tsl 100 screen grid resistors

[bmd]

marshall jcm 2000 tsl 100 anyone have thoughts on using 5k6 screen grid resistors. It came from factory w/ 220k's .The schematic actually shows 5k6

[Enzo]

Hi bmd, welcome to the forum.


Um... we need to get some terms straight.

Screen grids are grid #2 on the pentodes. That is pin 4 on the tube. The screen resistors are those 1k 5 watt rectangular cement ones up on stilts. R60,65,74.76.

The control grids, or just grids, are pin 5.

What schematic number do you have? Mine shows 220k grid stoppers. Mine is TL60-10-02.DGM, issue 3.

[bmd]

Hi Enzo,
You've helped me a lot before with this same amp. It's been working fine, however, I saw this thing on the internet where this guy said to replace grid blockers, R7, R10, R66 & R70. My schematic drawing TSL100/TSL122 # TL10-60-02.DGM iss 5. I actually replaced those with 5K6, amp seems to work fine & has a lot bluesier tone. I did notice my input power transformer was a little warm to the touch, never really paid attention to that before so I don't know if that is normal. Do you think this will hurt the amp because I like the tone? Thanks for your time and input.

[Enzo]

220k is a lot larger than I normally expect for grid stoppers, so no it won;t hurt the amp to install 5k6. Those resistor values have nothing to do with transformer heating.

[ogeecheeman]

Hi Enzo,
Gordo here.have a JCM2000 with a burned foil that was repaired by ?
The trace ties pin 4 of valves 3 and 4 (screen) to output tranny. I am curious as to why (aside from a possible bad tube and/or socket) what might cause a repeat of this with new fresh tubes.Same socket,this time the tube was burned before the HT fuse opened.
Your thoughts ,as always, appreciated.

[Jazz P Bass]

Not too sure how you are numbering the pins.
Pin 3 is the plate, high voltage pin that connects to one half of the output transformer primary.
Pin 4 is indeed the screen pin, but it does not (and should not) get connected to the OPT.
Link: http://www.hometheaterhifi.com/volum...be-diagram.gif
Burned foil is burned foil.
It became a fuse from an overcurrent condition.

[drewl]

There has been alot written about these amps and certain problems that occur.
Yes, those 220K resistors are odd, and most people swap them out for the standard 5.6K

here's a site with alot of useful info:
The Marshall TSL122 JCM2000 Repair/Mods Page