Denco coil.

[mickm3for]

Hi, I have 2 range 1 yellow coils. One reads main winding pins 1-6 3528uH coupling pins 8-9 80.2uH. The other one main 3522uH coupling 335.6uH. Both are 9 pin DP coils. Is this a fault in winding from factory as coils have not been touched from new? How long is that guarantee? Oh no just a few days over.

Mick.

[Philips210]

Hi.

I wonder if the difference could be due to the core being in a different position in relation to the windings. I suppose a check with both cores unscrewed may clear the suspicion on the windings.

Regards,
Symon

[mickm3for]

Hi I have checked the core the core is in the same place on both. Looking at them side by side the smaller uH coil the dia. of the winding is smaller (less turns) but as far as I know not tampered with and looks untouched.

Mick.

[snowman_al]

Is one a 'transistor' coil and the other a 'valve' coil?

[mickm3for]

Hi how do you tell the DP coil from the transistor coil Mick

[snowman_al]

Difficult now.
The originals were just valve coils obviously. The aluminium can they came in had the range and colour label on the lid and then 'DP' printed on it.
The transistor age saw the same label with a 'T' printed in place of the DP.
Over time the can is lost and the coils all look very similar...

I just wondered if the one with the least turns was a transistor coil.
The coil associated with the tuned circuit would be similar or the same whereas the coupling coil would have less turns to match the transistor input impedance?
Alan

A quick google finds plenty of pictures still, and some winding data, you may be lucky and match yours to a picture(s).

[frsimen]

Transistor coils have three windings, so use 6 pins on the base. Dual purpose coils have two windings with only 4 pins used on the base, except for the green variant which have three windings and use 6 pins.

Denco did occasionally use the yellow formers for other types of coil. I have a transistor range 2 blue coil on a yellow former. There is a spot of blue paint to indicate that is actually a blue type.

Paula

[snowman_al]

Paula,
''Transistor coils have three windings'', that is an excellent 'catch'. Of course they have, I should of given it a little more thought...
Alan

[Marconi_MPT4]

According to the Denco General Component Catalogue, they did manufacture a different set of tuning coils for valve and transistor circuits. Both yellow range 1 coils were designed to cover 150kHz to 400kHz with the recommended 300pF tuning capacitor and designed around a B9A base. It appears these were ordered just by description i.e. type, colour, range.

When using a 500pF capacitor, valve range 1 covers 150kHz to 350kHz

A description for the valve type is stated as having a 'signal grid coil with intervalve coupling winding', and for the transistor version, 'interstage RF coil with couplings'. Unfortunately no inductance values are given but apparently these might be found in technical bulletin DTB.4.

Rich