Music Man Heater Current

[jbltwin1]

Anybody know what the PT in a Music Man 2275-65(65 watt with 12ax7PI) is capable of in the heater circuit?

[soundguruman]

Put a current meter in line with the heater winding.
Add loads, like more 12AX7 filaments...clip them on externally for example.
Now how much AC current can you get before the voltage drops below 6.3 volts?
You answered the question.

[jbltwin1]

I know I could do that. I was hoping somebody had the specs for what it was RATED at.

[Jazz P Bass]

I'd like to know where you think the PT heater rating info would come from?

It's not exactly something the manufacturer would publish.

[52 Bill]

You can also work backwards from what the amp uses. Two 6CA7s and one 12AX7, add up the heater currents and add a bit for safety factor, 4 amps?

But if it has an original Type 1 transformer, that they used a few different model amps like the 130 watt heads, with 4 6CA7s, then 7 amps?

Just a guess.

[jbltwin1]

I have seen manufacturer data published on transformers for sale when they are new. It's one of the specs people look at when they design an amp. I was just hoping some old data was still around for MM's.

[g1]

What is the part number of the transformer? That will tell whether it is type 1 or not.

[Enzo]

MM didn't buy the transformers out of a manufacturer's catalog, they were wound to spec. Custom made in other words. Guys designing amps in their basement look at catalog specs because that is the only source of transformers they have. Engineers in the business of designing amps determine the current they need, then add a margin for safety and then specify those ratings to a transformer company to be made.

[J M Fahey]

I have seen manufacturer data published on transformers for sale when they are new. It's one of the specs people look at when they design an amp. I was just hoping some old data was still around for MM's.

Well, not likely.

I guess it went the other way round.

MM first designed the amp, and then ordered custom made transformers, from their OEM supplier.
I very much doubt they shopped around to see what commercial/off the shelf transformer they could use.

So definitely somebody had data and specs on those transformers: MM Engineering Dept and the involved manufacturers.

Data which does not need to be spread to the general public, not even to MM AWSC which would simply order "a Sixty Five transformer, part number xxxxx " or something similar, if ever needed.

*Maybe* Mercury Magnetics, classic transformer cloners, could have such data (ask them) but even so, it must have been reverse engineered, not pulled from moth and rat chewed humid blueprints.

[Gtr_tech]

I have seen a heater winding go open in the 2-6CA7 version with tube PI, so I'm thinking they were a bit under rated.