Leak Troughline 1. Are they really this insensitive?

[unclemanly]

I've got a Leak Troughline mk1 connected to a rooftop dipole FM aerial. The aerial is in line of sight of the Crosspool transmitter in Sheffield and about a mile from it. Ideal conditions you might think, but in fact I can only pickup one station (Radio 3) consistantly well. Then the sound is lovely. Reception of all other stations is poor in varying degrees. Attempting to tune to Radio 1 barely moves the magic eye tuning indicator.

I read confilicting information about the sensitivity of theses tuners. The suggestion here is that they need an excellent aerial in line of sight of the transmitter:
https://theartofsound.net/forum/show...uner-a-History

An alternative view is that they are so sensitive they only need a short length of wire in the aerial socket:
https://sparcradio.ca/wp-content/upl...estoration.pdf

I must say, I find it hard to believe that Leak would launch a flagship tuner that sounded poor in any but the most ideal locations, so I assume there is something wrong with my tuner. Any idea where to start looking?

[Andrew2]

Clearly something is wrong. Could it be overloading due to the multiple very strong signals hitting its front end? Perhaps try it with a short wire in the aerial socket.

[Radio Wrangler]

Sensitivity problems are quite difficult to trace.

Ideally, you need a good signal generator which covers the frequency ranges of both the IF and the RF. It needs to be well-screened with a good output attenuator. There's no point in trying to adjust the RF level down low if more leaks out of the sig gen than is supposed to be coming out of its output socket.

You inject an audio signal into the output of the frequency discriminator and make sure that at least it makes it to the output socket (embarrassing if you leap into the RF sections and it turns out to be a fault right at the end in the audio section...) Then you drive the final IF stage and see if the sensitivity is reasonable... work back to the antenna checking that you can drop the signal leve, by the amount og gain you'd expect in that stage. eventually you get to the antenna port having cleared up a few issues along the way.

It's likely that decoupling capacitors have gone leaky and resistors have gone high resistance, starving a valve or two along the way of bias voltage. You may find a valve or two along the way low on emission and consequently gain.

You don't know what's wrong with it, but it does and it can't speak. So you need test equipment to fill in for it.

You could try without the fancy gear and just verify DC conditions throughout the tuner but if you don't hit a bad component at DC, you get no clues about where to look next.

THese were not hyper sensitive tuners, but they also weren't deaf. You need a reliable, controlled level test signal in order to know where you are.

David

[mole42uk]

My mother lives almost under that Crosspool transmitter mast and has lots of trouble receiving anything at all - most receiver front ends are swamped if they have any sort of aerial. It may be worthwhile experimenting with a short wire instread of the rooftop dipole.

[paulsherwin]

The Crosspool FM transmitters are actually pretty weedy - only about 300W. That's not to say that there isn't a problem with the Troughline, but it may be an idea to hook up a modern tuner and see what the signal's like on that.

[unclemanly]

Thanks for the replies. I've tried a short length of wire in the aerial socket and I just get a poorer signal, and I've had a Quad FM2 running fine here in the past so I think the problem does lie with the tuner.
Diagnosing the problem as Radio Wrangler suggests is well above my technical level so it looks like I'll have to pack the tuner off to somebody with relevant expertise. Not so easy to find these days....

[mancunian69]

I've had Troughline 2 and 3's over the years on my hi-fi system.

Even when used with my Galaxy 17 antenna pointed towards Winter Hill transmitter, it was still not very sensitive, or selective. That was 20 years ago.

I think the reason for this is that back in the day the FM band was not as crowded as what it is now, so no need for the tuner to be highly selective.

Don't get me wrong, depending on who you talk to, they are one of the best sounding FM tuners you can get - even today. LEAK opted to use the Foster/Sealy discriminator and (BBC approved) Zenith/GE format for FM and would not budge from that.

The Hi-Fi mags raved about them back in the 90's and coupled them with all kinds of FM stereo decoders. They sold for mega money.

The set you have there has limited frequency response. What you would need is a Troughline 2 or 3 for full FM coverage. As for the Stereofetic, sorry, stereopathetic, don't go there.

Michael

[Mr 1936]

Hi unclemanly

Older tuners like yours were a bit less sensitive than modern ones because they were designed for use with a dipole 30 feet above ground at up to say 30 miles from a main transmitter of maybe 30 kilowatts ERP. Modern users expect to be able to use a room mounted aerial on the ground floor.

Your local transmitter may be only 300 watts ( 20 dB weaker than my example ) but the very short path of only 1 mile should mean that the radio path loss is perhaps 40 dB or more less than it would be at 30 miles. So the signal presented to your tuner should be more than enough.

In short, your tuner should work fine. Clearly it doesn't and is extremely "deaf" which could be for all sorts of reasons. The fact that the various main stations behave differently despite being transmitted at more or less the same power is rather unusual.

Bofore embarking on third party repairs, I suggest you re-check that your dipole and its coax is all OK, especially any connections which should be reliably screwed or soldered. Where you have coax braid, check that there aren't any stray strands shorting to the inner. I'd recommend that the dipole is more or less horizontal, and roughly broadside on to the transmitter direction. Keep it away from water tanks, and don't let the ends touch anything.

