Leak Troughline 3 Stereo Radio Tuner

[LucasAdamson]

Hi everybody,

This is my first post on this forum, as I've just bought a lovely, working Troughline 3 Stereo Radio Tuner in excellent condition. It came with a Leak Stereo 30+ and a Goldring Lenco 75 for £87 and a 60 mile round trip. Not bad, I suppose. I only really wanted this radio especially.

I must say that I am impressed with the sound, even though it has been is storage for 15 years completely unused. I have been waiting for the electrolytic caps to pop and lose all sound, but nothing yet! There is, however, the distinct smell of "old electronics," not unlike burning flux and dust filing the room. I like it

Anyway, I have purchased new electrolytic caps as a matter of course, and wanted to ask some advice about that. There is a triple cap, with a shared earth case and 3x 40uF supply caps inside, which I am replacing with 3x 450v 47uF Panasonic caps without hiding them in the old cap body (as I'm not such a purist - shame on me!). Will this increase tend towards a reduction in liveliness in your experience? I have heard that over capacitance in valve rectified circuits can do so, but have no experience with valve rectifiers, so...I humbly ask.

I am matching exact values with all other electros and leaving all of the tiny pF caps in place. I may test them for value accuracy at a later stage, but for now, I will trust that they are mostly ok, as they tend to be more reliable than electros, and the radio is working fine. I know some will ask why I intend on replacing the electros, but it's because they are a.) of rubbish quality originally by modern standards, b.) probably drier than they were originally, c.) it will improve reliability and d.) it's cheap (£9 total from Farnell) and easy to do.

There is a 1000uF 30v supply cap to the transistor MPX stereo decoder, which I will replace with a 3300uF Panasonic FC I have, and I will certainly be designing a new decoder at some point.

I have an embarrassing question. Embarrassing only because it reveals the depth of my tube ignorance:

What are the tall square section towers next to the valves? The ones with the hole in the top and a spiral inside. I have looked on the schematic, and they look to be transformers of some sort, but I can't be sure, as I've never come across them before, and the only tube circuit I've built is an SRPP for my DAC output stage.

Many thanks
Lucas

[DangerMan]

Hi Lucas,
Yes, the square aluminium "towers" are transformers.
They are tuned to the intermediate frequency and provide coupling between the stages of amplification and also the tuned circuits for the FM "detector".
Their adjustment is critical to the performance of the tuner (they define the bandwith and the discriminator's linearity) and, unless you have the equipment and know exactly how to align them, they are best left well alone !
Pete

[Alistair D]

Hi Lucas

Do a Google search on superhet(rodyne) radio theory. Hopefully you can find a description of how radio receivers work which is not too technical.

The values you have chosen for the electrolytic capacitors all seem fine to me. To be quite honest, if there is no hum on the signal and the tuner seems to be sensitive enough I would consider leaving it as original as possible.

Al

[DangerMan]

Hi Lucas,
in case you haven't found it, there is an excellent website covering Leak products here: http://www.44bx.com/leak/
The book is very interesting too ! (no connection, etc.. just a satisfied owner)
TTFN
Pete

[LucasAdamson]

Originally Posted by DangerMan

Hi Lucas,
Yes, the square aluminium "towers" are transformers.
They are tuned to the intermediate frequency and provide coupling between the stages of amplification and also the tuned circuits for the FM "detector".
Their adjustment is critical to the performance of the tuner (they define the bandwith and the discriminator's linearity) and, unless you have the equipment and know exactly how to align them, they are best left well alone !
Pete

I will certainly leave them well be. Radio 3 sounds really heavenly with this tuner - even in Stereo and an indoor aerial. I have read many times that the aerial needs to be first rate and the decoder is appalling on this thing. Maybe so, but when I say it sounds "heavenly" I mean that it is by far and away the nicest I've ever heard radio sound.

Other popier stations sounded awful, and I suspect that this is due at least in part to "radio edit" versions of songs on Radio 1, with no bass and a highly compressed frequency range generally, for the standard 2" speaker.

I must get a roof-top aerial now - I'm inspired to get this thing as good as it reasonably gets.

[LucasAdamson]

Originally Posted by Alistair D

Hi Lucas

Do a Google search on superhet(rodyne) radio theory. Hopefully you can find a description of how radio receivers work which is not too technical.

The values you have chosen for the electrolytic capacitors all seem fine to me. To be quite honest, if there is no hum on the signal and the tuner seems to be sensitive enough I would consider leaving it as original as possible.

Al

Even though it's all OK, isn't there any wisdom in replacing caps? I mean, although they work, there must be some leakage going on, surely. I know there are different schools of thought on this, and that the vintage school is mostly to leave well be until it breaks, but I can't resist trying to squeeze out a bit more magic from the thing.

