The Amp Garage

If your talking about the NFB loop, I'm using one 22k resistor, but each preamp has it's own lead to that resistor. I see a couple of problems with the way the NFB is employed here. First, that cap looks like a dead short to ground to the NFB circuit. Look a the schematic for a tweed champ to see h...

Don't mean to hijack but....

Structo, I have one of those exact chassis sitting in my shop. Can I ask how you shorten the chassis and what did you end up building with it?

I'm just starting a mono d-lator. I'm using a hammond 261C6. It will mount on the inside of the 1U rack chassis on the side (too tall to mount on the bottom of the chassis). As with the Allen, you need to use a full wave rectifier instead of the doubler.

Finally did what you suggested. I pulled the board out and biased with a 9v. I settled on 22k and a 2.2k giving me 22vsupply and 12v on the drain.

Now, how do I adjust the trimmer on the FET board? Right now I have it about 3/4 of the way up.

Thanks for the help,
Dave

It's one of Funk's boards. Got these parts years ago, just getting around to building it now. Here' a pic of the back side of the board.

Resistance from source tracks perfectly with rotation of the temporary pot I have installed.

I'm getting the same results with the MPF102 as well. Please have a look at the board and see if I have wired incorrectly, I am unable to find an error.

FET board looks just like in this post:

http://ampgarage.com/forum/viewtopic.php?t=3205

and I double checked the spec sheet. I think I have an MPF102 to try from rat shack.

I forgot to mention, I did check the drain resister, it measures a full 10k. Yes powering with the amp's PS. I get a range of voltages up to 16v, they track down toward 0, but I haven't used the full range of the pot (wasn't sure if shorting the drain to ground would harm it).

I am trying to bias the FET before completing the finally tweaking of the plate voltage in the preamp for the #102 of finishing up. I have a 25k pot in place of the 12k resistor shown in the schematic. I used a 2N4416 FET in the circuit. Problem is, I have the same voltage on either side of the the ...

@Luthierwnc

May I ask the value of the mid pot your using with the strat switch?

I have a few of extra 820mH Wilco inductors, seems like the value might be close. If anyone wants one, they can have it (I'll keep one for myself). PM me.

How do you like the sound? I mean when you use it as an effect. It's been a while since I've fired it up, but it sounded great as a stand alone amp (plugged into a pair of vintage Jensen P12Qs) and ok in front a the fender blackface clone (all I had at the time). I think it would sound better throu...

I built a PTP Herzog (the first version, not the one with the relay) last year. A friend of Gar Gillies gave me an NOS Herzog chassis.

I added the switched speaker jack from the second version and switchable NFB. Allows me to use it as a slightly higher gain Champ.

That picture is practically my desktop background right now, although I'm doing a high-plate non-HRM.