Transformers, anyone interested?

[Grim]

I am thinking of designing a standard range of transformers for guitar amps, as I know a lot of people want to build an amp, and hit a problem when trying to purchase a small quantity.

would this be something you're interested in?

[Steve Conner]

I live in the UK, and I get Hammond transformers through Bluebell Audio.

I've also seen remnants of the old "Maplin Millenium 4-20" transformers kicking around, and Maplin were recently selling Oxford Electronics 30 watt OPTs for £25 each. I bought two, but ended up swapping them with a friend, for an OPT from a Sound City 120.

But anyway, you should take a look at Hammond's range and prices to see what you're up against. There will be import duty and markups, for sure, I recently paid £80 for a 290KX PT.

[Grim]

prices wouldn't be a problem, as these are direct from the manufacturer, with no middlemen

100W output for about £50 delivered? 100W mains, around £60 depending upon actual power needed.

What people don't always realise is that small batches and specials don't cost a lot more to make, as all the materials are the same as the high volume stuff.

Having a standard range gets rid of the design overhead too, so you get the benefits of using the same manufacturer as the biggest amp builders use, without a price penalty.

not sure if there any rules about advertising on here though

[Steve Conner]

Well, yep, sounds like a good idea then.

My transformer cupboard is pretty full just now, but I'm sure there are quite a few other UK builders here who might be interested, so let's hear your opinion folks.

Bear in mind everybody will want something different! It might be a good idea to just do one transformer set for a popular amp and tell them what they're going to get. I'd vote for the 18 watt Marshall, or maybe the Fender 5E3, what do others think?

I don't know of any restrictions on advertising. Pickup makers pimp, er, showcase their work here regularly.

[Alex/Tubewonder]

What about compliance with current CE norm 61558? ROHS?
Custom 1-3 pcs?

[Grim]

The parts would not be 'Approved' to 61558 or 60065, but 'designed, built and tested in accordance with'. As you rightly point out, no one is going to submit 3 parts to a test house and have them approved.

Our internal technical files will support the construction and design principals are identical to the vast number of parts we supply to OEMs, which have been independantly approved.

All of our parts have been ROHS compliant for many years, and of course, lead free

We also have UL yellow cards for all our critical components.

From experience, as soon as it's in your amplifier, a test house will want to double check everything anyway.

[MWJB]

Hammond PTs are fine but, in the UK, it's not easy to find lay down types that fit into existing chassis. Torres already do reasonable 50W & 100W types that run 345-0-345VAC, or thereabouts, but something running 370-0-370 @ 200mA, or 375-0-375 @ 350mA for 50W & 100W handling would be good (for Brown tolex/BF style voltages, no current replacement for 67233 PT available in UK), especially if they could handle decent heater current, like 6A & 8A respectively, for EL34 & up to 6x 12AX7?

What they (Torres) don't do is a 330-0-330VAC @ 120mA, 6.3VAC @ 3.5A centre tapped, 5VAC @ 3A - ideal for champ upgrades (1x6V6 up to 1x 6L6/EL34/KT88, or 2x6V6 a la 5E3 with enough reserve to run 6L6 with a couple of 12AX7). Great for Champ, Princeton, Tweed Deluxe style builds. Especially if it could be made in 2 footprints, 2"x2 1/2" & 2 7/8"x2 1/4". If necessary, 3A for the smaller footprint, 4A for the larger?

I wouldn't go for a straight copy of the 5F1/5E3...from the posts I see, lots of folks want to try them with 6L6/EL34 or 5U4, so makes sense to build that capability straight in.

5F1/5F2A/5E3/5E3x2 seem to be popular kits/projects for hobbyists.

In fact, if you matched them up with reasonable pre punched chassis kits (steel would do, + faceplate) it would make a handy bundle...am I getting carried away now?

[Alex/Tubewonder]

The parts would not be 'Approved' to 61558 or 60065, but 'designed, built and tested in accordance with'. As you rightly point out, no one is going to submit 3 parts to a test house and have them approved.

Our internal technical files will support the construction and design principals are identical to the vast number of parts we supply to OEMs, which have been independantly approved.

That's standard procedure. Based on your test protocols you can apply CE mark on the transformer and issue CE 61558 declaration.

All of our parts have been ROHS compliant for many years, and of course, lead free

We also have UL yellow cards for all our critical components.

Fair enough

From experience, as soon as it's in your amplifier, a test house will want to double check everything anyway.

That depends on the test house. Generally, if a transformer carries CE mark they will test the amp as such and not bother with testing transformers separately, unless failure to comply with 60065 is traced to transformer misbehaving. In that case it'll be a dispute between you and me whether transformer is being used within its specs or if it is norm compliant.
That's why I provide very detailed specs when I order custom transformers, down to specific isolation materials, HV test voltages etc. Good dialogue with manufacturer prior to releasing to production is best way to avoid future disputes.

I'll be in touch when the time comes