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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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3rd Mar 2018, 9:54 pm | #21 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,088
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Re: Mullard Lockfit transistor failure survey
Yes, I've seen some of those DIL IC's which have obviously been sawn apart. They do look confidence-inspiring.
Somehow, I would expect modern epoxies to be higher temperature resistant than those of a few decades ago, though. Not only are there vast amounts of surface mount devices used, where the whole package has to withstand the full soldering temperature, but we have moved to lead-free solders which need higher temperatures anyway. |
10th Mar 2018, 1:41 pm | #22 |
Pentode
Join Date: Aug 2005
Location: Shrewsbury, Shropshire, UK.
Posts: 149
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Re: Mullard Lockfit transistor failure survey
I'm currently restoring an amplifier which originally used BFW60 and BFW90 Lockfit devices. Any thoughts as to the reliability of these?
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10th Mar 2018, 2:19 pm | #23 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
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Re: Mullard Lockfit transistor failure survey
I've no experience with those types, but I would treat them with suspicion and consider swapping them out. They don't appear to be anything special and superficially seem to be similar to the 2N2222/2N2907 or BC337/BC327.
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11th Mar 2018, 1:04 pm | #24 |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
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Re: Mullard Lockfit transistor failure survey
I'm still wondering if there's any difference in Mullard made and continental made lockfits.
On the other hand I've never seen these BFW types so I can't really comment on their reliability. BC635/BC636 (or higher) are possible replacements. |
11th Mar 2018, 8:24 pm | #25 |
Dekatron
Join Date: Aug 2006
Location: Madrid, Spain / Wirral, UK
Posts: 7,498
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Re: Mullard Lockfit transistor failure survey
I've had a few fail in Dual/Bettor record players and music centres (These were as common in Spain and Germany in the 70s and 80s as Thorn/Ferguson kit was in the UK). Fortunately my Tandberg language equipment, which is full of 'em, doesn't seem overly affected yet.
__________________
Regards, Ben. |
12th Mar 2018, 12:00 pm | #26 | |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,858
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Re: Mullard Lockfit transistor failure survey
Quote:
Before working with valuable vintage Mullard transistors - have a practice with some gash veroboard & some short lengths of tinned copper wire. You'll soon learn how long to leave the bit in contact, and at what temperature, before the perforated copper strip starts to lift &/or the wire's pvc insulation starts to shrink excessively or carbonise. I can vaguely remember teaching RAF apprentices, back in the early 70's, soldering techniques with 14 pin DIL IC's, using small sized soldering bits & then leading up to spade bits. They all seem to master the technique after a while. Most modern-ish DMM's can take a temperature probe attachment. Try applying your soldering iron to the leads of an old u/s transistor, whilst monitoring the temp at the point where the wire enters the encapsulation. Jesus - you've only a second or so. So speed is of the essence. Regards, David |
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12th Mar 2018, 1:54 pm | #27 | |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,088
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Re: Mullard Lockfit transistor failure survey
Quote:
So those of us who stick with 60/40, we are soldering components which are less susceptible to heat damage than before, but using the same trusty techniques. Win-win. But the point is, WHY are Lockfits dying when TO92's and TO220's are seemingly OK? |
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12th Mar 2018, 2:23 pm | #28 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,554
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Re: Mullard Lockfit transistor failure survey
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12th Mar 2018, 2:50 pm | #29 |
Moderator
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Re: Mullard Lockfit transistor failure survey
The general consensus does seem to be that it's something to do with the inflexible pins. It's a bit ironic that Mullard marketed the Lockfit standard as having improved reliability when it was introduced.
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12th Mar 2018, 3:05 pm | #30 | |
No Longer a Member
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Re: Mullard Lockfit transistor failure survey
Quote:
Number 1 is the awe and confidence inspiring early Texas Instrument resin package, these were typical of late 1960's TTL from TI, you can see the saw cut marks at the end. Ignoring the fact that this specimen is a 16 pin type, the whole package is thicker, even the pins are tougher, its like a T.Rex. Number 2 is a type of grey resin Signetics used, hard to see the label, its a 1972 vintage 7410. This is an extremely hard grey resin. When it is scratched it acts like granite, but its not as hard as ceramic but its extremely heat resistant. I always wondered if it contained some type of glass filler. Number 3 is a late manufacture 7410 of the typical black epoxy on modern IC's. (Which after attempting to drill and burn it, I don't think its as tough as the other two). Obviously its pretty difficult to beat ceramic, which is why all the mil spec TTL's were ceramic. I don't really know how lockfits compare or if it is some sort of resin defect that causes them to fail at times. |
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12th Mar 2018, 3:14 pm | #31 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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Re: Mullard Lockfit transistor failure survey
I suspect that the Lockfits *would* have been overall more-reliable on a production-line using automatic-assembly/wave soldering machines: more-reliable, that is, in the sense that fewer failed boards would come off the line than with conventional wire-legged transistors whose legs would sometimes miss a hole.
