6g3 power transformer - amp gurus...

[StrummersOfThunder]

Looking at PTs for 6g3 deluxe brownface builds.

In the collective wisdom of the forums amp gurus do you think the sedcondary impedence of the high voltage windings being mismatched between vintage spec PTs and the reproduction hammond 290bx is likely to cause an issue.
I read that the hammond has all the right figures in terms of VAC and mA current but the impedence is 112.5ohm d.c which apparently is about half of that of the vintage fender 125p2a.

Im assuming this will result in higher voltages if there is less resistance?

Ive seem some comments suggesting adding a 55ohm resistor between the secondaries and the rectifier plate.

The other option is ignoring this.
Or getting a cork sniffy mercury magnetics that apparently should emmulate the vintage closer.

Appreciate your thoughts on the topic per usual

[MikeC]

Impedance is a combination of the effects of resistance, ([capacitance & inductance]=reluctance) and is frequency dependent. In your case, 50HZ. In the USA, 60HZ. There are design/winding calculations that take mains frequency into account but I'd be surprised if it will be a detectable thing to your ear. Calling Jaret!!!

[sizzlingbadger]

110v vs 240v, I would expect there to a be difference in dc resistance between them.

[Jay]

Consider it is black box. If Hammond's engineers state that it is a replacement for the original than who cares what's inside the box

[StrummersOfThunder]

This is on the secondary side in referring to
330-0-330 v
Hammond spec sheet 112 ohm red red secondary
https://www.hammfg.com/files/parts/pdf/ ... 1697661948


Secondary for the vintage fender is about twice that

That should be independent of the primary ac voltage no ?

[StrummersOfThunder]

Consider it is black box. If Hammond's engineers state that it is a replacement for the original than who cares what's inside the box

I just wonder if it would negate all the efforts to replicate the fender circuit of the voltages / sag of the amp will be different due to different PT characteristics

[GrantB]

My layman's brain suggests volts is volts from a tranny, and impedance relating to the delivery of said volts is somewhat irrelevant.

But I'm also a hairdresser.

[RectifiedAmps]

I assume you’re talking secondary DC resistance here - not impedance? You’re measuring resistance but I think impedance is what would would matter more in terms of transformer differences.

The PT shouldn’t be generating much sag unless you’re drawing beyond its rated amperage, especially if it’s driving a valve rectifier. The rectifier’s series resistance should be the main factor creating sag but you could try series resistors between the secondaries and rectifier if things sound too ‘stiff’. The rectifier’s series resistance is more dynamic than a resistor (changes with current) but it’d be close enough! Or you could try saggier rectifiers (5U4 or 5Y3).

[MikeC]

I assume you’re talking secondary DC resistance here - not impedance? You’re measuring resistance but I think impedance is what would would matter more in terms of transformer differences.

The PT shouldn’t be generating much sag unless you’re drawing beyond its rated amperage, especially if it’s driving a valve rectifier. The rectifier’s series resistance should be the main factor creating sag but you could try series resistors between the secondaries and rectifier if things sound too ‘stiff’. The rectifier’s series resistance is more dynamic than a resistor (changes with current) but it’d be close enough! Or you could try saggier rectifiers (5U4 or 5Y3).

I think the typical 20% tolerance of the components in the old ones (that's 20% in value up or down) will make for way more variance in tone between 2 "identical" amps.

[RectifiedAmps]

I assume you’re talking secondary DC resistance here - not impedance? You’re measuring resistance but I think impedance is what would would matter more in terms of transformer differences.

The PT shouldn’t be generating much sag unless you’re drawing beyond its rated amperage, especially if it’s driving a valve rectifier. The rectifier’s series resistance should be the main factor creating sag but you could try series resistors between the secondaries and rectifier if things sound too ‘stiff’. The rectifier’s series resistance is more dynamic than a resistor (changes with current) but it’d be close enough! Or you could try saggier rectifiers (5U4 or 5Y3).

I think the typical 20% tolerance of the components in the old ones (that's 20% in value up or down) will make for way more variance in tone between 2 "identical" amps.

Yep, plus with a 3:1 ratio, a +/-5VAC difference coming from your wall due to variations in the power grid will result in +/-15VAC difference in the secondary output of the PT, which would be about +/-10VDC.

[sizzlingbadger]

The dc resistance is dependant on the amount of wire and it's thickness, it has no (appreciable) bearing on the voltage ratio's of the transformer under normal conditions. Transformers do suffer from "copper" and "iron" losses, effecting efficiency but it's not something I would expect you to be able to hear in the amp.

[StrummersOfThunder]

Cool info amp gurus collective

I think @rectifieramps has nailed it. Appologies for my non learned lexicon

[StrummersOfThunder]

Always impressed with the knowledge depth of this place

[StrummersOfThunder]

My layman's brain suggests volts is volts from a tranny, and impedance relating to the delivery of said volts is somewhat irrelevant.

But I'm also a hairdresser.

And a damn fine one !