Help with new 36 watt build

[JohnDandry]

I built a one TMB channel 36 watt. The overdrive sounds very ratty and thin, harsh. Volume seems about right, it sounds like the problem it is in the preamp All voltages in the amp are about right except screens are a little low.. The way I did it is with a 500k volume to a 470k resistor into the 2nd gain stage. I have a 220k plate resistor on the 1st pretube- and the 2nd half is not connected. on the 2nd stage I have the standard 100ks and a 2.7k/1uf cathode resistor...reads 1.3v. It kinda sounds like blocking distortion. Any suggestions? Is there a voltage problem by not having the other channel there? Thanks!! John

[Mooreamps]

We might need to see a schematic is see what is going on with this.

-g

[zaphod_phil]

Yes, it could well be blocking distortion. One of the causes of this can be parasitic ultrasonic oscillations. Is your layout and lead dress, nice and tidy, with short connections everywhere?

In addition to Gary's request for the schematic you're working from, some gut shots could be pretty useful.

Personally, I would also tie the unused triode in parallel with the other one in the same bottle, and reduce the load resistor to 100k. It's a shame to waste a triode, and you'll get a richer tone from a parallel triode preamp stage.

[brownnote]

Describe your power supply...how many nodes in the preamp?

[JohnDandry]

Well while the forum was down I kinda fixed it, it's alot better. I put a 470k in series and a 1meg to groung before the PI. Also raised the 2nd gain stage cathode resistor from 1.5k to 4.7k That helped. Now it seems a little blocky when ou hit the strings hard. I'm using the schematic from the 36watt group. Could it be a bias thing? Right now I have a bias resistor and cap for each pair of tubes, BUT...I blew out a pair of the matched quad so I have some old Mullards in 2 slots and Groove Tubes in the other 2. Would this cause the blocking distortion or harsh sounds when attacked?