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Re: Does anyone know what the difference are between the Heathkit W4AM and the Heathkit W4B

Electrical differences are very minor. W4B added a pair of 10K resistors between each side of the filament tap and ground, and has an on/off switch. Also the fuse was moved so that it just fuses the power transformer on the W4B, where on the W4A it also fused the AC outlet. I have schematics here for both, and a full manual for the W-4B version.

There is also an AA-71 which is even a later version of the same basic design.

Reducing the bias just involves increasing the value of the 360 ohm resistor on the cathode bias.

A lot of W4's didn't make it thru their first 45 years, so I wouldn't hold my breath on 50 more. Then again, we may not be here to find out :)



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