Express with Variable Voltage Regulator

[txbluesboy]

I just Installed a London Power Scaling Kit (SB-1) on my Express clone and so far am very pleased with it. I scaled only the power tubes and used what he calls the Improved bootstrap master volume for drive compensation. I think this master volume is an improvement to this amp even if you don't power scale. The volume control on my amp wasn't very usable because the best sound was just as the volume control barely came off 0, after that it was just driving the output to hard. Im not really a good enough player to say its perfect, however to my taste its a great improvement.

[UR12]

I just Installed a London Power Scaling Kit (SB-1) on my Express clone and so far am very pleased with it. I scaled only the power tubes and used what he calls the Improved bootstrap master volume for drive compensation. I think this master volume is an improvement to this amp even if you don't power scale. The volume control on my amp wasn't very usable because the best sound was just as the volume control barely came off 0, after that it was just driving the output to hard. Im not really a good enough player to say its perfect, however to my taste its a great improvement.

What did you guys who scaled the Express do in regards to a heat sink or was one needed?

[UR12]

Double post

[txbluesboy]

I bolted the MOSFET's directly to the aluminum chassis with insulators. So far the heat hasn't been that noticeable, but I'll keep you posted.

[UR12]

Just a quick update. I have the wiring done on the power supply and am moving on to the heaters and tube socket wiring. Here is a few pics of the power supply section after I got it finished and tested. I had to change the 220k in the bias circuit to 150k to get the bias in the range I wanted. I don't think this had anything to do with the VVR as I have had to do this on my other Express I built. I have also dropped the two 100k 3w bleeder resistors in favor of one 470k bleeder resistor,

[gearhead]

Coolio, looking good!

Watching and waiting to see how this one turns out. Thanks for being such a trailblazer, Dana!

Dave

[drz400]

I just Installed a London Power Scaling Kit (SB-1) on my Express clone and so far am very pleased with it. I scaled only the power tubes and used what he calls the Improved bootstrap master volume for drive compensation. I think this master volume is an improvement to this amp even if you don't power scale. The volume control on my amp wasn't very usable because the best sound was just as the volume control barely came off 0, after that it was just driving the output to hard. Im not really a good enough player to say its perfect, however to my taste its a great improvement.

What did you guys who scaled the Express do in regards to a heat sink or was one needed?

I used a thick .125" oxide thermal pad bolted to the chassis using the aluminum chassis as the heatsink, since when I used the thin insulators or mica I had a stituation where any piece of crap caught between cord cause a short to chassis

[UR12]

What did you guys who scaled the Express do in regards to a heat sink or was one needed?

I used a thick .125" oxide thermal pad bolted to the chassis using the aluminum chassis as the heatsink, since when I used the thin insulators or mica I had a stituation where any piece of crap caught between cord cause a short to chassis[/quote]

Sounds cool, (Excuse the pun ). I usually take a piece of fine sandpaper and sand the area where I drilled the hole for the mosfet. I try and make sure there are no burs or shavings left over from the drilling before I install the pad and mosfet.

Coolio, looking good!

Watching and waiting to see how this one turns out. Thanks for being such a trailblazer, Dana!

Dave

Daniel Boone I'm not I'm on to wiring up the heaters and tube sockets tonight.

[RB]

I just Installed a London Power Scaling Kit (SB-1) on my Express clone and so far am very pleased with it. I scaled only the power tubes and used what he calls the Improved bootstrap master volume for drive compensation. I think this master volume is an improvement to this amp even if you don't power scale. The volume control on my amp wasn't very usable because the best sound was just as the volume control barely came off 0, after that it was just driving the output to hard. Im not really a good enough player to say its perfect, however to my taste its a great improvement.

What did you guys who scaled the Express do in regards to a heat sink or was one needed?

I used a thick .125" oxide thermal pad bolted to the chassis using the aluminum chassis as the heatsink, since when I used the thin insulators or mica I had a stituation where any piece of crap caught between cord cause a short to chassis

I have been tring to find the .125 oxide (Aluminum I assume) material. Was it bulk or was it a precut pad for the mosfet? I would like to experiment with this approach.

[mdroberts1243]

I bolted the MOSFET's directly to the aluminum chassis with insulators. So far the heat hasn't been that noticeable, but I'll keep you posted.

Hi TxBluesboy,
Do you have pictures of how/where you installed the SB-1 kit (or just a good description)? I have one on order that I want to put into my Ceriatone-derived Express clone and I've been trying to decide where to put the power scaling.

Thanks,

[UR12]

Duplicate post.

[UR12]

I finished up the amp yesterday and it fired up with no problems. I have the crappy tubes in there for startup and am going to try and get it biased up with a set of NOS Siemens and some choice 12ax7s tonight at Richie's. So far, it appears to have all of the Express qualities that all of the other Expresses I have built have. Richie has a stock Express that we should be able to A/B against this one tonight. Preliminary tests shows all of the voltages correct and are tracking properly. I'll post more when we have had a chance to run the amp through it's paces this evening. In the meantime, here is a few pics of the competed amp.

[drhulsey]

Boy, those cap cans sure make for a tidy layout

[UR12]

Well so far so good. I got to take the amp to band practice and it ran perfectly for about 3 hours. I then took it over to Richie's to put on the bias probe and compare it to another Exress that was built with conventional stack-o-caps instead of the can caps and VVR. This amp sounded a little brighter to both of us but that is probably because of the different V1 tube. I will try a few others in the next few days. The VVR worked great and even after 3 hours at 1/2 to 3/4 power levels the chassis barely gets warm. I really like the can caps and really can't hear any difference to my ears. The amp is very quiet and has no hum at all. If you are tired of glueing up caps to the bottom of a chassis give these a try.

[sst4270]

I thought I'd been pretty vigilant here, but somewhere along the way I missed this... I built an Express last year using KOC's PS kit. Search: Marybeth. This VVR2 looks much simpler.
I used the chassis as a heat sink for the PS. During gigs it rarely gets warm. Tone is greatly affected at bedroom volumes, but otherwise the circuit works perfectly.

Dana, did you ever post a schematic of your circuit? Or are you simply selling the boards? I'm interested in purchasing and implementing into a recent Liverpool build.

Is there no extra transformer (as is used in Power-scaling) with VVR2? The extra x-fmr was a huge space hog inside an already cramped chassis.
I'm anxious to implement this into my current build before I CNC the chassis.

Thanks,

Steve