The AM Forum

So I got a Gonset G-76 hamfest find from KB3AHE, for which I will thank him for again here.

I was looking for a Cinch Jones S-310-CCT so I could rig up a test power cable to my Heathkit PS-23 to test it out, but it appears to be a real hen's tooth.
So I went out and bought a deep-cycle marine battery and a battery charger to power the DC PS that I bought with it from Frank.

I attached a dummy load just in case it started transmitting right off because of something wrong or a mistake on my part.
It powered up and seems to hear just fine.

I tracked down and fixed a missing wire in the DC PS that appears to have been wired for receive-only in the car (not wired to send power to the TR relays in the transceiver).
I was able to verify carrier with a watt meter and a scope.

Then I had to replace the mic socket which looked like a 1/4" stereo socket, but was really more like 7/32" or 3/16" (I did not measure it, just replaced it).
I was then able able to verify modulation with a scope.

So today I'm tring to track down some wire th throw into an tree for a very compromised horizontal 1/4 "vertical" with 2 short radials (i guess this might qualify as a very lazy L, not sure).

But what is quite annoying is the DC PS whine's like a gnat in my ear.  It used 2 PNP and 2 NPN to oscillate the primaries to make the LV and HV, so I know it is not a motor or vibrator makign the noise.  But I suspect it is somehting loose in a coil or a transformer rattling back and forth at the frequency of the oscillator.

Anyone out there with more experience with this or a similar type of DC PS have any idea what it is?

I attached the wav file so you can hear it.
NOTE: In the clip, the noise I am referring to runs between the 2sec mark and 10sec mark of this clip.  The first 1.5 and last 1.5 sec of the clip has a quiet whining which is the HD in my laptop spinning (which I can not hear with my ear) which you can hear because I had to crank up the internal mic's gain to pickup this high-pitched whine which is harder for this internal mic to detect at normal input levels.

>Then I had to replace the mic socket which looked like a 1/4" stereo socket, but was really more like 7/32" or >3/16" (I did not measure it, just replaced it).
>I was then able able to verify modulation with a scope.

Gonset used the socket that mated with the PL-68 plug. It is LIKE a 1/4", but a little different in construction. I know that the Gonset Communicators used those sockets. I wonder if it was because of the plentitude of military mics with PL-68 plugs...

>But what is quite annoying is the DC PS whine's like a gnat in my ear.  It used 2 PNP and 2 NPN to oscillate the >primaries to make the LV and HV, so I know it is not a motor or vibrator makign the noise.  But I suspect it is >something loose in a coil or a transformer rattling back and forth at the frequency of the oscillator.

Sounds very high in frequency, more like the effects of magnetostriction that loose components. The switched currents in the DC-DC converter may be mechanically squeezing and streching the core of the transformer at the oscillation frequency - the core laminations will cut down on eddy currents, but not this. There may not be anything you can do. I have seen/heard this in a number of DC-DC supplies. You can see this even in high power DC-DC supplies today.
 
My feel on Gonset equipment was that it was built to do a particular job at the lowest cost - it is alot like if somebody took the back homebrew equipment and began manufacturing it. Conveniences were eliminated, unusual designs are produced to make up shortfalls. The singing of the DC-DC may just be normal for that unit - can't say, never had one.


Dave Goncalves
W1EUJ

Dave & Dave,
                   the Whine is normal from those inverter power supplies. That is why they were usually installed somewhat away from the radio so you didnt have to listen to them. My old Motorola Motrac VHF mobile rigs sound exactly the same. the Multivibrator used in them is a big step up from the old electromechanical vibrators used in the earlier supplies.  Sit the powa supply in a box under the desk. As long as they are singing you know they are working.

If it is that bothersome, you might try mounting the powa supply transfoma on some rubber standoffs so the case doesnt act like the cone in a speaker. That might help.

I will be curious how you do with a loose wire antenner, those radios will load into a wide variety of impedances. try it on the low powa setting first and you cant hurt it. I'll be listening tonight.

