Denco green MW coil inductance?

[mickm3for]

Hi, anyone know the inductance of the feedback winding on the Denco range 2 (MW) coil or any for sale, thanking you. Mick

[Cobaltblue]

There are loads of Denco coils on EBay although the price is a bit eye watering. At the last RWB meet there was a chap selling them for £2 a go new in cans. As the EBay ones are mostly BIN might be worth making an offer

Cheers Mike T

[Biggles]

Hi Mick, can you be a bit more specific on which coil you mean. Is it the oscillator coil feedback winding or the third winding on the 2T transistor RF stage coil? Is it the DP (valve) version or the T (transistor) one? I have both so I can do a quick check on inductance if no one else can help you out. There is also a green version I think intended for regenerative sets. The data sheets give the inductance of the main winding but not of the others. They are also variable but I can find out minimum and maximum values if you require them.
Alan.

[mickm3for]

Hi yes its the range 2 mw green coil and its the inductance of the reaction (tickler)winding thanks i will repost Mick

[mickm3for]

Hi looking for the inductance of the green r2 mw reaction (tickler) winding thanks in advance Mick

[Herald1360]

Its mutual inductance with the main winding might be more important......

[David G4EBT]

Originally Posted by Herald1360

Its mutual inductance with the main winding might be more important......

That's true.

From time to time, the topic of the Repanco DRR2 MW/LW coil crops up.

Back in 2012 I borrowed a DRR2 from a friend to make a replica coil to make the BBC 'Focus' radio from 1959. (As an aside, anyone who built that diode+2 transistor radio - if they could follow the atrocious instructions - would have been very disappointed with it's performance due to lack of selectivity as compared to a 1-valve TRF. Six stations received - all on top of each other.).

In analysing the inductances of the DRR2, I discovered that the inductances of the tapped MW coil were individually 30µH & 70µH, but end to end, the total coil inductance was not as might have been expected - L1+L2 = 100µH, but nearer to 170µH. That's because only when coils are wound separately along a former does the total inductance = L1+L2+L3 etc. Otherwise, mutual inductance comes into play.

Though not directly relevant to the Denco MW coil (the only one that most are really interested in), the same caveat needs to be borne in mind. I've attached the Repanco DRR2 datasheet that I annotated back in 2012, and a picture of the DRR2 coil which explains things in a bit more detail.

Hope that might be of interest and relevance.

[G8HQP Dave]

Yes, the inductance of two coils is L1+L2+2M, where M is the mutual inductance. For very tight coupling M=sqrt(L1 x L2), so the total could be 190uH for your two coils. It is less than that because the coupling is not as tight.