Ampeg Jet J12-A power trans

[CB Amp]

Hello,

I've got an Ampeg Jet J12-A (1962 I think) with a blown power trans. I would like to order a new one to a transformer builder, but I don't know the value of the AC high voltage of the rectifier taps.

If someone has such an amp and could measure it, or know the values, I would gladly appreciate your help.

Thank you very much.

[Johnhenry]

I put a Delux Power Tranny in a friend's Jet about 5 yr's ago and it's still goin strong, if your getting a custom wound the winder should know what he need's for a 5Y3 rectifier.
Johnhenry

[CaseyJones]

Hello,

I've got an Ampeg Jet J12-A (1962 I think) with a blown power trans. I would like to order a new one to a transformer builder, but I don't know the value of the AC high voltage of the rectifier taps.

270-0-270 to 300-0-300 @ 120ma on the high voltage. 275-0-275 to 280-0-280 is ideal. More current is better, if the original had more current it wouldn't be zorched now would it?

6.3V CT @ 4A is good. More current is mo' betta.

5V @ 3A helps to make sure that future owners won't cook the PT by using a rectifier more demanding than the original 5Y3.

A budget replacement can probably be salvaged from an old phonograph or tube radio. The only caveat is to make sure you get the 5V winding for the rectifier. 60% to 70% of the phonograph amps I salvage don't have a 5V winding.

[Phil_S]

Assuming Casey is correct (no reason to doubt him), the PT275 is appropriate and dirt cheap:
http://www.musicalpowersupplies.com/4.html
The pair of 7591's need 0.8A each and the two 12AX7's need 0.3A each for filament current. That's 6.3v @ 2.2A. The 5Y3 needs 2.0A.

[CaseyJones]

Oh cool, there's the link to the low buck PTs. Weber just jacked the prices on his, it stands to reason... copper is goin' sky high, copper is high because the Chinese are buyin', then the Chinese charge top dollar for products that contain copper like transformers. The weak dollar doesn't help, either.

I like to go overboard on filament current for two reasons: If I have substantially more filament current than I need and the PT is running hot I don't have to second guess which winding is at fault. Oh, I'll check but less to think about is still less to think about.

The over-rated 5V winding is important. Tube swapping is gettin' to be a popular activity, I've had a couple amps sent back lately with damage caused by incorrect tubes subs. When I overbuild by 100% and the unit comes back cooked I know somethin' funny is goin' on.

[Phil_S]

Casey: I understand about wanting to de-rate your PT, but I don't expect to find 5V@4A + 6.3V@5A + HT winding for $33. Basically, you can't have your cake and eat it, too. For this kind of rating, I would look at Edcor for quality and price. http://www.edcorusa.com/products/transformers.html

You might look at these torroidal models. I don't recall seeing one with a 5V winding. http://www.toroid-transformer.com/trans.html I used one of these for a fixed bias VibroChamp (another story, another time). I took the bias supply from the 12.6V winding. I found the filament voltage was a little on the low side of 6.3v. When I called it to his attention, he gave me nothing but lip service. I would have much rather heard from him, "well, that's the way they are." This is in a 3 tube amp pulling maybe 1.5A of the filament supply. There is no excuse for that.

[CaseyJones]

Casey: I understand about wanting to de-rate your PT, but I don't expect to find 5V@4A

5V@3A. That's the minimum spec for our Brave New World. Now that every chucklehead who owns a tube amp has heard that you can sub a 5U4G fora 5Y3 you can't expect 'em not to.

+ 6.3V@5A + HT winding for $33.

I also want to make sure I have enough filament to sub EL34s... again, now that every yo-yo on God's Green Earth has heard you can... you can be sure they will. Never mind that 7591s have a different pinout, apparently there's another urban legend afoot that 6V6s are a straight no soldering sub for 7591s. Urban legend bein' what it is you can be sure that word will quickly spread that "all beam power tubes work in the same socket". Which is sorta true but of course not universally true.

I sleep better at night knowin' that my PT will at least survive a fraction of a minute when some boy genius stuffs a tube in there with a broken reference pin. YEAH the fuse should blow first which is why the truly innovative among us use much larger fuses. I check the value of the fuse the moment an amp hits my bench. 30 amp automotive fuses and power transformers glued to the amp with their own melted guts... now THERE'S a popular combination!

Basically, you can't have your cake and eat it, too.

Sure I can! But not the way you'd expect. I'm constantly on the lookout for good electronics salvage so it's just a quick trip to "the boneyard" for something like vintage Paeco iron from some old Hewlett-Packard tube junk.

Ten more bucks buys a whole lot more transformer new/retail. I'd prefer to spend ten bucks more and get more transformer than save ten bucks and get less. In the long run I save money. Experience has shown that when I use cheap parts unhappy customers return pissed off with zorched amps. Bottomfeeders can complain that I'm a grumpy pain in the ass and I'm not going to argue... they're right!

You might look at these torroidal models. I don't recall seeing one with a 5V winding.

I'm old school, I've never seen one of those donut thingies in a vintage amp. The 5V can be supplied by an extra toroid... if chassis space is available.

[CB Amp]

Thanks a lot for your help, the data and the links, I hope it can help the community.
Casey, I totally share your point of view, so don't worry, I'll keep this amp, and I'm no foolish adventurer

Thanks again.

[CaseyJones]

Thanks a lot for your help, the data and the links, I hope it can help the community.
Casey, I totally share your point of view, so don't worry, I'll keep this amp, and I'm no foolish adventurer

Thanks again.

Those Jets are a very cool amp especially the 6V6 version. Once every tweed every to roll outta Fullerton is in a collection somewhere the prices are going to go up.