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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 14th Mar 2018, 11:02 pm   #41
mark2collection
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Default Re: Mullard Lockfit transistor failure survey

I've been watching this post with great interest, & having read Marks article (many thanks for the link David), it certainly explains my Hacker Sovereign ...

I can set the idle current fine, only, the quiescent 'noise' through the loudspeaker is annoying on quiet passages, to the point I sadly have to admit to not using/enjoying the set. You know when your ear 'tunes' to that annoying rattle in the car, or 50Hz hum on a transformer, same for me & the foreground 'Sssssssssssssss' on the Hacker, irrespective of volume/tone settings.

Plus, everytime you switch the set on, it sounds weak & feeble, very poor low frequency response & anything above 1/3rd volume leads to masses of distortion with no further gain in sound output. Adjusting the pot on the front end of the amplifier improves things massively, but it doesn't last, until you re-adjust again ...

Amplifier aside, when it's going, it's a great sounding radio, works fantastic on all bands & when 'set-up' (twiddle amp front-end pot) it's most enjoyable indeed.

I'm now taking a very serious view to a re-visit, most likely late summer/autumn. I know the caps & resistors check out ok, but never considered the Lokfit transistors! (Silly really, there's nothing else left Aside from perhaps a winky pot). Owing to other commitments, it's been placed safely to one side, almost forgotten, a great shame ... But there's hope it would seem

About 3 years ago I finally repaired the module in my Roberts R707, usual Germanium transistor issues, would be nice to bring the Hacker back, both fantastic looking sets, great performers when correctly setup & astonishing build quality, especially the Hacker.

Mark
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Old 15th Mar 2018, 10:34 am   #42
David Simpson
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Default Re: Mullard Lockfit transistor failure survey

Right enough, this is a really interesting topic. I'm tempted to get my TITS out along with one of my transistor testers, if I could find some old Mullard Lockfits. Sadly I don't have any, and with the onset of spring - little available time. However, this would be a fine winter project. If anyone has a couple of spare transistors, one decent & one on the blink, perhaps they could send them to me - then I could send them on to another testing enthusiast. Just a thought.

Regards, David
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Old 15th Mar 2018, 11:06 am   #43
paulsherwin
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Default Re: Mullard Lockfit transistor failure survey

In the past I've just binned them, but next time I come across one I'll save it and offer it here. In most cases they appear OK on a tester though, at least using my fairly basic test gear.
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Old 15th Mar 2018, 1:57 pm   #44
ukcol
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Default Re: Mullard Lockfit transistor failure survey

We are getting a good picture of the fault symptoms experienced with Lockfit failures from various contributions to this thread and the Mark Hennessy article. There have been a number of suggestions as to the mechanism of failure but we will have to wait until someone has the time and the means to come up with a definitive answer.

I remember being of the opinion that the tin whisker problem was confined to the T07 case and that the T01 case was free from the problem. I was soon put right by Mark Hennessy and others and finally experienced a tin whisker failure in an AC128 myself which I was able to prove by cutting it open.

I mention the above because the picture one has of the reliability of a particular type of component comes largely from one's own (often limited) experience and it is very useful to hear the experience of others to get the bigger picture.
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Old 17th Mar 2018, 9:46 am   #45
mark2collection
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Default Re: Mullard Lockfit transistor failure survey

At work, we've very recently been 'gifted' a Tektronix 576(?) curve tracer!

Just need to figure out the various adapters, read through the vast manual & have a set of known (faulty & good) transistors.

The Hacker has just gone up the list a further notch ...

Mark
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