Raspy treble from 2203 amp

[solderhead]

D'oh! Somehow I thought we were talking about 100k plate resistors in the preamp. I completely mis-read the OP's comment about a 100k cathode resistor. thanks for clarifying that for me. I'm on the right page now.

[Mark]

What was the cause of the 880K CF resistor? Was it damaged or was it a mistake? Either way, it might be worth checking other component values also to see if they might be contributing.

All CC resistors tend to age upwards, but I have to admit that a 100k resistor that measured 880k is farther out of spec than anything I've seen as a result of age. Wow.

I think it’s the old Fender issue where they used 1/2 watt resistors on the anode/plates of the valves when they should have used 1 watt resistors. I replaced the resistors with 1 watt ones.

I understand your line of thought, but how much power actually gets dissipated across those plate resistors? My recollection from calculations many yeas ago is that the power dissipation across the resistors in the preamp stages of the supply line is so low as to be negligible. I obviously don't have the rail and plate voltages for your amp to confirm this, but if I assume that there's 100V across the 100k resistor, the math comes out to what? About 100mW? If that's correct then it would seem that a 1/2W resistor provides s 5x margin of protection. I've got to be missing something. I was always under the impression that the decision to use 1W resistors on the plates was intended for the purpose of hiss reduction.

I have seen Fender plate resistors go high though as you say they are mostly carbon comp resistors which increase in value over time. It was an instant fix replacing the 880K cathode follower resistor. The amp sounded horrible, I have seen circuits where they increase the value of the cathode resistor but 880K seems to be stretching the friendship.
The 880K sounded very mid heavy and compressed from memory.

[matt1969]

I put a 220k resistor on the volume control's wiper to treble control and it made huge difference. It really smooths out the taper helping to dial in the volume. I highly recommend it! Probably my favorite of all of the mods I tried.

Don’t you mean from the treble controls wiped to the top of the master volume?

Yes that's what I meant! Thanks! it works great. You can go as High a 470K if you want.