JCM 800...name that mystery knob...

[RJF]

Just picked up a JCM800 2203 horiz input with a 1960AV cab and it has 7 knobs. THe knob doesn't do anything at all, and other than that it appears to be stock. Anyone tell me what this might be, by looking at the wiring?

 

[RJF]

Also, ballpark figure on what these are going for? 1986 horizontal input 2203 with a 5/10 condition headshell with tan cloth. Got this through a trade deal and am not sure I want to keep it.

 

[311boogieman]

Interesting for sure.

It doesn't do a damn thing? The pics don't blow up for me very well but I guess I'm assuming it is some sort of master volume mod. I'm not an Amp Techie type person though.

Congrats on the amp non-the-less.

There is a cool Look Up link in my sig (allofcraigs) that might help answer your question on value.

 

[Shawn Lutz]

I can't really tell but almost looks like it is tied to the inputs like selecting high or low inputs

 

[RJF]

There is a cool Look Up link in my sig (allofcraigs) that might help answer your question on value.

That is a cool link!

Another thing is there is no label on the tubes. All it says is "made in Germany" across the bottom of the glass and they have black basses. EL34L's too btw.

 

[LP Freak]

Try pulling the knob out.

 

[glip22]

Try pulling the knob out.

Exactly. It has an added tube right there. Does no one see this. Pull pot engages the stage. Should be added gain stage or even two stages. Looks like another pull knob on the preamp pot. Probably adds in two gain stages. That amp should cook if done right. Mods look clean. Wire you see coming from the jacks goes to the grid of the added tube.

 

[Kapo_Polenton]

Try pulling the knob out.

Exactly. It has an added tube right there. Does no one see this. Pull pot engages the stage. Should be added gain stage or even two stages. Looks like another pull knob on the preamp pot. Probably adds in two gain stages. That amp should cook if done right. Mods look clean. Wire you see coming from the jacks goes to the grid of the added tube.

I was about to say, I see a preamp tube socket and a pull pot. That to me would mean gain stage. You guys need to spend more time on RT looking at amp guts and arguing about authenticity!

 

[PBGas]

I thought it looked like the mysterious Van Halen "dimmer switch".

 

[RJF]

OMG, I'm a freakin' idiot. PULL THE KNOB OUT!

Woah..... uh yeah.... it adds another gain stage.... Sounds like a REALLY HOT tube screamer or something up front. This thing cooks pretty good.

Pictured is the only two stickers I see on the chassis. Anybody recognize anything? I thought the city of LA sticker was kind of weird.

Obviously it must of had a pair of stickers on the grill cloth of the head, but am thinking about trying to dye that black or something. The tolex is in decent shape actually.

 

[LP Freak]

Try pulling the knob out.

Exactly. It has an added tube right there. Does no one see this. Pull pot engages the stage. Should be added gain stage or even two stages. Looks like another pull knob on the preamp pot. Probably adds in two gain stages. That amp should cook if done right. Mods look clean. Wire you see coming from the jacks goes to the grid of the added tube.

 

[glip22]

OMG, I'm a freakin' idiot. PULL THE KNOB OUT!

Woah..... uh yeah.... it adds another gain stage.... Sounds like a REALLY HOT tube screamer or something up front. This thing cooks pretty good.

Pictured is the only two stickers I see on the chassis. Anybody recognize anything? I thought the city of LA sticker was kind of weird.

Obviously it must of had a pair of stickers on the grill cloth of the head, but am thinking about trying to dye that black or something. The tolex is in decent shape actually.

La sticker might mean whoever did mod was a pro and placed the electrical safety sticker of LA county there meaning they may be certified or something to say the work is safe electrically.

 

[RJF]

OMG, I'm a freakin' idiot. PULL THE KNOB OUT!

Woah..... uh yeah.... it adds another gain stage.... Sounds like a REALLY HOT tube screamer or something up front. This thing cooks pretty good.

Pictured is the only two stickers I see on the chassis. Anybody recognize anything? I thought the city of LA sticker was kind of weird.

Obviously it must of had a pair of stickers on the grill cloth of the head, but am thinking about trying to dye that black or something. The tolex is in decent shape actually.

La sticker might mean whoever did mod was a pro and placed the electrical safety sticker of LA county there meaning they may be certified or something to say the work is safe electrically.

Sweet.

 

[OUTLAW1969]

......Or that the amp was originally bought and "utilized" by an LA County teaching facility, before the mod was done years later. My cousin works at a state teaching facility where everything is inventoried in a similar fashion (except updated to barcodes these days), and all electronics have to be maintained quarterly.

 

[RJF]

Well, who ever did the mod must have known what they were doing. This thing sounds great. Been jamming away at ear bleed volume for the last few hours. For some reason, the more I play through it, the harder it is to put the guitar down. Sounds just so "alive." I can see why some of you guys really like 800's. It has so much gain with that knob pulled out, thick and crunchy with minimal compression. Sounds so "open." I prefer the knob pulled out vs. it pushed in (stock) and a TS808 in front. This amp needs no boost. Plenty of gain on tap. More gain than my old 4100 dual reverb. I figured I would just turn around and sell this, but I'm struggling with that idea...

 

[glip22]

Ask Friedman to take a look at it. It looks like it's an HBE mod copy. I see that stamp on it. 1 meg Alpha pull pot,, small upright tag board at the added tube, etc.. What does the other pull pot do, add even more gain? Hard to see where the leads run.

 

[RJF]

Ask Friedman to take a look at it. It looks like it's an HBE mod copy. I see that stamp on it. 1 meg Alpha pull pot,, small upright tag board at the added tube, etc.. What does the other pull pot do, add even more gain? Hard to see where the leads run.

Wait, there is ANOTHER push pull pot?

I'll be back....

I'm back....

Holy crap. METAL! This thing has loads of gain with the second knob pulled and sounds awesome. The funniest part is the PO on this amp didn't even know that this existed. I asked "whats this 7th knob over here do?" He said "I'm not sure, I doesn't do anything."

 

[glip22]

Ask Friedman to take a look at it. It looks like it's an HBE mod copy. I see that stamp on it. 1 meg Alpha pull pot,, small upright tag board at the added tube, etc.. What does the other pull pot do, add even more gain? Hard to see where the leads run.

Wait, there is ANOTHER push pull pot?

I'll be back....

I'm back....

Holy crap. METAL! This thing has loads of gain with the second knob pulled and sounds awesome. The funniest part is the PO on this amp didn't even know that this existed. I asked "whats this 7th knob over here do?" He said "I'm not sure, I doesn't do anything."

Thats what it looked like to me. First pull pot engages another gain stage(half of added tube). Second pull pot engages yet another, other half of added tube.

 

[RJF]

I just emailed Friedman amps. Hopefully he will be gracious enough to take a quick look at the pics.

 

[londaxe]

I think I might have ended up with this amp. It seems to have had a few things changed since this thread was started, but nothing major.

Did anyone ever find out who did the modifications? It sounds incredible.