Can you help me identify an input transformer ?

[PeteC]

Hi

many years ago I gutted a second-hand Valve PA to build up a 50Watt ODS Clone for my backline.

I kept the surplus parts knowing that they would come in handy sometime in the future.

Looking through my parts bins I found a cylindrical input transformer - but it has no manufacturer markings.

Measuring with my DVM I find its got 2 windings :

1) Red - Brown - Black  which measure 2.7Ohms and 2.7Ohms between centre tap and ends.
2) Yellow - ~Orange    which measures just over 2.6K across the winding

It feels nice and weighty and of good quality.

I rigged up my DVM and a simple signal generator putting out 1v at 100Hz into the Yell-Orange winding and I read 7.9mv across each of the other two windings ( the centre tapped one )

So I figure I've got an input transformer with a 125:1 ratio - is that right ?

What sort of input would this be for ?
what could I use it for ?

looks like its far too high a ration to be any use in my Bo Hansen DI box build ( I was planning to use an OEP )

Any advice welcomed !
cheers
PeteC

 

[MikeClev]

You saw 7.9mv on each primary... well who uses just one primary winding? So its 16mv on the primary for 1v on the secondary, so 1:64ish.

That seems unusually high for any transformer outside of Ribbon mics!

 

[CJ]

your generator is probably 600 ohms output, so plug it into the 600 ohm pri of the transformer under tst.

the z balance will energize the core and the signal taken at the secondary will be much larger, 7.9 milli volts is really close to the noise floor of most scopes and volt meters,

so you want to measure the sec. voltage, because it is higher and will therfore give you more accurate readings from the dvm or scope, since the noise is now out of the equation.

i do not think the xfmr is 64 to 1.

a better ratio check will verify this,

also, try 1 k hz,

less distortion, if the xfmr is weak in the bass dept, the 100 hz signal will be distorted.

 

[PeteC]

OK,

i tried a 1v signal at 1KHz into the centre tapped primary and got 20V across the secondary.
So I guess i Have a 1:20 input TX.
What woud it be any good for ?
cheers
PeteC

 

[ruffrecords]

OK,

i tried a 1v signal at 1KHz into the centre tapped primary and got 20V across the secondary.
So I guess i Have a 1:20 input TX.
What woud it be any good for ?
cheers
PeteC

Tube mic pre of course!!

Cheers

Ian

 

[CJ]

you might have been on the center tap and an outside lead, which would double the ratio,

so it might be a 1:10. a typical input ratio

although i have seen some geo transformers with high ratios,

 

[PeteC]

thanks CJ -  i made sure to use the 2 outside leads of the winding so must be a 1:20 i guess.

Ian - tell me more about tube mic pre - whats a good novice single channel  mic pre ? Is NYD's one bottle a good bet for this tx ?

cheers
PeteC

 

[lassoharp]

What brand was the PA head?


Chances are probably good that the input transformer is budget quality in terms of response & headroom so think 'color pre' usage - something fun & cheap to build but still potentially useful.

The classic DIY dilemma with cheaper iron is - is it worth going to the effort & expense of building an entire mic pre from scratch for what will likely be a one trick pony, although it may turn out to be a very cool one.

I wasn't sure what your expectations were but I wanted to point that out in case you were hoping for something else.  If you just wanted a fun color pre, things like the old Akai/Roberts tape recorder modules or other similar units are great for this purpose.  The chassis and power supply are already intact and basically all you have to do is add the input transformer and remove some non essentials and you're ready to go.

 

[PeteC]

thanks Lassoharp

the PA was a RADIOVOX brand made in UK.  Cant find out much about them other than the guy who owned them lived in the next village to me apparently ( Bramhope, near Leeds in the UK )  Many parts were early RS, with Partridge TXs.

most parts seemed to be of very good quality and the wiring was meticulous - think early Hiwatt Mil Spec wiring.
There were originally 2 KT66 tubes in there with german ECC83s and EF86s.

Its now a *umble 50watt ODS clone  :-[  but sounds good 

I think a coloured tube mic pre would be great . I have tons of self built valve stuff - I like coloured !!

Rgds
PeteC

 

[lassoharp]

Thanks Pete,

I don't know much about the UK stuff but it sounds like it might be a cut above the budget amps. 

Keep us posted on the build!

 

[ruffrecords]

Ian - tell me more about tube mic pre - whats a good novice single channel  mic pre ? Is NYD's one bottle a good bet for this tx ?

cheers
PeteC

I would expect NYD's one bottle would be fine with this transformer.

Cheers

Ian

 

[PeteC]

I will lassoharp

I just have my Bo Hansen DI, dual green pre, and the second of my G Pultecs metalwork to complete first :
Oh , and theres a Loftin White on a breadboard as a monitoring amp as well at the moment
Need to get back to some songwriting and recording ...

Thanks for the thoughts on a mic pre project. I'll definitely do this.

Cheers
PeteC

 

[PeteC]

Thanks Ian,

so,........looks like NYDs one bottle is the project for this TX

thanks all
PeteC

 

[CJ]

kt66 and tele tubes , sounds like a rather good rig,

genelex brown base kt's are about 500 bucks a pair,
tele ef86 probaly 50 to 100 bucks a pop for th real ones,

sweep the xfmr up to 20 k and see where the dips are