Re: TR-4 Decreased Sensitivity on High Bands
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Two minor clarifications:
The cap across the neutralizing variable cap allows me to set a proper null so that the variable cap can swing through that at about the point where the rotor is meshed approximately half-way (it wouldn't do that with the original cap).
The loading equipment for the injection coupler alignment is called an "alignment load", not necessarily a "dummy load" as I referred to it and I didn't want to cause confusion with the antenna dummy load (and I still wonder about the etymology of that phrase).
Gary, This morning, as I tuned up (into a dummy load) across all bands and I noticed that the XMTR GAIN seems to saturate at about the same point for all bands.? I seem to recall that a few weeks ago (before I started touching up the alignment points), I could get a LOT more gain out of the lower bands. The only component work I've done is to replace the cap across the PA neutralizing cap and have that so I can minimize the spurious oscillations with the appropriate power peak at the valley (dip) of the plate tuning cap rotation.? I also replaced the cathode resistors with new 15R 1W metal film caps as the originals were out of spec and were not well-matched. Maybe I've botched the alignment(s) and, perhaps, I need to revisit those.? Disappointing as I'd hoped to make things better and apparently that's not the case but I don't yet know what I might have done wrong (yes, I did use the designated dummy load when tweaking the injection couplers which I know is essential to getting those correct). Thanks again,
Barry - N4BUQ
From: "Gary Follett via groups.io" <xntrick1948@...>
One test I have found to be useful is to plot output power on a given band versus position of the TX gain pot on the different bands. If you find that ?the saturation point of output (the point at which increasing the gain position produces no increase in output) versus position of the pot does not change as you go up in bands, then likely you have an alignment issue or a drive issue before the final mixer, because these earlier stages should produce more output than needed on the low bands to make up for poorer efficiency on the higher bands. In other words, you should be able to drive the heck out of the radio on 80 meters well before the saturation point of the TX gain pot.? Receiver gain issues track TX gain issues religiously. If TX gain is weak, receiver gain will be weak too. Gary W0DVN On Apr 28, 2025, at 7:44?PM, Ham Radio via groups.io <bernard.murphy@...> wrote:
Steve: I assume you meant AGC. ? I have a TR-4 that has the same issue. ? Fine on TX but low on RX. ? See attached file.
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73, Bernie. VE3FWF
Real?radios glow in the dark
<TR-4-tubes-sensitivity.xls>
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