JTM 45/100 build

Repairs, trouble shooting, modding and so on.

Re: JTM 45/100 build

Postby neikeel » Wed Jan 01, 2014 9:13 am

David B wrote:Schematic for the SVT, has 22-ohm/1watt screen resistors & 10 ohm / 5watt plate resistors...
Question is in a typical Marshall circuit will a 3watt screen resistor shut down the tube faster than the HT fuse?

http://www.webphix.com/schematic%20heav ... p6146b.pdf


I doubt it would be faster than a fuse. No the leak did not have an HT fuse - common mod wast to fit one discretely. Sadly I sold mine to buy more guitar orientated stuff! (of course Jim Marshall's first amps were leak powered IIRC?
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Re: JTM 45/100 build

Postby Stu » Wed Jan 01, 2014 11:45 am

I didn't know that. I think I'd read something about early Matamps being based on a Leak design, but I could have imagined that. :?:
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Re: JTM 45/100 build

Postby dai h. » Wed Jan 01, 2014 6:50 pm

a dedicated screen fuse would seem to give more protection (as suggested by "cerrem" on a PP thread recently, although having no resistor there (as the amp user seemed to favor in terms of the sound in *that* thread(not this one)) wouldn't give any protection (current limiting) while in operation I would think). I also (very vaguely) recall somebody (Randall Aiken?) saying (essentially) that a "ceramic wirewound resistor fuse" (as KFischer suggested over the hardier vitreous enamel-type wirewound) wouldn't make a very reliable fuse.
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Re: JTM 45/100 build

Postby neikeel » Wed Jan 01, 2014 8:01 pm

Stu wrote:I didn't know that. I think I'd read something about early Matamps being based on a Leak design, but I could have imagined that. :?:


Apparently he started making Bass amps with a 1x18 cab using Leaks before Ken Bran and Dudley Craven became involved.
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Re: JTM 45/100 build

Postby David B » Thu Jan 02, 2014 10:52 pm

dai h. wrote:a dedicated screen fuse would seem to give more protection (as suggested by "cerrem" on a PP thread recently, although having no resistor there (as the amp user seemed to favor in terms of the sound in *that* thread(not this one)) wouldn't give any protection (current limiting) while in operation I would think). I also (very vaguely) recall somebody (Randall Aiken?) saying (essentially) that a "ceramic wirewound resistor fuse" (as KFischer suggested over the hardier vitreous enamel-type wirewound) wouldn't make a very reliable fuse.



I was reading some of Kens stuff, he said some early metal panel 100's had 2 watt screen resistors and if they haven't burned open yet to replace them with 5watt resistors.

Also mentioned Hiwatts had one weakness that being small wattage screen resistors and again recommended larger 5watt ww resistors in all models as well..Using a fuse is interesting but probably overkill...
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