Classictone Trainwreck PT

[Tony Bones]

I'm looking for an PT suitable for a 4x6V6 build and found the Classictone Trainwreck PT 40-18065. The thing is manly! Way overrated filament and rectifier windings: 7.5A @ 6.3V and 5A @ 5V.

I'm just curious, is this a clone of a transformer that Ken scavenged from some other application, or did he spec it that way?

[Tony Bones]

Maybe never mind... I visited the website for the Z-Wreck and opened a fax from Ken to Dr Z. Last page is a blurry schematic for a Westrex AE 293 amp. It apparently has two rectifiers (can't read what kind) 4xKT88 and 4x6SJ7. That just about covers all of the filament windings. Though 300V @ 300mA seems a little low for a quad of KT88.

Anyone have a readable schematic of the AE 293 amp?

[M Fowler]

Ken started off using off the shelf PT's with mA rating of around 250mA then he increased that to around 280mA.

Current crop of TW transformers are around 300mA and yes the filament windings are stout as well. No sag in that bitch.


Just fine a PT for about 50w power handling perhaps 2000mA to 250mA and sufficient filament and rectifier voltage for your needs.


Some more opinions will be along soon.


Mark

[Tony Bones]

Well, I think I like a lot about this transformer for my application. 300mA @ 300V is just about right. Most PTs meant for a pair of 6L6 or EL34 have higher voltage with not quite enough current.

The fact that this PT uses a big stack of slightly smaller lamination is a plus too. I can cut the mounting tabs off and it will make a lay-down transformer with a compact footprint.

[aynirar27]

I believe the triode electronics express kit uses that PT if you are looking for a layout or schematic to see it in

[Tony Bones]

Thanks. The project I'm putting together is nothing like a Trainwreck. I was just interested in any history behind this transformer. It has an unusual set of specs as well as an unusual form factor. It makes sense that it's a copy of a tranny from the 30's or 40's. For some reason they often used a tall stack of smallish laminations back then. Starting in the 50's it became more common to see a shorter stack of larger laminations. More window area but a longer flux path.

FWIW, the transformer in the Westrex amp mentioned in that fax had two separate 5V windings for two separate supply voltages. The Classictone PT has 300V and 260V taps. I think the original Westrex was something like 500V and 260V, hence the two separate rectifiers. There's some writing on the schematic from Ken, but it's hard to read.

p.s. Why'd it take you 8 years to make your first post?

[Tony Bones]

Thinking about it, I realized that the early form factor (tall stack of small lams) results in higher losses in the winding and lower losses in the core. The typical design goal is to make the copper and iron losses equal. That results in the lowest overall losses. It's plausible that better quality core materials became available somewhere in there. The lower loss core made the change in aspect ratio appropriate from an engineering standpoint.

I'm probably the only one on this forum that finds this interesting, but I thought I'd share it anyway.