Bringing a B-52 ATX100 back to life!

[andrewsrea]

A fully functional B-52 ATX100 head is selling for $300. If you like Fender clean, Mesa dirt and need an amp head that can handle the bedroom to a small theater no problem, then I recommend this amp (with a required mod listed below).

It is mostly a 3 channel Mesa Recto-verb 100w, with reverb on al channels, an effects loop and only the diode rectifier. It doesn't have the simul-class or some of the other scaling/tone features, but it nails the high-headroom Fender clean in channel 1 and Mesa high gain in channels 2 & 3. All foot switchable with effects loop.

This year I started repairing for the local Music Go Round, who recently took this B-52 in trade which was an awful deal for them. It was missing all 10 tubes (about $281 replacement for basic tubes at Sweetwater) and the back panel with fan (which isn't needed). They smartly decided to take it at a loss and 'trash it.' Instead of making me dumpster dive, they kindly gave it to me.

Luckily, I had all the required tubes in my 'used, but great' tube stock (worth about $170 in repair value to me). While I was diagnosing it on my bench, I found four of the filter caps were not functioning and the amp had an unbearable hum. Looking closer, I realized this was under-designed B+ power supply circuit (the second I've encountered this year). Basically, the amp was designed for 115v house power, which would provide 475v B+ when the tubes were installed and biased correctly. Most homes today exceed 115v and here in Missouri, 123v is common which results in >510v B+. The filter caps are rated at an absolute max of 500v (250v + 250v). Not enough overvoltage to blow them up, but enough to wear them to the point of intolerable hum in a few months of play.

MY REDESIGN of the FILTER CAP MOD: Replace the (2) 220uF-250v radial and the (2) 100uF-250V Chinese electrolytic caps, with (2) 220uF-350v and (2) 100uF-350v Rubycon (22k hours lifespan) electrolytic caps. Mouser part numbers: 232-350BXW220MEFR18X and 232-350BXW100MEFR18X. This mod adds about 90v of over-voltage protection and should last 20 years. Cost me <$25 delivered.

I am going to play this one a bit and then sell it off. PM me if you are interested.

20221113_102556.jpg

20221113_102610.jpg

20221113_102704.jpg

20221113_102713.jpg

[Rollin Hand]

I have wanted to futz with one of those beasts for some time now, but it's hard to justify 100 watts for home play (and believe me I've tried) when modelers can do what they do in headphones.

By the same token, every time a Traynor Custom Special 100 comes up nearby, I get interested.

[andrewsrea]

I have wanted to futz with one of those beasts for some time now, but it's hard to justify 100 watts for home play (and believe me I've tried) when modelers can do what they do in headphones.

By the same token, every time a Traynor Custom Special 100 comes up nearby, I get interested.

It has one of the best master volumes I've ever heard and can actually do very good 70dB conversation-type volumes, with a great tone. The drawback is it doesn't do a rock or country 'edge-of-breakup tone. It has a super-high headroom 'V-shaped' clean and Mesa type distortions.

[Rollin Hand]

That was one of the things about Bugera: on the 6262, the master has a nice,smooth sweep. On the Peavey it copied, the master seemed to be "nothing...nothing...nothing...TINNITUS!"

[andrewsrea]

That was one of the things about Bugera: on the 6262, the master has a nice,smooth sweep. On the Peavey it copied, the master seemed to be "nothing...nothing...nothing...TINNITUS!"

JCM800's are like that as well as many others.

[Rollin Hand]

The Traynor CS100 has a huge advantage in that it's switchable down to 30W operation. I wish more big amps would do that, as it really helps guys like me not get divorced or killed by the neighbours.

Right now, the most tube watts I have is 20 (my red stripe Bandit has more). And I am OK with that.