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Ampeg B-15N needs help

7/21/1999 6:35 PM
Craig	Ampeg B-15N needs help I was asked to look at an Ampeg B-15N (not the point-to-point one; uses a circuit card) that has been blowing fuses and recently blew a Chinese 5AR4 w/Mojo Tone's stamp. I only just got it unloaded late last night after a gig, so I haven't done any troubleshooting yet. All I did was test the rectifier and found that it was dead. I asked what size fuse they had been using, but that info wasn't known. (3rd party transaction). This amp is currently being used in an college jazz program, and is primarily used by acoustic bassists, although some of the bebop guitarists dig it for its dark tones. I was wondering if anyone had any advice re: reliability of current production 5AR4s. The amp also has Sovtek 6L6s. Any comments re: these would be helpful too. The 6SL7s will all be replaced w/NOS JAN's where necessary. So far all I have been able to glean from opening the chassis is that the 1st filter cap (30uf/600vdc) is the original Mallory. So that will get replaced and obviously might be part of the problem. Didn't have any blisters or goup though. The last 3 filter caps, which are supposed to be 40uf/500vdc, are instead 47uf/500vdc, and appear to be fairly new. Any thoughts on the relative merits of returning to the spec'd 40uf would be welcome too. Also, anyone know a good source for Ampeg tolex and/or the rubber grommet chassis attachment parts that allow the chassis to hang upside-down when stored? This amp is pretty beat, cosmetically, and I want to encourage the school to restore it, and treat it from now on like an investment. Its totally stock except for the replaced electrolytics, and structurally sound. The chrome will clean up nicely I think - no major pitting or rust. It just needs a little TLC. Thanks, Craig

7/21/1999 6:35 PM

Craig

Ampeg B-15N needs help

I was asked to look at an Ampeg B-15N (not the point-to-point one; uses a circuit card) that has been blowing fuses and recently blew a Chinese 5AR4 w/Mojo Tone's stamp. I only just got it unloaded late last night after a gig, so I haven't done any troubleshooting yet. All I did was test the rectifier and found that it was dead. I asked what size fuse they had been using, but that info wasn't known. (3rd party transaction). This amp is currently being used in an college jazz program, and is primarily used by acoustic bassists, although some of the bebop guitarists dig it for its dark tones.

I was wondering if anyone had any advice re: reliability of current production 5AR4s. The amp also has Sovtek 6L6s. Any comments re: these would be helpful too. The 6SL7s will all be replaced w/NOS JAN's where necessary.

So far all I have been able to glean from opening the chassis is that the 1st filter cap (30uf/600vdc) is the original Mallory. So that will get replaced and obviously might be part of the problem. Didn't have any blisters or goup though. The last 3 filter caps, which are supposed to be 40uf/500vdc, are instead 47uf/500vdc, and appear to be fairly new. Any thoughts on the relative merits of returning to the spec'd 40uf would be welcome too.

Also, anyone know a good source for Ampeg tolex and/or the rubber grommet chassis attachment parts that allow the chassis to hang upside-down when stored? This amp is pretty beat, cosmetically, and I want to encourage the school to restore it, and treat it from now on like an investment. Its totally stock except for the replaced electrolytics, and structurally sound. The chrome will clean up nicely I think - no major pitting or rust. It just needs a little TLC.

Thanks, Craig

Replies:

Jim S. I have not had any problems with th... -- 7/21/1999 10:25 PM
john Martin Get a pair of NOS 7581 output tubes... -- 7/22/1999 2:29 PM