|
General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
|
Thread Tools |
22nd Jun 2019, 12:10 pm | #21 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,871
|
Re: Tester for Germanium devices, is there one?
It's a 30uA movement, though in a different housing.
I dismantled the movement and took the coil out. There was a fused strand quite visible on the top layer of the winding, right on one of the corners. I considered re-winding it, but hadn't any wire of the right gauge with thin enough varnish. It would have just been a matter of filing up a mandrel to sit over a rod to be held in my panavise and 30 minutes of careful winding. Anyway, I had an Ernest Turner meter in a newer style that does OK. Just need to make a scale. David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
22nd Jun 2019, 6:15 pm | #22 |
Octode
Join Date: Oct 2007
Location: Exeter, Devon, UK.
Posts: 1,554
|
Re: Tester for Germanium devices, is there one?
Tester for germanium transistor: the Avo CT537.
Interesting David - RadioWrangler's comment on a 30ua meter in his CT537. Avo must have changed the meter. I have a CT537 with a 50ua, 2.4k 1% meter. It is in a metal housing, with a small button knob reset on the lower right side of the panel. My manual (1965) comments: The military version CT537 uses an "Avo fuly sealed instrument with cut-out which breaks the It circuit. This cut out replaces the It fuse on the civilian model". The It fuse is 1 amp for the current test circuit. The civilian version TT537 uses "a Taylor 50ua meter, with no cutout." Both have a Int Rect 6F5 silicon diode (CV7384, 50v,6A) across the meter terminals as a limiter, + to +. One reason I don't use mine often is that I have burnt out several transistors under test even at low currents, low voltage and with no heating. I rather suspect the switches marked break before make do not always operate as they are meant to. I would be interested to hear what experience RadioWrangler and others have with theirs. wme_bill Last edited by WME_bill; 22nd Jun 2019 at 6:23 pm. |
22nd Jun 2019, 6:44 pm | #23 | |
Heptode
Join Date: Dec 2014
Location: Lincoln, Lincolnshire, UK.
Posts: 583
|
Re: Tester for Germanium devices, is there one?
Quote:
My suggestion to anyone who cannot or does not wish to obtain an old tester would be to lookup the old circuits available and build one as they are fairly simple. |
|
22nd Jun 2019, 6:54 pm | #24 |
Heptode
Join Date: Jul 2010
Location: Wellington, New Zealand.
Posts: 653
|
Re: Tester for Germanium devices, is there one?
PE had a really good design for a tester in the late 60's - basically a flip flop (2 x OC44) fed an ac signal into the base of the testing transistor and to another transistor whose output was used to 'null out' the test transistor's audio output via a pot which was calibrated for alpha(? going off memory = dynamic gain). A 5ma meter showed the input current/leakage via various switching arrangements. I built it an used it for years (still have it somewhere) but cannot recall the article or author's name. Awkward thing nowadays would be getting the original transistors to build it and the 95 ohm min speaker I used (presumably modern transistors could be used and a miniature radio output transformer). Mine never seemed to 'null out' completely but took it down to the lowest level.
|
22nd Jun 2019, 7:31 pm | #25 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,871
|
Re: Tester for Germanium devices, is there one?
It might well be a 50uA movement, I was just running on memory from a few years back. It's definitely in a Taylor case.
No devices destroyed yet, but I usually have the bias backed off before moving any switches. David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
22nd Jun 2019, 8:35 pm | #26 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,853
|
Re: Tester for Germanium devices, is there one?
Just a quick thought - if anyone was considering a standardised spec for Ge transistors, perhaps something like a DTG1200 or 2400 as a power one, and a 2GT182(more modern OC71 eq.) for a small amp one.
After I'd started the st'd valve project, I was amazed at the software produced graphs that some participants produced. They put my hand-drawn efforts to shame. I'm sure these same computer experts could come up with something decent for Ge, or any type of transistors. Regards, David |
25th Jun 2019, 2:53 pm | #27 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,853
|
Re: Tester for Germanium devices, is there one?
I'm sure Specmaster has by now quite a handful of advice. My final two-pennoth is some info from a 1965 Practical Electronics magazine. It takes up several pages. So if anyone wants them scanned, please let me know.
Regards, David |
25th Jun 2019, 5:58 pm | #28 |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,761
|
Re: Tester for Germanium devices, is there one?
The August 1965 issue (along with other issues of P.E. Mag from 1964, and most other UK radio mags too) is archived on the marvellous American Radio Hisory website. Here's the link to the Aug 1965 issue, with full constructional details of the transistor tester. Fittingly perhaps, it uses two long-since obsolete OC171 transistors:
https://www.americanradiohistory.com...cs-1965-08.pdf
__________________
David. BVWS Member. G-QRP Club member 1339. |
25th Jun 2019, 6:50 pm | #29 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Tester for Germanium devices, is there one?
The notion of testing transistors in a simple tester is about or equally limited to to that of testing valves in valve testers. It probably explains why I do not own and have never owned a transistor tester of any kind.
There might be some benefit for screening out duds and rough comparisons. They are fraught with issues in "matching devices" unless there is a very complex test protocol at the frequencies of the intended circuit or at least over a range that covers that and curve tracing. As is the case with valves, where a transconductance test alone is of limited but some utility value, an hfe on its own is too. The best test you can perform is in the actual circuit the device will be used in, which includes the transistor's DC bias conditions in that circuit and its dynamic performance over the range of operating frequencies it will be used with. Signal generators & a good scope & meter are required. Certainly for matching pairs of devices that are intended in a circuit where some sort of balance, either push pull amplification or signal nulling is required, dynamic testing is required for a close match. Generally, testers can set the working conditions up which may well be far removed from the circuit you plan to use the device in. Also, for RF germanium types the C-B feedback capacitance is very important and you would also have to measure that and the transition frequency. These values are a factor of 10 different for say an OC45 vs an AF125 and have a profound effect on the operation of a radio frequency circuit using them, but an ordinary transistor tester won't shed any light on this. So for example, if you plan to use a germanium transistor in a 455kHz IF stage, set it up in one. Measure the signal gain, does it require neutralization, this can indicate a high range C-B feedback capacitance. For an audio device set it up in a stage with the DC conditions it will be used in. Again apply a test signal output/scope measurements. Compare devices that way and it will not only tell you if the device is ok for the intended task, but if it is a reasonable specimen compared to its peers for its intended application and you can match them for some application if required. |
25th Jun 2019, 6:51 pm | #30 |
Rest in Peace
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
|
Re: Tester for Germanium devices, is there one?
I wouldn't use OC170/171 transistors in anything. They are essentially AF11x devices with different (pre Pro-Electron) type numbers, and are as prone to the 'tin-whisker' fault as others of their ilk. In a cupboard I still have a radio I built over 40 years ago, which uses 3 x OC170. If I wanted to make use of it again, I'd replace the OC170s with some of those Russian Ge transistors.
|
25th Jun 2019, 6:59 pm | #31 | |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Tester for Germanium devices, is there one?
Quote:
|
|