TF144 Turret Tuner

 During my experiments with reception of long waves it was clear that the best coils are wound with Litz wire. The chief reason being that their overall quality was better.... meaning less signal loss and you can tune to a sharper peak thus minimising interference. The reason for this has been known for many decades and is that alternating currents flow chiefly in the skin of a conductor. That means the least resistance to AC is achieved if one uses a good electrical conductor having the best surface area. One way to meet this requirement is to use a large diameter copper wire, but as the centre of the wire isn't really used much by the AC the majority of the expensive copper content is wasted. A long time ago someone realised that a better alternative was to use a large number of very thin insulated copper wires bundled together and joined at their ends. This "Litz wire" provided the maximum surface area for the weight of copper.

I spotted this coil assembly carrying loads of coils and bought one. It turned out to be a New Old Stock spare turret tuner for the TF144H signal generator.

One potential project is to use it as a preselector for an SDR or even as the basis for a simple signal generator. Either case will involve some tricky metalworking and construction to use the turret tuner feature although, if the design was limited to HF and lower frequency ranges a rotary selector switch might be a much simpler option. Below are pictures of the coil assembly...

 

 

 

The first step is to evaluate exactly what's present and examination of the TF144 manual supplies some information. For example the signal generator has no less than 12 ranges using three different tuning condenser and coil connections as listed below. The three gang tuning condenser C101/102/103 has 200pF sections and the trimmers C152 etc are 4-20.5pF, usually with a fixed capacitor across it as shown below. Using these figures the tuning coil inductance can be worked out. Not too easily I might add because large coils can have a sizeable self-capacitance. To work out the coil inductances I assumed the tuning condenser minimum plus miscellanous strays were about 20pF and trimmers were set at 12pF. Given all these numbers I worked out the likely self-capacitance of each coil, Cs as shown below. I didn't bother with effects of mutual inductance because this won't materially affect re-use of the coils and I assumed the effects of dust cores are included in the coil inductances shown below.

 RANGE

 Min

Max

 Tuning condenser configuration

Fixed

 Fixed pF

 Trimmer

 Tuning coil

 Cs pF

Inductance

 A

 10KHz

20KHz 

C101+C102 in parallel with C103

 C153

 82

 C152

 L114

 72

323mH

 B

 20KHz

40KHz

C101+C102 in parallel with C103

C156

 91

 C155

 L115

 64

80.4mH

 40KHz

80KHz

C101+C102 in parallel with C103

C159

 82

 C158

 L116

 72

20.2mH

 D

 80KHz

200KHz

C101+C102 in parallel with C103 

 C193

 10

 C161

 L117

 60

5.6mH

 E

 200KHz

 535KHz

C101+C102 in parallel with C103 

-

 -

 C164

 L119

 54

925uH

 F

 535KHz

1605KHz

C101+C102 in parallel with C103 

-

 -

 C167

 L121

 31

133uH

 G

 1MHz

2MHz

C101+C102 in parallel with C103 

C171

 91

 C170

  L123

 62

32.5uH

 H

 2MHz

4MHz

C101+C102 in parallel with C103 

C174

 91

 C173

 L125

 62

8.1uH

 I

 4MHz

8MHz

C101+C102 in parallel with C103 

C177

 82

 C176

 L127

 52

2.1uH

 J

 8MHz

16MHz

C101+C102 in parallel with C103 

C180+C194

 100+10

C179 

 L129

 40

0.51uH

 K

 16MHz

32MHz

 C101+C102 in series with C103

C183

 10

 C182

 L131

 20

0.51uH

 L

 30MHz

72MHz

C103 

 C198

 10

 C184

L133 

 12

 0.11uH
 

 

 Click on the picture below to see detail.

 

 pending
 

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