I run my TR7 with a QRO Technologies HF2500 (pr of GU74b's) with the ALC connected and have no problem. I also have the ALC on the TR7 cranked back somewhat.
Paul AD3G -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Don Cunningham Sent: Sunday, March 01, 2009 2:03 PM To: [email protected]; [email protected] Subject: Re: [Drakelist] TR7 with Modern Linear Garey, et al, I tried the "fake ALC" method with my old KWM-380 and an Alpha 91b after fiddling with ALC on the 91b with little success. I had no more success with the fake ALC circuit I found on a site. While it DID work at lowering the output (that could be witnessed in the CW mode with carrier turned down), the Collins had a leading edge spike that was a killer. The Alpha faulted on that spike, EVERY time. I have read a few places on the net hinting that the same might be true for the TR7. Anyone had experience with that?? Also, I was reading some time ago that the output of the driver board has been successfully used as a "0dbm" input for transverters. My thought was to remove the original PA in a TR7, build a small 30 or 40w amp to take it's place and drive the Alpha from that. I have since sold the Alpha and the KWM-380, and have a nice 2 tube, 3-500z amp whose ALC works well. I have NOT tried it as yet with the TR7, hence my question about the "leading edge spike", althought the amp would take it, 150w into this amp will give you 2k into a dummy load, hi. 73 and thanks for your input Garey, Don, WB5HAK ----- Original Message ----- From: "Garey Barrell" <[email protected]> To: <[email protected]> Sent: Sunday, March 01, 2009 12:12 PM Subject: Re: [Drakelist] TR7 with Modern Linear > Jim - > > Some good points there. However, most are related to the "dynamic" > action of ALC, NOT a fixed gain adjustment as I described. I and > others have used this technique with success for a long time, but > there is always new information! > > Of course there's always the argument that says "all this for less > than one S-Unit?!??" > > 73, Garey - K4OAH > Glen Allen, VA > > Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs <www.k4oah.com> > > > > Jim Shorney wrote: >> On Sun, 1 Mar 2009 09:26:20 -0000, John Stringer wrote: >> >> >>> The linear requires only 20watts drive for 400 watts out (our limit). >>> In SSB the only output control on the TR7 is the Mic Gain.It is a real >>> fiddle to adjust this for 20 watts and more so to keep it there. The >>> smallest touch on the gain control can double the output and also it >>> cannot >>> cope with peaks. >>> Modern radios have SSB output level separated from Mic Gain. >>> Any ideas on how to get around this situation? >>> >> >> A couple of things come to mind. Does tha amplifier have an ALC output? >> This can be used to limit your drive. You don't mention what kind of >> amp it is, but if there is no ALC output, you might be able to look at >> how Drake implemented the ALC in the L-4B/L-7 and add it to your amp. >> >> A power attenuator could be added inline. The difficulties there are >> that you have to find non-inductive resistors of sufficient power >> rating to soak up the extra exciter power, and provide T/R switching >> somewhow. >> >> A *good* external RF speech processor (SP75 or equivalent) could be >> used to limit the output level. I've found that my SP75 does a good job >> of limiting the peak output to a certian level. Or you could try >> adjusting the ALC control inside the rig for 20 watts maximum output. >> You might have to change some component values in the ALC circuit, but >> it should be do-able. >> >> The problem with reducing the output from a 150 watt amp to 20 watts is >> that you are operating closer to the crossover point of the >> transistors, and you could have higher IMD on your transmit signal. >> There can also be also other problems associated with using ALC to >> control your output level as is done in "modern" rigs: >> >> http://www.nitehawk.com/sm5bsz/dynrange/alc.htm >> >> From a spectral purity standpoint, it's probably better to have an >> attenuator in the input side of the linear than use any of the other >> methods. The National NCL2000 comes to mind here. The grid circuit is a >> 50-Ohm dummy load with two taps - one for high power and one for low >> power (~20 watts) drive. But that's a grid-driven amp, you may need >> something a little different if your amp is grounded-grid. >> >> 73 >> >> -Jim >> >> >> -- >> Ham Radio NU0C >> Lincoln, Nebraska, U.S.S.A. >> TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, >> GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time! >> >> "Give a man a URL, and he will learn for an hour; teach him to Google, >> and he will learn for a lifetime." >> >> HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ >> http://radiojim.exofire.net >> http://incolor.inetnebr.com/jshorney >> http://www.nebraskaghosts.org >> >> >> >> _______________________________________________ >> Drakelist mailing list >> [email protected] >> http://mailman.zerobeat.net/mailman/listinfo/drakelist >> >> > > _______________________________________________ > Drakelist mailing list > [email protected] > http://mailman.zerobeat.net/mailman/listinfo/drakelist > ------------------------------------------------------------------------ -------- No virus found in this incoming message. 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