UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - "Tatiana" a clone of "Sweetheart" using Russian Rod Pentodes

neon indicator · 13th Aug 2011, 9:26 pm

I got the schematic of the "sweetheart" type 31/1 here http://www.cryptomuseum.com/spy/sweetheart/index.htm

Using a coil designing program I concluded the 1/2" former has a core of some kind and the photo elsewhere of the insides/rear shows a slotted screw protruding. (pictures here http://www.techtir.ie/construction/sweetheart-clone)

Has anyone here got one and/or can confirm that?

Is it about 3MHz to 8MHz? Or?

What sort of length of aerial wire?

I think using 3 x 1j24b, 2 x miniature "polycon tuners" from transistor AM/FM sets and a 5mm x 30mm ferrite rod I can fit it all into a 110 x 60 x 31 mm Eddystone box including 3 x AA cell LT and 12 x CR2032 coin cell (36V) HT. Not using screw terminals or tag strip, but veroboard.

The coil in the AM/FM set is on a 5mm x 30mm round core and is one tapped coil rather than two sections. One part is 120uH and the other part 250uH, so I can use that for a slightly shorter aerial wire with a choice of two taps. Without the core I measured 17uH and 36uH. So I calculated how many turns for about 1/7th of the inductance for L2 and L3, which amazingly was about 18 and 25 (the original on unknown core and 12.5mm former). I wound the L3 at one end of rod and it is 16.2uH rather than desired 14. 24 is 15.4uH

The 18T on top of the existing 120 + 250 is 9.8uH. Taking 1T off gives 8.8uH

So provided the Ferrite material is OK at 3.5MHz to 7.5MHz, the coil should work, leaving original MW coil as aerial L1 coil as it's less critical?

The Polycon in the €2 "Jensen" AM/FM Radio is 2x +9pF trimmers on VHF section and 2 x +11pF trimmers on MW section

VHF dual gang 6 to 30pf (trimmers at minimum)
MW 6 to 84pF and 7 to 149pF (trimmers at minimum)
The Sweetheart uses 60pF for Reaction (minimum value unknown) and 100pF (minimum value unknown) for Tuning, so dismembering €4 worth of "Jensen" radios (from local "poundland" like Euro bargain store) gives two polycons (one used as 6 to 84pf, one used 7 to 149pF) and rod/coil for L1. Cheaper than buying parts online?

Can anyone see any snags to this idea of using 1 part of two separate of the four gang polys for the tuning and reaction?

Is there a reduction gear on Sweetheart tuning?

13th Aug 2011, 9:26 pm	#1
neon indicator Retired Dormant Member Join Date: Jun 2010 Location: Co. Limerick, Ireland. Posts: 1,183	"Tatiana" a clone of "Sweetheart" using Russian Rod Pentodes I got the schematic of the "sweetheart" type 31/1 here http://www.cryptomuseum.com/spy/sweetheart/index.htm Using a coil designing program I concluded the 1/2" former has a core of some kind and the photo elsewhere of the insides/rear shows a slotted screw protruding. (pictures here http://www.techtir.ie/construction/sweetheart-clone) Has anyone here got one and/or can confirm that? Is it about 3MHz to 8MHz? Or? What sort of length of aerial wire? I think using 3 x 1j24b, 2 x miniature "polycon tuners" from transistor AM/FM sets and a 5mm x 30mm ferrite rod I can fit it all into a 110 x 60 x 31 mm Eddystone box including 3 x AA cell LT and 12 x CR2032 coin cell (36V) HT. Not using screw terminals or tag strip, but veroboard. The coil in the AM/FM set is on a 5mm x 30mm round core and is one tapped coil rather than two sections. One part is 120uH and the other part 250uH, so I can use that for a slightly shorter aerial wire with a choice of two taps. Without the core I measured 17uH and 36uH. So I calculated how many turns for about 1/7th of the inductance for L2 and L3, which amazingly was about 18 and 25 (the original on unknown core and 12.5mm former). I wound the L3 at one end of rod and it is 16.2uH rather than desired 14. 24 is 15.4uH The 18T on top of the existing 120 + 250 is 9.8uH. Taking 1T off gives 8.8uH So provided the Ferrite material is OK at 3.5MHz to 7.5MHz, the coil should work, leaving original MW coil as aerial L1 coil as it's less critical? The Polycon in the €2 "Jensen" AM/FM Radio is 2x +9pF trimmers on VHF section and 2 x +11pF trimmers on MW section VHF dual gang 6 to 30pf (trimmers at minimum) MW 6 to 84pF and 7 to 149pF (trimmers at minimum) The Sweetheart uses 60pF for Reaction (minimum value unknown) and 100pF (minimum value unknown) for Tuning, so dismembering €4 worth of "Jensen" radios (from local "poundland" like Euro bargain store) gives two polycons (one used as 6 to 84pf, one used 7 to 149pF) and rod/coil for L1. Cheaper than buying parts online? Can anyone see any snags to this idea of using 1 part of two separate of the four gang polys for the tuning and reaction? Is there a reduction gear on Sweetheart tuning?