trinityamps.com

Hello,

Just finish to build my plexi 18W based on Richard Johnson and the Brown mods topic. It's in between the two schematics.
First time I powered it up, and all was fine! It sounds really great and cleans are awesome.
I put some chinese power tubes (valveart) in it, rectifier and preamp tubes are JJ's. Works fine.

I do have a new set of JJ EL84. So I tried them. But something I never encountered happened : I switch off the standy switch, then I have sound, but 5 seconds after that, I have no guitar signal, but hum like wallwart tension instead, maybe pitched higher. The tubes glows but there is only that strange sound. each time I do this, the amp behave the same way.

So I put back the ValveArt set and the amp worked fine again.

Is it possible that my JJ set is wrong?

thanks for any comment that could help me to understand this.

rgds,

Ed.

More than likely tubes if one set works and the others don't .
Some times you get bad tubes
Might have been nice to try them before the changes

Which Richard Johnson schematic are you working from?

Did you make any power supply changes ?

Hello sazafraz,

thanks for your message.
I suppose one of the tubes is bad but since it's the first time I see this ( I always buy JJ's, i like them in my other amps, princeton and deluxe, and have never had a problem). But sure, if the amp works fine with the valveart, it should work with other tubes.

I've worked with the layout you can find on the 18W forum. I've also found on another site the schematic that matches.
I've started with what I've already had : a 18W tremolo from Ceri@tone, I build a couple of years ago.
For the power supply, I've taken values from Johnson's layout. The only difference would come from one less 16uF/450 cap with 8.2k resistor, as seen on the plexi 18W from Trinity, because my layout is based on Trinity.
I haven't made all the brown mods, described by Stephen on this site. Do you think it could also come from the power supply?

rgds,

I've just made a test :

1) I've put one Valveart and one JJ : the amp works.
2) I've put the same Valvart, with the other JJ : the noise was back... seems that this last tube doesn't work.

These one schematic out there where theres an extra power supply node like a traditional plexi . where its

cap 1.5k cap 10k cap 10k cap 10k cap. ive tried it any various on it but the ez81 goes out screaming every time. (think it has something to do with the max negative sink current ) but have never figured it out.

yes, that's this schematic. I didn't put this extra node. I followed the layout of Unimind/Stephen and made a mix with Johnson's. The power supply is very close to Stephen's layout. I took Johnson's value for the tonestack and some others caps, components that "shapes" the sound and not related to how tubes are powered. I guess that was a good idea to do this

thanks,

Ed.