On my TR-4, when I switch to AM mode I get no audio output at all.  Can someone please suggest a way to troubleshoot this?

I thought that if I touched the grid of the last audio amplifier with a screwdriver, I'd get a pretty loud buzz, etc., from the speaker but I don't get anything with that little test (crude, yes, but I was trying to see where the signal stopped).

I presume injecting a modulated CW signal back through the chain should eventually find where it stops but not sure about that.  Any hints are welcome.

Thanks,
Barry - N4BUQ

Barry,

To receive AM with the TR4 the Function switch must be set to "SSB"
not "X-AM". Setting the Function switch to "X-AM" will key up the
transmitter, disabling the receiver.

Operating AM with the TR4 is done as follows.

Tune the AM station until the receiving stations AM carrier beat note drops
to zero (no beat note heard). This leaves the AM audio heard in the speaker.

Transmitting AM, the Side Band switch MUST be set to "X" and the Function
switch is set to "X-AM".

Setting the Function switch to "X-AM", keys the transmitter producing
a low level of RF output carrier of approximately 8 to 10 watts.

As you speak into the microphone, the speech amplifier output is applied
to the CCSM Modulator V14 13DE7. The output of V14 varies at the same
rate at the speech amp audio, varying the level of screen voltage to the
final tubes, producing CCSM AM output ifrom the final amplifier.
You cannot switch side bands in X-AM mode. The side band switch must
remain in "X" for X-AM to work.

The microphone audio in X-AM mode is controlled by the XMTR GAIN control,
same as in normal SSB mode. Operating in X-AM mode there is NO AGC voltage
produced like in SSB Mode, to control the gain of the CCSM AM transmit signal.

To switch back to AM receive, the Function switch is set to "SSB".

To operate SSB or X-AM, the KEY socket MUST be shorted to ground. The KEY
socket is connected to the V4 transmit mixer's grid. Inserting a 1/4" mono plug
from a CW key or keyer into the KEY socket removes the ground, providing
a high negative grid block voltage to the grid of V4, biasing V4 to cut off. Shorting
the KEY socket to ground, reduces the grid block negative voltage to V4's grid turning
V4 ON. The KEY socket MUST be shorted to ground for SSB and X-AM to work.

This is covered in the TR4 manual.

73
Mike W5RKL

On 5/22/25 11:39 PM, n4buq via groups.io wrote:

On my TR-4, when I switch to AM mode I get no audio output at all.  Can someone please suggest a way to troubleshoot this?

I thought that if I touched the grid of the last audio amplifier with a screwdriver, I'd get a pretty loud buzz, etc., from the speaker but I don't get anything with that little test (crude, yes, but I was trying to see where the signal stopped).

I presume injecting a modulated CW signal back through the chain should eventually find where it stops but not sure about that.  Any hints are welcome.

Thanks,
Barry - N4BUQ

Having just listened a bit to some AM on my TR-4, ?and having read Mike's comment, I'll point out that the manual indicates that you can receive AM in the X-AM function switch position. ? I have a Push-to-talk Shure 444 in the mic plug. ? I think that is the difference in the procedure.

?

If you don't have a key in the key receptacle, and you don't have a mic with an open PTT switch, then switching to X-AM will trigger the the transmit function and mute the receiver.?

?

The last sentence in the instruction manual regarding AM transmission indicates that if you want to receive AM using the product detector, you need to switch the function switch back to SSB. ?Also the manual states that in X-AM a diode detector is in use in that made for receiving.?

Randal,

This is exactly what I was trying to do.? I have a key in the key receptacle, no mic in the mic receptacle, and when I switch to X-AM, the audio goes dead.? To me, that doesn't seem correct and, based on your comment, I don't think it is so I'm not sure where to go from here.? It's as if I have a problem with the MODE switch but, so far, I haven't proven that.

I've tested all the tubes and since everything seems to work properly in SSB, unless V2 is not working, then I'm not sure why this isn't working.

Thanks so much for the reply,

Barry - N4BUQ

Having just listened a bit to some AM on my TR-4, ?and having read Mike's comment, I'll point out that the manual indicates that you can receive AM in the X-AM function switch position. ? I have a Push-to-talk Shure 444 in the mic plug. ? I think that is the difference in the procedure.

