THE CENTRAL ELECTRONICS
20A Rack Mount

The CE20A rack mount model was acquired from E-bay also and I drove to Ohio to pick it up, since I didn't want

it damaged in shipping. Someone had made some modifications to the unit to try and get more power output? I did

not understand his/her thinking it is only a pair of 6AG7 tubes running in linear mode, AB1 in fact. They removed the

5U4 rectifier and added some kind of voltage doubling diode arrangement, which ended up causing lots of problems

in the unit. The magic eye could light up the room with the green glow it had more than 600 volts on the plates. The

6AG7 tubes were running wide open and hot enough to boil the paint off the tubes. The biggest problem was the

6BA7 screen was getting no voltage as the 10 K ohm screen resistor burned open, leaving the 6AG7s to amplify

all the noise out of the preceding stage (6BA7) and running all out to do it with again 600+ volts on both the plates

and the screens. I found the driver screen problem by the simple test of plugging in a crystal to check the unit and

there was no output at all, when the unit should have been in straight through mode and running on the frequency of the

crystal. I checked the voltage at the 6BA7 driver/Xtal osc and viola no screen volts, which lead to the burned out

10K resistor.

I removed the mods put the unit back to original, by inserting the 5U4 rectifier, brought the plate voltage back to 360

volts, replaced the 10K ohm resistor, did an alignment of the stages and tried it out barefoot for a quick 10 meter

QSO. I then tried to drive the Thunderbolt with the unit, got close to 400 watts of carrier using the 20A as a driver.

NOTE:  The cover for the rf plate circuit for the 6AG7s should be in place in the rack mount and desktop model,

otherwise the unit suffers from feedback and microphonics when driving a linear amplifier.