                                               The Slab Bacon

Oh, I forgot to mention, the transformer is toroidal.

Excellent idea.  I will have to see if I can manage this after I actually have the satisfaction of radiating RF with it first.


I was planning on using a johnson matchbox to match it.  But i may try to use the tx alone just to see if it works.

I was hoping, but getting the antenna radiator in the tree took more time than I had hoped.  I never did get any RF out.  I am hoping on getting it on the air tomorrow night (saturday night), whininig PS and all..

> Oh, I forgot to mention, the transformer is toroidal.

The effect occurs for any magnetic material, in nearly any shape. At my workplace, we get a screaming hiss from a set of surface mounted ferrite coils we use in a high current low voltage dc-dc converter.

Dave Goncalves

 ::) 

Look, here's whatcha do.

Grab the thing. Walk it out back of the building. Slap it silly. Give it a good talking to, slap it around some more. And then tell it to just shut up! :o :o

That should do the trick?

                   _-_-bear

TEACHER:
Good morning, Torroid. Good morning, Torroid. Torroid? Torroid!? SHUT UP!!!!! Thank you.

WA1GFZ:
Far out, man!

TEACHER:
Now that`s fine, young Torroid!

WA1GFZ :
...High permeability too...

Yessir
I remember the VHF Motrac days and the "T" Power radios with a whoppin 25 watts of power.
The 100W UHF Motracs with the tiny ceramic final were quite interesting too. Nice stuff, hard to break. But the tube finals always needed "retuning".
The whining supply noise never got into anything, though. 600vdc, If I member correctly.
Fred

that whine is a comforting sound. it usually means you are on the air. when it stops it's often followed by the smell of burning transformer and a 30 amp fuse blowing in the 12 volt supply. a word to the wise- lay in a few spare inverter transistors if you have to run the rig off DC, and test them for leakage before you need them. also don't make long old buzzard transmissions on the inverter supply (see loss of whine and smoke).

Fred,

I used too install those Motracs into squad cars when I lived in Montana shortly after I was married. I started at the Motorola plant as an engineer worked for couple of year and took a year off to grow dental floss. A year off meant living off the land - my wife got a job in a resturant and I walked into a cowboy Motorola Service center. Boy did I learn a lot about Motracs! They were happy to have a real ENGINNIEER to make fun of.

The cars would wear out after a few years and they would come to the shop to have the radio removed tuned up, tunbes replaced and installed into the replacement vehicle. This was repeated over and over and over.

"Don't you guys ever replace these old radios?" I asked and they looked at me like I had three heads.

Moral of story - take the year off when you are 24 - not 74. That year was a big deal and life went on when I returned to the rat race. I miss that place every day.

Mike WU2D

i had a pair of 'tracs stuffed behind the seat of my 88 Ford ranger pickup up to just a couple years ago. One was permanent, a T74MST 100w uhf rocked for my repeater. the otha one got swapped between  a 110w high band on 2m simplex and another 110w low band om 6m simplex. I used to love to hear them "sing" when you gently squeeeeze th mic. But the T74 MST would almost kill the little 2.0 engine if you didnt put your foot on the gas. I had all 3 of them stuffed into the trunk of a Fairmont before the ranger. Kinda like a "tri band mobile" Frank style!

They were old when I got them, I put ova 300,000 miles on them and they are still workable to this day. I love those things, they are definately a mans radio!

I still have 2 dozen or so of them stuffed behind the furnace in my basement. The thought of throwing out all of the spare units is breaking my heart.

                                        The Slab Bacon

For a real whine....(or growl?) try a 60 watt GE pre-Progress line mobile with an 829B in the final and BIG dynamotor!!  Or...better still a pair of Motorola 30D/FMTR "coffin boxes" with big ol dynamotor.  Key that big heavy carbon mike switch and watch the car rock and the lights dim!  Now that's a real Man's radio!  Back to the 50's

 :o ;D

73,  Jack, W9GT