Educate me on these 2 Princeton Schematics


I have an amp built using Weber 6A14HP (High Powered Princeton) Kit. It has now been modded to Deluxe Reverb Size Transformers using 6v6 and GZ34 instead of 6L6 and Weber Copper Cap.

Looking at the 6A14 & 6A14HP schematics from Weber, I noticed there are a few different values of parts. 2 of them are in the red square box above the Power Transformer. 10k and 22k on the 6A14, 4.7k and 15k on the HP.
And there is an extra 20uf capacitor(?) right to the PT on the HP.

What functions are those parts serve and what tonal different would those variations make?
Since I swapped to 6V6 and DR Transformers, should I stay with the 4.7K and 15k or change back to original 10k and 22k? What about the extra Cap, should I keep or remove it?

Here are the schematics:



Thanks everyone!
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Silver Supporting Member
That little board is for the bias voltage supply. The resistance value used will depend on the voltage supplied from the PT. The amp with the higher value resistors most likely has a higher voltage secondary on the PT, so the higher value resistors are needed to bring the voltage in the bias circuit down. It may take some tweaking on your part to end up with the proper negative bias voltage.

Blue Strat

Bias supply, as mentioned. The different values are because one amp has 6V6s and the other has 6L6s. Those tubes have very different bias points.


Gold Supporting Member
Thanks @Blue Strat.
So do you think it's best if I change those parts to the 6A14 value?

It's important to set the bias correctly for the power tubes. You must learn to measure the bias voltage and operating current--you risk burning your power tubes and your power transformer if you don't. See: The Last Word On Biasing - Aiken Amps

Second question, about the added 20uF filter cap--you can use or not use, based on preference. Without, you get a slightly "slower" or "saggier" power supply and possibly higher hum at idle.

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