ID Fender amp circuit + Tech. question

[EightySix]

Hi everybody,
This is a 68 Showman, but I'm not sure if this is AB763 or AC568? I think it's fairly original, but can anyone spot any mods here?

Also a technical question - The power transformer was replaced with a repro 4 ohm New Sensor, but the output transformer is still the original 8 ohm Showman (not Dual Showman) transformer. Does having two different impedance transformers affect anything?







Thanks

[SatelliteAmps]

No such thing as a 4Ω power transformer. Looks like a handful of resistors were changed, but no major mods. And without looking it up, that looks like the AB763 layout.

[phsyconoodler]

Plate resistor changes at the phase inverter.Nothing drastic.
The output transformer needs to be identified as needing either a 4 or 8 ohm load,that does not say what the primary impedance is.It's likely 4k or 4.2k or something along those lines.Mr Satellite wants people to know the difference.
A layman says a '4 ohm' transformer' and what he should say is that it has 4 or 8 ohm taps on the secondary for what the speaker should be.
To properly ID the transformer we need to know the make,model and part number.

[SatelliteAmps]

Again, there is no such designation as a 4Ω power transformer. Why does the OP refer to it like that?

No idea of what Psycho thinks I want people to know. Whatever the stock output transformer is makes zero difference in a replaced power transformer.

[phsyconoodler]

You know exactly what I mean.You want people to use correct terminology when describing stuff so we can better help them out.

We are here to help and educate at the same time.

To the OP: what you SHOULD be saying is it has an 8 or 4 ohm speaker load tap.
The field guide says a blackface showman wants to see an 8 ohm load,circuit AA763.

[jay42]

Not that experienced....the '66 I know best does not have the green wire coiled around the bundle coming from the trem channel pots. Other than that, looks like AB763 with a few replaced parts.

Is it a drip-edge amp?

[EightySix]

Originally Posted by phsyconoodler

Plate resistor changes at the phase inverter.Nothing drastic.
The output transformer needs to be identified as needing either a 4 or 8 ohm load,that does not say what the primary impedance is.It's likely 4k or 4.2k or something along those lines.Mr Satellite wants people to know the difference.
A layman says a '4 ohm' transformer' and what he should say is that it has 4 or 8 ohm taps on the secondary for what the speaker should be.
To properly ID the transformer we need to know the make,model and part number.

Sorry, should have been more specific...

Power Trans - 'NSC022756 Rev. B' / '238-9608' -- "New Sensor/Schumacker Power transformer for Twin Reverb, Dual Showman, Bassman 100. 100 watts"
Output Trans - 'Fender 022897' -- Original 8 ohm OT

What made me question if this is the right PT is it's showing it should be used for the Dual showman, which is the 4 ohm version of my amp... Not sure if it matters or not?

[EightySix]

Originally Posted by jay42

Is it a drip-edge amp?

It's missing the original faceplate/grill cloth. The # on the choke/OT make it an early silverface. I was checking the transformers to find out if it was a Showman or Dual Showman when I noticed the PT had been replaced.

Thanks for the help, everybody

[jay42]

Originally Posted by EightySix

What made me question if this is the right PT is it's showing it should be used for the Dual showman, which is the 4 ohm version of my amp... Not sure if it matters or not?

ah...it doesn't matter.

[SatelliteAmps]

Originally Posted by phsyconoodler

You know exactly what I mean.You want people to use correct terminology when describing stuff so we can better help them out.

We are here to help and educate at the same time.

To the OP: what you SHOULD be saying is it has an 8 or 4 ohm speaker load tap.
The field guide says a blackface showman wants to see an 8 ohm load,circuit AA763.

I do want people to use proper terminology and to properly address the issues asked. You never once mention in your "educating" that you are only talking about OT's, not PT's as asked by the OP.

And as we found out in the follow up, your suggestion for what the OP "SHOULD" be saying is not quite correct, as the PT still has no bearing on what the output impedance of the OT is.