Major Minor Iron question

[jojokeo]

Aloha all,


I have studio friends that own a lot of the usual vintage Fenders and Marshalls almost all of which I've worked on including a special one that Jose Arredondo made a few of famous mods on. I can assure you that maybe they were special in his time and the mojo they provided but it was nothing that we don't do routinely these days but that's another thread and story. I can share this info if wanted later? There's one particular guy that doesn't like distortion coming from his amp and instead likes it clean and punchy to use as a platform for his pedals, etc.


I was given a Fender Hot Rod Deluxe to use as a blank canvas. Rather than put this on Timbo's thread and distract from it I am creating a new one to ask: I would like to transform this into a Major Minor using the PT and only would require buying a new OT? Going by the old rule of parts being +/-20% I think it can be done but would like a little reassurance please?
The KT88 specs are 1.6A x 2 = 3.2A. With 3 - 12A_7's totaling  0.9A for a heater total = 4.1A it is over the PT spec of 3.75A. BUT it's only about 9% over... Am I being too optimistic on the heaters?
The PT specs are:
495Vdc unloaded
440Vac @ 65.7mA
388Vdc @ 200mA
Heaters:
6.6Vac @ 3.75A
*I am not planning on using the 53.6Vac @ 1.58A winding...


Thank you in advance,
Jojo

[SILVERGUN]

ALoha jojo,

The KT88 specs are 1.6A x 2 = 3.2A. With 3 - 12A_7's totaling  0.9A for a heater total = 4.1A it is over the PT spec of 3.75A. BUT it's only about 9% over... Am I being too optimistic on the heaters?

I don't think so. You could pre-test by putting a load on the winding and see how far it sags down, or just go for it. The only resulting problem would be eventual heat failure. Transformer windings are pretty resilient and usually rated so that you get the listed voltage AT the listed current. Who knows what max current available is?...smoke is a good indicator.

*I am not planning on using the 53.6Vac @ 1.58A winding...

Running cathode bias?


Are you gonna do a UL OT?
You wouldn't want the Major Numbskull committee coming after you. I mean, now They are not being Drama Queens anymore.

[jojokeo]

Thanks SG. Mr 88's still carries mistreatment issues akin to what others display in their political correctness boycott ways. This is not good under any circumstance but especially not good in today's crazy upside down world. It's a lose lose and nobody wins.


I am going by the elder's (Sluckey & PRR's) +/-20 rule as said earlier and past experiences adding and changing tubes in numerous Hammond chassis amps. And by not utilizing the extra winding it's helping prevent it from being overly worked in total capacity. The amp will likely rarely if ever be pegged with "everything on 10" anyways so I'm thinking I will roll the dice on it? I don't want to pour any extra money into it that necessary. I will order a UL OT and was planning on cathode biased. By maybe considering any extra headroom by fixed bias and not having to screw around with multiple bias resistors and caps will make this decision and set-up easier? I do not care about anything but headroom and punch on this one. Overdrive and distortion is unwanted and unwelcome 'round these parts... sort of like that MO JOJ/JOB kook :) if you can talk sense into him you'd be the first? ;)

[SILVERGUN]

.....planning on cathode biased. By maybe considering any extra headroom by fixed bias and not having to screw around with multiple bias resistors and caps will make this decision and set-up easier? I do not care about anything but headroom and punch on this one. Overdrive and distortion is unwanted and unwelcome 'round these parts...

Well, yeah, it will run cooler in fixed bias and if the winding is there and you want headroom, why not use it? As Timbo found out: KT88 = headroom. How do you think J-Blo's head got soooooo big?

Since that 53.6Vac winding won't be seeing any current as a fixed bias supply it won't add any tax to the heavily taxed xfmr.
Also, depending on how tight your chassis is you might wat to ix-nay on the esitor-rays

It's your soup Buddy, I'm just glad there's no one around to pee in it.

[jojokeo]

Thanks SG, found the reply in my spam folder of an email I have to use for EL34.com unfortunately. I'm still going forward on this just not at the speed I'd like... yet! Yes, J-Bo is still being a Karen and no matter how much grief I give he's being a total donkey. It appears a new UL OT is all I'll need to fork out for? I may re-mount it to the oppo end and I should have plenty of room? I'm hoping to be able to use the tube sockets of the original chassis? Room "shouldn't" be an issue hopefully. But not sure about the speaker and new OT and possibly an external cap can and just thought about the choke... a new red back Celestion may also be a nice addition or possibly an EV12L??? Still planning things at this point then it'll be designing the fit and finish...