More sparkle from vibrochamp?

[Rick1114]

I've been thinking about tweaking my 66' Vibrochamp to see if I can get a little more chime on the top end. I'm using a Weber 8A100 speaker which sounds beefy for an 8 inch but can get a little muddy at times. I'd like a little more top end to come through, and maybe tame the bass a hair. I've got a fairly bright 6V6 tube in there already (Tung Sol RI) and a Mullard 12Ax7.

Here's a few ideas & issues I'm wondering about:

A) I recently replaced the cathode resistor/cap with a 1K resistor and a 50uf/50V capacitor because the stock values ran the 6V6 too hot. Should I try a smaller bypass capacitor, maybe 25uf with the 1K resistor to achieve more highs/less bass?

B) My plate resistors are measuring in at 125K (should be 100k). I'm hesistant to replace anything original in this amp, but would this cause loss of high end?

C) The most obvious thing would be to replace the speaker, but It's *not* that far off from what I want, and good speakers are costly . If nothing else works right I'll consider it.

Any thoughts?

Thanks,

Rick

[chipaudette]

One approach is to add a "bright" cap across the volume knob. Assuming that you've got a black-face/silver-face style champ, try a 47pF cap (1 kV tolerance) from the high side of the volume pot to the wiper.

Many Fender amps have this cap wired to a "bright" switch so that you can cut it in and out. That's a good approach. On the deluxe reverbs, though, it is permanently wired in. That works, too.

If you generally like the sound, but it's just not quite right, you can adjust the value of the cap to taste. Or, if the "bright" is just a little too bright, you can also add a resistor in series with the cap (50kOhm? 100kOhm? 200 kOhm?) to reduce the magnitude of the effect.

Good luck.

Chip