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View Full Version : Leak Troughline III tuner mystery partly resolved



Barry
03-05-2010, 22:39
A while back I bought, from a well know purveyor of used classic audio equipment, a Leak Troughline III tuner, in excellent condition complete with wood sleeve. This purchase was made following enthusiastic comments made both in the pages of Hi Fi World magazine and by some members here on AoS. I was not unfamiliar with this Leak tuner, having owned one long ago. The tuner was described as being in full working order and indeed it was; well at least in the sense that it ably received several radio stations. I reported my initial findings, comparing the Troughline tuner with my then current Quad FM3 in:

http://theartofsound.net/forum/showthread.php?t=3007.

My concern then was that the Leak tuner displayed an unacceptable bass bias; making speech sound excessively chesty and deep. At best it could be described as a 'bloom', at worse it was actually 'boomy'.

It was suggested at the time that replacing the output cathode follower might bring about an improvement. The tuner had come with a full compliment of Mullard valves (with the ‘shield’ logo). The output cathode follower was an ECC88. This was replaced in turn with a Siemens E88CC, a Philips ECG 6922, a Mullard E88CC (with the stylized ‘M’ logo), as well as a Mullard ECC88 (another sample with the ‘shield’ logo). None of these substitutions brought about any real improvement. I was thinking of trying a Mullard PCC88 (7v heater) but had to check as to whether the heater supply could cope with the higher current drawn by a PCC88.

By shear coincidence, I have just stumbled across the manufacturer’s user notes for this tuner. On inspection of the circuit diagram (in those days manufacturers readily published the circuit details of their products), I noticed that the output cathode follower is the triode half of an ECF80. No wonder changing the output valve for a variety of ECC88 designs didn’t work! Yet the ECC88 was the valve type that had been fitted to my tuner, and it would seem, to others. The valve line up quoted by Leak is as follows:

2 x ECF80, ECC84, ECC85, EF80, EM84 and EZ80.

Does this tally with the valve line up of Leak Troughline III’s used by other members? I have ordered some Mullard ECF80 valves to try out, but I am still puzzled as to why this valve had been changed and yet the tuner still ‘worked’.

To be continued ….

Spectral Morn
03-05-2010, 22:54
I will dig mine out tomorrow and have a look........ However this is interesting.


Regards D S D L

Spectral Morn
05-05-2010, 16:23
A while back I bought, from a well know purveyor of used classic audio equipment, a Leak Troughline III tuner, in excellent condition complete with wood sleeve. This purchase was made following enthusiastic comments made both in the pages of Hi Fi World magazine and by some members here on AoS. I was not unfamiliar with this Leak tuner, having owned one long ago. The tuner was described as being in full working order and indeed it was; well at least in the sense that it ably received several radio stations. I reported my initial findings, comparing the Troughline tuner with my then current Quad FM3 in:

http://theartofsound.net/forum/showthread.php?t=3007.

My concern then was that the Leak tuner displayed an unacceptable bass bias; making speech sound excessively chesty and deep. At best it could be described as a 'bloom', at worse it was actually 'boomy'.

It was suggested at the time that replacing the output cathode follower might bring about an improvement. The tuner had come with a full compliment of Mullard valves (with the ‘shield’ logo). The output cathode follower was an ECC88. This was replaced in turn with a Siemens E88CC, a Philips ECG 6922, a Mullard E88CC (with the stylized ‘M’ logo), as well as a Mullard ECC88 (another sample with the ‘shield’ logo). None of these substitutions brought about any real improvement. I was thinking of trying a Mullard PCC88 (7v heater) but had to check as to whether the heater supply could cope with the higher current drawn by a PCC88.

By shear coincidence, I have just stumbled across the manufacturer’s user notes for this tuner. On inspection of the circuit diagram (in those days manufacturers readily published the circuit details of their products), I noticed that the output cathode follower is the triode half of an ECF80. No wonder changing the output valve for a variety of ECC88 designs didn’t work! Yet the ECC88 was the valve type that had been fitted to my tuner, and it would seem, to others. The valve line up quoted by Leak is as follows:

2 x ECF80, ECC84, ECC85, EF80, EM84 and EZ80.

Does this tally with the valve line up of Leak Troughline III’s used by other members? I have ordered some Mullard ECF80 valves to try out, but I am still puzzled as to why this valve had been changed and yet the tuner still ‘worked’.

To be continued ….

Hi Barry

My mk 3 is (without a Stereo or mono decoder) ECF 80 x2, ECC84,EF80, EZ80, ECC85 and EM84.That is what is fitted in mine.

The Trough-Line Stereo has an ECC 88 as the output valve.

Hope that helps. My Trough-lines where buried behind a pile of Pioneer tuners and other tuners :doh:


Regards D S D L

Barry
05-05-2010, 19:21
Hi Neil,

Thanks for going to the trouble of checking the valve line up of your Troughline 3 for me. I have just got mine out to check the valve line up too and so appreciate the trouble caused.

