Petrucci's amp that they modeled the JP-2C after..

[GJgo]

So we all know it's a HRG. Here's what I don't know. Was it a factory or a modded c? Now, I don't care about that, what I'm getting after is I wonder what transformer is in it? More specifically which transformer did they use when they reverse engineered it for the JP-2C?

I've felt from the beginning of having mine that it has some sag. I've been reading about the differences between the 100 & X101 that ran more of a normal voltage out of the transformer and had some sag vs. the 105 that runs hotter and thus has more attack and headroom.

You guys have any thoughts on this?

 

[GJgo]

Well, I measured what I have for comparison. The power transformer in the JP is 3 7/8" deep. The X101 PT in the IIC I just picked up D) is 3 7/8" deep. Hmm..

I read an old post where a guy said his 105 PT was 3 1/2" deep, maybe someone here who has one can verify? Same question to any guys who have a 100 PT?

 

[bandit2013]

I am going to throw this out just because.... If they reverse engineered the actual transformer, it would have been destroyed in the process. However, what you may see on the outside does not mean you will have the same on the inside. Many things have changed over the years in terms of materials used, type of insulating system, varnish, copper alloy, laminations materials (what type of steel is it) and its efficiency. It is what is inside the core is what makes a difference. I would not go by outside dimensions as the means to verify if one is the same as the other that was made some 30-40 years ago unless you are comparing something that was made in the same era.

 

[GJgo]

Well then, I guess it's time to see what plate voltage the JP PT is running. Copied from elsewhere-

Early 100 - 100-162318 - 448V
Simul/60-100 Power - 105-162318 -483V+
X101-162318 – Export - 448-460V
180W - 0180322 Coliseum - 500V+

 

[bandit2013]

That would definitely be a better comparison..... Voltage at load would say much more than the dimensions of the steel laminations of the Transformer if comparing models from different years vs something new and something old.

 

[GJgo]

I have a bias tester probe, just need to find the motivation to pull the chassis out!

 

[GJgo]

I tested my X101, the PV is 444v. I'll test my 105 & the JP later.

That said, I was chatting with Mike B. about something else & asked him this question- he told me that when designing the JP transformer the 105 was the objective, however they did back off the plate voltage.

 

[GJgo]

My 105 PT is running 515 PV. Learning more about this I can see why they chose to back it off- the only tubes Mesa has that will take that abuse are the STR-425s. I'm betting they backed it off so they could run STR-440s in it. At the 105 voltage you really should be springing for old 415 / 416s.

 

[IronSean]

So why the suspence GJgo? What did the JP-2C measure at?

 

[GJgo]

Sorry, I'll have to pull the chassis to measure it & I haven't done that yet. When I do, I will report.

 

[Silverwulf]

The JP2C transformer was reversed engineered from the 105 PT. As stated earlier, they just reduced the plate voltage.

From everything I've seen, Petrucci's go-to Mark IIC+ amps have been factory originals. You can see the "Pull Deep" script on the faceplates of them. Being short heads, it would be very unlikely those were upgrades. Not impossible, but very unlikely. Not to mention Petrucci has stated how he studied up and learned the differences in upgrade vs non, transformers, etc.

 

[imotep06]

Sorry, I'll have to pull the chassis to measure it & I haven't done that yet. When I do, I will report.

And ofc, that never happened :lol: :arrow:

 

[GJgo]

Oops. I don't remember exactly, but it was right around 450pv. The JP2C transformer was more or less the same as the X101 in both dimensions & performance.