Specs for OT 784-139

[flatart]

I would like to build a replica of 784-139 OT for Marshall 50W plexi.
I've looked all over the net to find all details but I've collected just few info.
I know that these are considered precious secrets and people are doing their business with it ... anyway I try
Here the result of my search, as you can see I miss a lot of info

- winding pattern it seems to be: 0.25 PRIMARY || SECONDARY ||0.5 PRIMARY || SECONDARY ||0.25 PRIMARY
- primary should be 1760 windings, diam 0.31mm
- So I should have: 440 turns PRIMARY || SECONDARY || 880 turns PRIMARY || SECONDARY || 440 turns PRIMARY
- About secondary windings: I dont know if they are connected in series (two windings of 60 turns) or in parallel (like dagnall C1998, so two windings of 120 turns, first 0-16, second 0-4-8-16) and how they are distributed.
- I don't know even secondary diameter, doing some math it should be 1.08mm, but I would like to know exact diameter
- About iron it should be classical "I-E" 96mm x 80mm, 58 laminations x 0.65mm (tot 38mm)
- For iron type I should go for M6

Moreover: I dont know the meanings of "self leads" or " flying leads", can you explain me?

I hope that someone will give me missing infos or at least confirm what I found (even directly to my email)

[Structo]

Can't help you with the tranny build but self leads refer to the leads coming off of the various taps which are the same wire as it is wound with I believe, they slide insulation over the wires.
So this is solid core enameled wire. It can be rather fragile and doesn't take many bends to break them.

Flying leads mean the windings are terminated and new wires (usually stranded) are soldered on to the tap wires and color coded for the windings.

[Richie]

contact Brian Wallace, wallace amplification, he has some already made,and knows more about the marshall transformers than about anyone. He also has a nice list and record sheet of marshall amps and what trannys they used.


http://www.wallaceamps.com/

http://marstran.com/

[flatart]

I know Brian because I bought some of his trannies and they are amazing. I don't ask him because what I'm looking for is "his secret", he has unwound original Drake and Dagnal OTs and obviously he knows everything but this is his business.
My problem is that if I buy Marstran or metropoulos or mercury OTs, I have to pay a lot of money for shipping and tax (and EUR/USD change is going down...). so I'm trying to get exact specs to give to a professional OT maker here.

[epis]

Hi,
Thanks for sharing.Only what I could tell you,two 60 windings in parallel is for 4Ohm,in series for 8Ohm output.For 16Ohm you would need 4 windings.Good Luck with project

[flatart]

two 60 windings in parallel is for 4Ohm,in series for 8Ohm

Hi epis, this is not correct, we are not speaking about resistance, we are speaking about coil windings, so if 60 windings are 4ohm impedence, then two 60 windings in series (120) is 16ohm impedence

[epis]

You are right,sorry ,but,check out this:
http://forum.metroamp.com/viewtopic.php?t=16305
http://forum.gtlab.net/cgi-bin/yabb2/Ya ... 1166911150
It is in Russian but you can see the pictures of secondary wiring and get some ideas.

[flatart]

Hi epis, I'm posting in 5 different forums and you are the only one that helped me. Thanks for this picture.

Your exact link does not work and I can't do any search in this cirillic forum. I tried also with babel fish translator but with no success

Your picture is the winding schema for Marshall 100W OT Dagnall C1998. In fact I'm looking for the same info but for Marshall 50W OT Drake 784-139. I suppose it's the same, but I dont know for sure, consider that we are talking about 2 different builders (drake and dagnall)

[flatart]

http://forum.gtlab.net/cgi-bin/yabb2/Ya ... 1166911150

cirillic but grreat link

Thanks again epis

[flatart]

Sorry, this is the correct C1998 OT dagnall winding schematics

[INDIAN.LN]

Hi
I'am sorry for my ENGLISH.
Is not werry well......

I'am man, who sometimes read this kind of forums and i take notice, that nobody ( from comunity of people who knows ) will help to people who want know, what is inside this 50W Drake output transformers.

So.
Possibly I'am a mad.
But, I took best sounding plexi 1987 ( with 440V on anodes - not handwired! ) from our district and I make reverse engineering of output transformer.

It was a DRAKE from 06/1999

So, it was a shitty rendition of second simplyest version of output transformer.

I can't believe, that it can sounds so good as sounds.


On plastic bobbin was:

1st winding - 426 turns, starting from white anode wire and finish is connected to start of 7th winding (inside OT)

2nd winding is started from orange wire ( GND of repro circuit ) and have 40t. Finish is connected to start of 4th winding.

3th winding is started from brown wire ( mid of primar - and is conected to finish of 7th winding in paralell ) and by 852t finished in red anode wire.

4th winding have 20t and start is conected ( internally ) to finish of 2nd winding. Finish is conected to start of 5th winding and is 4 Ohm output at the same time. ( yellow wire )

Finish of 5th winding is 8 Ohm output ( green wire ) and is together conected to start of 6th winding.

5th winding have 24 turns.

6th winding have 35t and finish is 16 Ohm output ( grey wire )

7th winding have 426t and start is internally conected to finish of 1st winding.
Finish is conected to start of 3th winding and together are center of primar winding ( + )

Between windings are some ( 2 or 3 ) turns of sticky paper tape.

No paper between each layers ( or each second ) -

primars looking like wild winding - wires are oftentimes failing to lover layers.

Unbelievable bad craft!

But sounds like a God!

Now is temporarily Dagnall txop 00005 inside this 1987 ( which I buy from official Marshall service center ) and is boring. Or I dont know how it say??
Simply no fun....
My friend says, that sounds closer to Slash or that sounds little bit modern.

For me it is not acceptable sound. Now it sounds like other plexis in our region - nothing special!

So, Drake must get back!



Good luck!

INDI

[Phil_S]

flatart: If you bring the information you have and have acquired (particularly the last post from INDI) to an experienced winder, explain the amp (wattage, voltage, etc., bring a schematic), from all this, he should be able to figure the correct secondary wire gauge, turns, and interleaving, as well as the appropriate lams. You'll probably get a darn good transformer and you will then have the "formula".

A note on the lams. The idea is to figure the dimensions of the bobbin after winding and size the lams accordingly. An experienced winder should be able to do this easily, particularly if you can suggest what appears to be the correct choice. I've fooled with this a little bit in attempting to rewind a small SE OT that was bad. It is surprisingly simple to estimate how many turns of wire will fill the "window" and that is your limiting factor.

I actually think you are "there." Now you can find out what a one-off wind will cost you! It may be cheaper just to buy one from the fellow who has already reverse engineered the OT.

INDI: Thank you for your posting. Your English is not perfect but your information is very clear.

[epis]

Hi Indian, thanks for your post. Could you, please, post what magnet wire gauge (wire diameter) was used for that transformer. Thanks.

[INDIAN.LN]

Hi

For America: Primary wire is 29 AWG and secondary 20 AWG

For others: Primary 31 SWG and secondary 21 SWG

( measured without insulation )

Primary wire have clear insulation, looking like classical plain enamel and secondary is red.

[Phil_S]

Magnet or transformer wire comes in a variety of colors. As far as I know, the color has no meaning. It is probably good to use different colors for each winding so you are not confused when interleaving. However, 20AWG and 29AWG will not be mistaken. One is fairly thick. The other is not quite hair thin.