Now it's red-face time for me, as I have to tell you that whereas I thought I was changing the output valve, one half of V5 (an ECF80), in fact all along I have been changing V1, an ECC88 for another ECC88! :doh: I can justify my error by stating that both valves are situated between two IF transformers. It of course explains why no change was found, so changing V4 with a new EFC80 may bring about an improvement.

I could also say that I got the ouput valve confused for an ECC88, since as you have stated, your Leak Troughline Stereo has an ECC88 for the output valve. My Troughline is a Troughline III, and since it has a built in stereo decoder, I assumed it would be the same as a Troughline Stereo. Hence I went looking for an ECC88 and found it, though it was the wrong valve. :o

So the situation now is as follows: all the valves in my tuner are present and correct. V1, originally a Mullard, is now a Siemens and V5 is the original Mullard ECF80. I have ordered a new Mullard ECF80, so will subsitute this valve when it arrives. Perhaps that will bring about the improvement I seek.

At least all this explains why my tuner continued to work.

Sorry to have mucked you about, and as I said:

to be continued ...........

Regards

Spectral Morn
05-05-2010, 19:24
Hi Neil,

Thanks for going to the trouble of checking the valve line up of your Troughline 3 for me. I have just got mine out to check the valve line up too and so appreciate the trouble caused.

Now it's red-face time for me, as I have to tell you that whereas I thought I was changing the output valve, one half of V5 (an ECF80), in fact all along I have been changing V1, an ECC88 for another ECC88! :doh: I can justify my error by stating that both valves are situated between two IF transformers. It of course explains why no change was found, so changing V4 with a new EFC80 may bring about an improvement.

I could also say that I got the ouput valve confused for an ECC88, since as you have stated, your Leak Troughline Stereo has an ECC88 for the output valve. My Troughline is a Troughline III, and since it has a built in stereo decoder, I assumed it would be the same as a Troughline Stereo. Hence I went looking for an ECC88 and found it, though it was the wrong valve. :o

So the situation now is as follows: all the valves in my tuner are present and correct. V1, originally a Mullard, is now a Siemens and V5 is the original Mullard ECF80. I have ordered a new Mullard ECF80, so will subsitute this valve when it arrives. Perhaps that will bring about the improvement I seek.

At least all this explains why my tuner continued to work.

Sorry to have mucked you about, and as I said:

to be continued ...........

Regards


Not a problem Barry.

I look forward to reading what your valve swaps reveal.


Regards D S D L

Barry
17-05-2010, 19:57
In some of my previous postings I’ve mentioned that my Leak Troughline Stereo tuner displayed an unacceptable bass-heavy tonal balance. This was described in my post:

http://theartofsound.net/forum/showthread.php?t=3007.

To put this in perspective, I found I could equalise the tonal balance by using a –2/+2dB ‘tilt’ plus a bass roll off –3dB at 150Hz. With this setting the tonal balance was very similar to that of the Quad FM3 I use. Otherwise voices were unnaturally chesty and deep.

Following my initial post Neil, suggested that I might try changing the output cathode follower; erroneously stated to be an ECC88. I did so; in fact I did some tube ‘rolling’ here, all of course to no avail as I was changing the wrong valve! Having now found out that the cathode follower is in fact an ECF80, I have replaced the original Mullard valve with an NOS Mullard ECF80. Mirabile dictu – it’s worked; not only is the tonal balance much better, the output level has increased to 63mV for full deviation. Before, the output was only ~22mV compared to 100mV for the Quad.

I had thought that my mistake over the output valve might have been due to the fact that my tuner is designated a Leak “Trough Line Stereo”, whereas Neil’s tuner is designated a Leak “Trough Line III”. To further confuse the situation, the rear of my tuner is actually marked “Leak Trough Line 3”. In order to try and resolve matters I did some research. To be precise, the Trough Line 3, has the following valve line up:

V1, cascode RF triode ECC84; V2, triode mixer ECC85; V3, triode oscillator and pentode IF ECF80; V4, pentode limiter EF80 and V5, 2nd pentode limiter and cathode follower ECF80.

The ‘Trough Line Stereo’ incorporated minor circuit revisions, as well as incorporating a simple stereo decoder. The circuit changes are as follows:
ECC88 replacing the ECC84;
C6 1000pF
R5 33Ω
C29 200pF
C40 50pF
C41, 42, 43, 44 150pF
C47 0.47uF
C53 1uF
and
R38 47kΩ.

There is also a bypass capacitor of 5000pF (C58) fitted between one of the anodes of the EZ80 rectifier (V7). Curiously the HT rail is now marked as 148V.

http://44bx.com/leak/Leak/Circuits/TroughLine2.gif

and

http://www.44bx.com/leak/Troughline3Stereo.html.