[This ease-of-auto-insertion was also one of the touted reasons for those 1960s resistors which consisted of a carbon-stick with tubular brass caps-with-sideways-sticking-out tabs pressed on the ends. I've seen plenty of these where the brass has embrittled with age, cracked and lost its grip on the carbon-rod] |
12th Mar 2018, 6:52 pm | #32 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,858
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Re: Mullard Lockfit transistor failure survey
This debate has released another memory from the early 70's. At that time, the RAF had been getting fed up with the failure rate of some American DIL & other epoxy encapsulated semi-conductor circuitry. Transatlantic costs were getting higher & higher. Solution - send some avionics technicians from 30MU at RAF Sealand to the nearby Liverpool Dental School. These guys became experts at using dental equipment to repair connection failures between the wee legs or pins & the chip inside. Loose legs & epoxy breakdown, enhanced by vibration, being the main problem.
To digress slightly, wallets of cheapo dental picks, scrapers, scalpels, etc.can be bought on the internet. A must for folk working a lot with electronic components. Particularly the diddy dentists mirrors. Regards, David |
12th Mar 2018, 7:01 pm | #33 |
Hexode
Join Date: Dec 2013
Location: Torrington, Devon UK.
Posts: 446
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Re: Mullard Lockfit transistor failure survey
I repaired a Roberts Rambler last week with a failed BF195C lockfit in the IF section. I replaced it with a BF495C pulled from a later Rambler. I was surprised at the cost and lack of availability of a NOS BF495C. I have got a few MPSH10’s here but didn’t think of trying one so thanks Paul for the reminder.
Regards Graham |
12th Mar 2018, 7:33 pm | #34 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
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Re: Mullard Lockfit transistor failure survey
The 2SC2999 is also very cheap from Chinese eBay sellers and has always worked well on the few occasions I've used it. Watch the leadout though.
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12th Mar 2018, 7:49 pm | #35 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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Re: Mullard Lockfit transistor failure survey
For the typical MW/LW/FM radio IFs, a humble BC109C has enough gain at the required frequencies to work just fine. For higher-Ft requirements like FM-broadcast-radio local-oscillators or RF amps you can use the likes of a BF115.
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13th Mar 2018, 11:27 am | #36 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,858
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Re: Mullard Lockfit transistor failure survey
Perhaps Colin, to establish the cause of failure, you could have a shot at delving inside one of your duff Lockfit transistors. I believe that some Forum members in the past have attempted to remove encapsulation material using a Dremel & very thin small circular blades & grinding discs.
Once or twice in the past, I've attempted to repair broken leads out of TO5's etc., by using minute hobbyist drills & a dental pick, but it was extremely fiddly and not always successful. Regards, David |
13th Mar 2018, 12:49 pm | #37 | |
Rest in Peace
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Location: Harlaxton, Lincolnshire, UK.
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Re: Mullard Lockfit transistor failure survey
Quote:
I am sorry that I have been repeating myself but I was trying to get an idea of failure rate from those of you who have seen, in recent years, significant numbers of this type of transistor. |
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13th Mar 2018, 12:59 pm | #38 |
Moderator
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Re: Mullard Lockfit transistor failure survey
There is usually only one bad transistor in a radio, and replacing it cures any fault, but I usually swap them all out if replacement is easy. I haven't had a failure in a Mullard module yet, which is just as well as they're awkward to replace.
I reckon about half the radios with Lockfits I've encountered had some sort of transistor problem. I don't work on large numbers of sets though, so I don't know how typical that is. Obviously some people will see a lot of Lockfit faults and others few or none. |
14th Mar 2018, 5:26 pm | #39 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,858
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Re: Mullard Lockfit transistor failure survey
Hey - what a bunch of Silly Billys we all are - I've just Googled "Mullard Lockfit Transistors" & discovered a heap of failure info by Mark Hennessy :-
http://www.markhennessy.co.uk/articl...ransistors.htm Well worth a good read. Regards, David |
14th Mar 2018, 7:55 pm | #40 |
Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
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Re: Mullard Lockfit transistor failure survey
Thanks for the link David. As you say, anything from Mark is well worth reading.
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