?

If you don't have a key in the key receptacle, and you don't have a mic with an open PTT switch, then switching to X-AM will trigger the the transmit function and mute the receiver.?

?

The last sentence in the instruction manual regarding AM transmission indicates that if you want to receive AM using the product detector, you need to switch the function switch back to SSB. ?Also the manual states that in X-AM a diode detector is in use in that made for receiving.?

The TR-3 uses the a product detector for AM reception, and needs to be switched to SSB for receive, but on the? various TR-4, TR-4C, and TR-4Cw's I have used on AM for both transmit and receive, the key must be unplugged, or the key closed when using AM and the mode switch remains in AM for both transmit and receive.? The same rule applies for SSB transmit.? Since I operate also operate CW, I usually rubber band one of my bugs to one side when operating phone on either mode. You'll hear the T/R relay click when you first close the circuit, but it releases just as fast.

I was about half-way through writing a reply to you when I decided to, yet again, read the section on AM operation.? That's when I realized that I had mistakenly been trying to receive in X-AM with the key inserted and open.? I was thinking that closing the key (or removing the key plug from the jack) would cause rig to start transmitting a carrier, similarly to how a fully plate-modulated transmitter would but that's not the case.? Since it uses CSSM, it only transmits when audio is supplied from the mic (at least that's the way I understand it); otherwise, it's effectively in receive mode.? I tried this and, somewhat to my surprise, AM receive is working.? I feel like such a klutz.

Thanks for all the replies to this.? It finally set in.? I now want to recheck those tube voltages with the rig set up this way.? I suspect the cathode and grid voltages will be much closer to what's in the chart.

Barry - N4BUQ

The TR-3 uses the a product detector for AM reception, and needs to be switched to SSB for receive, but on the? various TR-4, TR-4C, and TR-4Cw's I have used on AM for both transmit and receive, the key must be unplugged, or the key closed when using AM and the mode switch remains in AM for both transmit and receive.? The same rule applies for SSB transmit.? Since I operate also operate CW, I usually rubber band one of my bugs to one side when operating phone on either mode. You'll hear the T/R relay click when you first close the circuit, but it releases just as fast.

I was about half-way through writing a reply to you when I decided to, yet again, read the section on AM operation.? That's when I realized that I had mistakenly been trying to receive in X-AM with the key inserted and open.? I was thinking that closing the key (or removing the key plug from the jack) would cause rig to start transmitting a carrier, similarly to how a fully plate-modulated transmitter would but that's not the case.? Since it uses CSSM, it only transmits when audio is supplied from the mic (at least that's the way I understand it); otherwise, it's effectively in receive mode.? I tried this and, somewhat to my surprise, AM receive is working.? I feel like such a klutz.

Thanks for all the replies to this.? It finally set in.? I now want to recheck those tube voltages with the rig set up this way.? I suspect the cathode and grid voltages will be much closer to what's in the chart.

Barry - N4BUQ

The TR-3 uses the a product detector for AM reception, and needs to be switched to SSB for receive, but on the? various TR-4, TR-4C, and TR-4Cw's I have used on AM for both transmit and receive, the key must be unplugged, or the key closed when using AM and the mode switch remains in AM for both transmit and receive.? The same rule applies for SSB transmit.? Since I operate also operate CW, I usually rubber band one of my bugs to one side when operating phone on either mode. You'll hear the T/R relay click when you first close the circuit, but it releases just as fast.

From: "Mike W5RKL via groups.io" <mikew5rkl@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Monday, May 26, 2025 1:00:35 AM
Subject: Re: [DRAKE-RADIO] TR-4 AM Mode

Just to help me understand this:

To enable receive mode, it is necessary to close the key circuit but one is still not transmitting.

To transmit, either PTT needs to be closed or VOX enabled.

Looking at the schematic, I think that's correct but would like to confirm.

