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Leak

We offer RF/IF and MPX alignment services for Leak Troughline tuners.
We also provide a complete renovation service for these wonderful tuners.
We can supply and fit a modern LM4500-based stereo decoder to any TroughLine for a surprisingly low cost.
We can even repair and align the original Leak decoders, although frankly this is a fool's errand!

Troughline tuners

The Leak Troughline is an FM tuner with two RF stages, two IF stages, two limiters, a Foster-Seely phase-detector discriminator, and a cathode-follower output stage on the mono output. A separate MPX output socket is provided for driving FM stereo decoders. The design exhibits some unusual features such as the 'Troughline' quarter-wave resonator used to stabilize the IF frequency in conjuction with temperature-compensation and a small amount of automatic frequency control (AFC), resulting in an unusually stable tuner.

The discriminator uses germanium diodes (rather than a dual-diode valve like the Quad FM tuners). This means that if you're listening to it in stereo, the fabled 'Troughline' sound has nothing to do with it being a valve tuner: what you're listening to is basically germanium. If you're listening in mono there is a cathode-follower valve output stage but this is still not really the source of the sound, which appears to me to be a result of (i) oscillator stability; (ii) very good AM limiting; and (ii) the concentration of the distortion into the 2nd harmonic.

The design is substantially constant over the four versions described below, with some layout differences between the Troughline I and the subsequent models, and just a few valve and passive component changes between all the rest.

Stereofetic tuner

The StereoFetic tuner is a solid-state tuner using a FET front end, ceramic filters and ICs in the IF strip, a ratio detector using AA119 diodes, and an integral stereo decoder based around an IC.

The Stereofetic has never enjoyed the acclaim of the Troughline range, although it was intended by design to perform at least as well. There may be some 'valve snobbery' involved in this, although as it was a brand-new design, is it certainly true that no 'magic ingredients were carried over from the Troughline. Never having heard one I can't comment further.

Troughline tuners

Photo by Stephen Robinson

Troughline I

This is the first version of the Troughline. Do not buy: it only tunes from 88-100mHz which cuts out the top half the FM VHF band including all our favourite stations.

Troughline II

This is the earliest version of the Troughline that is still usable today. At some point during production the IF and discriminator transformers were respecified, the earlier versions being only suitable for monophonic reproduction. The later version is found with and more often without a factory stereo decoder.

Troughline 3

This is internally identical to the later Troughline II with just a different faceplate (Harold Leak's poorly designed and poorly manufactured 'Leica look', which the US dealers sensibly refused to take, so Leak had to make another series of faceplates for the American market). It is found with and more often without a factory stereo decoder.

Troughline Stereo

This is essentially a Troughline 3 with

one valve change
some component-value differences in the IF and discriminator stages to increase IF bandwidth
a circuit change at the sound take-off point to buffer the discriminator output.

An internal 3-transistor stereo decoder, of rather poor quality, was fitted as standard equipment - it sounds reasonably OK but makes no attempt to filter the 19kHz or 38kHz switching tones, which can fry your tweeters.

Alignment notes

Notes on aligning the Troughline tuners.

There are various sets of Troughline alignment notes floating around the Internet. None of them makes complete sense: one of the most frequently seen (a) obviously consists of two sets of notes jammed together and (b) contains a major implausibility about detuning the oscillator coil by 50%, when the normal practice would be to reduce the signal generator output to 50% below limiting at this point.

However, if you know what you're doing the Troughline is not hard to align from first principles: all you really need to know is that the IF frequency is 12.5MHz, which may cause its own difficulties with test equipment. The orange trimmer capacitor C8 is best left alone, as is the entire RF front end, as it is extremely stable: normal alignment should concentrate on IFT1, IFT2, and the discriminator coil.