JTM45 to plexi50

[Jsinca]

Hello,
Ive searched the fourum looking for an answer and couldnt not find it. Not for my particular situation. So i apologise if this has been answered before.

I switched my metro JTM45 to a 1987 spec. Well almost.

Kept the filtering at Jtm45 spec.
kept the transformers JTM45 spec
kept the Choke JTM45 spec

Everything else is now a plexi 50 watt spec.

So my question is. What SOUND and FEEL changes should i expect if i replaced the transformers and caps to an all out plexi 50 watter?

Could I just replace the caps? Will the PT handle it?

Thanks

[neikeel]

The PT will be fine (350-0-350v at 150mA or so) you need to decide what to do with the recifier, diodes or valve?

A 50watt diode rectified amp with 100uF mains filtering is tighter and crisper in pick attack, palm muting etc (assuming you went for 0.022uF to 0.047uF PI couplers replacing the 0.1s and decreased the NFB and changed the tone stack). There is less power supply sag with diodes and higher filtering.

Ideally for EL34s you would need a 784-139 type OT if you go to diodes, for EL34s and a valve rectifier then a 789-128 is more correct, but I guess you could use 6L6s with the existing OT, depends on where you are heading. You can use the existing OT with EL34s. Georges Metro 45 OT is an 8k primary vs the 3.4k primary of an EL34 OT so you would need to alter your impedence selector 1 step up than the load with EL34s in that amp, so with an 8ohm cab set the selector to 16ohms with EL34s. No tdisastrous if you don't just not how the valves are supposed to operate.

[Jsinca]

Thanks for the reply

I have 392 volts on the output plates. Would that be higher with the 1202-118? And If so what sound changes would i expect to hear?

I have gone to a bridge rectifier. Ill try paralleling some larger caps in the mains and see if I like it.
I installed a 100k pot in the NFB circuit. And have changed the PI caps and all other components to the 50 watter spec.

I have compensated for the impedance mismatch in the 784-103. I am running a 4ohm cab setting the selector on 8ohms.
That brings up another question. Not using the 16 ohm tap do i loose some output from not using all the windings on the transformer?

So my last question. What will I hear in tone change between the 784-139 and the 784-103?

Thanks
John