Dentron Clipperton-L 3x GI-7B Conversion

 This is a Dentron Clipperton-L I converted to 3ea GI7B ceramic triodes. It was originally 4ea 572 tubes. Those are very expensive, and its difficult to get good 572B tubes, any more. The end result of this conversion was very nice, and GI7B tubes are plentiful and cheap.

 The original filaments were 6v @ 16 a, the GI7Bs are 12v @ abt 4a total. I repurposed the 12v control power winding (good for abt 5a) in the xfmr for the new tube fils, and build a doubler for the old 6v fil winding to provide 12vdc for the controls. 

Here's some vids, pics, and explanations...

Vid 1...

Vid 2...

Vid 3...

Finished conversion...

Rear panel, pre-conv...

Front panel, pre-conv...

Interior, pre-conv...

Gutting begins...

More parts coming out...

With this area gutted, I'll cut the perforated floor out to build a raised sub-chassis...

Will use this space for a lv doubler...

Filament current test...  2.7a total. The original was 16A!!!

Testing 12v winding loading...

Mockup of matl for raised sub-chassis...

Amp chassis now cut...

New sub-chassis cut and prepped...

Fabricating new tube mounts. The control grid flange of the tubes will be bolted directly to the new sub-chassis...

Tube mounts being fab'd...

Plenty of clearance for tubes...

Tubes modified for plate connections...

Tubes mounted...

Plate choke and parasitic chokes mounted...

Filament and cathode connection clamps...

Plating removed and clamps tinned for connection...

Fan speed dropping resistors in place...

Fan recounted to blow in across plates and Filament connections...

Plate glitch resistors installed...

Lower compartment wired...

Total Filament current, when installed with lower resistance, 3.5a. Much better than the OEM 16 amps!

Fan seen cooling top and bottom of tubes...

Testing begins...

HV transistor for bias circuit seen on left...

Lv Doubler on term strip on right...

High Voltage interrupter relay installed...

Idle current approx 125ma...

Plate temp...

Filament and cathode terminal temp...