[Drakelist] TR-7 - More Info Cont'd
To everybody who has written thus far, I thank you. Still working on it... - I have double-checked the ground connections on the tuner and radio. All is good there. - To Gary who suggested that the external tuner indicated that the problem was past that point, I hooked my Tentec up to the same tuner/antenna and it is rock solid at full power output into the same configuration. I also don't think I have a break in the ladder line for the same reason. I have connected my MFJ-259 to the tuner input and the antenna is about 58+j7 in terms of impedance. Looks rock solid on the 259...no fluctuation. - I can't induce the problem on 20m...only 40m. I ran 20m CW into the same doublet/ladder line antenna and it's fine...at least through a short test. - During testing, I notice that I can induce the problem by unkeying the radio a fairly high percentage of the time. So, if I put it in CW and key up, all will be well until I unkey. When I unkey, the reflected power will frequently jump. Same on SSB if I key the mic with no input audio. If I just key the mic with basically zero RF going out and then unkey, I will see the reflected needle jump when I let off the PTT switch. This is what had me thinking about the T/R relay. I tried this on 20m and didn't see the same thing. It operated normally. When I aligned this radio (I don't recall the exact S/N but I think it's around 4900), I had trouble keeping it from oscillating when I followed the instructions. I tried to follow the service manual carefully but it wanted to oscillate. I had to fiddle with it a fair amount going between the two adjustment pots to make it happy. Maybe it's still too hot. My meter says I'm getting about 125W out on 40m. Dave K8JD ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR-7 - More Info Cont'd
On Sat, 16 Oct 2010 16:50:50 -0400, K8JDC wrote: I had trouble keeping it from oscillating when I followed the instructions. I tried to follow the service manual carefully but it wanted to oscillate. I had to fiddle with it a fair amount going between the two adjustment pots to make it happy. Maybe it's still too hot. My meter says I'm getting about 125W out on 40m. I would bet that if you had a frequency counter coupled to it, you would find that it is oscillating somewhere in the 9 MHz area. That is the symptom of the 40 Meter oscillation problem that I found. 125 Watts is below the spec that Drake says to align it to, so you should be able to get more out. I would have to go back and look at my notes, but I think 330 Ohms paralleled across R2203 on the REV. 2 predriver board was what I used to increase the amount negative feedback at lower frequencies. It may be possible or necessary to go even lower in value, but this is what worked for me on two samples that I had. I was just able to make rated output through adjustment of the predriver pot and ALC pot without oscillation. It's hard to get it to oscillate into a dummy load, it seems to need an antenna to take off. 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 Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] TR-7 - More Info Cont'd
?I was plagued with the 40M oscillation problem with the same symptoms - a 40M antenna with a bit of reactance resulted in the oscillation. I decided to build the PIN diode attenuator per the PA1HFO design and solved the problem that way. That allows you to set the signal level fed to the pre-driver stage to a different level on each band. You can then adjust each band so that the drive control can be left in the same position as you switch bands and you don't have to adjust it for every band change. With the input signal thus attenuated on 40M, the oscillation was never heard from again. There are other advantages to the attenuator and the whole thing is described in an article on WB4HFN's site. The mods to the original TR7 are minimal - the attenuator sits in the coax feed to the PA brick and you have to pick up the supply voltage and band switch information from points on the motherboard. The entire mod can be removed in very short order if desired. 73, K8AC - Original Message - From: Jim Shorney jshor...@inebraska.com To: drakelist@zerobeat.net Sent: Saturday, October 16, 2010 6:09 PM Subject: Re: [Drakelist] TR-7 - More Info Cont'd On Sat, 16 Oct 2010 16:50:50 -0400, K8JDC wrote: I had trouble keeping it from oscillating when I followed the instructions. I tried to follow the service manual carefully but it wanted to oscillate. I had to fiddle with it a fair amount going between the two adjustment pots to make it happy. Maybe it's still too hot. My meter says I'm getting about 125W out on 40m. I would bet that if you had a frequency counter coupled to it, you would find that it is oscillating somewhere in the 9 MHz area. That is the symptom of the 40 Meter oscillation problem that I found. 125 Watts is below the spec that Drake says to align it to, so you should be able to get more out. I would have to go back and look at my notes, but I think 330 Ohms paralleled across R2203 on the REV. 2 predriver board was what I used to increase the amount negative feedback at lower frequencies. It may be possible or necessary to go even lower in value, but this is what worked for me on two samples that I had. I was just able to make rated output through adjustment of the predriver pot and ALC pot without oscillation. It's hard to get it to oscillate into a dummy load, it seems to need an antenna to take off. 73 ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
