Xtian.
Contrary to common misconceptions that are quoted in all the magazines, a true class A amplifier is not running at full power all the time, whether at idle or full output. The plate dissipation of the output tube (or tubes) is usually highest at idle (they are typically biased to max dissipation, or even slightly higher in some guitar amps), and the plate dissipation decreases as it starts delivering power to the load.This is because the plate voltage and plate current in an output tube are 180 degrees out of phase, so when the plate voltage is at max, the plate current is at zero, and vice-versa, so the instantaneous power, which is the product of the voltage and current, is zero at all times.
Hope This Helps and congrats on the sweet build..
Tony
" The psychics on my bench is the same as Dumble'"
xtian wrote:I installed a Hall VVR3 on the front panel of RJ's TW chassis. It took a lot of visualizing and rotation of parts, but I think I arrived at the only valid solution. The Rectifier is mounted on the chassis with thermal paste and the mica sheet it came with, and the leads are extended to reach the PCB.
Can't wait to test it out!
Nice job on your amps, How do you like your VVR? I wanted mine closer to the power supply but could not without making a new faceplate, so I choose to install it on the back panel. I like how it works. I am guessing yours scales all the B+ voltages in the amp? Did you have to add caps and resistors to yours? I read a post someone did not have to in their build, tried without but I ended up adding them to get rid of noise. If you did what value cap did you use? Again nice job on the amps...
For what it's worth regarding how hot the EL84's are biased, my Blues Jr. came stock from Fender biased at 12W per tube. I crank it all the time, and so far no redplating, and no burnt-out tubes. I've had it a couple of years, now.
Granted, it's got the stock Fender chinese EL84's, but it sounds fine, so I never bothered to do the Bill M bias mod.
It may shorten the tube life to run them that hot, but I agree, it's in the years, not hours category.
I'd be more concerned with the overall impact on tone.
VVR report: It works, and I like it! Better by far than the Weber Mini Mass I just bought (yuck). Better even than the PPIMV I put in a Bassman. My VVR is scaling all the B+ voltages.
I installed the VVR without adding the extra coupling caps as mentioned in the instructions, and indeed, there is DC on the Volume pot, and worse, on the Volume control on my guitar! If it was just the Volume on the amp, I wouldn't mind at all, because I never move that knob while playing. The Volume knob on the guitar however…
OH! Another MAJOR benefit to the VVR? When you turn it down just 10 or 20 percent from max, all 60Hz hum vanishes, and the amp is still LOUD. Nice nice nice.
I made Hall's recommended mods to the input resistor and added a 0.022uF cap prior to first triode's grid. Still left a little DC scratchiness on the Rocket Dog's Volume pot, but none on the guitar's Volume, which is exactly what I was hoping for. I'm not going to bother putting Hall's mods in the second stage.
Played for an hour at bedroom volume--SO GOOD! I put a clean boost in front of the amp and dimed the volume, with the VVR scaled low. Got a great Crazy Train hi-gain sound, with full note articulation. Man, this amp has a LOT of range.
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I made Hall's recommended mods to the input resistor and added a 0.022uF cap prior to first triode's grid. Still left a little DC scratchiness on the Rocket Dog's Volume pot, but none on the guitar's Volume, which is exactly what I was hoping for. I'm not going to bother putting Hall's mods in the second stage.
Played for an hour at bedroom volume--SO GOOD! I put a clean boost in front of the amp and dimed the volume, with the VVR scaled low. Got a great Crazy Train hi-gain sound, with full note articulation. Man, this amp has a LOT of range.
Looking good, I added .04 and .047 caps to the first and second stages and the 1meg resistor to the second stage, it got rid of all scratchiness in the controls. These amps sound good by themselves, and also work well with pedals, I tried a Durham Sexdrive clean boost and a Hughes and Kettner Tube Factor,both sound good. I liked the VVR mod enough to order a couple more. Any ideas for a cabinet?
Yep. Figured maple cabs coming in a week or two from Jeff in Redding, CA, and laser etched maple faceplates from RJ. Sweeeet.
Can't wait to see it, I have to make 2 more cabinets yet myself, waiting on cherry wood for one. Almost went with Tiger maple for one but found Tiger figured cherry enough for a head and 2x12 speaker cab. May make a maple one in the future for maybe an Express????
The VVR was such a success in Rocket Dog #2, that the client wanted it in #1. I mounted the VVR's MOSFET in a different place--it's still pretty tight in there.
The VVR works just as well in #1. But earlier, I mentioned that I had installed the cathode bypass switch to service the first preamp stage, instead of the second as recommended by the schematic. Now that the VVR is in place, my cathode bypass made very little difference in sound. So I moved the cathode bypass to the second preamp stage, per spec. Better.
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Any ideas for a cabinet?
