[R-390] PRC-77 batteries
Sandy Geiger
[email protected]
Wed, 16 Jan 2002 11:58:17 -0500
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<P>Hello-I picked up a couple of functioning PRC-77s at a gun show Sunday. The batteries are weak;anybody know where I can get replacements ? TIA,Sandy G.<BR><BR> </P></DIV>
<DIV></DIV>C.H.(Sandy)Geiger III
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<DIV></DIV>>From: "AI2Q Alex"<[email protected]>
<DIV></DIV>>Reply-To:<[email protected]>
<DIV></DIV>>To: "'Steve Goode'"<[email protected]> ,<[email protected]> , "'Roger L Ruszkowski'"<[email protected]>
<DIV></DIV>>Subject: RE: [R-390] 6DC6 Replacement
<DIV></DIV>>Date: Wed, 16 Jan 2002 11:38:37 -0500
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<DIV></DIV>>
<DIV></DIV>>Hi Steve:
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<DIV></DIV>>I confess! I've poked JFETs into both 26C6 mixers on my R-392, and those
<DIV></DIV>>24-V stages work really well. I used a Dremel tool cutter to scribe the
<DIV></DIV>>glass of 7-pin miniature tubes, cracking them open and removing the innards.
<DIV></DIV>>I then soldered the JFETs with drain source and gate connected to the old
<DIV></DIV>>plate, cathode, and grid leads, respectively. After inserting a label with
<DIV></DIV>>my callsign on it, I then glued the glass envelopes closed. I popped 'em
<DIV></DIV>>into the R-392, where these solid-state jobbies perform flawlessly. I can
<DIV></DIV>>elaborate about the glass cutting procedure if you're interested.
<DIV></DIV>>
<DIV></DIV>>As per the 1977 QST article, last night I fired up an 1800-volt bipolar
<DIV></DIV>>junction transistor in the relay circuit of an old Drake TR4. The device is
<DIV></DIV>>a TV horizontal output transistor.
<DIV></DIV>>
<DIV></DIV>>I pulled the relay driver tube and put my little solid-state jobbie (fabbed
<DIV></DIV>>on a scrap of circuit board) in there with some clip leads, with my VTVM
<DIV></DIV>>hanging in to see what's happening with the switching levels. I also put a
<DIV></DIV>>reverse-biased diode across the driven relay in order to quash any possible
<DIV></DIV>>counter-EMF that might do in the transistor. The xstr that drives the relay
<DIV></DIV>>is in turn driven by a cheap N-channel JFET such as an MPF-102 or MPF-105,
<DIV></DIV>>which derives its Vdd from a diode and a 300 uF cap hanging off the filament
<DIV></DIV>>line as a simple halfwave rectifier/filter. The FET gate is extremely
<DIV></DIV>>high-Z, and sees the control voltage at a VOX/anti-VOX summing point. Works
<DIV></DIV>>like a champ and offloads the filament line.
<DIV></DIV>>
<DIV></DIV>>Now on to RF "replacements." Finding suitable high-voltage FETs for the
<DIV></DIV>>cascode circuits may be a problem. The Idss of the output FETs in these
<DIV></DIV>>pairs has to complement the input FET. As for dual-gate MOSFETs, I know that
<DIV></DIV>>Dan's Small Parts has some.
<DIV></DIV>>
<DIV></DIV>>Your thoughts?
<DIV></DIV>>
<DIV></DIV>>Vy 73, AI2Q, Alex in Kennebunk, Maine .-.-.
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<DIV></DIV>>
<DIV></DIV>>-----Original Message-----
<DIV></DIV>>From: [email protected] [mailto:[email protected]]On
<DIV></DIV>>Behalf Of Steve Goode
<DIV></DIV>>Sent: Wednesday, January 16, 2002 10:41 AM
<DIV></DIV>>To: [email protected]; Roger L Ruszkowski
<DIV></DIV>>Subject: Re: [R-390] 6DC6 Replacement
<DIV></DIV>>
<DIV></DIV>>
<DIV></DIV>>Alright! I must confess that I have had similar evil thoughts.
<DIV></DIV>>
<DIV></DIV>>WARNING---SAND STATE THOUGHTS TO FOLLOW!!!!
<DIV></DIV>>
<DIV></DIV>>I love the way my R-390A performs. Right now the only sand in it is the
<DIV></DIV>>Navy approved power supply changes. It even has a working ballast tube.
<DIV></DIV>>But I want this receiver to work forever! So what happens when I run out of
<DIV></DIV>>tubes? My thoughts are that anything behind the mechanical filters is fair
<DIV></DIV>>game since that should have minimal performance hits in dynamic range,
<DIV></DIV>>sensitivity, etc. So I was thinking of looking at the IF, detector, agc,
<DIV></DIV>>calibrator circuits to start experimenting on. What I have found so far in
<DIV></DIV>>discussions with others who have actually done solid state conversions is an
<DIV></DIV>>article from the April 1977 QST (it is not the April fool article). This
<DIV></DIV>>article shows how to make plug in solid state replacements for any tube
<DIV></DIV>>using JET or MOSFETs in cascode with high voltage transistors. This is as
<DIV></DIV>>far as I have gotten. Anyone else willing to confess? Anyone actually
<DIV></DIV>>succeeding in doing a solid state conversion?
<DIV></DIV>>
<DIV></DIV>>Steve, K9NG
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