Thanks Gary. Will let you know what I find. I might have missed another switch problem. I thought I checked for continuity with all the sections bur maybe not.? Thanks for the help.
On Thu, Mar 20, 2025, 5:13?PM Gary Follett via <xntrick1948=
[email protected]> wrote:
Correction to V2 analysis:
Pin 5 is the AM detector. In AM, the radio uses V2 as the AM detector and as the first audio amplifier, but only in AM.
I also added some more paths for the sidetone path. In addition, I added in red the path that the sidetone takes to get to the audio output. You can see that, if the Anti-Vox were set too high, you might have difficulty keying.
Gary
W0DVN
Analysis of V2:
Pin 1 should be 0 if there is no key plugged in or a key is plugged in and the key is keyed. In key up position, this pin should be negative SOMETHING (in RX) because this is the grid block keying line for the TX mixer and the TX driver in CW only.
Pin 2 can only be 0 if radio is in CW position. This would be true in both TX and RX. If you are in CW, you are getting the right answer.
Pin 3 filament is a bit low, lower than I would expect. Do you have low line voltage?
Pin 4 is correct
Pin 5 should rectify the AC audio tone in the sidetone oscillator, producing a negative voltage at pin 5, which is what you are seeing, but only when keyed in CW. I don¡¯t see any way this pin could rest at 0.9 volts positive, as shown in the ¡°spec"
Pin 6 is not connected
Pin 7 is a bit low, no concern
I think V2 is operating as it should.
Remove V19 and V2 and measure the resistance between V19 pin 7 and ground, and V19 pin 7 to C100 both ends, in CW position, then in SSB position.
While I had said earlier that the Anti-Vox was not needed in CW (It isn¡¯t) it is still in the circuit, so try CW keying with the Anti-Vox full CCW and full CW to see if there is any effect. Also, try CW keying with the receiver AF gain set to nearly zero.
Gary
W0DVN
I got back to the TR4C today.
I disassembled, completely cleaned and inspected the mode switch, found a couple of bent fingers and straightened them and cleaned the switch fully.
I did get the AM Mode back, but the CW is still being evasive.?
The problem definitely seems to be in the V-2 stage.
I checked the voltages?and resistor values in that stage.
Found some interesting things. Ran out of time this afternoon. I had a spare tube and changed it with no change.
It still keys the cw for a split second then unkeys. The sidetone stays constant?while the key is down. the momentary cw creates a momentary bump on the wattmeter and dummy load.
Obviously there is a voltage missing and some that are not correct.??
V2 back in that back corner?is such a nice spacious place to work!!
Going to have to burn some more midnight oil on this one.
V-2 12AV6 voltages
pin?????? Measured?????? Spec
1 ???????? -18 v? RX????????? 0
??????????? -.73? TX??????????? -1.6
2????????? 0????????????????????? 13.0?????
3????????? 11.8 AC??????????? 12.6 AC
4????????? 0????????????????????? 0
5????????? -.41 RX???????????? 0
??????????? -.57 TX ??????????? .9
6????????? 0????????????????????? 0
7????????? 239????????????????? 255? ? ??
On Mon, Mar 17, 2025 at 9:12?PM Terry WB0VQP via
??<TLNixon357=
[email protected]> wrote:
Thanks Gary!
I have had the entire front panel off the radio in order to get to that S-2 and clean it.? Not to say I got it all clean and working. I was suspicious of that as well.?
This radio? belonged to our local club The Davenport Radio Amateur Club INC for many years.? It was in the basement shack of our President when lightning struck his power lines and set his house on fire.? The electrical panel was only a few feet from his shack.? The whole family almost died in the fire.?
Although it did not have any heat or fire damage, it was really smoked-up and had some water damage.? ?So a little at a time I am trying to restore it.? ?It was given to me by the President when our insurance company bought us two new rigs to replace this one and an Icom damaged by the fire.
The SSB TX was intermittent?on it, and I discovered the key jack had some corrosion around it and was not grounding properly when the key was unplugged. .? Cleaned that all up and it is reliably working on SSB, but would like to make it fully functional.??
I still have an R4B and T4XC twins and another TR4 here. I love this Drake equipment.
Thanks Again!
Terry WB0VQP
On Sun, Mar 16, 2025 at 7:58?PM Gary Follett via
??<xntrick1948=
[email protected]> wrote:
Shown in magenta on the attached schematic is the path the sidetone oscillator signal takes to get to the VOX tube, V19A, in order to key the relays. This tube amplifies that sidetone signal just like it would an audio signal from the microphone input. This is rectified by D5 and fed to the keying triode V19B.
My most likely bet is that the contacts on S2 are not making good contact so the sidetone is not getting to the grid of V19A.
Also, while the VOX sensitivity pot has no impact on the CW ¡°VOX¡±, the Anti-Vox and Delay do affect CW ¡°VOX". Try turning Anti-Vox all the way CCW to see if that is an issue since you do NOT need Anti-Vox on CW.
Gary
W0DVN
<PastedGraphic-1.tiff>
On Sun, Mar 16, 2025 at 2:56?PM Gary Follett via
??<xntrick1948=
[email protected]> wrote:
Can you answer the question I already asked, "Do you have steady sidetone when key is held down?¡±?
Gary
W0DVN
On Mar 16, 2025, at 12:43?PM, Gary Follett via
??<xntrick1948=
[email protected]> wrote:
Do you have steady sidetone when key is held down?
