| Author | Message | ||
     Peter Maziar (mosfet) Username: mosfet Registered: 11-2006 |
OK, I am asking the big guns for some help. Particularly, Steve Kennedy and Ed Goforth, + any other music man gurus out there. I am working on creating the King Daddy Channel-Switching Music Man HD150 amp of them all, incorporating FET channel switching, automatic reverb and phase channel switching, the LED DRIVE (see my other mod topic), and both stages of a 12ax7 tube on the distortion channel. I have designed a modified and hot-rodded Fender tube distortion circuit for my HD-150 distortion channel. Problem is (last night I realized), that the supply voltage to the 12ax7 will drop to about 64% on LO, due to the standby switch taking power from a center tap. I estimate current to the 12ax7 will drop by 1/3 on LO power. Can anyone contribute to this project by designing a way to get a steady supply out of the amp for the tube? 350 Volts is what I am after. The standby switch is DPDT, and one set of poles is unused. Thanks, all. | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Without dropping? A separate power supply transformer is the only way that I see. Then you could get the same voltage on high or low. It would mean a separate filter section though and a compltet second power supply. Probably more room than you have unless you are using a different chassis. | ||
| Peter Maziar (mosfet) Username: mosfet Registered: 11-2006 |
Brainstorm: run the 12ax7 at 200v, taking supply from the source to the power tube screen grid resistors, using a small, high wattage series resistor and filter cap like in a rd50 amp, raising that resistance to make the voltage the same when in high power mode, using the spare poles on the standby switch to do the resistor switch. The factors that concern me are voltage spikes when going from standby, and what effect tapping off that supply will have on the screen grid voltage to the power tubes. Comments or design suggestions? | ||
| Steve Kennedy (admin) Username: admin Registered: 03-2002 |
Have you considered hanging a couple of MR510 diodes, a 150k resistor and a 100uF, 450Vdc cap off the low-power side of the power switch (built in the same configuration as the amp's plate rectifier/filter that comes off the the pole of the Hi/Standby/Lo switch)? This would provide about 350Vdc no matter what position the mode selector switch is in. Replicating the plate circuit is a bit of overkill but the concept is right there and should work (if you are careful). This method also does not potentially interfere with the operation of the output tubes as you are isolated by this separate rectifier circuit. Steve | ||
| Peter Maziar (mosfet) Username: mosfet Registered: 11-2006 |
My tube circuit is built on a special board I constructed that will allow me to change out components to dial in the sound and gain. I have included a switch, so I can drive the circuit with or without the factory distortion circuit in front of the 12ax7. I will be running a battery of tests before inserting the circuit, so I can match the levels to factory original. I am trying the power supply as in the RD50, as I mentioned before, using the free poles on the standby to keep supply constant on HI and LO. If there are any issues, I will consider the method you are suggesting, though I am hesitant - if my power supply scheme works, it will be cheaper, and take up less space. I appreciate your input/interest very very much, Steve, thanks.  | ||
| Peter Maziar (mosfet) Username: mosfet Registered: 11-2006 |
Update: It works!!! Imagine that !! A 150 watt Music Man with a high-gain tube distortion circuit to replace the solid state clipping stage!! Voltages were hardly affected (in LO setting, I still haven't worked out HI yet, tomorrow is soon enough). All I need to do now is refine the circuits tone!! By the way, thanks for the diode info, Steve. You were a big help. | ||
| Peter Maziar (mosfet) Username: mosfet Registered: 11-2006 |
Update: Well, it sounds kind of like a cross between a Fender, a Marshall, and a Boogie, but still has a Music Man flavour. Pretty hot, and pretty much as high gain as I want it. I am having a ball playing with all of the parameters. Frequencies are beating. I may decide to revoice this entire channel to take advantage of the new tube circuit. So far, it is a great big thumbs up. I'm keeping the clean channel essentially stock. Do any of you have an opinion on how the dirty channel should sound in this amp? | ||
| Peter Maziar (mosfet) Username: mosfet Registered: 11-2006 |
Well, if anybody out there is interested, my dirty channel is pure tube now, with no solid state distortion at all. I can make it sound like a Fender, then with a flick of a switch, make it into a Boogie with TONS of gain! And I can turn down my guitar, and clean it up. Maybe the best part is that the first channel is stock, so I fully retain the original tones too! As soon as I have physically installed the circuit into the amp, channel switching is next, including phase and reverb. This is going to be one badass HD150! Nobody will ever be able to complain about the solid state in this amp ever again!!! I wish everybody out there could hear what I am hearing! It is just plain mean!!! |