Quote:
Originally Posted by David G4EBT
I've got three transistor testers:
Peak Atlas DCA50, which thinks JFETS are diodes
Peak Atlas DCA55 (bought cheap when on offer from Maplins). Sees it as a JFET, and states 'drain and source not identified' but correctly identifies the gate.
Cheapo Chinese jobby, which obligingly gives three options according to which test lead is connected to which pin!
Basically, none are any use whatsoever in this regard!
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Hi David,
I had rather hoped you would respond as it was your posts in the original thread I had been reading.
I must confess I have never felt the need to buy a transistor tester. I have always tested bipolar types in circuit with an analogue meter. Black to the base of an NPN and away you go! I never got used to doing it with a DMM as the leads are the wrong way round!!
I don't know how a FET would test out though on the AVO:- although it's a bit academic as it's not here anyway!
I have a BF256b so I'll go with your drawing and see what happens!
Second anomaly concerns the coils. One winding has a tapping which I assume is the primary? This is fairly obvious for L1, the oscillator coil but not so for L2, the aerial coil.
I would have assumed that the primary (the side with three pins) would be connected to the BC109 with the tapping unused. The secondary with two pins would go to the 270pf cap and the aerial.
Looking at your PCB layout, it looks like your L2 coil is connected the other way round- ie the three pin side goes to the aerial?
I have been involved in several projects some years ago where we made our own PCB's. I seem to remember that the artwork had to be printed on paper from an inkjet printer and then photocopied onto transparent film and then UV exposed onto photoresist board. Getting enough density from the photocopies was always a problem. We did have access to an early laser printer but had issues with accuracy. We were making eurocard sized boards with a dozen or so TTL chips and a CPU plus a full width edge connector. Double sided print as well!!
My mate did the artwork with only a manual PCB routing program- no autoroute! His head very nearly exploded!
I drilled the million holes with a pillar drill and loaded the boards.
All done in his flat with minimal equipment- madness really but we did manage to produce pretty good boards! Ferric chloride and something nasty to develop the boards which got upset on the kitchen floor and dissolved all the cardboard boxes....
I guess there are some much better ways to do it now. Even getting small runs of boards made nowadays is quite cheap.
But for this project it's not taken long to build it on the perf board so a PCB is not really necessary but would make a much more professional looking job.
Many thanks for your help and to the other respondents to the thread.
All the best
Nick