Dear OMs on this thread, (Do not try to visualize this) Here is my report I promised yesterday:
While I was checking cold solder joints, I checked the conductance of the tuning coil. The tap in the middle was fine, but the wire was broken near the rear-end terminal. The meter would jump a little and then show the infinite R. So I think it was a very fine "crack". Here is a picture that shows what it looked like after I de-soldered the PCB from the terminal and lifted the broken end. I soldered it back and now the PTO works fine. Thanks for useful tips. http://kihwal.fayoly.net/ham/pto_broken_wire.jpg Kihwal, K9SUL (ex-HL1SUL) ----- Original Message ----- From: Kihwal Lee <kih...@yahoo.com> To: "k4...@mindspring.com" <k4...@mindspring.com>; drakelist <Drakelist@zerobeat.net> Cc: Sent: Monday, May 9, 2011 12:46 PM Subject: Re: [Drakelist] R-4A PTO Hi Garey, Thanks for the wonderful tips. I will let the list know what I find. I know of a person who redesigned the TR-4 PTO circuit to get the better stability. I do not know what effect it had on the linearity though. I will ask him whether he is okay with sharing the information. 73, Kihwal, K9SUL (ex-HL1SUL) ----- Original Message ----- From: Garey Barrell <k4...@mindspring.com> To: drakelist <Drakelist@zerobeat.net> Cc: Sent: Monday, May 9, 2011 12:25 PM Subject: Re: [Drakelist] R-4A PTO Kiwahl - First, that's a 2N3858 in the Buffer position, a 2N3904 will replace. The 2N706 is still available from Mouser and others. Other transistors 'may' work, but 'may' also corrupt the linearity. I don't know..... I've been looking for a defunct PTO to conduct these sorts of experiments on, and can't bring myself to mess up a working unit! :-) There are several other, more likely, causes of PTO failure. Top of the list is bad solder joints, particularly the tap on the coil. The 10V Zener sometimes shorts. Leaky or shorted Dur-Mica (brown, dog-bone) cap. Leaky or intermittent disc ceramic cap. Roughly in that order! The Buffer should read about 8 VDC on the Collector, 2.5 VDC on the Base, and 1.9 VDC on the Emitter. The Oscillator should read about 9 VDC on the C, 5.6 VDC on the B, and 5 VDC on the E. The Collector reading may be 'anything', depending upon the characteristics of your meter probe. It may kill the oscillations completely. The important reading here is the Base to be about 0.6 V above the Emitter. If this is true, the transistor is almost certainly ok. Let us know what you find!! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs <www.k4oah.com> Kihwal Lee wrote: > The PTO in my R-4A failed a few days ago. I replaced it with a spare I had, > but I still want to fix it as it has better linearity. In case the > transistors are bad, what are the proper substitutes? It has a 2N3058 and a > 2N706. > > Kihwal, K9SUL > _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
