11 posts in less than 12 hours in answer to my question-that is very impressive support from this group! Thank you all. I will try the "fake" ALC first as that is the easiest and come back to report. My Linear is the ACOM 1000 which I believe is similar to the Alpha 91. It has no ALC connection. John. GI3KDR
-----Original Message----- From: [email protected] [mailto:[email protected]]on Behalf Of Don Cunningham Sent: 01 March 2009 19:46 To: [email protected]; [email protected] Subject: Re: [Drakelist] TR7 with Modern Linear Thanks for the thoughts, Garey. The amps I have now all have ALC outputs, so I'll report back later if they have any problem with the TR7 if there is any interest. 73, Don, WB5HAK ----- Original Message ----- From: "Garey Barrell" <[email protected]> To: <[email protected]> Sent: Sunday, March 01, 2009 1:35 PM Subject: Re: [Drakelist] TR7 with Modern Linear > Don - > > Dunno, never tried it on a TR-7. Doesn't seem like there should be a > problem, since the "fake" ALC voltage is present before the transceiver > is keyed. There was a blurb about a "keying" spike when the TR-7 was > first powered on in the early units, but I didn't think it applied to CW > or SSB operation. > > The INPUT to the PA block on the TR-7 is about +4 dBm at 50 ohms. > > The only problem with replacing the PA with a smaller unit is that you > then MUST use the amp for all operations or drop back to the 20W level. > In that case you might as well just stick a 10 dB pad in FRONT of the PA > block. > > 73, Garey - K4OAH > Glen Allen, VA > > Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs > <www.k4oah.com> > > > > Don Cunningham wrote: >> 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 >>>> > > _______________________________________________ > Drakelist mailing list > [email protected] > http://mailman.zerobeat.net/mailman/listinfo/drakelist > ---------------------------------------------------------------------------- ---- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.0.237 / Virus Database: 270.11.5/1978 - Release Date: 03/01/09 07:04:00 _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
