Thanks to Gary and Jim,
I think the finals in this rig are original, but not sure. I'll look closer
next week and play with it some more. I had an ALC light on 28.7....full
brightness... at full CCW on the predriver with carrier control set at
maximum CW. I may go back to 150w and have another go at it that way, but
it seems like that should not make a difference?
Other issues: I had tweeked the S-meter some, but still reads high. I've
noticed at least 4 S-units higher than my Omni VI+ and about 5 S-units
higher than my TR4C which I think reads a bit low. On Calibrate, CW, on the
null, its 20-30 over.
On the plus side, .....the TR-7 receives great, had very good transmit audio
reports, and A,B,C tests between the 3 radios are quite amazing. You'd
thing the Omni VI+ would knock the old Drakes dead, but NOT SO. In fact, I
cannot tell much difference between them. (except when using the Omni's
DSP)
If anyone has any ideas on the high S-meter reading, let me know, but until
then, I'll do some more checking.
Thanks,
David
----- Original Message -----
From: "Jim Shorney" <jshor...@inebraska.com>
To: <drakelist@zerobeat.net>
Sent: Sunday, February 08, 2009 6:27 PM
Subject: Re: [Drakelist] TR-7 Alignment
On Sun, 8 Feb 2009 17:36:01 -0500, Gary Poland wrote:
If I remember correctly the explaination I got from Drake for lowering the
power to 120 watts was for PA stability on 40 meters, keeping the
predriver below 1/2 turn.
I ran into the 40 meter instability problem on two rigs in the 3000
serial number range, my own TR7 with 2sc2879 replacement finals and one
that I picked up recently for resale with a completely stock PA. Both
had the version 2 predriver. I found that the situation could be
improved somewhat by increasing the low frequency negative feedback at
Q2201, by reducing the value of R2203. It's possible that doing the
same thing to Q2202/R2212 might help as well. Even with this mod, the
second TR7 required a delicate balance between ALC setting and
predriver gain setting to avoid 40 Meter oscillation with specified
power out. I think I ended up with the predriver gain set just below
maximum by a little ways. There appears to be a broad but definite gain
peak in the 9.3 to 9.7 MHz area, and I believe this is responsible for
the instability problem. I don't know what the root cause is at this
point, and it does not seem to affect all units.
73
-Jim
--
Ham Radio NU0C
TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A,
GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time!
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
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