tubes age 14
Otherwise the common 1N914 like silicon switching diodes are too slow for
good RF detection. And that 0.6 volt conduction threshold (.2 in germanium,
less in schottky) messes up weak signal detection. Good tube vintage tube
manuals show curves for detector diodes like 6H6 and 6AL5.
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Date: Fri, 27 Aug 1999 10:39:21 MDT
Subject: [R-390] solid state vis hollowstate
One of the many things I like about tube type gear is the pleasure of using
macho tools, big honking wire cutters, soldiering guns (with POWER), big
screw drivers. It's a pain looking at a board and trying to decide if the speck you
are looking at is a surface mount part or a fly speck. When I am asked the
difference between solid sate and tube type gear I tell them, with solid state you
are always worried about hurting it with static, overcooking parts, etc. On the
otherhand with tubes you are always worried about getting yourself nailed by
high voltage, either from the big electrolytic with the bad bleeder resistor you
didn't know about, or when testing with instruments. In other words with
soldstate you are worried about killing it, with tube type you are worried about it
killing you.
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Date: Fri, 27 Aug 1999 12:58:59 -0500
Subject: Re: [R-390] Why use a tube when Solid State will do!
Yes it would be tough to do. I got a sack of new SOT-143 silicon double gate
MOSFETs from Farnell in GB two days ago. Took one week from placing my
order on their secure web page, cost .45 US per transistor, .65 shipping when I
ordered only 35. Shipping likely would have been the same for 300... And cost
per transistor probably lower since 25 was their first price break. These are
good though better than 1 GHz, the package is about 4 mm in diameter with
radial leads. At least this week, that's not bad availability. The part number is
BF-988. I found a data sheet somewhere on the web in .pdf format.
I'm no fan of multiple conversion receivers. Mixers, especially tube mixers are
obnoxious noise sources and have rotten strong signal handling capabilities.
The tracking tuned circuits of the 390 family are there precisely to minimize the
strong signals getting to the mixers. The big problem is that the modern double
balanced ring mixer that has good signal handling capability is low impedance
and all the 390 circuits are high impedance...
At the moment, I'm thinking that the single conversion receiver will outperform
the 390 family. The state of the art is probably a Norton feedback RF amplifier
feeding a diode ring double balanced mixer that's properly terminated with wide
band terminations feeding the initial receiver selectivity after a low gain wide
band first IF stage. That initial selectivity should be most of the receiver's
(14 pages)
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