Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
TR-4C "Rel_Out" Knob (Load pushed in) Not Working Correctly
|
I am a Drake newbie and have a TR-4C that was gone over by an expert and working well prior to shipping.
Here's what I am seeing when tuning up at 3.6 MHz: ? ?
At this point, with the Load knob pushed all the way in, if I rotate the knob clockwise power start dropping down from 135 to about 100W with knob pushed in and I stopped around mid-way.? ? Once I release the knob, meter current is back again.? If I try to increase Load knob (not pushed in) slowly while re-dipping plate current, output drops progressively. ? I assume I¡¯m not seeing maximum output because the pushed-in Load knob is either mechanically or electrically broken and therefore not matching the PA finals to the 50 ohm load. |
|
Your analysis makes sense. I assume you have an external power meter of some sort. Can you take the cover off the unit and inspect what is happening with the Load/Relative Power knob? With power off of course. if there is a mechanical problem it should be visible. I don't have a TR-4C and it is enough different from the TR-4 (which I do have) so that my idea may not be valid.
toggle quoted message
Show quoted text
On 2/1/2024 1:36 PM, Jerry NY2KW wrote:
I am a Drake newbie and have a TR-4C that was gone over by an expert and working well prior to shipping. --
Richard Knoppow Los Angeles WB6KBL SKCC 19998 |
|
Jerry: Common issue....clean the slide switch behind the front?panel on the LOADING control shaft.? If dirty, it can affect both Plate Current and Output readings.? Spray some De-Oxit D5 into the switch and work it a bunch of times.? That should clear up the problem.? Also check the resistor on the slide switch (R13A) to make sure it isn't missing?or burned up.? Value is selected during production. To me....your LOAD control is behaving?normally.? You are just not seeing?the RF being picked up and sent to the TR-4C meter. 73 Peter VE7PS On Thu, Feb 1, 2024 at 1:36?PM Jerry NY2KW <josternmd@...> wrote: I am a Drake newbie and have a TR-4C that was gone over by an expert and working well prior to shipping. |
|
Jerry: Yes - the slide switch just switches between Plate Current and Relative?Output Power.? Rotating the LOAD control changes the loading cap and will result in a change in output....likely lower, if you have already dipped and loaded for max output on your external meter. I tend to ALWAYS use an external?output meter for tuning and avoid using the internal RF Output meter.? Of course I DO use the meter in Plate Current mode! Keeping that switch clean is really important, especially as I have seen it prevent seeing ANY Plate Current when trying to set the bias as a 1st step. Cleaning it is always part of any routine pre-operational check up on a new-to-me tx/xcvr. 73 and GL! Peter VE7PS On Thu, Feb 1, 2024 at 2:02?PM Jerry NY2KW <josternmd@...> wrote: Hi Peter, |
|
Hi Peter,
Thanks for these great tips.? Can you help me understand how the Load slide function knob works?? Am I correct that is doesn't matter if pushed in or not, the Load knob remains mechanically linked to C95 capacitor and this loading cap is being moved same way regardless of whether knob is pushed in or not?? So I should be able to tune without pushing it in by only using my external wattmeter and the plate current?? ?I think something else is off though as peak output is not coinciding with plate dip... I guess that's part of a neutralization issue? 73 Jerry NY2KW |
|
Jerry: Correct......the load control is always adjusting the LOAD cap as it is rotated, regardless of whether it's pushed in or not.? Pushing it in just disconnects the meter as a Plate Current Meter and connects it as a Relative Output Meter. So are you seeing RF Output on the internal meter with the LOAD control depressed now? R13A is actually part of the Plate Current metering circuit, not the relative Output circuit.? I may have misled you on that earlier. So...to tune the PA you do not need to push in on the LOAD control at all while you watch an external RF Output meter connected to the output of the PA.? Typically you start off with the load control at about 10 o'clock or a bit less, and TUNE for a plate current dip, with reduced TX Gain.? Increase gain a bit at a time, dip again and rotate the LOAD control clockwise slightly.? RF output should?go up slightly.? Gradually increase the tx gain, dipping the plate current, and increase LOAD slightly until you kind of max out on all 3 controls.? This is harder to explain?that it is in real?life!? Once you get used to it, you can do all of it in about 20 seconds.? On the XCVR's?(with 3 good PA tubes), you should see 150+ watts (or even more) on 75m, dropping to maybe 100w or so on 10m. If the Plate Current dip does not coincide with a peak in output...and you are using a known good 50 ohm load.... yes, neutralization should be checked.? I don't like the method described in the Drake manuals, and have had much better success by disconnecting the SCREEN voltage, putting a coaxial?TEE in the output?line with one lead going to the dummy load and the other going to an oscilloscope...BUT ONLY connect the scope AFTER you have tuned up on 10m with?screen voltage still connected.? ONLY connect the scope to the TEE AFTER you have disconnected the screen voltage.? Screen voltage is easily disconnected at the feedthrough capacitor where it passes through a shield to the 68 ohm screen resistors under the PA cage.? Make sure you prevent your disconnected lead from shorting out.? Make sure power is off when you do this and bleed off the?+700V line too! Or better yet...just disconnect the AC-4!? Don't touch the tuning controls - they should remain where you were tuned up on 10m. If you see Plate Current jumping around while tuning up on 10m, you may have to neutralize on 15m after tuning up there first.? Unplug the AC-4 at the xcvr, disconnect screen voltage, plug in the AC4 and power up again, connect the scope to the tee and adjust the neutralization cap with an insulated screwdriver for a minimum output shown on the scope.? Then shut down, unplug the AC-4 supply at the xcvr, reconnect the screen voltage wire, apply power again, tune up on 10m (scope disconnected!), then power down/disconnect the AC-4, re-disconnect screen voltage, connect the scope again and repeat on 10m for a minimum. If you are uncomfortable messing about with HV, get some help or have someone who is, do it for you.? You don't want to blow up your scope, or worse yet....get yourself zapped with either the 300V screen voltage or especially the 700V HV! Once you get used to doing this way, you'll never use the neutralization method in the Drake manual.? Kenwood made this easy for us with their hybrid tx and xcvr's by putting in an SG switch (screen grid) which allowed you to disconnect the screen voltage with the flick of a switch on the rear panels.? It was meant for transverter use, to provide minimal drive to a VHF transverter, but sure makes neutralization with a scope easy! Safety FIRST!? Be very careful!? Take each step slowly and make sure that any time you are sticking your hands in the bottom of the radio that the AC-4 is off and is disconnected at the xcvr. 73 Peter VE7PS On Thu, Feb 1, 2024 at 3:00?PM Jerry NY2KW <josternmd@...> wrote: Hi Peter, |
to navigate to use esc to dismiss