Thanks,

Barry - N4BUQ

---

From: "Mike W5RKL via groups.io" <mikew5rkl@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Monday, May 26, 2025 1:00:35 AM
Subject: Re: [DRAKE-RADIO] TR-4 AM Mode

The TR3, TR4, TR4C, and TR4CW transceivers operate "CCSM" (Controlled
Carrier Screen Modulation) AM in one side band only. The side band switch
must be kept in "X" which limits the AM transmit in one side band.

In AM transmit without speaking into the microphone, the AM Modulator reduces the
final tube Screen voltage, allowing an initial low level RF output of approximately
8 to 10 watts. As you speak into the microphone, the speech amplifier audio is
applied to the AM Modulator causing the AM Modulator's output to vary the
final tube screen voltage at the same rate as the speech amplifier's audio, hence
CCSM AM transmit.

Operating AM, the XMTR GAIN control should be adjusted to limit the peak plate current
indication of 200 to 250ma (0.2 to 0.25 amps) since transmit AGC is not used in AM.

73
Mike W5RKL

On 5/25/25 9:43 PM, n4buq via groups.io wrote:

I was about half-way through writing a reply to you when I decided to, yet again, read the section on AM operation.? That's when I realized that I had mistakenly been trying to receive in X-AM with the key inserted and open.? I was thinking that closing the key (or removing the key plug from the jack) would cause rig to start transmitting a carrier, similarly to how a fully plate-modulated transmitter would but that's not the case.? Since it uses CSSM, it only transmits when audio is supplied from the mic (at least that's the way I understand it); otherwise, it's effectively in receive mode.? I tried this and, somewhat to my surprise, AM receive is working.? I feel like such a klutz.

Thanks for all the replies to this.? It finally set in.? I now want to recheck those tube voltages with the rig set up this way.? I suspect the cathode and grid voltages will be much closer to what's in the chart.

Barry - N4BUQ

The TR-3 uses the a product detector for AM reception, and needs to be switched to SSB for receive, but on the? various TR-4, TR-4C, and TR-4Cw's I have used on AM for both transmit and receive, the key must be unplugged, or the key closed when using AM and the mode switch remains in AM for both transmit and receive.? The same rule applies for SSB transmit.? Since I operate also operate CW, I usually rubber band one of my bugs to one side when operating phone on either mode. You'll hear the T/R relay click when you first close the circuit, but it releases just as fast.

Barry,

Yes, you have to remove the 1/4" plug from the KEY socket or short the 1/4" plug
when operating AM. This is clearly stated on page 16 paragraph "6" titled "KEY"
in the TR4 manual (see "KEY" socket discussed in the TR4C manual below). The
same KEY plug is the same in the TR4C and TR4CW as it is in the TR4. "Key
being close" means to short the KEY socket or pull the CW key/keyer 1/4" plug
from the KEY socket. If you do not remove or short the 1/4" plug at the KEY socket
then the transmitter is disabled in ALL mode and AM receiver will not work.



If you use a J38 straight key that has the slide switch, simply move the slide switch
so it shorts the J38 key terminals.

Yes, PTT and VOX work the same in AM mode as they do in SSB mode.

73
Mike W5RKL

On 5/26/25 8:39 AM, n4buq via groups.io wrote:

Just to help me understand this:

To enable receive mode, it is necessary to close the key circuit but one is still not transmitting.

To transmit, either PTT needs to be closed or VOX enabled.

Looking at the schematic, I think that's correct but would like to confirm.

Thanks,

Barry - N4BUQ

---

From: "Mike W5RKL via groups.io" <mikew5rkl@...>
To: "DRAKE-RADIO" <[email protected]>
Sent: Monday, May 26, 2025 1:00:35 AM
Subject: Re: [DRAKE-RADIO] TR-4 AM Mode

The TR3, TR4, TR4C, and TR4CW transceivers operate "CCSM" (Controlled
Carrier Screen Modulation) AM in one side band only. The side band switch
must be kept in "X" which limits the AM transmit in one side band.

In AM transmit without speaking into the microphone, the AM Modulator reduces the
final tube Screen voltage, allowing an initial low level RF output of approximately
8 to 10 watts. As you speak into the microphone, the speech amplifier audio is
applied to the AM Modulator causing the AM Modulator's output to vary the
final tube screen voltage at the same rate as the speech amplifier's audio, hence
CCSM AM transmit.

