Express Transformer Allignment

[BIG Dave]

I'm about to drill the holes in the chassis for my first Express build. Going by the Ron Worley Express Build Guide page 11, it appears to me the transformers are not aligned along their center (front to back). The diagram shows a hole at the rear corner of the chassis for the OT positioned 5/8" from the rear panel and 1 5/8" from the side. The hole at the front corner for the PT appears to be 7/8" from the front and 3/4" from the side. I marked the holes with a Sharpie and then positioned the transformers using the corner hole marks as a guide. In this position, the transformers are not aligned (from front to back). The OT is closer to the center of the chassis by about 1/2". Before I go ahead and drill the holes, I just wanted to verify the transformers should not be aligned. Is this correct?

[M Fowler]

The OT is smaller then the PT so they would not be aligned.

Watch out for the front valance thickness hitting the transformer I always adjust for that before I mark and drill. Remember it is only a guide your transformers may be different from original in overall size.

Mark

[BIG Dave]

Thank you Mark. The PDF you attached shows the PT and OT aligned along their centers. On the other hand, the Worley Build document (page 11) shows eight red dots denoting four OT mounting holes and four PT mounting holes with the OT mounting holes shifted too far away from the outside edge of the chassis for the two transformers to align along their centers. I searched the Internet looking for a "top down" view of an Express for comparison however I wasn't able to find a picture from that angle. There is however an RJ pre drilled chassis in the FOR SALE section and the hole pattern appears to match the PDF that you posted (I'm using an Alyn Myers chassis and the transformer holes are not drilled). I'm leaning towards going wih the pattern you posted...

[M Fowler]

Here is an original TW Express top view.

[martin manning]

Do you think Ken might have been tweaking the alignment of the transformers to minimize hum? My recent experience says putting them on the same centerline is best, but maybe some sets are quieter if they're off-set.

[M Fowler]

Not sure Martin but I set mine where they line up the best and I try to center line them too.

I watch the side and front valance positioning then mark and drill. I haven't used the headphone trick to place the transformers.

Mark

[BIG Dave]

https://tubeamparchive.com/download/file.php?id=29236

From the photo provided by Mark, it is clear KF mounted the OT off-center relative to the PT. Yet Martin and Mark had good results aligning the transformers. It appears the placement isn't critical as good results are achieved either way. My sense of symmetry is making me lean towards aligning the transformers. Decisions, decisions....

[xtian]

Use the headphone trick and use your ears!

[martin manning]

For me it's easier to just clip my DVM on the OT and minimize the millivolts.

[BIG Dave]

Use the headphone trick and use your ears!

For me it's easier to just clip my DVM on the OT and minimize the millivolts.

Please confirm I have the Headphone Trick correct. I attach the 120 VAC primaries of the PT to 120 VAC wall voltage. All other leads including the secondaries are taped off separately. The 16 ohm output and the ground of the OT are connected to headphones. All other leads including the primaries are taped off separately. Then I move the OT until I hear the least hum in the headphones. Correct?

Regarding Martin's comment, the PT hookup would be the same, but instead of hooking the 16 ohm and ground to headphones, those leads are connected to my VOM set to MV? Correct? Thanks again for everyone's help!

[JazzGuitarGimp]

Use the headphone trick and use your ears!

For me it's easier to just clip my DVM on the OT and minimize the millivolts.

Please confirm I have the Headphone Trick correct. I attach the 120 VAC primaries of the PT to 120 VAC wall voltage. All other leads including the secondaries are taped off separately. The 16 ohm output and the ground of the OT are connected to headphones. All other leads including the primaries are taped off separately. Then I move the OT until I hear the least hum in the headphones. Correct?

Regarding Martin's comment, the PT hookup would be the same, but instead of hooking the 16 ohm and ground to headphones, those leads are connected to my VOM set to MV? Correct? Thanks again for everyone's help!

Correct. You'll want to set your meter to AC mV.

[Bob S]

This works - either way.
Don't be surprised if the OT needs to be a hair skewed.
Well worth the effort.

[geetarpicker]

Dave,
I left a PM, but basically yes Ken offset them slightly. Like the pics show the OT is perhaps 1/4 to 3/8" closer to the output tubes compared to truly on the center line. I do know Ken believed that transformer placement can even effect tone, and he used the old Marshall plexi 100s as an example. The earlier Marshalls 100s had quite different OT placements compared to the metal panel amps and Ken mentioned there was different coupling going on between the OT and the power tubes because of this and a tonal effect. Still, in the wreck the offset is only slight but it all is part of the recipe so I'd stick with the way Ken did it. If you change it I'd surely then use the headphone trick to compare hum pickup from the PT to the OT with different placements. Keep in mind though Ken's reasons for the transformer placements may have also been for more than just minimizing hum.

Also it seems perhaps about half the Express/Liverpool clone builds are starting out with stability issues so I'd be careful messing with the recipe Ken had, at least for starters. My two clones were built simply following my '89 and they are 100% stable fully dimed, even with the bottom ground panel missing and no grid stoppers and only shielded cable on the input lead. I know following Ken's layout might just be a monkey see monkey do mentality, but it's probably the safest way to start out.

[bgkyt1]

Maybe Ken just moved the OT further in so there was room for the board mounting screw and ground screw.

Having tried the headphone trick to position transformers, I have found that having them that close produces a lot of hum, and offsetting them a little might not make it worse. But even though it hums a lot through headphones, maybe it's not as bad through the speaker in a room situation?

[Richie]

Also don't forget before mounting the transformers, make sure you have the mounting holes for the power supply board. Some of the holes are under the transformers. And if you don't do this first, you'll have an AH crap moment. Any holes under the transformer, I usually counter sink them so they are flush with the chassis, and put a nut on the bolt to hole it in place till I mount the boards. But again, I sometimes do things a little different. I use nylon spaces and bolts, and no standoffs for the boards.

I like Allyns' undrilled chassis because people use different transformers. And you can make you own mounting holes for whatever set your going to use. Those pics sure look like there is more space between the transformers.