Fender Twin Reverb, too bright?

[shiner555]

Hey Everyone,

May be a dumb question....but I figured it'd be worth a try! I've been rebuilding an amp that is a copy of a blackface twin. I've gotten it up and running, had to replace the verb xfrm, but when I crank up the verb it get's really bright and a little too harsh for my tastes. Any ideas on what I could do to dull it down just a tad?

Thanks!
-Jason

[Bruce / Mission Amps]

Are you using a cathode bypass cap across the 12AT7 driver and or the recovery triode? If so try a 1000 to 2200 ohm biasing resistor on the 12AT7 with no bypass cap.
A 12AZ7 is a little duller sounding and you can bring the cathode resistor down to 680 to 820 on that tube.
I'd try this first though, use little snubber cap on the recovery triode.
Drop a .0022uF to .0033uF 400v cap across and in parallel with the 100K plate load resistor of the recovery triode.
Start with the .0022uF cap but you'll have to experiment with the cap value (.001uF to .0033uF) to get the high freq attenuation you want.

[shiner555]

Are you using a cathode bypass cap across the 12AT7 driver and or the recovery triode? If so try a 1000 to 2200 ohm biasing resistor on the 12AT7 with no bypass cap.
A 12AZ7 is a little duller sounding and you can bring the cathode resistor down to 680 to 820 on that tube.
I'd try this first though, use little snubber cap on the recovery triode.
Drop a .0022uF to .0033uF 400v cap across and in parallel with the 100K plate load resistor of the recovery triode.
Start with the .0022uF cap but you'll have to experiment with the cap value (.001uF to .0033uF) to get the high freq attenuation you want.

Hi Bruce!

Thanks a bunch for the suggestions. I am currently using a bypass cap across the cathode, on the driver tube and the recovery tube, according to the fender schematic.

On your second suggestion, do you mean put a cap in series and in parallel to ground with the 100K plate resistor?

Thanks,
-Jason

[Bruce / Mission Amps]

Hi Bruce!

...

On your second suggestion, do you mean put a cap in series and in parallel to ground with the 100K plate resistor?

Thanks,
-Jason

Try it without the cathode bypass cap and see if you like it better.
With respect to the little .001uF to. 0033uF cap, what I meant was, a small value snubbing cap directly across the reverb recovery tube's plate resistor.
The high frequency signals from the plate will see the little cap as another way to drain off before the next stage. Like a tone control would do.
The 100K plate load is connected to your B+ rail and filter caps, which are AC grounded, so the signal siphoned off will go right to ground anyhow.