Weber 5E3 OT polarity

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I was reading through some old threads the other night, and came across one that pointed out a discrepancy between the Weber 5E3 schematic and layout drawings regarding the OT primaries. Out of curiosity, I improvised a NFB loop with a 100k resistor, lifted the bypass cap from the PI and clipped it in. The amp oscillated like crazy.
I know it's an easy fix. My question is, how big a deal is this on an amp with no NFB? It seems like at the very least it would also reverse the secondaries and the speaker leads. Could it also contribute to hum?

[loudthud]

If it picks up hum due to proximity or orentation to the power transformer, polarity won't matter, it will pick up hum either way. It will make a difference as to absolute phase. Some people claim they can hear a difference but you could just reverse the wires at the speaker.

[pdf64]

For good layouts/lead dress, for an open loop tube guitar power amp, the polarity of the output with respect to the input is immaterial. With a bad layout, or very high gain (not 5E3), the stability might be better one way than the other.
But it also depends on whether you think overall polarity matters. Peter.

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Thank you both for the reply. Tried swapping the speaker wires but couldn't really hear a difference. As for the question of overall polarity, I'm gonna hold that one in abeyance until I learn a lot more about electronics. Thanks for easing my mind, guys!
All the best,
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[Bruce / Mission Amps]

... My question is, how big a deal is this on an amp with no NFB? It seems like at the very least it would also reverse the secondaries and the speaker leads. Could it also contribute to hum?

Not a big deal and normally not much of an issue when there is no NFB, but I have run into situations where reversing the OT leads did make the amp sound very slightly cleaner, especially... when driven hard.
I can only assume it had something to do with random capacitive coupling (read that as sloppy wiring, ha ha) which was negatively impacting the circuit in a tonally sense and reversing the primary leads helped in a very small way.
Also.... with respect to your above comment ("...It seems like at the very least it would also reverse the secondaries and the speaker leads")....
the speaker leads are the secondary in an output transformer. You might have the leads of the OT momentarily confused with the power transformer, who's high voltage secondary is connected to the OT's primary.
The primary leads to the power tubes is what you would reverse.

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Hi Bruce. Thanks for your reply. I think I will reverse the OT primaries. Even though it's not the problem I thought it might be, it seems like that would be the more correct way to wire them. Also, thanks to you and Tubeswell for your advice on using a 5Y3 in my amp. I still haven't found the resistor you suggested but have played out a couple of times with no problems.

[PremiumPlus]

The only reason I can imagine that the amp might sound cleaner when driven hard, (as opposed to wiring the OT 'backwards') would have to do with the power supply sag and the preamp tubes being affected by amplifying the other half of the signal; i.e. while the preamp is 'pushing' the power amp would be 'pulling' the signal. But I would imagine that that would be countered somewhat by the lag in current (remember current lags voltage by 90 degrees) being supplied by the filter caps. This would also be affected by having a choke in the filter network too. Just something to muse about, probably not that important.

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Hi PremiumPlus, Thank for the reply. The consensus seems to be that it doesn't matter much, except for the secondaries being reversed at the speaker hookup. Do you remember that little polarity test guys used to do with a 9 volt battery, where the speaker would move outwards or backwards depending on how you touched the battery to the lugs? I'm not even sure that would be a major problem. It might slow your transient response a nano-second or two. On the other hand, that might be exactly the sound somebody's looking for...