New Half Power Express

[Littlewyan]

As some of you may know, JM offers a half power Express that still uses 2 x EL34s but is actually cheaper than the full power Express ($4000 USD).

How on earth is JM only getting 18W out of 2 EL34s? Someone suggested before he might be running them in a parallel single ended configuration. I'm not sure though as surely that would sound completely different from the standard push pull 36W Express. I guess he could be running the amp on a lower voltage but then surely the clean to mean wouldn't work?

[Firestorm]

Triode? Wouldn't sound the same either. Maybe big power resistors on the output to suck up half the power.

[Littlewyan]

Doesn't explain how he managed to lower the cost though.

[lpd]

Triode is my guess too although it will sound different. Curious how it would sound as triode always seemed thinner (or less weight) with more chime in the hifi systems I've owned :/

[Littlewyan]

I guess its possible. He must be using smaller transformers hence the cost decrease. Unless there is such a big margin on these amps that he can afford to lower the cost.

[RockinRocket]

Using a preset powerscale and smaller transformers wouldn't affect the clean to mean right?

[Littlewyan]

Well I've done some tests in a simulation and the lower voltage does affect it a bit. Hopefully someone who has installed VVR can chime in and let us know.

The odd thing is the transformers used don't look any smaller than the standard ones. The PT I will say does look larger though. I always thought the Express PT and OT were of similar size.

[RockinRocket]

I don't know where VVR is at now but the earlier ones definitely gained up the amp more and more as VVR was being introduced into the circuit. Is there a reason folks don't just use London power over the cost?

Pacific Express transformers are a bit different sized by the way

[Littlewyan]

I don't know enough about VVR or London Power if I'm honest. I've never used it.

Maybe it is Single Ended. That OT looks pretty much the same as the standard Pacific OT that I used in my amp though. I might be cheeky and leave a comment on the photo on Facebook asking

[John_P_WI]

There are several fundamental differences between VVR and London Power's power scaling. London power allows you to maintain the rail voltages at the caps simplifying what is scaled. I"m in the scale the plates and screens, clamp the PI and pre voltages camp. This coupled with a good master volume such as an improved master, limit the tonal and gain changes as the amp is dialed up and down.

It has been fun following KOC's power scaling evolution over the last 15 plus years.

Both VVR and PS have been proven to work in their intended applications and use.

[norburybrook]

VVR works great on an express, just don't expect it to take it down to bedroom levels. It works well taking the edge off the volume on a small gig, studio sessions etc

Also the express takes OD pedals well so with a nice OD and the VVR you have a versatile amp that will sound great on all kinds of gigs.

A fiend played me a track from a recent session he'd done using his VVR express with a Boss blues driver. Tack was done using a telecaster and the amp shown below in the picture with my Rocket.

The cleans were beautiful and the OD sound was just to die for...... really was.


Marcus

[strelok]

My guess is its a lower B+ voltage. Mostly likely just a scaled down PT, and the lower wattage would allow the OT to be scaled down as well, decreasing the cost some. The OT could also be running a higher primary ratio which would also reduce the power output. Granted that would change the sound, too.

[Littlewyan]

Ah ok, I'll have to look into London Power and VVR a bit more.

I guess it might just be lower voltage and different OT impedance. I know Marshall got a single ended EL34 amp (SL5) down to 5W by only having a 250V HT. Not sure what the impedance is though.

[M Fowler]

A local guy builds MoWreck amps and advertise's his Express as

16-24w with 6V6

28-50w with EL34

32-60w with 6L6GC

Same transformers no VVR or PS.

[Littlewyan]

Well done Mark now you've just confused the situation .

Same transformers?! What is this trickery? I know Firestorm said big resistors on the output, but what about resistors in series between the EL34s and the OT?