The AM Forum

Waiting for the tables for my shack, I couldn't sit down and started revising 3 receivers of the GRC9's. I have two complete sets and a loose receiver.
After mounting a few cells of 9 Volts batteries inside the negative supply batteries inside the receivers, just did switch them on. Surprise, they all worked directly. The only problem I noticed was that the sliders of the volume potmeters did not make good contact , but a little spray did solve that.
So next the alignment. And an other surprise, for all 3 receivers hardly necessary, they still were almost smack on after more than 50 years. Also, no tube change required.  ;D
Really nice little receivers, very well made!!
When the shack is ready, it is time to revise the transmitters and the LV80 and two DY88,s I have 3 of those powersupplies, so one will be modified to run at 115 VAC

Nice job. I have one complete unit and one loose receiver. Both have homebrew power supplies. I don't get good positive going modulation on the tx for some reason. Maybe about 50%. Negative is good. Have some accessories for it. the whip ant set with case and radio mount, ground screen wires with  spool and field strength meter. Fun stuff.
Larry

Indeed fun stuff Larry
The modulation is quite dependent of the load of the final, not uncommon for modulation at the third grid. The T1154 transmitter suffers from that problem as well. If you load too much, no good positive modulation. The output is quite limited at AM, the book says it is 7 Watts for AM. But it also depends upon the state of the final tube the 2E22. A fresh tube may improve the modulation as well.

Oh yes, the loading. I will try that and watch the scope while talking into the hifi T-17. I forgot about that. I have another 2E22 if needed too.
Larry

Please keep me posted with the results, I have to do the same when the shack is ready...

Hi!
All this GRC-9 talk made med curious about modulation pattern. So, brougt the scope and started or tried to start the Angry nine... It was a no go situation. Problem traced to the power cable, all fine on the outside completly rotten on the inside, so... I will have arrange with a new cable. Wish me luck...

And those cables are not very abundant.. :'(
But you have the connectors, so you always can make new ones.
Wish you luck...

Sorry about the cable rot. But just make a new one with the connectors. They are hard to find. I made my own cable some years ago after I found a connector at a hamfest. I never found a power supply for it, so I built my own also. So I went through my GRC-9 this weekend and got it up to working condition again. The bandswitch in the receiver needed cleaning, and the dial tracking is not very good, so I re calibrated the rx to be fairly close in the ham bands. The transmitter puts out good power, but the modulation is still not good in the positive direction for some reason. Adjusting the loading made no difference. I installed a cable to connect a Heathkit Q multiplier at one time and it is much better on cw now.
LB

When my shack is ready, I will revise my GRC9 as well and keep you posted about the results.

I recall someone had discussed several mods to the GRC-9, perhaps WU2D, that addressed transmitter chirp reduction on CW and improving the positve modulation peaks. Most likely was in ER magazine.  Was that you Mike?

I did test the modulation of my AN-GRC9 and got the same results. Upto 50% modulation it looks real nice, If more, the positive doesn't increase much. At 90% negative, the positive is approx 60%. More modulation results in both negative and positive soft clipping
On the low power setting, the modulation is worse and there is distortion above 50%
Time to open the set and start measuring......

Hi!

Well, finally I got the time to make a new cable, so my GRC-9 is back in business!
So far, a few CW QSO´s in log, will test AM later today.
Checking on a oscilloscope, voice pattern looks OK.

I don't know which AN-GRC9 you have, but the French ones are sometimes highly radio active, the lettering is painted with radium paint. I did dump one because the geiger Muller counter did peg!!!. These sets will give off some Radon gas, not really good for you. In other brands only the freqency dial of the trasmitter is radio active, but not too much, that's no problem.

Hi!

It is a Telefunken, faceplate is in German, it appears to be non radioactive, no glow in the dark...

The glow in the dark is long gone before the radium paint decays. I don't think a telefunken is active. Whenever you have access to a geiger counter, you can test it. The transmitter frequency dial may be, but not a dangerous level like the French sets. Just enjoy it.

Hi!

I'm aware of the fact that the luminous intensity drops off long long before the radium has decayed to marginal.
But, I have found on some old meters from aero planes that if I take a strong torch and give the meter a good blast of light, there will be a short lived glow, that fades out quickly.

The Telefunken GRC-9 does not glow when doing this test and the lettering is so white and thin my conclusion is that it is "just white paint". If I'm wrong in my conclusion, please let me know!

I have noticed that if I activate the dial lights when operating CW, the light will increase slightly when pressing the key.
Is this "normal behavior" or something I need to have a look at.
There is a slight chirp, did some checks on 7 MHz yester day, there is approx. 150 Hz of drift "chirp".
It doesn't sound bad, it actually quite charming...    ;)

When I was at Fort Gordon GA in 1971, we used an FM transceiver that was mounted in our jeeps, and I was told it was a "VRC76," It had a dynamotor to power the transmitter, and a carbon mic.

If any of this sounds familiar to anyone on here, please get in touch. TIA.

73,

Bill, W4EWH

I am sorry Bill, the VRC76 is unknown to me.
SM6OID, I am sure your conclusion is right, just white paint.
I never saw the dial light intensity change during CW transmissions, I will check. May be a voltage drop in the return of the cable to the power supply adding to the 1,5 Volts filament voltage. A few tents of a volt will be noticable. 
Thats a good test with the torch!!. Clever, I did not think about that. I have a Geiger counter, so I didn't need it.
Indeed all GRC9 will chirp a little. I had 3 and all did, as you say, just charming...