Yeah, it's weird.? I tuned to the "other" null and that seems to have done it.? Initially, it was pegging the meter over most of the tune range.? Only on 20.? Very strange.
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
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On Saturday, January 11th, 2025 at 6:43 PM, John K5MO via groups.io <johnk5mo@...> wrote:
Steve
I think I'd follow your nose and plug in another set of PA tubes and see what happens. It's the easiest least-invasive step at this point.
Kinda surprised it doesn't take off on 10, but does on 20.
John
On Sat, Jan 11, 2025 at 4:21?PM Steve Wedge, W1ES/4 via <w1es=
[email protected]> wrote:
Interestingly, I have seen the following:
Disconnected one tube's plate cap at a time. No problems.
Put rig on 28.7 and checked the neut. I dipped with loading cap at 0, removed screen lead, nulled the output signal on scope x10 probe. I noticed that some positions of the RF TUNE control give suddenly high-amplitude signals. Also noticed that there are two nulls on the neut cap that are 4 clock directions from each other (i.e., if one is at 10, the other is at 2). I tuned to one of them.
Reconnected screen lead. 10m loads up fine. I still can get 20m to break into whatever it's breaking into but it's at a very small place on the RF TUNE dial that's nowhere near where the receive and transmit signal peak..
I put these tubes in a few months ago but haven't played with it much. They COULD be the tubes from the scrapped TR-4C -- tubes with gremlins? For now, I seem to have tamed it. Interestingly, getting a dip on 80m is very broad. The other bands are fine. Close to 200W out on 80 and 40, about 175W on 20, dropping to 150W on 15 and a little over 120W on 10.
Has anyone out there seen the neut cap have two nulls when neutralising by disconnecting the screen lead?
I still think these tubes are suspect but I may as well use them, as they're stronger than what was in there.
73,
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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On Saturday, January 11th, 2025 at 3:14 PM, Steve Wedge, W1ES/4 via <w1es=
[email protected]> wrote:
I had taken my TR-4Cw RIT offline and to the bench to use for comparison to Ronnie's similar rig (only difference is mine has a NB and is about a month or so older than his).
I figured that I'd go through some transmitter testing (the receive seems to be okay but has a parsimonious S meter, like many do). On 10m midband, the neutralisation looks okay (I'd done it a couple of years ago)., I bring the rig onto 20m and the plate meter pins! Connections are fine and 10m shows a little over 100W out (yeah, the finals aren't new). I can only get 20 to behave with the RF TUNE control down near 1 - 2, which isn't at peak receive.
I had another, rather ugly TR-4C that had a similar problem and I could never fix it. I finally wound up scrapping it for parts (it was pretty ugly, anyway) but there's no way I am going to scrap this rarest of all TR-4 rigs.
Any ideas?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
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