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Old 13th Aug 2011, 9:26 pm   #1
neon indicator
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Default "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?
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Old 13th Aug 2011, 10:32 pm   #2
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Default Re: "Tatiana" a clone of "Sweetheart" using Russian Rod Pentodes

6 to 12MHz. Dial calibrated in metres.
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Old 13th Aug 2011, 10:57 pm   #3
neon indicator
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Default Re: "Tatiana" a clone of "Sweetheart" using Russian Rod Pentodes

Thanks Graham.

The Polish radio sometimes also called a "Sweetheart" aka "OP-3 Type 30/1" does look very similar, but the 2nd knob is near middle. It looks like a superhet. Is there a schematic anywhere? One just sold for serious money, nearly 1K, no logic to it really. I added photo of it to the blog / article.

Well, I will get the RF section working in next few days with 1j24b rather than the DF91/1T4 and see what it does. I suspect I might have slightly more tuning range (50% more capacitance, so maybe down to about 4.8MHz rather than 6MHz. Having somewhat more inductance to get down to 3.5MHz seems feasible.

It's not like it's a copy using identical coil, valves and tuning capacitors in a reproduction box. More a bit of fun using the identical design so adjusting the frequency band isn't a deal breaker?

I'll be happily surprised if I can resolve CW or SSB on it though!
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Old 13th Aug 2011, 11:31 pm   #4
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Default Re: "Tatiana" a clone of "Sweetheart" using Russian Rod Pentodes

Hello NI have you checked out the RBZ receiver ..American..nicely made.
Your doing a grand job.

Lawrence.
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Old 14th Aug 2011, 12:29 am   #5
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Default Re: "Tatiana" a clone of "Sweetheart" using Russian Rod Pentodes

Quote:
Originally Posted by neon indicator
The Polish radio sometimes also called a "Sweetheart" aka "OP-3 Type 30/1" does look very similar
Circuit in Wireless For The Warrior Volume 4. It is a superhet.
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Old 14th Aug 2011, 12:44 am   #6
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Yes, the RBZ is cute. http://www.qsl.net/i0jx/rbz.html
http://www.cryptomuseum.com/spy/rbz/index.htm

I have the schematic saved. Difficult to make as it uses THREE ganged tuning coils, like old car radio Permeability tuning.

I'm into "simple" at the moment. I'll do one more TRF/Regen, the Gilbert Davies "fun with Radio" recycled also as the BBC one valver in I think 1957. https://www.vintage-radio.net/forum/...ad.php?t=71222, but modified to do LW and MW as R4 is good and the only strong AM daytime signal here is 252kHz RTE1. It will use a 500ml "Lilt" bottle as the coil former and maybe be entirely screw together.

Then I'll do a superhet with dual conversion and SSB. Still haven't got to grips with the 1j37b as a mixer.

Also I have two audio amps for speakers:
Class AB using 1j29b (maybe 500mW or more)
Class AB using 1p24b (maybe 5W or more)

Plenty other ideas. But slow progress due to bad sinus trouble.
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Old 14th Aug 2011, 7:06 pm   #7
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Default Re: "Tatiana" a clone of "Sweetheart" using Russian Rod Pentodes

OK, a 1st draft of the schematic for the 1j24b russian pentodes is done http://www.techtir.ie/construction/tatiana-design
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Old 15th Aug 2011, 11:24 pm   #8
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Default Re: "Tatiana" a clone of "Sweetheart" using Russian Rod Pentodes

Started assembly. All parts for main veroboard mount apart from a few wire links. The coil and variable capacitors on a sub-board.

http://www.techtir.ie/construction/t...in-veroboard-1

Definitely fits 110 x 60 x 31 Eddystone diecast box.

The components are all at least 50V, some are 63V or 100V. So fine for the max HT of about 44V with fresh batteries (HT battery nominal 36V and LT nominal 4.5V). But the miniature capacitors likely not high enough rating for a 90V set.

Photos too large to attach here. But no adverts, popups or registration needed to view link.
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