ZTX series transistors. Is this a co-incidence?

[Biggles]

I have a circuit for an amplifier which I am trying to reverse engineer but unfortunately there are three transistors in e-line packages which are unmarked. There are both PNP and NPN devices used in the circuit. They look very much like ZTX something or others to me. I have some ZTX107, 108 and 109, 300 and 500's, and even a ZTX3702 but I was wondering if the 107 etc numbering was an equivalent to say a BC107, but made by Zetex. If this is the case are these intentional, direct equivalents or is it just some kind of co-incidence? The transistors I am looking to substitute are plain old low level AF stages, in which I suppose you could use a whole range of transistors, but I would like to keep it as authentic as possible. I don't have much info on Zetex transistors, so any suggestions would be helpful.
Alan.

[paulsherwin]

There are datasheets on all these Zetex transistors if you google them. I don't see any reason why you shouldn't use them if they look the part. As you say, a large number of general purpose Si types are likely to sub without problems.

http://www.alldatasheet.com/datashee...EX/ZTX107.html

However, do you have a good reason to suspect the original transistors are bad?

[Biggles]

I am trying to copy a couple of Bi-Pak AL60 amplifier modules I have from years ago and have traced out the circuit successfully and identified all the components apart from those unmarked transistors. I wish to use transistors from old stock I already have and among these are the random collection of ZTX type transistors. I also have a large collection of NOS general BC type devices, but for the sake of making "authentic" copies I would rather use ZTXxxx types. Probably me being a touch pedantic, but I would like to stay as close to the originals as possible. This has been on the to do pile for a long time. I also plan to make a pre-amp and tone control circuit using discrete components to complete the amplifier when I have time. The originals performed very well, hence the desire to replicate them.
Alan.

[paulsherwin]

I think ZTX107 = BC107 etc, and the specs seem to support that, but I haven't found any hard references.

[Brian R Pateman]

I've always assumed (foolish I know) that ZTXnnn = BCxxx.

I don't remember the basis for this assumption but Towers gives specs which are close enough.

[Mr Moose]

Hello,
The problem with unmarked ZTX series e-line transistors is that their collector currents can vary from 100ma to at least 5A.
For instance the ZTX849 has a collector current of 5A https://www.digchip.com/datasheets/p...ZTX849-pdf.php
Yours, Richard

[Herald1360]

Only some ZTXxxx = BCxxx, ZTX849 definitely ain't a BC849 sub. Some ZTxxxx also carry over to 2Nxxxx. I suspect on a few common or popular bits.

ZTX types I've always liked- they're small and (were?) available in many varieties. That ZTX849 sounds like an ultralow VCEsat switching type. Most also had the advantage (to one brought up on OC types) of being centre lead base with collector marked by a moulding flash on the top.

[Bill]

The Ferranti ZTX107,8 and 9 were equal to the BCs. The 300 and 500s are not equivalent to anything, numberwise. Ferranti got the cost of production of the e-lines down to one penny each, the least we sold them for was 4p, these being the ones that just about transisted.The automatic testers sorted devices into about 20 different bins, depending on gain,leakage,breakdown voltage or just rejects (there were many!). I'm talking early 1970s here- I suspect there are a lot more new ZTX types developed by Zetex and whatever the company is called these days(something "Diode"?).
I am not suggesting that Ferranti semiconductors were in any way inferior, there were many unidentifiable "SQ" devices with custom numbers for the likes of MoD and Tektronix.

Bill

[Skywave]

Originally Posted by Brian R Pateman

I don't remember the basis for this assumption but Towers gives specs which are close enough.

IMHO, every electronics enthusiast should have a copy (or copies, including back numbers) of T.I.T.S. (Tower's International Transistor Selector) within easy reach. Just as essential as a soldering iron.

Al.

[Biggles]

I regret not taking the copies of Tower's with me when I left various jobs in the past. I think I was the only one to look at them, being into home construction. Usually when repairing radio equipment at work, you had the genuine spares, Motorola, Pye, Storno, etc from stores and replaced like for like, so you never really had to look equivalents up. Motorola had their own house numbered devices in many cases anyway.
Alan.

[Biggles]

Just a quick update on this one. I eventually decided to use ZTX300's and ZTX500's for the unmarked transistors, as I had a few in stock. Probably a little over rated for the application but as they are apparently complementary and presumably matched, I took a punt. They work very well and I have now constructed and tested two amplifier modules. They sound terrific and I am well pleased with them. I am now going to build a matching pre-amp as the one I tested the amps with was borrowed from another project. Thanks for all your input.
Alan.

[paulsherwin]

They are unlikely to be matched closely, but that probably doesn't matter.