just bought an ampeg b25b

toobalicious · #1 06-04-2010, 10:03 PM

got what i think was a great deal on it.... apparently, movers had broken one of the power tubes some years ago, and it has sat in the closet since. it appears in very good, but dirty condition. blah blah...

i have 6L6GC's out the yin-yang, so i installed a pair at dude's house and powered it up before i bought it, to which it happily complied. one of the preamp tubes is badly microphonic, and the pots are scratchy, but it is doing what it is supposed to. oh yes, the ground pin has been broken off of the plug---- i like to live on the edge, i guess. of course i will replace it post-haste.

yes, yes, i know it is old, that the caps need changing, that the bias needs to be checked...

so.... my first amp with 7027a. i know that the 'pegs are wired as such that 6L6-type tubes can be substituted, but i have also read about the sky-high voltages present in said 7027a 'pegs, and i realize that the sovtek-made 6L6's i tested it with may not be up to the task.

any tube recommendations? ive been kind of hung up on JJ 6L6's recently, but that is mostly because of the reliability i have experienced--- and the amps they are installed in sort of dont suck... since under my ownership this amp will likely never see a stage, emphasis can be placed on "great-sounding" as opposed to "long-lasting", within reason, of course.

any thing else i should take into account? i am excited to get this thing checked out so i can play it.

pics to prove it:

JimmyM · #2 06-04-2010, 10:32 PM

why not jj's? almost recommended going nos for them, but then i priced them...no thanks!

jimbilly · #3 06-05-2010, 12:08 AM

Nice!, that looks clean too! My tech tells me that the 'coin base' Sovtek 5881 (6L6GC equivalent) handles high voltages.

MAMMOTHvolume · #4 06-05-2010, 04:26 AM

el34's will take it aswell if the PT is up to it

coreyfyfe · #5 06-05-2010, 07:23 AM

6L6GCs are designed for higher voltages and should hold up ok. Why not just order some 7027s? They're in production from JJ and Sovtek.

toobalicious · #6 06-05-2010, 08:28 AM

well, thats right... there are 7027a's in current production. and in fact, the "normal" jj 6L6GC can be "run... in place of 7027A’s in the old Ampeg gear at 600 plate volts with no problem" (from eurotubes website). i mentioned before that i have been a jj fanboy for a minute, and they are cheap enough, so i suppose that is a likely avenue.

but what about this 7199? it appears to me that NO ONE makes this tube anymore. sovtek did, but they seem to be NLA, aside from the fact that sovtek tubes, in general, arent incredibly exciting. and beyond that, i havent actually found any for sale yet. NOS ones are $$$ and hard to find. is rewiring for 6U8 a reasonable and recommended option? i am cool with adaptation, but i generally hate to change things in vintage amps that arent normal wear items (caps, tubes) or a danger (2-prong power cords), not to mention the potential disaster of inserting the wrong tube during a brain fart or whatever.

i dont know if the 7199 even needs replacing, just getting the ducks in a line... apparently, i have some more reading to do!

toobalicious · #7 06-05-2010, 08:34 AM

BTW, i remember those "coin-base" 5881's.... rather, i *think* they are the same as what i referred to as "wafer-base". and yes, i know they are durable. for several years i had a pair of them basically rolling around in a gigbag for emergency use.

but they sounded....... kinda flat. kinda unexciting and bland. at least in my fenders (which is all i had at the time). i sold them on ebay to a jukebox guy... am i correct in thinking that these were never designed to pass audio? "russian military servo tube" is the phrase that sticks out, whatever exactly that is....

are those even made anymore?

toobalicious · #8 06-05-2010, 08:37 AM

last one, i promise....

fliptops.com is gone? dang!

coreyfyfe · #9 06-05-2010, 08:57 AM

www.fliptops.net

The 7199 is the driver tube, and probably will be fine with the one you have, but if you want to snag a few NOS ones as backup should there ever be an issue that would be my personal preference to modding for 6U8, were it my amp.

anderbass · #10 06-05-2010, 11:49 AM

Quote:

Originally Posted by toobalicious

any thing else i should take into account?

What ohm cab will you be using?

throbbinnut posted some good info you should check out in this thread:
Ampeg B25B Question!

BassmanPaul · #11 06-05-2010, 11:56 AM

Quote:

Originally Posted by jimbilly

Nice!, that looks clean too! My tech tells me that the 'coin base' Sovtek 5881 (6L6GC equivalent) handles high voltages.

Sorry but they are NOT equivalent. 5881 equates to a 6L6WGB not a GC. Has less plate dissipation than the GC which is why guitar players like them. They run out of steam earlier than the GC. In an amp designed for GCs they'll provide less output.

Paul

toobalicious · #12 06-05-2010, 12:16 PM

well, i guess it will have to be an 8 ohm one... currently, the only 8 ohm cab i have is a small-ish 1x15 that sounds its best when it is being pushed (which obviously isnt going to happen with the b25b). i do have a 4ohm 2x15 that i could stand to rewire to 16 ohms, but then i wouldnt be able to really use it with anything else (not that i really do now). ideally, i will find an original b25b 2x15 cab (at a good price, even), but i am not holding my breath.

paul, that is what i thought i remembered about those sovteks--- lower output and easier to drive into distortion. probably *not* what i want from a +/- 50 watt bass amp!

coreyfyfe · #13 06-05-2010, 12:20 PM

Quote:

Originally Posted by toobalicious

i do have a 4ohm 2x15 that i could stand to rewire to 16 ohms, but then i wouldnt be able to really use it with anything else (not that i really do now).

You could have it wired with a switch like the original B25 cabs. There was a thread a few weeks ago (maybe longer) about that, someone had a few wiring diagrams for how to wiring the switch. The only thing I'm not sure about is what kind of switch you would need, ie is there a specific quality/current handling capacity that needs to be maintained.

Edit - I found the thread, and I even posted a diagram in that thread

. 5 amp DPDT switch should do it.
Ampeg cab with ohm switch help

toobalicious · #14 06-05-2010, 12:30 PM

nice... that could be the magic stick. the switching idea had crossed my mind, but it was a fleeting thought. the jackplate on the 2x15 is plenty big to accommodate this, and a switch like that is too cheap to *not* try it.

GeneralElectric · #15 06-05-2010, 12:35 PM

I play a B25B that looks a lot like yours. I have it with NOS GeneralElectric 6L6s and I've got Mullards in the preamp now for the 12ax7s (or was it 12au7s? I don't remember now) the rectifier tube was what came on it from Ampeg in 69.

FWIW I gig and play mine regularly with all sorts of different bands in all sorts of different venues.