Steve, Although some have been confused by the readings at first, I don't see any advantage in modifying the internal voltmeter to read the external supply voltage - what it reads is the actual voltage the K2 is operating at - but if changing it is your choice, by all means do it - it should be a simple task of padding R10 (or lowering its value a bit).
By process of elimination, the more 'critical' voltage regulator is the 8 volt low dropout regulator. The main thing the 5 volts drives is the front panel and control board digital stuff and as long as the voltage is within the tolerances for digital components, it will be close enough. The really critical circuit - the PLL is regulated by a secondary regulator down to 5 volts driven from the 8 volt line. The major parts of the K2 driven from the 8 volt regulator are the IF amp and product detector, the AGC, and the low level transmit stages - the devices used in those stages are not particularly sensitive to the voltage level. The only thing really sensitive to the exact voltage level is the AGC threshold since it is a resistive divider. I would think you could better 'improve' your K2 by carefully setting the AGC threshold level by changing the Control Board R1 value and leave the regulator as it is. As I recall, you may have optimized the AGC Threshold the last time you 'tweaked' your K2. 73, Don W3FPR > -----Original Message----- > > NB: this posting is about an Elecraft radio > > ;-) > > * * * > > I was thinking about doing two things to my vereable > K2 #0771, as I wait for new Elecraft toys: > > ... one is to re-jigger the divider resistors to > offset the K2 voltmeter so it reads what my actual > input-port voltage is, rather than the "internal" > voltage > > and > > ...two was changing the TO-220 regulator(s) to some > kind of precision type ... could not remember if it > was the 8V LVDO or the plain-old 7805 type that set > the reference voltage for other measurements. Wasn't > obvious from the schematic, at first. > > On the matter of the offset, I suppose that the > voltmeter's ultimate accuracy will be reduced a bit > because a fixed offset won't compensate for the > actual, varying drop through the polarity-protect > diode, as that will vary over the IsubF ... however, > I've switched mine to the newer Schottky type -- and > aren't they V-drop-flatter over the current curve than > the original? > > And on the second matter of the regulator precision, > maybe I am mistaken about the availability of > more-accurate TO-220 parts. What is the typical load > that the 8V rail has? I'm guessing a 1 amp regulator > will suffice. > > Which regulator was the "critical" voltage unit? It > was the +5v, right? > > Steve KZ1X/4 > > -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.338 / Virus Database: 267.9.4/57 - Release Date: 7/22/2005 _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
