Output Trans cooked - Help for a friend:

[Lanticus]

My buddy Joe (Pallbearer) posted this question in the Little Rock Gear Nerds group on fb.  Figured I'd take it here to the source for my brother!  I'll pass on any help to him, or better yet, get him to join srlives. 

(Man, yall shoulda seen it!  The thing shot smoke and flames on the outro guitar solo of their last song of the set!  ROCK AND ROLL!!)

From Joe:
Figured there would be a few people in here who could give me a general answer on this.

Recently had a fairly rare vintage point-to-point tube amp cook its output transformer. I'm just curious how difficult it would be to replace the OT with something from say, Mercury Magnetics. They won't carry something with the exact specs I'm sure, but the amp is essentially voiced like a Sunn Model T (70's era,) and uses 2 KT88's in the power section, so I wondered if one of their drop-in SUNN OT replacements might be a close enough fit to work. Will a good bit of the components need to be changed to different values to make this viable? I'm a moron at the electrical engineering side of amplifiers so any input would be helpful so I can decide whether the work is worth it. Love the amp's tone, so saving it is preferable to scrapping it.

[VOLVO)))]

Have him join here, Nick/Hemi could probably steer him correct. I just want that dude on here, I'm a huge fan, hahaha.

[Lanticus]

I sent him an email telling him to join!  My man would fit right in the jamroom.  One of the biggest gear heads I've ever met!

[VOLVO)))]

-excited-

[servantofthedead]

Alright, Joe Pallbearer here, joined up at the behest of Lanticus! Nothing really to add to the above info, apart from giving the amp model and any other specs I can dig up upon request.

[VOLVO)))]

Any additional info helps, pics, model, schematics, etc. We've got some talented chaps around here, I'm sure you'll find what you need.

...and of course...


WELCOME. Huge fan, here. Glad to have you. Make yourself at home, and enjoy.

[servantofthedead]

Thanks man. I'll see what I can dig up.

The amp itself is an AIMS VTB-120 Tube Amp, uses 2 KT88 tubes in the power section, and 3 pre-amp tubes, all 12ax7's if I recall. It's intended to be bass amp, but I've found it sounds better for guitar, as its voiced pretty brightly, so Brett (vocals/guitar) was using it to power half of his full-stack. No issues until the end of the show, when, as described by Lanticus, the thing literally went up in smoke. The OT is definitely fried, you can see (and smell) the burnt edges on it.

These are not pictures of my personal amp, but it's a similar make. curiously enough, mine might be slightly older as it only has 3 sockets for pre-amp tubes:





I have not managed to get a schematic, but I might be able to take gutshots at a later time. Honestly, I may very well be mistaken about it being PTP as well, because I see in looking online that there are a few models that are slightly different than mine that have a simple PCB.

[VOLVO)))]

Gutshots would be helpful. It looks awesome, to say the least... How's the money situation? You may be able to pull it, and have MM rewind it or wind you a new one. Their Sunn transformers are outrageous... 500 bones for the full set of iron, at least.

Ay kids, don't this look like one of 'dem Kustom/Univox dealios? Any idea where it was built?

[Mr. Foxen]

If you can figure the spec, these guys can make to order: http://www.kh-audio.com/e-productinfo.asp?id=1288


Their English is dodge, but I've bought lots of parts from them and they've been sound.

[servantofthedead]

I'm not in any huge hurry to get it fixed, but I would be willing to drop a decent amount of cash on the thing to get it bulletproof for live use again. I'm in a situation now, for the first time ever really, that I'm actually managing to not be constantly in the hole regarding gear purchases.

I'll try to get gutshots when I can! We're preparing for SXSW next week, so it might be a bit of a wait on having time to disassemble the chassis and do all that.

[servantofthedead]

If you can figure the spec, these guys can make to order: http://www.kh-audio.com/e-productinfo.asp?id=1288

Their English is dodge, but I've bought lots of parts from them and they've been sound.

