Building 5F2-A from scratch transformer quest.

[chikov]

Hello Friends. In January this year I moved from Houston ,TX to Moscow Russia and now I am attempting to build Prinston tweed amp for a friend. I want to buy most of my parts locally, however, to buy both POWR and OT I have to order them. I went to a small place where they said they would build me one if I give them all the info. My first question is this, if you were to build an OT what would you need to know? the number of turns, or the ratio or the impedance? What those numbers would be for the 5F2-A OT and may be What will I need to tell him about the PT? just that on B+ it is 325Vac and two more windings for 6.3 V and 5V? I am blazing the new trail over here and I appreciate all your help. Thank you.

[pompeiisneaks]

There's actually quite a bit of art to transformers.

lamination material
core size
gauge of the primary and secondary wires
etc.

I don't know if you can just give them the exact information. You can try to give them dimensions of the transformers as well as primary and secondary voltages, impedances, current capacity etc. and they 'might' get the figures correct, but still have a crappy OT, if it doesn't have the right kinds of 'magic' done to it like core gap and some other stuff I only vaguely understand. Sadly, it's becoming a lost art I think.

For non audio applications it's a lot less important I think, just slap some windings into E I laminations and you're golden

I once researched if I could build a transformer winder with a raspberry pi/arduino and a few stepper motors, but realized quickly the really thick books you need to read/master to understand transformers, I became quickly disenchanted with the idea

~Phil

[Phil_S]

To build on what the other Phil says, there's a great deal to know about a transformer and the chances of getting it right are limited.

You might do OK on power transformer if you know the voltage, current, and overall wattage.

An output transformer is a whole other thing. You'd really want to know the number of turns, wire gauge, etc. In addition, it is important to know if there is interleaving or not. This amp has a single ended output, so an air gap is required.

Read this. Look for Roberto's post with winding specs and questions. You'll get the idea of what you need to know.
https://ampgarage.com/forum/viewtopic.p ... ve#p379241

See if you are able to purchase Hammond replacement transformers or get someone in the US to buy you what you need and ship it to you.

[chikov]

Oh wow, thank you guys for the info. I will talk to the guy tomorrow and let you know what he said. At the shop they had some PT looking like a big donut (no core at all). I think guitar tube amps need a metal core on their amps, correct?

[pompeiisneaks]

Those are called torroidal transformers, they have a donut core instead. They work as well, but I've not used them. They're becoming a lot more common than the old style square ones. I don't know enough about how the core works, but 'core saturation' is important for transformers in some cases related to audio... again, I only vaguely understand the how/why of it.

I don't know if you can make output transformers of toroids, though... I've only seen power myself.

~Phil

[ChopSauce]

Not at all (in reply to chikov). I built two amps with toroidal power transformers.

If you can't or don't want to buy Hammond, which seems to export massively, or inMADout, latter which is a "european" company, I'd be surprised that you can't simply give the characteristics of the power section you plan to use and have something build accordingly. Whether the outcome will (or not) be tonewise "close" to the original is another story but I think buying straight from the USA is the safest, in that respect.

[Phil_S]

Show the schematic to the winder. It may give him enough information to get it done right.

[chikov]

I got a message from the Transformer guy - he saw the diagram I sent him but he needs to know the diameter of the wire and the number of winds. does anyone know where can I find this info?

[pompeiisneaks]

That gets back to pretty much what I was indicating at first. It's unlikely that you'll find that kind of information without destructively pulling apart a known transformer to get the wire gauge and do some windings ratio tests to see how it's setup etc.

Some of that special mojo that makes transformers what they are.

You can try to contact on of the us manufacturers and ask, stating you're not in the US so you can't get us transformers, but they still likely won't want to give away the secret sauce.

~Phil

[Phil_S]

Here, this looks like it might help.
https://www.youtube.com/watch?v=k6b7ND8dCoA
For $10 you can purchase the single ended plans, which what you need. I can't say if they are worth it or if they are any good, but it looks cheap enough to take a chance.
https://www.delatsch.com/shop/

[chikov]

Here, this looks like it might help.
https://www.youtube.com/watch?v=k6b7ND8dCoA
For $10 you can purchase the single ended plans, which what you need. I can't say if they are worth it or if they are any good, but it looks cheap enough to take a chance.
https://www.delatsch.com/shop/

Thank you so much for this info! I did spend $10 and and got some good information on OT build and Exell sheet that helps to calculate all the info to build one from scratch. I talked to the guy here in Moscow who winds transformers and he said that he is not that good at OT ones because so much matters in their construction ( the Primary and Secondary winds have to interchange and the core pieces have to be put tothether the certain way with the pieces of paper in between. He said it will be $35 for him to make one and I can get Champ OT from Stewmac for $28 and free shipping (I have a membership with them). So I told him not to bother - I will buy one from US. It might be an interesting endeavor to start making my own transformers though... The guy from the link above sells the winder for $100...

[Phil_S]

Good choice. I'm not surprised about what the winder said. Making an audio transformer is much more complicated than power transformer.

I suggest you think carefully about spending $100 for the winding machine. That is only the beginning. There will be other things you need to buy. Patrick Turner, an expert winder has retired, but his website is still running: http://www.turneraudio.com.au/ Reading will show you there is a great deal to know and equipment needed.

[2L man]

If you need to order parts consider Uraltone here in Finland. I believe they are used to mail to Russia as I have read positive customer comments from their site. I just built a 5F2 and for it I bought Hammond 1760C and most other components from Uraltone but its PIO capacitors came from Russia If you ever build Deluxe, 5E5, 5E7, 5F7 etc the Uraltone 5E3 Eyelet Board is beautiful design!

Esa

[katopan]

Output transformer winding details (wire dia, turns and layering) are almost guarded secrets for those who have put in the time and money to tear down and analyse old original transformers. You can find some designs on the web. Sometimes you come across discussions with other people and are lucky to have a classic design shared. And no, I'm sorry but I don't have the details for 5F2-A transformers or I'd be happy to post them.

The 'proper' design info for winding a transformer was covered in my Uni course, but gave me no practical capability for winding my own. Then years ago one of the guys on the 18 Watt forum was openly talking about transformer design 'rules of thumb' that simplified the process and make it practical. Then there's the actual winding itself which takes thinking through in detail and there are a number of approaches used. But with his mentoring and other online discussions I've had with people I was able to construct a simple hand winder and proceeded to wind a few PTs and OTs. Those included sets for a 6P1P-EV push-pull amp as well as a Wreck Express. After that I upgraded the winding machine to be stepper driven and Arduino controlled. I've made another set since the automation and those are currently in my 6G6-B Bassman build.

When you don't know the proper details of vintage transformers but still want to wind your own, you are left with designing the wind yourself. That involves making your own educated decisions about the design choices, which are all compromises.

Winding your own transformers can be very rewarding and fun. On the other hand it is hugely time consuming for individual one-off builds and even if you do it cheap as possible (like I did) you will still spend more on the materials set up that the first set of transformers will cost you commercially. The savings only come once you have wound a few. But did I mention the time involved? Making the transformers will become the most time consuming bit of building an amp.