More Mods for my JCM800: New Grounding Scheme, Rework the Bright Cap Switch, Add a Switchable Clipping Circuit!!!

eSGEe said:
--- wait wait wait -- I have a solid state Peavey that was BLOWN UP in a NUCLEAR accident -- and I BUILT a SH-iTTY wood cab for it -- and it works -- was THAT "maintenance"?
View attachment 42593

wow ----- the Jackson Lives with Robert in Californication----- the KUSTOM is long gone the MESA is left the realm of logic.........................still have the Hartke-- the strat and the dog toy! BUWAHAHAHHAHAHAHAH
Click to expand...

Did you check that with a Geiger counter?
 
:bump:

I can't get myself to just button-up this amp and enjoy its awesomeness. The last couple of weeks I've been experimenting with other minor tweaks...:

1: Removed the 470pF bypass cap at the plate of the first gain stage that I added on a long time ago. No need for a bypass cap here.

2: Repositioned the V1 shielded grid wires, for aesthetic reasons only.

3: Replaced the Preamp control's silver mica bright caps with a pair of polystyrene caps at the suggestion from 67plexi. I likes what I hear... thanks, 67plexi!

4: I experimented with different values of the input grid stopper resistor. Stock is 68k. I tried 33k and 10k. I think I like the 33k the best. The smaller the resistor value is at this position, it will allow a tiny bit more highs, but it will add more sensitivity and response to the feel of the amp. 10k was too much, and I settled on the 33k. No added RF interference was noticed with the smaller valued resistors.

5: Completely rebuilt a back panel assembly for the amp's combo cab. This would be the 2nd time I've done this to this cab.

6: Replaced the damaged Scumback speaker with a new Scumback speaker. And yeah, I still haven't gotten over my oops on this... :BH:.

But wait... There's more before I'll shut up, ha ha! As I wait yet for more parts to come in...:
1: I'll be making the 33k grid stopper resistor permanent after I get one with a 2-watt rating.

2: Add a properly rated thermistor to achieve a soft-start inrush current limiting capabilities.

3: Add a .1uF DC-blocking cap between the added resonance control and impedance control.

4: One of the three filter caps is semi-old and looks out of place compared to the other two, and will be replaced.

5: Replace V1b's .015uF cathode bypass cap (Stock is .022uF) with a .01uF cap.

AND FINALLY... for now...:

6: The current power tubes are old have drifted quite aways apart. I have some SED Winged-C's in my stash just waiting for the right moment... :woohoo:
 
OK... For the grand finale in this latest round of mods for this old beast, I present y'all some more porn. As of today, with the exception of that little toggle switch, the front of this amp still looks very stock:
June 2020.JPG


This is the second time I've rebuilt the back panel. I also added labels for the Resonance, second Master Volume, Clipper, and gain-boosting controls. The swinging two-piecer:
Rear Panel Rebuilt 2020 (2).JPG


I got really lucky here! When sliding the chassis in and out, the bottom of the PT is gliding over the piano hinge:
Rear Panel Rebuilt 2020 (1).JPG


Spaghetti neatly assembled:
1026p_350p Bright Cap Switch (1).JPG


This is not a good pic of it... the cap and resistor treble peaking circuit is hiding the bright caps. But the added two-way bright cap switch is set up with the JCM's stock value of 1000p and alternate value of 350p. Lots of mojo with this combination:
1026p_350p Bright Cap Switch (2).JPG


I made an intended effort to install the a 'soft-rush' current limiting thermistor after the power switch:
NTC Thermistor after Switch.JPG
I don't understand why more amp manufacturers or boutique builders don't install these in their circuits? Fender and Mesa Boogie does! Cheap insurance for a dollar or so... :unsure:


And in the tube department, we have a couple Mesa branded 12AX7's, an old Philips JAN 12AX7, and a pair of semi-NOS Winged-C's:
June 2020 Tubes.JPG


In a nutshell: The amp can sound purdy and sweet, but it lives for viciousness and nastiness... :dood:
 
eSGEe said:
--- wait wait wait -- I have a solid state Peavey that was BLOWN UP in a NUCLEAR accident -- and I BUILT a SH-iTTY wood cab for it -- and it works -- was THAT "maintenance"?
View attachment 42593

wow ----- the Jackson Lives with Robert in Californication----- the KUSTOM is long gone the MESA is left the realm of logic.........................still have the Hartke-- the strat and the dog toy! BUWAHAHAHHAHAHAHAH
Click to expand...

Hey - that purple cable looks familiar.
 
Drumoid said:
Hey - that purple cable looks familiar.
Click to expand...
syscokid said:
:bump:

I can't get myself to just button-up this amp and enjoy its awesomeness. The last couple of weeks I've been experimenting with other minor tweaks...:

1: Removed the 470pF bypass cap at the plate of the first gain stage that I added on a long time ago. No need for a bypass cap here.

2: Repositioned the V1 shielded grid wires, for aesthetic reasons only.

3: Replaced the Preamp control's silver mica bright caps with a pair of polystyrene caps at the suggestion from 67plexi. I likes what I hear... thanks, 67plexi!

4: I experimented with different values of the input grid stopper resistor. Stock is 68k. I tried 33k and 10k. I think I like the 33k the best. The smaller the resistor value is at this position, it will allow a tiny bit more highs, but it will add more sensitivity and response to the feel of the amp. 10k was too much, and I settled on the 33k. No added RF interference was noticed with the smaller valued resistors.

5: Completely rebuilt a back panel assembly for the amp's combo cab. This would be the 2nd time I've done this to this cab.

6: Replaced the damaged Scumback speaker with a new Scumback speaker. And yeah, I still haven't gotten over my oops on this... :BH:.

But wait... There's more before I'll shut up, ha ha! As I wait yet for more parts to come in...:
1: I'll be making the 33k grid stopper resistor permanent after I get one with a 2-watt rating.

2: Add a properly rated thermistor to achieve a soft-start inrush current limiting capabilities.

3: Add a .1uF DC-blocking cap between the added resonance control and impedance control.

4: One of the three filter caps is semi-old and looks out of place compared to the other two, and will be replaced.

5: Replace V1b's .015uF cathode bypass cap (Stock is .022uF) with a .01uF cap.

AND FINALLY... for now...:

6: The current power tubes are old have drifted quite aways apart. I have some SED Winged-C's in my stash just waiting for the right moment... :woohoo:
Click to expand...

Well, this thread is the first thread that has me wanting to get a Marshall - lol. Probably because I like doing the very same things you've been doing to this amp - lol...
 
Amp Mad Scientist said:
Did you check that with a Geiger counter?
Click to expand...


Cut him some slack, New bro Ampmad. ;) Adrian just reported in recently that he soldered. I am so proud of him and glad he got to use a nice new Soldering Iron. Some other cool things to remember, ESgee,,,,,,,,, Flux can be your friend in helping solder nicely, and it is also good to remember to clean your work when finished soldering.
 
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