Encouraged by the improvement in tonal balance (the difference between the Leak and the Quad FM4, I now use, is less than 1dB, though there is still a bass ‘hump’ around 150 –200Hz which now gives an acceptable 'warmth'), I intend to replace all the valves in the signal path by NOS Mullards. I wont replace the EM84 tuning indicator, nor the EZ80 rectifier, since these are not part of signal path (though again some might challenge the latter). So far I have obtained NOS Mullard samples of all but the ECC85, but the search continues. When I have finished ‘fettling’ the tuner, I will do a full comparison with the Quad FM3, FM4 and, if possible, with a Quad FM2 (valve) tuner.

So thanks Neil for the advice, despite sending me off on a fool’s errand regarding the ECC88!

As before – to be continued

Regards

Spectral Morn
17-05-2010, 20:53
In some of my previous postings I’ve mentioned that my Leak Troughline Stereo tuner displayed an unacceptable bass-heavy tonal balance. This was described in my post:

http://theartofsound.net/forum/showthread.php?t=3007.

To put this in perspective, I found I could equalise the tonal balance by using a –2/+2dB ‘tilt’ plus a bass roll off –3dB at 150Hz. With this setting the tonal balance was very similar to that of the Quad FM3 I use. Otherwise voices were unnaturally chesty and deep.

Following my initial post Neil, suggested that I might try changing the output cathode follower; erroneously stated to be an ECC88. I did so; in fact I did some tube ‘rolling’ here, all of course to no avail as I was changing the wrong valve! Having now found out that the cathode follower is in fact an ECF80, I have replaced the original Mullard valve with an NOS Mullard ECF80. Mirabile dictu – it’s worked; not only is the tonal balance much better, the output level has increased to 63mV for full deviation. Before, the output was only ~22mV compared to 100mV for the Quad.

I had thought that my mistake over the output valve might have been due to the fact that my tuner is designated a Leak “Trough Line Stereo”, whereas Neil’s tuner is designated a Leak “Trough Line III”. To further confuse the situation, the rear of my tuner is actually marked “Leak Trough Line 3”. In order to try and resolve matters I did some research. To be precise, the Trough Line 3, has the following valve line up:

V1, cascode RF triode ECC84; V2, triode mixer ECC85; V3, triode oscillator and pentode IF ECF80; V4, pentode limiter EF80 and V5, 2nd pentode limiter and cathode follower ECF80.

The ‘Trough Line Stereo’ incorporated minor circuit revisions, as well as incorporating a simple stereo decoder. The circuit changes are as follows:
ECC88 replacing the ECC84;
C6 1000pF
R5 33Ω
C29 200pF
C40 50pF
C41, 42, 43, 44 150pF
C47 0.47uF
C53 1uF
and
R38 47kΩ.

There is also a bypass capacitor of 5000pF (C58) fitted between one of the anodes of the EZ80 rectifier (V7). Curiously the HT rail is now marked as 148V.

http://44bx.com/leak/Leak/Circuits/TroughLine2.gif

and

http://www.44bx.com/leak/Troughline3Stereo.html.

Encouraged by the improvement in tonal balance (the difference between the Leak and the Quad FM4, I now use, is less than 1dB, though there is still a bass ‘hump’ around 150 –200Hz which now gives an acceptable 'warmth'), I intend to replace all the valves in the signal path by NOS Mullards. I wont replace the EM84 tuning indicator, nor the EZ80 rectifier, since these are not part of signal path (though again some might challenge the latter). So far I have obtained NOS Mullard samples of all but the ECC85, but the search continues. When I have finished ‘fettling’ the tuner, I will do a full comparison with the Quad FM3, FM4 and, if possible, with a Quad FM2 (valve) tuner.

So thanks Neil for the advice, despite sending me off on a fool’s errand regarding the ECC88!

As before – to be continued

Regards

Scuse me ;) I thought you had a Trough-Line Stereo ( I may have taken you up wrong, it was awhile ago when we chatted about this)so the advice was right for that but wrong for a Trough-Line model 3. I would have had to go check that out as off the top of my head I would not have known what that valve was (I only have one 3 and as it has a slight fault I don't use it)whereas, as I have several stereos I knew it had an ECC 88.

Regards D S D L

Barry
17-05-2010, 21:29
Hi Neil,

I was only teasing you about sending me on a 'fool's errand' regarding the ECC88. ;)


My tuner is a 'Trough Line Stereo'. It's marked as such on the facia, despite being marked 'Trough Line 3' on the rear. The left hand knob on the facia is a three-way switch with three positions; 'off', 'mono' and 'stereo'. I have examined the component values (where visible), and they all correspond to the Trough Line Stereo as described.

Neither the 'Trough Line Stereo', nor the 'Trough Line 3' use an ECC88 for the cathode follower. They only use this valve for the cascode triode first stage amplifier.

This has been an interesting activity for me, and having now got the tonal balance back on keel, I must thank you again for suggesting I replace the output valve. The old girl is now sounding much as I remember. :)

As I said I intend replacing all the valves with NOS Mullards, and will report back when I have done so.

Regards