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VHT SP6 to P1x
#1
Hello,

I converted a VHT special 6 circuit to a P1 extreme.

I kept the original transformers and speaker.

The only changes I made from the 10-10-04 schematic was a 230R cathode resistor and a 22k B+3 power supply resistor. (May replace 22k with 27k to drop another 10v off B+3) I also kept the VHT triode/pentode switch and the 34k/68k lo/hi input resistors.

Clean and light crunch sound really nice, full on gain is not so pleasing. Triode mode is a bit dull too.

Looking for advice to sweeten the high gain.

Here are the voltages:
B+ 350v
B+1 342v
B+2 330v
B+3 285v

EL34
Pin 3 330v
Pin 4 320v
Pin 8 18.48v (cathode 230R)

12AX7
Pin 1 198v
Pin 6 164v

I'm considering the following for a more British tone and sweeter high gain.


1. Replace stock 10inch speaker with Emenence RF10C. Put the 8 ohm speaker on 16 ohm tap. (VHT OT impedance is 9000, I think the EL34 would be better at 4500)

2. Add a cathode bias toggle switch for use with 6V6. EL34 230R <> 6V6 470R.

3. Maybe convert Extreme to a P1 for earlier breakup. Drop 90v from B+1 by replacing 100R with 1k8 5W resistor, rebias for EL84 (I have the 6v6 to EL84 plugin adapter) Is this a safe way to drop 90v?

4. Or leave the P1x as is and just use a pedal for the high gain stuff.

Any advice is appreciated.
Mike

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#2
After doing some research, sounds like reducing B+ 90 volts with a power resistor is not a good option. So scratch the conversion to a P1 EL84 idea.

Strange that VHT offers the 6V6 to EL84 adapter given the voltage on the plate would exceed 300Vs.

Anyway, going to rebias the P1 extreme for a 6V6 and see if it helps with the higher gain settings.

Right now the amp sounds nice with the gain and volume controls up to about 2 0clock. Then it gets fizzy and harsh.

Question: Could this be the result of using the stock 16ohm speaker on the 16ohm tap with the EL34? (The VHT OT primary is 9000 ohms)



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