Darn mis labeled PT

[Randall]

So here's one I've not seen before. 1965 Deluxe-Amp comes in dead. Shorted filter cap. But it also had been converted to solid state rectifer with two extra 20uF filter caps added. I convinced the customer to put it back to stock. While I'n in there I notice the filament wires coming off the PT are wrong. One grren wire and the green/ yellow are going to the lamp, and the other green wire is chassis grounded. Well, that's clearly wrong, so I figured the guy who thought those other BS mods were a good idea must have done this, too. I wired like the schematic with both green wires to the lamp, and the green/yellow to ground. But then I could not get it bias up, and it sounded very weak.

I eventually found I had 7.3 Vac to ground on one side of the lamp, and 1.2 Vac on the other side. I disconnected everything, and I found it was wired correctly before I changed it. I had 7.5 Vac between one green wire and the green/yellow wire with the other green wire grounded, with all tubes removed in standby. So it turns out this darn PT has mislabled filament wires. Amp works fine now.

I have never come across this in all my travels. Have you?

[xtian]

No! What a nice surprise for you, special supernice.

[Mick Bailey]

The only time I came across a transformer with incorrect lead colours was a replacement toriodal PT for a Laney bass amp (from the manufacturer) and with it was a handwritten note saying it had been made with the correct colours but wired incorrectly. I put a note inside the chassis when I fitted it for the next guy.

[The Dude]

I don't recall ever seeing something like this. Imagine if this transformer was purchased/installed by a novice or someone doing their first build. It could take forever to figure out the problem.

[Leo_Gnardo]

I have never come across this in all my travels. Have you?

Can't say I've seen the like. It's amusing to consider somebody at the Fender factory ran across this problem, and knew enough to wire the filament connections correctly in spite of the insulation color mixup. Thereby sparing a relatively expensive transformer from the trash bin! Makes one wonder, were there more mis-labeled like this? After encountering one or two, on the production line they might have learned enough to look out for this problem.

[The Dude]

Which begs the question(s) - Is the transformer original? Has it been rewound? Is it a replacement? Was it indeed this way from the factory?

[Greg Robinson]

I see this fairly often - mostly on east-asian assembled amps that use Faston type connectors for their transformer connections where the silkscreen notes wire colour, but usually a slightly different type of error than described above.

Rather than a centre tap being colour coded incorrectly, it'll be something like the labelling says "RED-HT, RED/YEL-CT, RED-HT", but the actual lead colours are "BLK-HT, WHT-CT, BLK-HT" or similar.
That sort of error is fairly innocuous in-and-of-itself, but once or twice it's had further implications, like those silkscreen labelled colour codes are actually used for a different secondary - say that above example where the ACTUAL colour code of the HT winding is BLK-WHT-BLK, but the silkscreen indicates that as the heater winding, and the transformer colours for the heater are actually "GRN-3.3, GRN/YEL-CT, GRN-3.3". Careless note-taking could then easily result in a very expensive mistake if the silkscreen was followed.

Lesson from all this is to take notes, and to never assume, but confirm with measurements where required.

[catalin gramada]

As you know possible there are soldering terminals mounted to bobin. Anyone messed with the wiring of an open transformer may do a wiring mistake. You should open the bells and see if can wire the leads in a proper way for the next.

[Greg Robinson]

As you know there are soldered terminals mounted to bobin. Anyone messed with the wiring of an open transformer may do a wiring mistake. You should open the bells and wiring the leads in a proper way for the next.

Not always. In fact I'd argue that's rare to see. Most transformers these days have their flyout leads simply spliced directly to the magnet wire and then fastened under layers of insulation tape/paper.
There's no way to re-wire these without damaging the insulation, and there's no good way to repair/replace that once the laminations have been assembled and the transformer varnished, so is best left alone, with a note left for whoever is next in the chassis.

[catalin gramada]

You don't know till you don't open it. This is an original deluxe 1965 for instance, despite the fact it is a 125P23C and not an 125P23B as schematic states.

[Randall]

I do think the PT is original from the date code. No way to know much else than that.Pretty sure it came from Shumacher like that. I have a label maker, so I stuck one on the chassis that reads, "Mislabled Filament Wires On PT" maybe save the next from going thru that.

[The Dude]

......I have a label maker, so I stuck one on the chassis that reads, "Mislabled Filament Wires On PT" maybe save the next from going thru that.

You're a good egg, Randall!

[Chuck H]

This could have gone worse or taken longer. You reasoned it out pretty fast without damaging the original PT. So I'd call this a win for sure

I've never seen incorrect color codes on a PT. But I've had a couple of aftermarket Fender replacement OT's where the brown and blue primary leads are opposite of original resulting in a positive feedback situation. In fact I've seen this enough that now I tack solder the untrimmed plate leads to check for this. The first time this happened to me I has already trimmed and wrapped the leads on the socket pins. Only to find I had to lengthen one of the leads with a splice to correct the problem.

And I once bought an OT where the black lead for the final on the secondary was swapped with one of the colored leads. So orange was the grounded lead and black went to the impedance switch. I called the manufacturer about it and they basically said 'Yeah, that happens sometimes.'

[g1]

I've had a couple of aftermarket Fender replacement OT's where the brown and blue primary leads are opposite of original resulting in a positive feedback situation.

Same here, or at least with single ended OT's.
I guess if they are also single impedance, you can't really say whether it's the primary or secondary that is wrong phase.

[Chuck H]

Same here, or at least with single ended OT's.
I guess if they are also single impedance, you can't really say whether it's the primary or secondary that is wrong phase.

True!