Another Tram D201A Question

[troyota]

I am getting very close on this ole gal. I am noticing on AM may receive is about 3kc lower than it should be. Example, the frequency is 27.305, but to clear it up I have to move the vfo to 27.302, then in crystal mode the clarifier will not get there (about 27.304 or so. It is like this on all channels crystal or manual selection. AM TX is dead on frequency. I replaced the 5.8015 crystal with a spare I had (not sure if it has drifted). It did not make any difference. I have another very nice D201A that works 100% perfect. I will pull that 5.8015 crystal to check it with. When I was doing the 4mhz alignment, I noticed that my 4.4 crystal was at 4.2, all my 20mhz alignment came out fine after replacing 4 crystals. Would the 4.4 crystal cause the RX issue I am having? 1,5,9,13,17,21,26,31,and 36 all tuned to frequency. I was expecting those to be off a little due to the 4.4 crystal being off. Maybe, I am looking at that wrong. I do not have a scope or a frequency generator. But they are on the "to buy" list for sure. Anyway, any guidance to what may be the issue is greatly appreciated.
Thanks!

 

[troyota]

Wait! My 4mhz reading was not 4.2 for the 4.4 crystal. The reading was 4.3998. I read my notes wrong. I just ran through the 4mhz again. Ch 1 = 4.3998, Ch 2 = 4.4099, Ch 3 = 4.4199, Ch 4 = 4.4399, Ch 5 = 4.4299. This was as close as they will adjust. I don't think that is my issue, but I am not sure.

 

[nomadradio]

A difference between transmit and receive frequency on AM can sometimes be blamed on the 5.8015 MHz crystal X300 used for the 2nd conversion stage in AM. Sideband receive is single conversion, but AM gets converted down from 6.255 MHz to 455 kHz. The two tiny black 455 kHz ceramic filters can also be off frequency, but that crystal is more often to blame. Has no trimmer cap. At least it's in a socket. Barkett still sells that one if it's so far off you need to replace it. Best way to check it is with a receiver that's calibrated on frequency well enough to tune it in and tell that way. Poking a probe onto it for a frequency counter can change the frequency. The tip of the probe will add capacitance to the circuit and pull down the crystal frequency to some degree. And if all you have is a receiver that you can eavesdrop on that crystal, set it to sideband, tune in the 5.8015 and see if the tone changes when you touch a counter probe to the circuit. You'll hear the pitch change when that happens.

73

 

[troyota]

Thanks Nomad, I have a yaesu 990 tuned to 5.8015 LSB that I used as a sniffer. It does change when I touch the crystal with the probe. If I roll the vfo back and forth on the 990, I can hear a difference. It seemed to zero beat above 5.8015. ( i think) I was leaving for work out of town, so I was in a hurry. Wasn't sure if I could tell if the crystal was off by rolling the vfo to find what freq it was at. Didn't know if I was looking for loudest tone, highest signal, zero beat...or something else. Lol.
Thanks again

 

[nomadradio]

Maybe I'm overthinking this. There's a trimpot on the crystal board that sets the transmit frequency. The front-panel clarifier is for receive only. Might be the whole cause of the issue.

R143 is the trimpot closest to the channel selector. Probe the counter to J100B, the top RCA socket at the rear of the crystal board. Center clarifier on channel 1 should be 21.7085. Key the mike and set R143 to agree with the receive frequency.

73

 

[troyota]

Alright, thank you. I think I done that after I completed your vfo tx mod. I will check that when I get home Friday to be sure. I know AM and SSB uses different paths. SSB works great with the RX and TX on frequency with each other and the clarifier is very close to center. I have made contacts on 37LSB to Washington state, Arizona, Nevada, etc. AM works pretty good and is very usable, but my OCD will not let me accept it. In manual mode I notice the rx clears up and rx signal increases on the meter when I roll the vfo about 2.5-3 kcs down. In crystal mode I can't move the clarifier that far. I can get about 1 kc each way.
Thank you for your help

 

[troyota]

Ok, I checked tx freq and rx freq. They are dead on. I went back to my 990 tuned to 5.8015 and used my coax jumper sniffer probe speciality tool....lol. anyway, I get a tone. when I roll up on freq my signal increases in volume and on the meter of the 990. The highest reading is at 5.80349. Does that mean the crystal is off that much?

 

[troyota]

Alright, I tried my spare crystal and the crystal from my good working d201a and they are both the same way. So I guess it's not the crystal. Is there a way to check the small black filters? It seems like a while back i had a rx issue and tapping on one of them brought it back. I'm going by memory and that is dangerous.

 

[nomadradio]

Only way I know to check the 455 kHz filters is with a signal generator feeding 455 kHz into the receiver's AM IF section. You roll the sig gen's frequency above or below 455 to find the filters' center frequency. Use a signal level weak enough to hear some noise with the carrier. Center frequency will be where the pitch of the noise is lowest.

73

 

[troyota]

Ok, thanks. I don't have a signal gen. I do have a spare board from a 201a with those on it. I may switch them out to see if it helps. Is there a source somewhere to purchase these?

 

[kopcicle]

Ok, thanks. I don't have a signal gen. I do have a spare board from a 201a with those on it. I may switch them out to see if it helps. Is there a source somewhere to purchase these?

455 kHz Signal Generator

Simple modulated crystal controlled 455 kHz oscillator...

Hello All, Had been wanting to build a crystal controlled 455 kHz oscillator for alignment for quite some time. Found several circuits on-line and originally…

antiqueradios.com

LEAP#484 Crystal-Locked 455 kHz AM Oscillator

crystal-locked 455 kHz carrier oscillator with fixed-frequency audio tone amplitude modulation (AM) for IF alignment

leap.tardate.com

455 kHz Oscillator Circuit – Electronics Projects Circuits

3 transistors are used (bc548) supply voltage is 9 volts 455kHz RF signal is produced with ceramic crystal. Description of the circuit The 455kHz Modulated Osci

320volt.com

So I guess my point is (as if I ever have one) pick a flavor (or a language) and have at it .

 

[kopcicle]

Anecdotally,
I once built a 455 kHz , AM modulated power oscillator.
It was my road rage broadcasting station.
It's amazing how many devices you can get into within a 100' radius with 150W...

 

[troyota]

Thanks kopcicle, I will attempt to build one of those. I have not had a chance to get back to this d201a. I have had other things come up. I am still having a little am rx issues. I did get the replacement pot for the rf gain. I need to get that in there to see if it helps my am rx. Thanks to all for your help. I will try to get in this thing again this weekend.