Last Modified: 20 Apr 2013


Sat Aug 28, 2010

INALLY GOT THE DIPOLE INSTALLED in the attic today, and got a VHF lead ready for the Leak TL3(s), or the Ambit Tuner, whichever can be made to work. I mounted the dipole as vertical polarization to make it omni-directional. Seems to work so far.

But it can be a problem if you want a distant station in stereo, as suddenly you need lots of signal.


Tue Aug 31, 2010
Went to fetch the TL3's from my mate Phil today. Got home 4 pm!


Got one of them working!













This is the one with the funny foreign mains plug that had not been tried out by previous owner I believe (?) Also the one without the phono lead cut off short.

Rectifier valves were missing ('borrowed' by previous owner); a search revealed I hadn't got any EZ80's or EZ81's, so I bodged up a rectifier with two 1N4007's soldered onto the B9A socket instead.

Also that web page servicing article about the front panel control switches was right! They were OK for a bit while cold, then they started going open circuit. As they mostly only connect anything in one direction only I shorted the contacts together (by soldering bits of wire across the tags). This meant it was permanently AFC 'off' (incidentally when it's 'AFC' 'on', the EM84 indicator is turned off at its supply (?)) and so permanently on 'distant'.

The scale pointer position was quite a way out as well, so I moved it. E.g. as in the above photos 103.5 MHz is BBC Essex, North. Which it is.

As I'm in the South, so it's a bit 'distant'.

Sounds very nice indeed must be said!

Hello they've just played Spencer Davis Group Keep On Running and I do believe I could detect the old microphone pre-amp overload clipping thing going on.

Now onto A Whiter Shade Of Pale ....


I considered an ECC88 in position #1 (the standard is ECC84) just to see what would happen but to be honest as I've got a masthead amplifier in the loft it isn't necessary, in fact, there can be a problem with too much gain and as it subsequently turned out most often the Troughline needs 'local' sensitivity rather than 'distant' because of this.


How to move a cord driven tuning scale pointer ~

Grip the "string" strongly with tweeters or somesuch, on the side of the pointer that you want to slide it towards . Shove with thumbnail etc., the tweezers grip creates slack in the "string" so will slide though the slots of the pointer more easily.


Wed Sep 01, 2010
Here is the web page about repairing the switches:

www.keith-snook.info ... LEAK-Troughline.

He also mentions changing all the resistors, at least for the II versions, but according to the bottom photos it looks like he's used miniature metal films.

My TL3's have got all carbon composite resistors as per original type, except where a high power is needed.


Another photo ~ now with betterer knobs and a new indicator tube:





Still can't get the glue off where the paper labels were stuck on, seems it's sunk into the paint.

I'm trying out a small modification; because the local / distant is presently stuck on 'distant' (shorted with wire), I've increased the AGC slightly for the RF amp, by modifying the resistor divider, making it 2:1 instead of 3:1. Yellow area below, 220k to 470k.




Just as a matter of interest, the following is the original Mullard / Philips developed decoder circuit ~ as per the Troughline Stereo:




The audio output cathode follower is modified to remove the de-emphasis filter components, and no volume control.

According to the "blurb" they tried different sorts, starting with an all-valve affair, which "wasn't good enough", and then someone said you might have better luck with it if you stopped using a Foster-Seeley detector and went to ratio detector, Leak's response to that was was non, nien, niet, no-way hose; so somehow Philips got involved with Mullard stepping in with their recommendation of which transistors to use.

Thing about it is the outputs seriously need buffering, as it's quite high impedance, quite likely how a lot of the problems come about I'm guessing.

There is an article somewhere that explains replacing the ECC84 with an ECC88 to give greater sensitivity, this is necessary for stereo, and I believe a ECC88 is standard for the Troughline Stereo.

Just to be nosey I have currently got my Heathkit multimeter plugged into the MPX socket to monitor the DC offset. The point about having the 'trough-line' for the oscillator is to minimize frequency drift.

Now given that I haven't got AFC engaged, nevertheless the needle has hardly moved all day, so yes the oscillator frequency is very stable.

Some DC offset from the FM detector is normal. To be more correct it ought to be zero DC if tuned in properly (and not least, if aligned properly). But it can be positive or negative if going off-tune, hence 'tune' meters, and AFC.


Thu Sep 02, 2010
A bit more tinkering this afternoon ~ I had to find a way of making the local / distant option work (that is, making it possible to work in 'local' mode) because, what with it being hard-wired to distant, plus the masthead amplifier upstairs, it's a mite overloaded. Not all that obviously though, interestingly, but mainly manifests itself as more background noise and a sort of slight 'fuzzy' effect encroaching on complex classical music, or even loud pop type stuff.

Found a miniature toggle switch and bodged it up on a couple of flying leads.

Checked out the resistor values ~ so long as they're reasonably close, they can stay in, but there were four dodgy ones reading too high.

The dropper resistor which is inserted into the HT supply for the RF stage for distant mode was high resistance, and replaced.

Also RF amp cathode resistor, and two 47k's. Also had to change a 1k, only because I cut it out by mistake. I replaced these with same type carbon composite. Where resistance tests closely matched the correct value, I left the originals alone.


The other as yet untried TL3 won't work using its own mono audio output as the lead has broken off the 1uF cap for the volume pot, so that will need replacing. Also the phono lead for it has been cut off and also needs replacing.