Surely, given the availability of caps today, Mr Leak would have binned those old caps himself. Don't worry, I won't be putting metal film resistors, a toroidal transformer and new valves in there.

[Tractorfan]

Hi,
I don't know anything about Leak tuners in particular, but personally I can't for the life of me see how changing the caps in the rectification circuit can alter the "liveliness" of the performance. All they do is smooth the HT supply, nothing more. DC is DC.That's it. Anyway, an increase of 7uF isn't that much considering component tolerance. If the existing ones work OK, I'd be inclined to leave them be. All caps leak a little bit and as long as it's not excessive (caps getting warm) I wouldn't worry, meself.
Hope this helps.
Cheers, Pete

[Alistair D]

What I would do here is to measure the voltages on the anodes and cathodes of every valve and compare them with the schematic. Only replacing components where the voltages are out of spec.

Alternatively, buy yourself an ESR meter so that you can measure the electrolytics in circuit.

Al

[DangerMan]

If the tuner sounds good now, it can't have a large amount of ripple (alias hum) on the supply rails. Therefore there's not a lot to be gained by swapping the HT smoothing capacitors. But it's your choice.
What I would do is check that the original electrolytics are not running hot. This could indicate leakage which could damage the mains transformer if it increases: but this is unlikely as there is no hum on the output.

There are a few things inside the tuner that could be affected by disturbing it: I'm largely thinking about the multiple earth points in the tuner that are made mechanically via rivets but there will be other things. Whilst you could go the whole hog and do some preventative maintenance on these, just imagine how you'd feel if it got worse and you didn't understand why !

There's a time-old adage... "never touch a runner", which is just meant for jobs like this

Enjoy it.. it'll still be there if you do decide to make some changes at a later date.
Meanwhile read up as much as you can on what makes it tick.

The stereo decoder is its weakness, and there are any number of more modern alternatives when you do update this.

TTFN

Pete

[G8HQP Dave]

When checking valve voltages, remember that "in spec" generally means within about 10-20% of the stated value. Similar tolerance when checking resistors. Exception is heaters, which should be 7-10%.

There has been suggestions that these Leak tuners sometimes have deemphasis capacitors which are too large, giving a muffled sound. Worth checking. The puzzle is how they got their sums wrong - or was it deliberate to ease the transition for ears used to AM?

[LucasAdamson]

Originally Posted by Tractorfan

Hi,
I don't know anything about Leak tuners in particular, but personally I can't for the life of me see how changing the caps in the rectification circuit can alter the "liveliness" of the performance. All they do is smooth the HT supply, nothing more. DC is DC.That's it. Anyway, an increase of 7uF isn't that much considering component tolerance. If the existing ones work OK, I'd be inclined to leave them be. All caps leak a little bit and as long as it's not excessive (caps getting warm) I wouldn't worry, meself.
Hope this helps.
Cheers, Pete

I have read several articles and discussions regarding smoothing capacitors and their effect on PRAT and bass response in particular. I have built several solid state devices and can confirm that there is a reality to some of this. In essence, the prevailing idea is that, in power amplifiers for example, large capacitance can help bass solidity, power and clarity, but over-capacitance can lead to a subtle slowing of responsiveness (pace, rhythm and timing). A particularly successful implementation of a Gainclone amplifier I have built uses way less capacitance than is normal for a power amp, and it lends a very lively and involving atmosphere to the whole system. I have read recently that this is particularly the case with tube rectified circuits - the discussion was on a forum where somebody was proposing to replace a 40uF supply cap with a 220uF supply cap, and more than one poster advised that the gains could be outweighed by a certain perceived sluggishness. I agree that this doesn't immediately make a whole heap of logical sense, but that doesn't make it not so.

[LucasAdamson]

Originally Posted by DangerMan

If the tuner sounds good now, it can't have a large amount of ripple (alias hum) on the supply rails. Therefore there's not a lot to be gained by swapping the HT smoothing capacitors. But it's your choice.
What I would do is check that the original electrolytics are not running hot. This could indicate leakage which could damage the mains transformer if it increases: but this is unlikely as there is no hum on the output.

There are a few things inside the tuner that could be affected by disturbing it: I'm largely thinking about the multiple earth points in the tuner that are made mechanically via rivets but there will be other things. Whilst you could go the whole hog and do some preventative maintenance on these, just imagine how you'd feel if it got worse and you didn't understand why !

There's a time-old adage... "never touch a runner", which is just meant for jobs like this

Enjoy it.. it'll still be there if you do decide to make some changes at a later date.
Meanwhile read up as much as you can on what makes it tick.

