What OT for my Z-wreck build

[rooster]

Drew, OK, passion for MM noted. And I appreciate passionate amp people. This said, I still find myself running to the MCI product - and yes! - $$ makes a difference to me, but I also have not had any issues with them or their product. I have talked with Paul @ MM and Joe @ MCI and where I find Paul more the interesting character than Joe, it might only be the fact that MM is making one-z, two-z trannys for various artists. Yeah I always dig the stories. But Joe is a just as knowledgable cat as Paul and been in the biz just as long. I think we have to conceed that MM started a vigorous ad campaign back in the 90's - starting with VG mag - to be the 'step up' tranny place, catering to one-offs for the vintage hounds and this has paid off. This has established them in the hearts and minds of many guitar players. Well, and then there'a the pretty red bell covers........ Eh, I like pretty, but I do try to find the beauty in just the delivery of the stated specs, too. And here MCI does this as well as anybody out there, IMO.

Anyway, back to crafty1 and specifically the 470 OT, do you have that number rating thing in place yet?

[Clyde]

I've had a few of the MCI's come across my bench lately and I have mixed emotions about them. I've seen some spec'd specifically for a certain vintage model where the voltages have been just dead wrong. Had another amp that had a HV short somewhere, couldn't find it in the amp, I'm somewhat suspicious of the transformers, either PT or OPT, but couldn't get it to reoccur. Judgement withheld.

[rooster]

Clyde, not sure that MM can nail the correct tweed Deluxe PT for that matter - they make 5-10 versions? So all you can be clear on with any manufacturer is that they deliver a PT with the stated taps and at the stated AC voltage on the secondary with the proper amperage. Right? I gave up expecting anybody to clone the exact finished voltages written on 40 year old schematics - that was 110 VAC from the wall, eh? That's the rub there. When anybody states they have cloned a tweed Deluxe/whatever from the exact original PT, well, when it delivers 15 more VAC on the secondary - well - IT WOULD, wouldnt it? Yeah so this is always a problem.

Think a about it, when Ken made his first TW the wall was 110. So this means that we shoot for 400 on the plates because a real Epress was measured with 400 volts on plate in the day? Or did he prefer 385VDC and we missed the boat? Ha, Glen would know - did his Express sound better 20 years ago?

Anyway, I happen to think that when MCI or MM says they have cloned something vintage, they probably have. Many times, however, I would prefer something with 15 VAC less on the secondary. Especially when dealing with EL84s and 6V6s. Is this what you are talking about maybe?

[Clyde]

No Rooster, not wall voltage variation. I've seen 40 volts less on the plates than there should be. For a Fender, that's not where I'd want it. It'd be a great Express transformer though.

[rooster]

Clyde, OK, I have two brand new MCI PTs here for some projects. One is for a Deluxe Reverb, (#40-18016), the other for a Marshall 18 watter (#40-18035). The first PT is said to be 330-0-330, the second 290-0-290. I am going to measure them right now and report what I find, including my wall current.....

To be 40 volts off, well, that's huge to me. So you are saying that you bought a particular PT that said it would be XXX-0-XXX and it was either higher or lower than this? In other words, it was not built to the stated spec voltages?
.....Or are you saying that you bought it based on it's application? Like they said it was cloned from an original Fender PT and you were replacing one in that particular amp? This is important to know.

Alright, back in a few minutes...

[rooster]

OK, back with the numbers. The DR was spec'd @ 330-0-330, it reads 358-0-358. The Marshall is spec'd @ 290-0-290, it reads 311-0-311. This is approx a 7% increase over projection, not so good in my world. If I was shooting for 425 plate, I might end up with 455 with a 7% increase - (but probably 440VDC under load given a typical tube compliment.) Still not what I am looking for, however.

My wall voltage is: 122.1VAC, and either piece is spec'd at 120VAC.

Further, you have to expect an overage as the PT is measured without a load - sure - but I can report a closer percentage with Heyboer iron and Hammond under the same conditions. For example, I have PTs from Heyboer here spec'd @ 300-0-300 and it measures 308-0-308, and another piece spec'd @ 270-0-270 and it reads 278-0-278. This is only 3% over the projected load voltage and will probably settle down to the target voltage under load.

?? So at this point, I agree with you, Clyde, the finished voltages are higher. No, not 40 volts like you spoke of but maybe 15. And, yes, I'm with you on this, in some cases even 15VDC over can ruin a great plan. !!

Lastly, I am building one of the amps this next week, and will try the MCI iron under load. I don't think it will come down to the projected numbers but it might. I will let you know.

[Clyde]

Wow, those voltages are really up there, and your wall voltage isn't overly high.
I've seen 125 here and I still don't see that overvoltage. No the transformer I spoke of was for a Vibroverb, which should have 440 on the plates but only had 400. There's nowhere to go with that.

Now I don't really mean to be an MM fanboy, but when I talk to Patrick or Paul, I can source different voltage PT's for a particular build or vintage piece and that's very valuable to me.

[rooster]

Clyde, what was the MCI number for that PT? I could actually use that. The fact that you have one under-voltage like that seems kind of odd. And also keep in mind, dealing with cloned DR PTs from other manufacterers, that I have seen 440VDC on the plates. Which is to say that both parties may well have cloned a real deal vintage PT. Amongst the many versions that MM produces, you can be sure that they have one of these, too.

I guess the thing is, what I want is something that clones a vintage piece, but in the direction of lower voltages, like the schematics from Fender, in this case.. People always say that those schematics were ballpark and that you won't ever find this in the real world. Not so sure about that. I have run a Variac on a vintage DR and things are pretty damn close. Sounds great, too.

OK, update me with that PT number please, I have sent an email to MCI about these two trannys I documented above to see if they have a comment. That company is really working hard at this process, it seems just a shame that they couldn't take a leap and make something that DELIVERS vintage voltage, and not just clone a PT.

Oh, P.S., has anybody used the Express clone PT from MCI yet? I wonder how close that PT comes to 400VDC on the plates. Er, even though Ken may have been shooting for 390 in 1985.

[Clyde]

Sorry, this wasn't my amp but I'm sure the website will have specs on it.

[crafty1]

Rooster,

Since i started my Wreck build over a year ago i have made some changes, particularly the transformers. The PT i had made here in Melbourne and i spec'd it the same as the Rocket PT - 280-250-0-250-280v @ 300ma. Check out RJ's site.
Choke now is a MM-10H-CH.
The OT i orginally went with was the A470s Dynaclone. Sounded fantastic but i found it very bass heavy or boomy ( for want of a better decsription ). Reducing the output tube bypass cap from 250uf to 220uf ( as per Rocket ) tamed it some what. The OT that is in it now is the experimenter OT from Tonesluts which they no longer sell.
The key thing i found with this OT is that it has a smaller stack and a much lower DC resistance in the primary windings. In combination with the choke, this has a significant effect on the amps ferquency range/response and touch sensitivity. Not to mention the voltage relationship between plate to screen on the power tubes.

If you were to look at MM's range of OT's i would steer towards the Haddon clone for the AC30. not sure about Magnetic components?

Cheers,

Rich