That's awesome. I'm not dead-set on Mercury Magnetics, just want something reliable, so I'll see what I can do to find out specs. I would imagine there's schem. floating around on one of these things. They're not so incredibly rare that one wouldn't exist I wouldn't imagine.

[VOLVO)))]

I have a feeling Univox had something to do with this based on cosmetics, or Kustom in the 80's... LINEAGE! Note the font/controls etc...




"VTB-line schematics are very similar to those of the Fender Bassman."

[servantofthedead]

The AIMS stuff was apparently pre-Randall. But, I've actually owned a couple of Univox amplifiers and currently Pallbearer uses a Univox 50w and 100w tube amp for live actions.

[dunwichamps]

buy this OT

its a remake of the Dynaco OTs used in original 2 x Kt88 amps. I have used it before in my own amps, fuckin killer

http://triodeelectronics.com/a4dyoutr43oh.html

They also have remakes of the PTs as well

Reasonable costs 2, $134 for that OT. Includes UL taps ect ect 4,8,16 output

[VOLVO)))]

Nick, is it just a drop in replacement? desolder/solder in the new, check bias and whatnot = good to go?

[servantofthedead]

Thanks, I'll bookmark that!

[dunwichamps]

Nick, is it just a drop in replacement? desolder/solder in the new, check bias and whatnot = good to go?

they are drop in replacements for 2 x Kt88 sunns exact dimensions of original Sunn PT and OTs which were just Dynaco Mk2/Mk3 transformers used in hi fi amps

check the descriptions and notes to see Sunn part numbers and dimensions.

[Hemisaurus]

Nothing to add, I'd pick the Magnetic Components over the Weber trannies as well.

Built in Chicago y'know

You might want to give the amp a complete overhaul, cap job etc. but if you're doing it on the cheap, just check none of the resistors fried, if you have a meter check the DC lines for excessive ripple that might indicate failing caps, usual stuff. You can do all that without putting the tubes in (unless it's got a tube rec, in which case leave that in)

[dunwichamps]

Nothing to add, I'd pick the Magnetic Components over the Weber trannies as well.

Built in Chicago y'know

You might want to give the amp a complete overhaul, cap job etc. but if you're doing it on the cheap, just check none of the resistors fried, if you have a meter check the DC lines for excessive ripple that might indicate failing caps, usual stuff. You can do all that without putting the tubes in (unless it's got a tube rec, in which case leave that in)

Weber doesnt make anything with the right primary for 2 x KT88 in this wattage range
Mag Comp has nice stuff but again ur not going to find a 4-4.3k primary with the wattage range u need.

Now you can run a 2k-2.2k tranny but the mismatch is annoying and if this amp does have a proper Dynaco OT it may not fit

[Hemisaurus]

Mag Comp make the tranny you recommended

Primary impedance is a factor of secondary impedance and turns ratio, Weber use that to their advantage in their kits. Suppose I could say any old 100W O/P can be used, providing you know how to wire and load it, but I think the MC/Triode is a good call. Unless he has some 100W tranny going spare.

[dunwichamps]

Mag Comp make the tranny you recommended

Primary impedance is a factor of secondary impedance and turns ratio, Weber use that to their advantage in their kits. Suppose I could say any old 100W O/P can be used, providing you know how to wire and load it, but I think the MC/Triode is a good call. Unless he has some 100W tranny going spare.

hmm not listed on their main site

I did buy the 240W 2.2k OT that triode has what a fuckin deal for a 200+W OT

[servantofthedead]

I'm not qualified or capable of working on the amp myself sadly. Mostly looking for general advice on what steps to take to have the tech use to get the amp up and running again.

[dunwichamps]

I'm not qualified or capable of working on the amp myself sadly. Mostly looking for general advice on what steps to take to have the tech use to get the amp up and running again.

no prob man, well if you want direct assistance email me

dunwichamps@gmail.com

I can guide you through it all

A possible schematic

http://www.aimsamps.com/g12vtb120schem.php

[VOLVO)))]

^^^^^^^ Listen to this cat, he's the man!

[chlorpromazine]

here are a couple of pics that I snapped as the magic smoke was being released from the amp