New build Garnet herzog inspired JCM800

[nandrewjackson]

A friend of mine was telling me about the Garnet Herzog, I'd never heard about it before.  For those that don't know,  its sort of a fender champ with a power resistor in place of a speaker,  and a line out, so you can use it like a distortion pedal. The amp, including the power tube, can be cranked all the way up, and since the line out comes after the power tube, you can run it into the front end of another,  larger amp, and get the sound of power tube overdrive at any volume.


Well,  I have some champ style transformers and most other components,  so I ordered a little hammond  10 x 6 x 2 box, and I'm building a full 2204 (jcm800) preamp into a single ended champ style output "herzog".


I've built jcm preamps and I've built a few champ circuits,  so I'm not expecting too many curveballs.  I just thought I'd share my project here on the forum. 


It will have diode rectifier.  I'm not installing a power switch or standby switch,  since it will be a pedal.


I will install a switching jack at the normal speaker connection,  so it can be ran into a speaker if desired. 


I plan on using a middle of the road cathode bias R/C on the output tube, to accommodate either 6L6, 6V6, or EL34 operation. I'm hoping to find a resistor value that will operate for all 3, maybe making some run hot, some cold. If one resistor value won't do it, I guess I'll add a switch that will need change power tube cathode resistor for each tube type. I haven't plugged any numbers into bias formula yet,  I'm hoping I don't need to install switchable resistors.  We'll see.  . . . .


I've only got transformers,  bypass switch,  pots, and "output" resistor mounted so far.

[nandrewjackson]

Pics. Its missing the 25k middle pot, I don't have any here.

[nandrewjackson]

Pic

[PRR]

> either 6L6, 6V6, or EL34 operation.

Randy doesn't play it right in the YouTubes I am finding. Find the January 1970 version. Now, how can you tell WHAT tube is in that racket?? This isn't the difference of 9% THD or 13% THD you might get from two tube types. It is ALL 369% THD or more.

Go ahead but _I_ think it is a mind-game, not a useful trick.

EDIT: https://www.amazon.com/Best-Guess-Who/dp/B00138F46S scroll down to track 5, sample plays in the browser.

[nandrewjackson]

 
I don't disagree,  PRR.


that's why it's got the 2204 preamp,  I'm *hoping* to hit the sweet spot on the power tube.


It will have 2204 gain, master vol, and line out pots. There should be real brown sound hiding in those 3 pots.


I'm only hoping in one hand, and keeping an open mind about what fills the other hand. 

[nandrewjackson]

Tube sockets, 1/4" jacks,  and power cable installed.  No circuit wiring yet.

[kagliostro]

Ciao Nandrewjackson

Nice idea 

Only one thing, don't forget the cap across the primary OT winding

http://el34world.com/Forum/index.php?topic=25594.msg277563#msg277563

(This must be used only when the amp is in Herzog Mode and if you have the treble problem)

Franco

[tubenit]

I built a D'Mars ODS some years ago and use a big resistor and a H&K Red Box so that it could be run into a PA system for a "zero volume stage" (can't remember the correct term?).

It worked out great and got years of good use until it was replaced by a Helix something.

With respect, Tubenit

[nandrewjackson]

It's up and running. It sounds like it should. 


I used Hoffman 5e1/5f1 specs for the output stage, with the addition of a 68k grid stopper on the driver triode grid.  And I jumpered pins 1 and 8 on power tube socket for EL34.


I plugged my DMM readings into rob robinette bias calculator for 6V6, 6L6, and EL34, all the are in the green.  I'm glad to not have to add different cathode resistors with a switch or something like that.


It's all point to point, I only used 1 terminal strip, and that is for the 4 rectifier diodes.  I used teflon tubing on the leads if they were about 1cm or more.


There's a 16 gauge bare ground buss zig zagging around.  One main chassis ground, and one main circuit ground. It's got noise. There are a couple signal lines that might get changed over to shielded .


I used a DPDT toggle switch to replicate the high/low input jacks. 


I haven't tried it all in herzog mode, I've been playing it into a speaker so far.

[shooter]

Nicely done !!

find a buddy with a quality packed 4 X 12 cab, play in a smallish "venue" with good acoustics,  heads will look up 

[nandrewjackson]

Thanks for the replies, everybody. 


I'll post again after I try it out in herzog mode in front of my 50 watt ab763 combo.


I tried to cut out a piece of clear lexan/plexiglass for a bottom cover plate, I thought that would look neat. The dang plastic broke, so I guess that was a sign to take a break from it for a minute  .

[nandrewjackson]

How did you like your D-style build, Tubenit?


I haven't tried to build one of those yet.  I haven't played one, either. 

[nandrewjackson]

Herzog mode was very harsh in the high frequencies.  I did add a cap for that, on the line out pot. Swiper to ground 0.003uF.


Kinda weird how that worked out, landing on 0.003uF. That's the stock value on some garnet schematics,  but it's placed from 6V6 plate to ground. I didn't want to place it there, because I plan on using this as an amp as well as a herzog, and I didn't want to alter the amp mode sounds. So I decided on swiper to ground for the placement. I tried several different caps, starting at 1000pF, and went up from there. I know the technical aspects of the 2 locations are very different.  Plate to ground at OT primary, and OT secondary  , wiper to ground after a 1M pot and a 150k resistor,  is it just coincidence that a 0.003uF works well in both places?


Really getting some good sounds,  in amp mode and herzog mode. 


A side note, I've built a few jcm800 2204 preamps,  and never bothered to include the hi/low input option.  I always wired them up hi input only. Well, well, well, the low input can get some nice sounds too :)


Schematic drawn up for those interested,  and screenshots from robinette bias calc.

[nandrewjackson]

EL34

[nandrewjackson]

6L6

[nandrewjackson]

6V6