Mullard Si modules - what transistors? - UK Vintage Radio Repair and Restoration Discussion Forum

paulsherwin · 24th Oct 2015, 3:38 pm

We all know that the early Mullard modules used AF11x series transistors, but has anybody dismantled one of the later Si ones used in the Roberts R606 and 606MB amongst others to find out what's inside? I have a nasty feeling that the answer will be B194/5 Lockfits. This info doesn't seem to be in any of the Mullard documentation.

I don't have an obviously faulty module at present but am a bit concerned about what the future holds, given the increasingly common Lockfit problems.

G6Tanuki · 24th Oct 2015, 4:52 pm

My R606 [S/N 30178 if that's relevant] seems to be running just fine - if/when I need to open it and investigate what's in the Mullard modules I'll report back.

In the days when I was rebuilding VHF mobile-radio gear the "generic" Si NPN RF/IF/oscillator/frequency-multiplier transistor I used for anything up to 200MHz was the BF115. I have a trayfull of them here 'just in case'.

paulsherwin · 24th Oct 2015, 5:07 pm

As I said, I don't have an immediate problem to address, but want the info for future reference.

mhennessy · 24th Oct 2015, 5:51 pm

I went inside the FM module of an R707 once. Inside was TO92 silicon - can't remember which types, but I think more details might be somewhere on this forum.

24th Oct 2015, 6:00 pm

Because the noted failure mode of the Lockfit transistors is leaking moisture down the leads how about a spray of conformal coating (posh varnish) onto the existing transistors, that may stop the rot, or even a silicone aerosol. Point into a hole and squirt. I have a can of Halfords silicone lubricant that I spray on any connector that becomes accessible when playing with my motorcycle. Seems to stop corrosion.

G6Tanuki · 24th Oct 2015, 7:11 pm

Quote:

Originally Posted by mhennessy

I went inside the FM module of an R707 once. Inside was TO92 silicon - can't remember which types, but I think more details might be somewhere on this forum.

I've not needed to pop the module-cans of my R707 - yet; its one lockfit-failure has been in the audio preamp/tone-control area.

If I do ever need to undertake future delveage into its Mullard Modules I'll note what's inside, and correlate this with any serial-numbers for the future guidance of others.

24th Oct 2015, 3:38 pm	#1
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,985	Mullard Si modules - what transistors? We all know that the early Mullard modules used AF11x series transistors, but has anybody dismantled one of the later Si ones used in the Roberts R606 and 606MB amongst others to find out what's inside? I have a nasty feeling that the answer will be B194/5 Lockfits. This info doesn't seem to be in any of the Mullard documentation. I don't have an obviously faulty module at present but am a bit concerned about what the future holds, given the increasingly common Lockfit problems.

24th Oct 2015, 4:52 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,010	Re: Mullard Si modules - what transistors? My R606 [S/N 30178 if that's relevant] seems to be running just fine - if/when I need to open it and investigate what's in the Mullard modules I'll report back. In the days when I was rebuilding VHF mobile-radio gear the "generic" Si NPN RF/IF/oscillator/frequency-multiplier transistor I used for anything up to 200MHz was the BF115. I have a trayfull of them here 'just in case'. Last edited by G6Tanuki; 24th Oct 2015 at 5:09 pm.

24th Oct 2015, 5:07 pm	#3
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,985	Re: Mullard Si modules - what transistors? As I said, I don't have an immediate problem to address, but want the info for future reference.

24th Oct 2015, 5:51 pm	#4
mhennessy Dekatron Join Date: Jul 2007 Location: Evesham, Worcestershire, UK. Posts: 4,244	Re: Mullard Si modules - what transistors? I went inside the FM module of an R707 once. Inside was TO92 silicon - can't remember which types, but I think more details might be somewhere on this forum.

24th Oct 2015, 6:00 pm	#5
Guest Guest Posts: n/a	Re: Mullard Si modules - what transistors? Because the noted failure mode of the Lockfit transistors is leaking moisture down the leads how about a spray of conformal coating (posh varnish) onto the existing transistors, that may stop the rot, or even a silicone aerosol. Point into a hole and squirt. I have a can of Halfords silicone lubricant that I spray on any connector that becomes accessible when playing with my motorcycle. Seems to stop corrosion.