Operating AM, the XMTR GAIN control should be adjusted to limit the peak plate current
indication of 200 to 250ma (0.2 to 0.25 amps) since transmit AGC is not used in AM.

73
Mike W5RKL

On 5/25/25 9:43 PM, n4buq via groups.io wrote:

I was about half-way through writing a reply to you when I decided to, yet again, read the section on AM operation.? That's when I realized that I had mistakenly been trying to receive in X-AM with the key inserted and open.? I was thinking that closing the key (or removing the key plug from the jack) would cause rig to start transmitting a carrier, similarly to how a fully plate-modulated transmitter would but that's not the case.? Since it uses CSSM, it only transmits when audio is supplied from the mic (at least that's the way I understand it); otherwise, it's effectively in receive mode.? I tried this and, somewhat to my surprise, AM receive is working.? I feel like such a klutz.

Thanks for all the replies to this.? It finally set in.? I now want to recheck those tube voltages with the rig set up this way.? I suspect the cathode and grid voltages will be much closer to what's in the chart.

Barry - N4BUQ

The TR-3 uses the a product detector for AM reception, and needs to be switched to SSB for receive, but on the? various TR-4, TR-4C, and TR-4Cw's I have used on AM for both transmit and receive, the key must be unplugged, or the key closed when using AM and the mode switch remains in AM for both transmit and receive.? The same rule applies for SSB transmit.? Since I operate also operate CW, I usually rubber band one of my bugs to one side when operating phone on either mode. You'll hear the T/R relay click when you first close the circuit, but it releases just as fast.

In thinking about this, I think I see what is going on.

?

Audio goes the the screen modulator which modulates the gain of the final..?? I think this is that same as the old novice rigs like

the T-60 or DX-40.?? The carrier does go up and down with the modulation.? But you can hear it with a normal AM (diode) detector.

Drake marketing made it seem like something new and special, but it's really just old fashioned screen modulation.

?

I think the audio does not go through the crystal filter, only the carrier and it is not modulated.? It is fully DSB and full fidelity should result.

?

Right?

73,

Gary

WB6OGD

The transmit speech amplifier's audio does not flow through the IF filters.
The "IF" filters are for "RF" not "AF".

The DSSC (Double Sideband Suppressed Carrier) signal from
the BM (Balance Modulator) flows through the LSB IF Filter (side
band switch must be set to "X" which selects the LSB filter).

To operate AM with a TR4 or any of the TR and T4/T4X<any>
transceivers or transmitter, the Side Band switch must be in
the "X" position which selects the "LSB" filter;

Any plug inserted into the "KEY" socket must be removed or
the plug shorted to ground in order to receive and transmit AM.
The same applies when operating SSB, the KEY socket must be
shorted to ground.

PTT and VOX work the same in AM mode as they do in SSB mode.

AM in the Drake TR series radios operates CCSM (Controlled
Carrier Screen Modulation). The Modulator stage controls the
level of the final amp's RF output. With no audio from the speech
amplifier applied to the Modulator stage, the Modulator stage keeps the final
amplifier's RF output at a low level, 8 to 10 watts. As the operator speaks
into the microphone, the speech amplifier audio applied to the AM modulator,
varies the final tubes screen voltage at the same rate as the speech amp
audio, hence CCSM AM is produced.

73
Mike W5RKL

On 5/26/25 12:43 PM, Gary WB6OGD via groups.io wrote:

In thinking about this, I think I see what is going on.

?

Audio goes the the screen modulator which modulates the gain of the final..?? I think this is that same as the old novice rigs like

the T-60 or DX-40.?? The carrier does go up and down with the modulation.? But you can hear it with a normal AM (diode) detector.

Drake marketing made it seem like something new and special, but it's really just old fashioned screen modulation.

?

I think the audio does not go through the crystal filter, only the carrier and it is not modulated.? It is fully DSB and full fidelity should result.

?

Right?

73,

Gary

WB6OGD