BBC transformers - anyone have experience?

[API]

Hi.

I own a BBC line mixer that have unbalanced inputs and i have been looking for some transformers for this to balance them.
Right now i see there are several lots of BBC transformers on Ebay and i was wondering if anyone here have any experience or knowledge on which to buy for a line input?
I have no docs on the mixer either and i suspect that it was either unbalanced or had remote transformers from the start.
Numbers i see on the Ebay ones are:
LL88ASC
LL81MSC
LG105MSC

 

[CJ]

there was a lot of hype on those orange pumpkin looking things,

but i forget if they were inputs or outputs,

LL88ASC, 12 of those for 45 bucks on evilbay but they are still bidding,,

 

[ruffrecords]

The ll88 is a 600:600 type. Quite chunky so not sure if it is intended for input or output. The ll81 is a10 k:10k type intended for line input and is just what you need. I tested both types some time ago when the group put together a document listing the basic inductance parameters of a range of transformers. You can find it here:

http://www.groupdiy.com/index.php?topic=47515.0

Both these transformers are well specified.
Cheers

Ian

 

[MatthisD]

I bought a lot of LL88ASC from the last round, worth it for the cans alone I thought.

Dull finish laminations, presumably radiometal 50/50 material. The exact same lam as in OEP A262 series.

Mu can 31.5mm OD, filled with wax (easy to melt and remove core)
Core: 24/25 EE
Stack: 38x 0.35mm (fully interleaved)
Structure: 1/2 primary, 1 turn of tape, 1/2 secondary, 1/2 secondary, 1 turn of tape, 1/2 primary.
turns: Outer winding (1/2 Primary) 372 +/-10 turns
Wire: 34AWG or near equivalent SWG

Inductance: 10H primary or secondary.

I think they are 1CT:1 there must have been insulation between the two halves of the secondary but I don't know if I left out the "1 turn of tape" or if it wasn't there which would mean the secondary is all one chunk. No copper shields.

If the can was any smaller then the core would not fit so LL81MSC must have a smaller lam size.

Regarding the LG105MSC there is an LG type datasheet here:
http://www.sowter.co.uk/pdf/BBC%20LG%2096A.pdf

Under LAM NO. it says; 187

see below, could be this size which would fit in the 25mm diameter can.
http://www.magmet.com/lamination/187ei.php

 

[MatthisD]

The one I took apart happens to be the one with lowest inductance, the other 11 that I measured range between 10.2H and 16.75H. DCR of the windings is almost the same for all of them, within about 1% (red - green 56.7 ohms).

The lids are held on with three blobs of solder and are easy to remove. Photo shows the two different versions, the lower 10.75H model on the left and 16.8H on the right.

 

[MatthisD]

Model number drawn with marker on one and printed on the other.

 

[MatthisD]

The brighter finish on the right comes from the transformer on the right from above post.