help me mod my Ampeg jet II

[electricJohnny]

I'm not too sure what to do to the circit of my amp to mod my Jet


I'd like a nudge in the right direction as to put a Master volume in and maybe if at all possible the switch Ive seen on other 15 watt amps that goes between pentode and triode or 15 and 7 watts

http://schematicheaven.com/ampegamps...12t_jet_ri.pdf
here's the amps particulars and things

[Chuck H]

Other than a volume reduction what do you want from the amp that you don't get now?

The triode/pentode switch is easy. But the tone does change in triode mode. A master volume won't get you to power tube distortion and that amp wont give you much preamp distortion. So a master volume would act more like a gain knob instead of a way to get more drive at lower volume.

Chuck

[electricJohnny]

I mostly want volume reduction out of this amp, its alittle too powerful right out of the gate for my taste

and don't discount the pre amp distortion of this amp, the reissues have el84's(only ampeg i can think of with these tubes), this amp roars when its opened up, it sounds almost marshall-ish, not oodles of headrooom

[Chuck H]

Originally Posted by electricJohnny

and don't discount the pre amp distortion of this amp, the reissues have el84's(only ampeg i can think of with these tubes), this amp roars when its opened up, it sounds almost marshall-ish, not oodles of headrooom

Be that as it seems 90% of this amps distortion is generated in the power tubes and PI. In that order. If you do want to try a master volume it should at least be a post PI type. And even then I think the results could be less than gratifying. Your amp uses a bias modulated trem so most post PI MV's won't work. I just worked out one that will about a week ago on another thread.

The triode/pentode switch would work fine for this amp.

I can't modify a PDF file with my stuff. If you provide a gif or jpg version of the schem I'll show you how to do the MV and T/P switch

Chuck

[electricJohnny]

I think I posted the jpg

thanks for the help Chuck

[Chuck H]

Here are the modifications. Changing the watt rating on the original 100R screen resistors is just an intelligent suggestion. You could leave the stock 1/2 watt resistors in there but they may fail due to the surge when switching. The 1k 3W resistors from the switch to the plates is also just a suggestion. You will get a bit more volume reduction if you use them. You could also use a jumper instead if it gives you enough volume reduction and this would simplify the circuit. If you do not use the 1k 3W resistors you should definitely replace the stock 100R screen resistors with 3W units.

Chuck

[WholeToneMusic]

You first might want to try installing some 12AY7's to reduce amplification.

[Guitarist]

I wonder if this might be a good candidate for the Cerrem resisitor mod from plate to plate of the el84s? I think it was a 10K resistor and here you might be able to use a 25 watt resistor. As el84s are cheap that would be an easy and toneful way to get what you want. You could interrupt with a big switch.

Otherwise ground one of the driver grids, pin 7, and go "single ended". You'll get a tad more hum but it works and I know an Laney el84er who loves it.

Guitarist