The stereo decoder is its weakness, and there are any number of more modern alternatives when you do update this.

TTFN

Pete

Yes, I'm more from the "if it works, break it, mend it better, then break it again and mend it some more" school. Dumb perhaps, but fun, and often educational.

My main forum is DIYAudio, where there is a lot of emphasis on building and understanding what you're building, in order to improve the circuit. Such a tuner as this deserves some new caps - I won't break it, I promise! I couldn't leave such dinosaurs in there, all dried out and leaky and off spec - I know from experience what a difference a cap change can make! In the same way, I have replaced the phono plugs.

I am considering going fully tubed stereo, and making a tube decoder. I found a circuit diagram, PCB print, parts list and instructions for a Dynaco FMX-3 Tube MPX Stereo Decoder. www.the-planet.org/dynaco/Tuner/FMX%203.pdf

Watcha think? Cool, eh? Need a matched quad of germanium diodes though, amongst some other crazy old stuff. Hmm...

[Silicon]

When I examined my Troughline Mk3 Mono tuner I decided to replace C53, the 1uF capacitor that the audio passes through, with a Polyester or Polypropylene capacitor. I can't remember which.
I also replaced C56, the 4uF capacitor on the anode of the output valve. I left the power supply capacitors in place. I checked the value of the resistors in case they changed value.
I replaced a worn out valve.
The sound is very clear and natural sounding. If I listen to radio 3 on headphones I feel that I could hear a pin drop in the studio.

Brendan

[LucasAdamson]

Thanks for that Brendan. I should check those resistors I suppose. Maybe down the road I will really go to town on it. Ever considered going stereo?

[G8HQP Dave]

My main forum is DIYAudio, where there is a lot of emphasis on building and understanding what you're building, in order to improve the circuit.

Emphasis on building, yes. Emphasis on understanding? Sometimes, but I find DIYaudio also contains a lot of post-modern nonsense and anti-science. I, and others, were recently criticised on there for suggesting that people ought to read a book about basic electronics before sharing their ignorance of how negative feedback works. Mind you, there are audio sites which are far worse.

[LucasAdamson]

Hi Dave. Yes, it's a shame when people let a little knowledge run ahead of them. There is also, of course, considerable stocks of snake-oil in the hi-fi trade, and even in DIY.

Do you remember which are the de-emphasis capacitors in the Troughline you mentioned in your last post? Or a post you could link to?

[Herald1360]

Originally Posted by LucasAdamson

Need a matched quad of germanium diodes though, amongst some other crazy old stuff. Hmm...

Wot, no EB or EA something or other valves

[G8HQP Dave]

Deemphasis is C50 (3nF) for mono, and C59/60 (2nF) for stereo.

On page 246 of "Firsts in High Fidelity" by Stephen Spicer he suggests that C50 should be 1nF. C59/60 should be 750pF. However, both should be higher if the following preamp has a low input impedance: 47K means C50 2nF, C59/60 1.4nF. This suggests that the Leak values assume a preamp input of nearer 30K - seems rather low.

Preemphasis caps which are maybe up to twice the right value will put a -6dB shelf in the treble above about 1.5kHz. This will lead to a very smooth sound, yet it might still sound detailed as higher treble is still present but at a lower level. It might embarrass a lot of audiophiles if they discovered that their favourite tuner sounds as nice as it does because of serious frequency response errors! This issue does not arise in earlier versions of the tuner.

The Ge diodes are in the stereo decoder, not the main circuit.

[LucasAdamson]

Thanks Dave. All fascinating stuff. It is true that sometimes a system sounds amazing because it's not full frequency. I have a very detailed and revealing system, and it just makes a lot of recordings sound horrible. I will buy some 1nF polypropylene or more likely polystyrene caps and try them out in the C50 position. As I am replacing the decoder, I don't think I will bother with C59 and C60 though, as it will be pretty irrelevant with the new decoder.

I am having second thoughts about building that Dynaco FMX-3 Tube decoder from scratch - too much parts sourcing (like the matched quad of unobtan/german-ium diodes for example) for so little advantage other than the genuine kudos of making such a thing. I will probably try and find one of the many good solid state designs that will fit in the case in place of the existing one. Probably this one, actually: Link

[Hybrid tellies]

Hi, you mentioned using a good rooftop aerial, where I live they are needed but there are parts of Bristol which gets superb FM reception from Either Wenvoe or the local relay at Bedminster Down. So if you are lucky enough to live in one of these areas where the FM signal is strong using a large rooftop aerial might actually overload the set causing all sorts of noise and intermodulation problems.