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previous: Tom Hi!I'm looking for ... -- 6/15/2000 4:06 PM

Re: Bluesbreaker/JTM45 schematic...

6/15/2000 4:32 PM
Peter S	Re: Bluesbreaker/JTM45 schematic... The JTM 45 differs from the 5F6a only slightly. They increased the size of the filter caps. The first Power supply resistor was changed from 4.7k to 10k. The mains B+ was dropped from 420-430VDC down to about 390VDC. The 27k Feedback resistor was taken from the 16ohm OT tap instead of 2ohms like on a Bassman. They used a 12AX7 in the first gain stage. Some models had a bypass cap on the summing resistors before the second gain stage. Some models had a larger bypass cap on the high treble volume control. Obviously they used a different OT and PT. I cant think of any other changes off hand without looking up the schematics. I'm sure there were a couple more. Most of these changes were pretty minor and it's obvious when you compare the tonal qualities of both amps....they sound very similar. As far as the schematic goes, it's quite readily available, but off hand I cant think of a place on the web to download it. I'm short on time right now but if no-one tells you where to get it by the time I check back in later, I'll scan a copy and send it to you. Peter S Kimerik Amps

6/15/2000 4:32 PM

Peter S

Re: Bluesbreaker/JTM45 schematic...

The JTM 45 differs from the 5F6a only slightly. They increased the size of the filter caps. The first Power supply resistor was changed from 4.7k to 10k. The mains B+ was dropped from 420-430VDC down to about 390VDC. The 27k Feedback resistor was taken from the 16ohm OT tap instead of 2ohms like on a Bassman. They used a 12AX7 in the first gain stage. Some models had a bypass cap on the summing resistors before the second gain stage. Some models had a larger bypass cap on the high treble volume control. Obviously they used a different OT and PT. I cant think of any other changes off hand without looking up the schematics. I'm sure there were a couple more. Most of these changes were pretty minor and it's obvious when you compare the tonal qualities of both amps....they sound very similar. As far as the schematic goes, it's quite readily available, but off hand I cant think of a place on the web to download it. I'm short on time right now but if no-one tells you where to get it by the time I check back in later, I'll scan a copy and send it to you.

Peter S
Kimerik Amps