power Transformer / Power Supply schematic wasn't present in the three drawings I received.
I did find a date code on the large clamped-in filter cap installed in the preamp chassis. Feb 64. So, actually this amp is more like 57-59 yrs old, depending on the shelf life of that filter cap. Vintage Celestion G12 speakers...Alnico magnets, I was told
The Schematics for the amp:
Zodiac Twin 30 Ch 1.pdf
Zodiac Twin 30 Ch 2 Trem & Magic Eye.pdf
Zodiac Twin 30 Ch Phase Splitter & Pwr Amp.pdf
It was recently serviced prior to it coming to me, but the pushbutton switch bank was still had intermittent behavior. I hadn't seen it yet, but had visions of horror tackling that. Not far from wrong.
The rear view image is with the upper and lower panels removed. Lower panel has a gold-colored perforated metal screen with sharp edges at the back of it to inflict injury to those reaching inside to follow a cable. I added rubber grommet edging to cure that.
Now to the switch bank, after removing the upper preamp chassis and opening it up.
These linear actuated switch contacts are similar in nature to typical rotary switch wafers, though the paired upper/lower rotor contacts terminals are not riveted to the phenolic panel which is set up with the moving interactive push-push switch actuators. I first had to go in with very fine round scub brush to clean all the surfaces at each location. I found the terminal where that green wire connects was not very stable, and trying to get additional tension on the upper/lower halves of the wiper blades was like herding cats. Plus the folded upper half of the terminal had fractured where it bends upwards to form the solder terminal before continuing onto the contact. After cleaning all those contacts/terminals, I went back and carefully soldered the terminals to the rectangular 'anchor blades that serve to hold each terminal in place. It did take two attempts to cure that one terminal where the green wire attaches. After that, I had reliable and repeatable results and the pushbutton array now works as intended. And a heavy sigh of relief from yours truly.
The owner of this also had a friend who reproduced an excellent set of schematics for this amp, which I've attached below.
There's physical damage from age on the side cleats behind the upper right rear panel so that lower panel screw presently is missing it's anchor point. There's a Magic Eye circuit that displays the Tremolo speed that's very cool. Preamp tubes are EF-86 pentodes. Power tubes are EL34's & cathode-biased. The Power Transformer / Power Supply schematic wasn't present in the three drawings I received.
I did find a date code on the large clamped-in filter cap installed in the preamp chassis. Feb 64. So, actually this amp is more like 57-59 yrs old, depending on the shelf life of that filter cap. Vintage Celestion G12 speakers...Alnico magnets, I was told
The Schematics for the amp:
Zodiac Twin 30 Ch 1.pdf
Zodiac Twin 30 Ch 2 Trem & Magic Eye.pdf
Zodiac Twin 30 Ch Phase Splitter & Pwr Amp.pdf
Attached Files
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