Transformer advice for #102

[Matt J]

Hey everyone,

This is my first time posting here in the Dumble forum but I have been an avid reader for a while. I used a lot of the information in the Trainwreck section to build my Express amp. The Express was a great amp, but it just wasn't for me, my younger brother now uses it some and it fits him as a player much more. I have been wanting to build a Dumble Overdrive Special as my next build for quite some time and have read here on the forum as much as I could about the various generations. Originally I was thinking about a 70s build, a 50 watter based off of ODS #40. After listening to many sound examples and considering what I'm wanting out of the amp I decided a high plate non-HRM100 watt model would be much better. I've settled on #102 as the one I want to build.

I've spent some time collecting the necessary parts. An amazing silverface CE chassis, a 1x12 combo cabinet, and an EV 12L speaker. I'm almost ready to start constructing things, I didn't want to jump ahead without having as much material and tools as possible. Pretty much any questions I have had I've been able to solve by searching around on the forum. There is only one thing left I need to decide on: what type of transformers to use. This is a VERY important part and I was hoping some of you could give me some advice or suggestions on this, especially if you have built a #102 yourself. I plan on taking a lot of photos and documenting the build on here as I work on it.

Tony's #102 layout posted on here (which is really awesome by the way) shows a Fender 026554 PT and a 022889 OT. The 026554 looks to be a multi voltage export version of a high powered Twin or Dual Showman 026477 PT. I am only needing to wire mind for 120v. The 022889 OT has a primary impedance of 2000 ohms.

Originally I was looking at Hammond transformers. However, after reading around on them I kept hearing that their voltages can be off by a considerable amount. I was looking at getting their 291FX and 1760W power and output trannies. The problem with the 291FX is that there is only 320v on the secondaries. Looking at the schematic and layout of #102 the power trannie is going to have to put out at least 340v on the secondaries. The 1760W still matches up well with the Fender 022889 because it has a 2K primary impedance. It also has the convenience of 4, 8, and 16 ohm taps.

One PT I am considering now is the Schumacher NSC022756. It is listed at NewSensor as being a 100watt replacements for a Twin Reverb/Dual Showman. The biggest issue I have is that I do not have any more detailed information such as secondary voltages whether it has a CT etc. I have emailed Schumacher asking them for more information, I'll post on here what they say. Two others I am considering are the Magnetic Components ClassicTone 40-18004 and the Mojo763 from Mojotone. A custom order from Heyboer is another possibility, but I have never ordered any custom item from them and don't know what type of time frame or cost I would be looking at.

As for the output transformer, most of the suppliers I have mentioned above have a matching Twin/Dual Showman style OTs with primaries in the 2k range. Not all have 16, 8, and 4 ohm taps, which is what I would prefer. However I'm willing to deal with only using a 4ohm tap (it will be feeding an 8ohm speaker) if the OT is one that will sound really nice with this circuit. I have also thought about using an ultra-linear OT like Mercury Mag's Dynaco DO-100 but I am not that familiar with UL OTs. This amp is for mainly home usage, it's not like I'll be cranking it up to it's limit every night.

These are just some thoughts I have. I am very open to suggestions and advice if anyone has any opinions. I am going to be taking a lot of pictures of the build as I go along and post them on here as a visual record in case anyone else is interested in building a #102. It may also help me catch any mistakes I make along the way!

Thanks!
-Matt J.

[ToneMerc]

Hi Matt, I order custom stuff from Heyboer all the time. One piece orders are welcome and lead times are about 2-2.5 weeks, sometimes quicker. There's lot of choices for iron and I have my personal faves but YMMV.

If you are on eBay, there was a guy selling MCI branded(Marvel) Twin PT, OT and chokes, free shipping.

[David Root]

How about MCI # 40-18042? 345 HT winding with a 320 tap. This is a Twin PT with enough juice for a Showman. Yes it's an export primary but the lamination stack is 1/4" thicker than 40-18004, which doesn't hurt.

On the OT, either the standard MCI Twin OT, or for a bigger bottom 40-18026, which is the Marshall JMP 100W OT. I'm about to put 40-18026 into my #183 type build.

[Matt J]

Thanks for the info everyone. I contacted Heyboer about a custom wind, they said that they actually make the PT and OT sold by Mojotone I have mentioned, they recommended I just buy those because it would be cheaper then a custom wind. So I'm heavily leaning towards getting them. I'm still waiting to hear back from the people at Schumacher.

-Matt J.