Mullard glass transistors
 

I recently bought an early 1960s Perdio Carnival transistor radio in nice condition and all working. Looking inside I was surprised to find that someone had carefully swapped the original Mullard glass germanium transistors (OC44 OC45 OC71) for equivalent Russian types. I wondered if the Mullard glass devices are going to become prize possessions along the lines of PX4 triode valves!

Re: Mullard glass transistors
 

They already are.

Certain guitar effects pedals used them back in the day. Modern guitarists lust after them because if they can only manage to get some of the original type transistors they can build a pedal and get that special magical tone that will soon make them as rich and famous as <insert name here>

So they do grab transistors from old portables. NOS germmanium devices go for silly money on auction sites. But I've not come across them fitting russian replacements to make the radio go again... it usually goes in the bin.

David

Re: Mullard glass transistors
 

Sorry David, I've got to disagree I'm afraid. Most guitarists (and I'm one of em) just want to find a 'sound' and these old transistors do that, well some of them do and they are highly variable, but then musical instruments by their very nature are like that. It's nowt to do with being rich and famous - if that's your ambition then best go on BGT or X Factor etc.

Cheers,
Steve.

Re: Mullard glass transistors
 

NOS glass transistors go for such silly money that they now have to be treated like money so much so that they have to be kept in money bags;D

Re: Mullard glass transistors
 

The thing that makes me smile is that there are a limited number of germanium transistors suited to the application of being on the front end of a guitar amp. I had to reverse engineer the missing treble boost amplifier in my Gretsch Jet Firebird & Rally guitars. Gretsch had lost the original schematics. The common garden OC44/45 etc are far too noisy and a poor option.

http://www.worldphaco.com/uploads/Gretschdoc.pdf

The most suited American made device is the 2N2613 (designed much like the UK/European AC107) for low noise tape deck preamps. The better made American effects pedals used these as did Gretsch. Realizing this I bought up a large number of them before this was common knowledge to make replica Gretsch Treble boost amplifiers, which I have supplied to very few including a guitarist from Dire Straits because I'm not normally in the business of making and selling electronic apparatus.

Of course the Europeans and the Americans were not the only ones to make low noise audio germanium transistors suited to the task at the time in the mid 1960's. Due to the fact that the Japanese basically pioneered battery portable audio tape recorders in that era they set their semiconductor houses to the task of manufacturing low noise germaniums for audio. There are quite a few examples such as the 2SB440. The Americans got onto these types and started using them in pairs 2SB439/440 in the front ends of their 8 track tape players.

Re: Mullard glass transistors
 

My tongue was firmly in cheek, my brother can be found in 'The best little blues band in Batley' and distortion/vintage pedals is an in-family wind-up. I gave him a Wien bridge oscillator and matching distortion meter 'So he could check he was getting enough' :-)

But, still, at the prices the NOS ones are fetching, there must be some very powerful motivation at work to spring that much money out of people.

I used to know Matt Mathias, the man behind Matamps, also sold under the Orange brand. He had a steady stream of quite well known names come into his shop on King Street, Huddersfield.

David

Re: Mullard glass transistors
 

But did you make sure your brother took the 'tone sucking capacitors' out of his electric guitar?? It is a well known fact that musicians who appear in pubs where the patrons are usually a little merry will be immediately booed for their sound if the caps have not been changed AND their amps do NOT have the NOS long plate 12AX7's. Go into any pub and you will hear 'Oh my GOD he's using a non gold plated, oxygen-free lead for his amp!!' or ' what a terrible sound - must be his Russian EL34 equivalents.' - ;D

Re: Mullard glass transistors
 

Speaking of Mullard glass transistors - did anyone here figure out a good way to open a later OC71 and get rid of the opaque goo so it was a phototransistor? The older ones you could scrape the black paint off, but not the later ones. I had a bit of success but found it was far to easy to damage the inside contents or connections.

Re: Mullard glass transistors
 

Stick it in a centrifuge AKA mum's spin dryer ;D

Re: Mullard glass transistors
 

Black silicone grease marks on the next load of washing? That's you in deep trouble, Chris.

David

Re: Mullard glass transistors
 

I have a couple of the ones that you can scrape the paint off to get a poor man's phototransistor. Apparently they really are phototransistors, but reject in some way: http://www.wylie.org.uk/technology/s...rd/Mullard.htm

Re: Mullard glass transistors
 

I did just that to make a photo transistor when constructing a tremolo pedal from a circuit in one of the magazines circa 1969 :)

Re: Mullard glass transistors
 

My Dad worked at Mullards Mitcham when the OCP71 really was a selected OC71 sold at a much higher price. When they became very popular a special production line was set up just for OCP71 but they were generally nothing like as good.

The spin dryer was a well known trick mentioned Practical Wireless, I seem to remember. I think I have some early unpainted no opaque goo samples somewhere.

Re: Mullard glass transistors
 

You don't have to open the package, just move the goo away from the chip.


Wasn't the goo blue?

That's where I would have seen the idea!

Re: Mullard glass transistors
 

It was white in the one I did, it looked like gel, you had to scrape the black paint off first of course

Re: Mullard glass transistors
 

My Mum used to work on the production line at Mullard’s Southampton factory. She was one of the girls on the line that tested transistors and depending on which way a centre zero meter ‘swang’ Painted the red dot on the package to indicate the emitter.

Re: Mullard glass transistors
 

Wasn't the red dot the collector?

I have hundreds of wrong way round glass transistors

Joe

Re: Mullard glass transistors
 

I was told that the goo was silicone grease. When trich was still around, that was quite good at dissolving silicone grease.

B

Re: Mullard glass transistors
 

red16v's mother has a lot to answer for!

Re: Mullard glass transistors
 

The red dot is the collector, but there is also a difference in the leadout spacing. They will work either way round, but with greatly reduced gain, maybe that's what is being tested.