Need help IDing vintage transformers

[Randall]

I pulled a power and output transformer from a too far gone 65 National Newport 50 combo amp. Scored some nice RCA tubes, too. I can't make sense of the codes on transformers. The PT has 33-3014 and 16649. The OT has 340-6528 and 166448. I've looked at several EIC lists, and these numbers just don't jive. One Google search pulled up a Reverb.com listing for a 65 Supro that said the 16649 was an original Magnetic Corp PT, but I don't know if that true or not.

Anyone have a better idea?

[The Dude]

Do you have a schematic for the amp the iron came out of?

[Randall]

Unfortunately, I have not been able to find one on any of the Valco sites I have found.

[mozz]

166
Chicago Electronic Engineering Co.
Chicago 47, ILL

[Enzo]

If you pulled it, you had the chassis? Would have been a good idea to apply power to transformer only and make measurements. You still can put 120v on the primary wires and see what results.

[Randall]

The thing was toast, wiring shot, etc. I think I can ID the winds OK, so I'm not sure how the chassis makes much difference. They both pass the neon lamp test, so what I want to find out is current and OT load mostly.

[The Dude]

I found this, and maybe you've already seen it. Posting anyway in case it can be of help.

https://www.premierguitar.com/articl...nal-newport-50

It was apparently a 17 watt amp and used a pair of 6973 tubes for the output. The tube compliment is in the link. It used a pair of 10 inch speakers, but I can't find or see speaker impedance anywhere. If you still have the original speakers, you could obviously figure out output impedance.

P.S. I also found that the model number was N6450TR if that helps.

[Enzo]

I think I can ID the winds OK, so I'm not sure how the chassis makes much difference.

If you can ID the wires, great. Just thinking that while still wired it might be a lot easier to obtain that information.

[Randall]

OK, two Jensen 8 ohm speakers, so 4 ohm OT, Duh. I guess I'll consider it 15 watts or maybe 20 watts?

With no load, the PT measures 342v-CT-342v on the reds, 5.7v on the yellows, 3.5v-CT-3.5v on the greens. It ran three 6973's and four 12AX7A's, so what would be a reasonable guess as to the filament current rating?

[Justin Thomas]

3 power tubes? Or was an extra one used for reverb or something? Was that a typo, or did it maybe take a 9-pin rectifier? Maybe that's what fried it in the first ?

Justin

[Dave H]

It ran three 6973's and four 12AX7A's, so what would be a reasonable guess as to the filament current rating?

That adds up to 3*0.45 + 4*0.3 = 2.55A.

[Randall]

Justin, no typo, two outputs and one in the preamp, probably the reverb driver. 5Y3 rectifier.

Dave H., could one assume it to be a 3A winding?

[Dave H]

Dave H., could one assume it to be a 3A winding?

I would

[mozz]

2.55A plus a 150ma dial lamp maybe? I wouldn't assume a 3A winding. I would say 2.5A and since it is used and old, i would only use it at less than that. Many amps were not overbuilt.

[bob p]

IMO the best way to decide what to do with hard to identify transformer set is to look to the schematic from the original device where it was used, not to exceed those loads under any circumstances, and to deliberately underspec your build.

What?!?

Although companies like Fender used very robust iron that would allow modders to push them beyond their deployment ratings, most manufacturers didn't do that. Like Mozz said, most amps in that era were NOT overbuilt. The reason for that is that overbuilding costs money and that represented a significant incremental manufacturing cost that most manufacturers were deliberate to avoid. In fact, most of the cheaper amps were deliberately UNDERBUILT as a cost-shaving measure. The result is that they would universally fail if you tried to push them to the specs that the rest of the circuit implied they could handle.

Look at the Dano and Valco manufactured Silvertones. They were built with lightweight iron and flimsy pressboard boxing. Their iron was underspec'd for the 2x6L6 applications, but in the early 60s the demands that guitarists placed on amps weren't that severe and they could get away with it. That all changed in late 60s-70s and we suddenly saw failures occurring at a higher rate as the loads on amps were increased. Many of those underbuilt amps are famous for failing if the amps get pushed for extended periods. The Silvertone Twin Twelve OT is famous for this.

My recommendation would be to proceed with caution. An underbuilt transformer set might be fine for low-demand applications, like a jazz guitar amp, but they're not likely to fare well in hard-driven rock-and-roll amps, or heaven forbid in an application where someone has the idea to use them with an attenuator, which is a prescription for certain death.

Maybe I'm just changing my outlook on things, but I've quit scavenging old iron like I used to. Back in the days before everything with a tube became expensive on ebay, it was worth my time to ferret out great deals. But now that every lunchbox type PA amp is marked up like it's a vintage collectible, re-purposing old gear just doesn't have the appeal that it used to have.

Because of the expansion of the builder's market, today there's a great aftermarket in inexpensive high quality iron ... it's much better than we had 30 years ago when we had to scavenge because the market was thin. Today I have the luxury of spending little money while being able to overspec iron to meet the needs of my build.

We live in a great time to be amp builders. To me, recycling old oddball iron just isn't worth the time it takes when new iron can be had so cheaply. Maybe my outlook is changing just I'm guarding my time more than my money these days.

Good luck with your build. Let us know how it turns out.