high gain lee jackson gp 1000

[billyz]

@billy, on most gp1000s it is an internal trimmer, but on mine it is a minipot on the back of the chassis

@rune, do you have a better schematic to work from? i would greatly appreciate an upload....

Oh yeah, I remember now. Getting old.

[Gorhrut]

rune, how much did you say the tech in finland would charge you to fix the pcb issues? i might be willing to go half in with you (send money via paypal) if you can promise me and billyz some high quality pics when its done so i can get the same fix.


im gonna try making my own with point to point wiring or mabe on an eyelet board or something but i may as well fix the one i got too.....


first and second stage were easy to draw up on a layout, just based it on a fender champ layout and changed the values. its gonna take some time to layout the rest though....end game, im thinking im gonna add the vht 2/90/2 circuit with this and just make it a complete head.

[Rune]

Distortion is connected to R201 on tube 1 for starters. That is a typo which fucks up the whole schematic.

[Gorhrut]

i know this is late but, whatev...

just checked and p100 on mine is for sure 1M, like the schematic says.

[Rune]

Very weird. Could swear it was 10k, have to recheck later.

[Gorhrut]

[img2176]http://i.imgur.com/GvnbJxC.jpg[/img]

i think this is fixed now???

if anyone sees mistakes could u fix it really quick with ms paint? thats alot easier than trying to figure out what people mean through text...

[billyz]

[img2176]http://i.imgur.com/GvnbJxC.jpg[/img]

i think this is fixed now???

if anyone sees mistakes could u fix it really quick with ms paint? thats alot easier than trying to figure out what people mean through text...

Without seeing the preamp again I don't know. I would not do it that way myself. I would use a more standard level control setup. With the pot to ground. But then I don't know bout r17 either. Also, I would check to see if it has a split plate load formed at r205/r206.

That is what would good about hand wiring one on a turret board. You could try different con figs more easily.

You can verify those things with an ohm meter first.

[Jana]

Delete P100
Connect R17 to ground
Delete everything related to Master 2
Connect C4 to P6

[Rune]

Oh forget what I said about distoetion being on first tube, it is on the second, but need to open my 88 to draw a new schematic, turns out the one I had for GPSP is wrong too. No wonder it's noisy when parts are totally messed up. Most of the resistors are messed up on the tubestages or simply not added at all. This schematic sucks, written by german amatures and my famous by that Jon Woodworm guy from Bodom forum.

Want proof, okay then tell me where R200,201 and why R207 is an ouput resistor and nowhere near the distortion then. I believe R202 should be connected to distortion, but I only got these old unclear pics to study at the moment.....

[Smokebreak]

Delete P100
Connect R17 to ground
Delete everything related to Master 2
Connect C4 to P6

^ That's what I was thinking, for a straight OD amp at least. Then again, Mesa had that Fender 3M3(220K/R17 here) in parallel with the whole OD section. MKIIC+ comes to mind.
I would think there has to be some attenuation between the 4th stage and the master(s), even with the higher Rk's. Maybe not.
Maybe the 220K goes to ground off 4th stage, and the OD pot isn't a rheostat but wired as a voltage divider. Maybe the entire OD section is just plain wrong. Either way, I don't see how this amp could not oscillate at full tilt, as drawn.
Interesting thread.

[Gorhrut]

i just erased all the push/pull features from the original schematic so its very likely that the OD section IS completely messed up....idk.

i guess this is where i try it all out and see....

[Meat&Beer]

Delete P100
Connect R17 to ground
Delete everything related to Master 2
Connect C4 to P6

That, yes. R17 may want to be a pot at first so you can decide what would be best for this grid leak portion of the divider going into V2A. When you have a happy result, measure the pot and replace with a fixed resistor.

+1 What BillyZ said about the gain pot, also. Lug 1 should be your input from C9, Pin 2 (pot wiper) should be the output to the voltage divider for V2A, and pin 3 to ground.

Do you guys really need two separate outputs as in Masters 1&2? I don't see a reason, really. Enlighten me if there is one, of course. That's a half a tube you could do something way more useful with there...

[Gorhrut]

[img2176]http://i.imgur.com/KN9oPrz.jpg[/img]


is this looking better?


i had the two masters on there because they were on the original. not really needed. stereo was the big buzz word at the time so lee jackson did this setup to sell it off as stereo amp

[Smokebreak]

Oh forget what I said about distoetion being on first tube, it is on the second, but need to open my 88 to draw a new schematic, turns out the one I had for GPSP is wrong too. No wonder it's noisy when parts are totally messed up. Most of the resistors are messed up on the tubestages or simply not added at all. This schematic sucks, written by german amatures and my famous by that Jon Woodworm guy from Bodom forum.

Want proof, okay then tell me where R200,201 and why R207 is an ouput resistor and nowhere near the distortion then. I believe R202 should be connected to distortion, but I only got these old unclear pics to study at the moment.....

You're saying the distortion/OD/P2 is between the 3rd and 4th stages?

R200,201 are virtual center taps for the heater winding, if that is indeed the case and have nothing to do with the signal path. However, they could be grounded anywhere, and this may provided clues. Wherever they meet, this a ground point. Can you tell where they are grounded?

[billyz]

Oh forget what I said

Want proof, okay then tell me where R200,201 and why R207 is an ouput resistor and nowhere near the distortion then. I believe R202 should be connected to distortion, but I only got these old unclear pics to study at the moment.....

I see r200/r201 as the heater string faux center tap.