开云体育

My interest in this project started some time ago when I happened to notice that the original LZ1AQ circuit using 2N2222A/PN2222A transistors couldn't hear my weakest daytime LF NDB using a 39" diameter small loop (2.4-2.5 uH inductance) but when trying other better RF transistors it could hear the NDB. Eventually I tried building just one section of the LZ1AQ balanced circuit as an "LF noise output test circuit", and replacing both transistors each time I wanted to compare different transistors (with the 2.5 uH iron powder toroid equivalent loop inductance on the loop input to ground). And after I discovered that the input transistor contributed all the sensitivity, then I just had to change one transistor for the LF output noise test, making for a quicker test. I eventually added the low current single transistor Norton preamp to give a 10 MHz gain and noise figure test as well, of course needing to change the transistor in that each time. These use NPN transistors; both test circuits use polarized electrolytic caps. To test PNP transistors I'd need to build two more circuits with the polarized caps reversed. I don't intend to do that, so you're on your own if you want to test PNP transistors for LF noise and for 10 MHz gain and NF! As far as I know there are no good RF PNPs being manufactured any longer. The 2N5583 leaded transistor was the primary one; the lower frequency 2N5160 (used in the complementary symmetry NPN PNP output stage of most function generators of the 1970-1990s) was also available. For SMD, the BFQ149 was popular--all these are no longer manufactured. For other NPNs, especially small-signal types such as 2N3906--those are not suitable for use in loop amps that are biassed for moderate to high current, and which see potentially large input signals. The only exception I've come across, and that was purely accidental--is the PZT2222A, which I discovered is used in the WBL-02 loop amp I recently reviewed. I'd never heard of this transistor before, and assumed it was just another of the 2N/PN2222A types--and was pleasantly surprised to find it's noticeably better, as shown in my transistor tests. For whatever reason it apparently uses a different die than the common 2N/PN2222A types.

(One experimenter emailed me saying his tests of the BFU590 did not go well, with a number of transistor failures when actually using that device in the loop amp with outside small loops. Apparently the BFU590 was not very robust. Since I have enough 2SC5551As for now, I have not actually tried the BFU590 except in bench tests. I know the 2SC5555A is very robust; neither N4CY Everett nor myself have had one damaged so far from use in any of our various preamps and loop amps; we have of course damaged them from accidental bench tests such as reverse polarity power supplies--oops.)???? :)

(And as I reported some time back, the OnSemi 2SC5555A does not appear to be discontinued or obsolete; one can place a current order with for a minimum order, $900 when I checked, and in about 6 months you could expect to receive your order.)

Steve AA7U