Also a brief check of some resistor values showed a few problems there as well. The HT dropper resistor for distant mode appears to be open circuit as I'm measuring 1.4 Megohms; it should be <=470k. But a job for later!


Fri Sep 03, 2010
Further to the above resistor replacements, there is indeed a discernible difference....

It's much louder!!!


Sat Sep 04, 2010
Further to a discussion elsewhere about mains earthing and possible shocks due to the lack thereof, here is a mod to TL3 for adding an mains earth wire, via a 100R lift resistor. Just soldered onto nearest convenient earth tag of a tag strip. Earth wire taped to twin core lead and attached to plug's earth pin.





Pretty colours!


Mon Sep 06, 2010
In case no-one has got schematics I found these on the web ~

First, Trough Line II ~ note TL2 did not have a coil between the two cascoded halves of V1, the ECC84.





Whereas the TL3 does (L3 ?) :





Next, Trough Line Stereo ~ Trough Line III is identical to this as far as I can tell but without the decoder module, hence TL3 has mono audio & MPX outputs same as TL2.





Wed Sep 08, 2010
The way the 'local' switch works is clever, seems a bizarre way of doing it but means the RF amp still works but "at starved power". Suspect it's a better way than putting a large negative bias on the grid, which is how other circuits I've got do it.


Mon Oct 11, 2010
Re TL3 (No. 1) ~ I have tonite replaced the 470k for the audio output de-emphasis (RC filter) with a new one, and another same value elsewhere. They were both getting on for 600k measured...

Pretty sure it's cleaned up and sharpened up the treble a noticeable tad and a half.


Tue Oct 12, 2010
I am having a go at renovating the other one. Taken the switches out, taken apart and cleaned, now have to figure out how to put them back.

The modus operandi is, the top silver part of the front panel is actually an insert.

Take the control nuts off and it virtually falls out revealing the rivets for everything attached to the back:




Watch it cos the perspex scale window is then loose as well! So best remove it for the duration. I washed them both in soapy water.

Drill out the rivets for the switches 'til they fall out the back (3.5mm bit and hand brace).




The one just in front of the big cord pulley for the tuning capacitor gang won't come out, not enough gap; so remove two side screws, and loosen the other two, just so that front panel will tilt forward a bit to get more room to get it out. Not too much cos of the dial drive cord!

Being silver plated, the contacts have most likely gone black and this is the reason for them not working terribly well:




To dismantle, bend up the four 'claws' that hold on the fibreboard or whatever it is made of backplate.

After scrubbing with contact cleaner and a switch cleaning strip:




The copper contact strips are probably quite bowed. Straighten them out flat and bend out the curved over end bits until at right-angles.

Temporarily reassemble and test all functions with Ohmeter. If OK crimp the 'claws' back firmly with long-nosed pliers.


I wasn't sure how to reattach them, considered countersunk M3 screws however, the bulk of the front panel is not metal but chrome plated plastic! So problee won't take too much abuse. Also time was at a premium (when isn't it?) so I tried something quick like 2.5mm blind ('pop') rivets, that worked a treat, only thing is the rivet heads are not completely flush so the silver insert plate is slightly raised at the bottom, doesn't notice that much though.

Sun Oct 17, 2010
Breaking news, I lost me lettering!

Dismantled front panel to get switches out, while I'm at it go wash the thin silver insert bit and tuning scale 'glass' in warm soapy water.

What I thought was "dirt" on the panel turned out to be some weird rubbery film, at least I've never seen lacquer like that. The lettering came off with it!

It was disgusting though and trying to peel off anyway. Although you can still see where the words have been.


#2. the overhauled switches seem to work. Though one did give me a bit of bother for a while making sure the contacts were making properly.

#3. Couple days ago got two coax splitters from Rapid, mainly for the purpose that they also act as –6 dB attenuators. So have now got two tuners running off one downlead, and the loft distribution amplifier gain is curbed somewhat so less overloading. Result. Also means can use the distant setting on the TL3 where it may be handy without the effect of merely increasing noise. Which is interesting in itself, didn't think it would make that much difference.


Mon Oct 18, 2010
Tip ~ if it's escaped anyone's notice earlier I moved the wire on the AFC switch that powers the EM84 indicator to the centre tag so that it's on all the time.


Tue Oct 19, 2010
Is there such a thing as too much gain? Yes, I've got it! More hiss is typically the result, I've read to be careful with strong signals with the TL as it's AGC is not sophisticated, so you can get kind of clipping, but doesn't sound like that it sounds more like recording tape saturation, bass that breaks up, possible crackling noises.

I am experimenting with 2 x 6 dB attenuators / signal splitters in series.


Fri Oct 22, 2010
The first one is inserted into the pattress (downfeed from distribution amplifier oop in't loft), the second is on one output, and a shorted plug in the other output.

The Leak and the Ambit both come off the second's two sockets.

The Leak is quite happy about this, traces of overloading on strong stations even in local mode seems absent now, and occasionally distant setting may be used for the weaker stations. Still not essential though.

The Ambit on the other hand has a lot of gain so still needed adapting somehow, like Radio 2 for instance raises noticable overloading effects.

While I had the lid off today tried an experiment by adding a resistor attenuator to the aerial socket, 68R in series and a 150R shunt across the socket. Probably not ideal I know as it does not take into account small inductances of the resistors but, necessity being the mother of wotsitsname, desperate measures needed resorting to.

I am still evaluating!

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