trouble with old brown Pro — OT?

[woodman]

my '62 Pro has developed an intermittent problem — at times, it'll drop to half-power or less. then, sometimes days later, it will kick back in with full power. this has happened twice at gigs, when the amp was hot, and once at home, when the amp hadn't bee cranked for days, and another time it was working fine at home but failed when i fired it up at a gig an hour later.

the power never cuts off completely — it just drops drastically and sounds like a Pignose turned up to about 3. i've rolled several sets of tubes into it but it's repeated the problem regardless of tubes. the amp was recapped a year and a half ago, so i doubt that's the problem.

my trusted amp tech has been through it twice (with a fine-tooth comb the second time) and can't find anything wrong ... this being the trouble with an intermittent problem: he has to witness it to get any solid idea what's wrong.

but just like when you take your car to the mechanic and it won't repeat the malfunction, the amp has fired up full power with no problem each time i took it in. no mechanical manipulations, like jiggling the tube sockets or speaker cord, will make it malfunction.

my tech has suggested it could be the output transformer giving up the ghost, as they can go intermittent when they're about to fail. he's offered to slap a loaner OT in there to see if it cures the problem — a sweet deal in this day and age. (he's an old friend and the only tube amp specialist i know of in the region.)

but before i do, wondered if anybody had any ideas on this? there's nothing more maddening than an intermittent problem! [BTW: the PT had to be replaced last year ... maybe these xformers have just gone as far as they can go.

[Groovey Records]

Very strong possibility but I'd try the Rectifier first

[woodman]

swapped out all tubes including recto, no change ... guess i'll go ahead with the OT swap and see if it solves the problem. it'll undoubtedly change the sound of the amp, but i need the dang thing to work dependably ... if the OT is the problem, maybe i can shop around for an equally sweet-sounding one (if they exist!).

[Groovey Records]

Try Skip Simmons he may have a old stock OT

http://www.skipsimmonsamps.com/

[DMace]

There are few things on earth more exasperating than an intermittent problem. I hope it's not the OT, because that's a good part of the tone of that amp. But I guess it's an inevitability with all old tube amps. Transformers, like most parts, have a lifespan. I'm dreading the day the OT goes on my '66 DR and '65 Princeton.

[refin]

Well,I had that problem once before in a BF Vibrolux Reverb...........it was an intermittent driver tube.I know that probably doesn't help,since you changed all the tubes.
BTW,woodman,still diggin you and your band,great sound!

[cousinpaul]

I had the same problem as refin. You might try cleaning and retensioning the PI tube socket before you do the OT swap. They can get loose and grungey over time. Best of luck. I'm hoping it turns out to be something simple.

[stantheman]

Woodman - I'm sure he checked this but the solder joint from the Ground Switch? Sounds like something is touching and arcing - perhaps that is why power is not completely lost.

[woodman]

we went through the whole amp from stem to stern again this afternoon, even flexing the board to make sure no solder joints were invisibly flooky ... nothing turned up.

so we went for the dreaded OT transplant! HERESY WARNING: actually, the $53 loaner he popped in there sounds better than the stock '62 xformer! more cut, more even frequency response, just generally ballsier. admittedly, my testing was in the friendly confines of the Woodshed — i'll test it onstage Friday night to make sure it's not illusory.

so: IF i get through the gig with no malfunction, thus indicating a strong likelihood that the OT is indeed the problem, is Mercury Magnetics worth the dough? i notice they've got two choices:

FBPRO-O Brown $100.00
FBPRO-OM Brown 2, 4 & 8Ω taps $150.00

what's the diff?

[DMace]

Originally Posted by woodman

we went through the whole amp from stem to stern again this afternoon, even flexing the board to make sure no solder joints were invisibly flooky ... nothing turned up.

so we went for the dreaded OT transplant! HERESY WARNING: actually, the $53 loaner he popped in there sounds better than the stock '62 xformer! more cut, more even frequency response, just generally ballsier. admittedly, my testing was in the friendly confines of the Woodshed — i'll test it onstage Friday night to make sure it's not illusory.

so: IF i get through the gig with no malfunction, thus indicating a strong likelihood that the OT is indeed the problem, is Mercury Magnetics worth the dough? i notice they've got two choices:

FBPRO-O Brown $100.00
FBPRO-OM Brown 2, 4 & 8Ω taps $150.00

what's the diff?

Q: if the $53 loaner sounds great, why not just get one of those?

[Groovey Records]

what speaker you going to use

Original Professional's and the TV pannel had a 15" field coil speaker

Later both the wide and narrow Pro a 15" Jenson

your brown A Jenson or Oxford 15"


All of these are 8 ohms

I think the more expensive OT may been used for more then one model

ie 2x12 or 2x10 0r 4x10 like the Tremolux blonde or Vibroverb Brown or Blonde Bassman

[woodman]

mine's totin' a Weber 15A150-O. works real well for me.

Q: if the $53 loaner sounds great, why not just get one of those?

Believe me, that's looming in my mind. but it's all theoretical til i try it in a gigging situation ... i've had too many great "living room" sounds that fizzled onstage to make a premature judgment. we'll see Friday night if it can rally that call to glory!