[Sideband]

For what it's worth, I have a Troughline Stereo and I find the sensitivity and selectivity adequate for my area. As an idea in Croydon, I'm about 25 miles from the Wrotham transmitter (as the crow flies....i.e in a straight line) where the main BBC stations are broadcast from. The tuning indicator is about three-quarters closed on R2 , slightly less on R3 and R4. I have a simple dipole indoors which is not ideal but it works. Locals broadcast from Crystal Palace which is about 6 miles as the crow flies (I can see the mast from the top of the hill) are also strong. I would agree about the selectivity.....it has trouble with a couple of the locals that are only 400Khz apart....fortunately I don't listen to either of them. The poor selectivity has to be accepted....the Troughline was designed when there were only three BBC stations available on FM at around 2.2 Mhz spacing each....it just didn't need the selectivity of a modern tuner. It is however one of the best, if not the best sounding FM tuner I have ever had and gives outstanding audio quality through my Leak Delta 70 amplifier.

[Ted Kendall]

Originally Posted by mancunian69

LEAK opted to use the...(BBC approved) Zenith/GE format for FM and would not budge from that.

Zenith/GE is the pilot tone stereo system, used by all stereo tuners.

Originally Posted by mancunian69

As for the Stereofetic, sorry, stereopathetic, don't go there.

Nonsense. A Stereofetic in good condition is no mean performer, even now. I listened for many happy hours to my Delta AM/FM, which is identical as far as FM is concerned.

[stevehertz]

You already know where the problem lies given that a Quad FM2 worked perfectly well using the same aerial/downlead set-up. So unless something has happened to the latter (a short or O/C), then by elimination it's the Leak that's either faulty or just struggling to cope with the local conditions. You can double check by trying (borrowing maybe) a modern hi-fi tuner or even a cheap, lo-fi 'all in one' stereo unit.

[Sideband]

Originally Posted by unclemanly

I've got a Leak Troughline mk1 connected to a rooftop dipole FM aerial. The aerial is in line of sight of the Crosspool transmitter in Sheffield and about a mile from it.

I must say, I find it hard to believe that Leak would launch a flagship tuner that sounded poor in any but the most ideal locations, so I assume there is something wrong with my tuner. Any idea where to start looking?

I would agree and like others here I would say that the Troughline needs attention or the aerial needs checking. The latter is the easiest by trying with another tuner.

Besides my own Troughline, I repaired another for a friend. His was slightly earlier and had the decoder mod. Checking his after changing the rectifier and front-end ECC88 against mine, both performed in a similar way.

[Radio Wrangler]

Yes, the ECC88 is well known for having a fairly short life, so a fresh one of those could be a stab at finding a quick fix.

DAvid

[Sideband]

I don't know the Troughline Mk1 so it may have an ECC85 instead of an 88....or maybe even something else? Either way, the front-end valves are probably a bit tired by now and need replacing.

[winston_1]

Originally Posted by Sideband

The poor selectivity has to be accepted....the Troughline was designed when there were only three BBC stations available on FM at around 2.2 Mhz spacing each....it just didn't need the selectivity of a modern tuner.

This is just not true. These tuners were also exported to the USA (The circuit shows the different de emphasis components for the USA). Back then the US FM band was as crowded as the UK one is now.

[unclemanly]

Troughline 1 valve lineup is:-

EZ80,
EB91,
2 x EF80,
3 x ECF80,
EM81

I'm tempted to replace the lot and see what happens (except perhaps the EM81 magic eye).

My aerial is OK by the way. I had the aerial man around last week and we spent some time establishing that.

[Sideband]

Replacing the lot may cure it BUT it's poking and hoping and you won't learn anything! The two EF80's are probably IF amps but with three ECF80's these could be used as IF amps as well. I'm going to make a guess and say the two EF80's are RF amp and self oscillating mixer (or maybe just a mixer with one of the ECF80 triodes used as oscillator. If that is the case then the EF80's need to be in top-notch condition so I would at least try those first. If you have a meter, check the HT supply as the EZ80 may be tired causing low HT which will also cause poor sensitivity. Perhaps someone with a Troughline 1 circuit can clarify which valves do what (I only have the Troughline II circuit).

[unclemanly]

Originally Posted by Sideband

Perhaps someone with a Troughline 1 circuit can clarify which valves do what.

Here's one along with a block diagram of the circuit.

[Sideband]

Originally Posted by winston_1

This is just not true. These tuners were also exported to the USA (The circuit shows the different de emphasis components for the USA). Back then the US FM band was as crowded as the UK one is now.

Well perhaps the wording was a little broad....The selectivity is nowhere near as good as a modern tuner. The one I have CAN select the two locals that are very close but there is no real transition between one and the other.....better with the AFC off of course. If you have a couple of locals only 400Khz apart I would be interested in how your tuner performs. In my case one station is on 105.4, the other is on 105.8. In fact there is another on 106.2 and all of these tend to 'blend in' while tuning.

[Nuvistor]

I am presuming the Troughline 1 was a 1950’s model. With reference to USA exports and FM stations, from magazine articles it seems FM was still in its infancy despite being around for a few years. There were 533 stations using FM in 1957 across the country compared with over 3000 AM medium wave stations.
Although the stations were probably grouped around large population areas there may not have been close in frequency to each other. They seem to be in general relatively low power station, 1kw.
Interesting article in the USA magazine December 1957 “ US Radio” page 22.”FM The Frustrated Medium”

https://worldradiohistory.com/Archiv...o-1957-Dec.pdf