Transformer binding

[erichayes]

Hi All,

The ST-70 thread on Jeff's "funny car" stereo 70 jogged my memory about something to keep in mind for you guys who are having transformer bells painted, plated or powder coated.

Toroidal transformers are not the only ones that can be screwed up due to improper mounting or enclosing. Your standard EI laminated-core transformer is subject to the same problems--they just manifest themselves a little differently.

If you disassemble a well built transformer, you'll find that there are fiber or plastic washers on the bolts holding the bells on. These are to break the "magnetic short circuit" that would be created due to metal-to-metal contact between the bolts and the laminations. Disassemble a really well built transformer and you'll also find insulating tubes in the lamination bores to further separate the bolts from the laminations.

The point is: when you get your customized bells back from the shop, don't forget to replace the insulating washers when you reassemble the transformers.

Since I receive my transformers disassembled to begin with (the bells are powder coated by another vendor), I can start the assembly from scratch using 304 stainless hardware, aka 18/8, which is nonmagnetic. This solves all the insulating problems completely. As a result, the power transformers run cooler (cold, in the case of the 1773) and the output transformers . . . well, ya gotta be there.

If you can't find 304 hardware locally, McMaster-Carr definitely has it and West Marine possibly does (I haven't checked).

[TomMcNally]

I noticed (and replaced) the nylon insulating washers and cardboard tubes when I replaced the stock end bells on my Triode ST-35 transformers with Ned's cool looking nickel plated versions. One thing that annoys me about almost all of the transformers, is that they use cheap steel bolts, and it looks like they just break the extra length off with a pair of pliers, rather than use the correct length hardware, or cut them properly.

I'm a big fan of Phillips head stainless hardware in my amplifier construction, it looks much better than cheezy zinc common head bolts. I may buy a box of 3" 8/32 size 18/8 stainless from boltdepot.com next time, and replace the transformer bolts in a few amps that look nasty.

I also like the nuts with the built in washer, but they only seem to come in zinc.

[mesherm]

Those nuts with the captive star washers are called K-locs. I absolutely love them. I use them in all my amps. McMaster-Carr has them in 18-8 stainless.
P/N 96278A005 for 4-40
P/N 96278A007 for 6-32
P/N 96278A009 for 8-32
P/N 96278A411 for 10-32

[TomMcNally]

Thanks - I've been getting 100 for 99 cents in Zinc ... the stainless from McMaster-Carr are about $ 9 a hundred, but I see boltdepot.com does have the 18/8 stainless variety for about $ 5.50 a hundred. Time to stock up ! I've been mounting medium size transformers with 8/32 hardware, and using 10/32 on the monster stuff.

... tom

[EWBrown]

I like the Magnequest look, so I've been using 8-32 brass bolts and some nice gray fiber washers which my local tiny-town hardware store has in stock. A repaint of the end bells, clean and paint the lams, then add the brass hardware, and any humble old tired looking trannie can look "high end". Yellow_Light_Colorz_PDT_08

/ed B in the frozen tundra wastelands

[erichayes]

Hi All,

The K-Loc is a brand name. If you ask your fastener guru for kepnuts or kepsnuts--I've seen it both ways--he'll know what you're talking about. BTW, the nut on a stainless kepnut is stainless, but the star washer on every one I've seen is regular steel and prone to rust.

I mentioned McMaster-Carr as a vendor because they carry everything known to man and beeste. I didn't mention that they are also one of the most expensive purveyors around. I buy all my fastener-related stuff from www.olander.com in Sunnyvale. They take plastic and don't have a minimum (and do have a WATS line).