Tweet
Hi Guys
I know this is a very old thread. But i think starting a new thread might be a bad idea.
I'm in the process of compiling a list of things to do to convert a Jcm 900 dual reverb to EL34.
Can anyone check my list and see if it it looks correct and maybe give me some feedback.
For starters I'm not sure about point 8. Some amps have a 47K feedback res while others have a 27k.
Herewith the list: (don't laugh)
1). Change the screen grids to 2k2 5W resistors.
2). Change the grid stopper arrangement so that each Grid has its own 5k6 resistor.
3). Remove the NFB components (56k//10n) that were added at the OT Violet wire on the 4ohm tap.
4). Change grid leaks R26 & R27 to 220k 1/4Watters.
5). Change R30 to 22k 1W in the supply line to the preamp tubes.
6). On the bias supply, change R29 to 15k 1/4W and R28 to 56k 1/4W.
7). Change PI plate load R23 to 91k 1/4W
8). Change NFB resistor R17 to 100k 1/4W
9). Remove the 4k7&22n network across R6
10). Add back the second 50uf section of the filter going to OT CT.
11). Change out C12 for a 630V related capacitor.
I know this is a very old thread. But i think starting a new thread might be a bad idea.
I'm in the process of compiling a list of things to do to convert a Jcm 900 dual reverb to EL34.
Can anyone check my list and see if it it looks correct and maybe give me some feedback.
For starters I'm not sure about point 8. Some amps have a 47K feedback res while others have a 27k.
Herewith the list: (don't laugh)
1). Change the screen grids to 2k2 5W resistors.
2). Change the grid stopper arrangement so that each Grid has its own 5k6 resistor.
3). Remove the NFB components (56k//10n) that were added at the OT Violet wire on the 4ohm tap.
4). Change grid leaks R26 & R27 to 220k 1/4Watters.
5). Change R30 to 22k 1W in the supply line to the preamp tubes.
6). On the bias supply, change R29 to 15k 1/4W and R28 to 56k 1/4W.
7). Change PI plate load R23 to 91k 1/4W
8). Change NFB resistor R17 to 100k 1/4W
9). Remove the 4k7&22n network across R6
10). Add back the second 50uf section of the filter going to OT CT.
11). Change out C12 for a 630V related capacitor.
Comment