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Author Topic: Tube Rig Alignment Audio Signal Generator  (Read 1724 times)

Posts: 298

« on: January 06, 2007, 10:02:02 AM »

I would like to check and perform,(if necessary)
an alignment on my 1973-77 vintage HF transciever.

In performing a carrier frequency adjustment.
The instructions are asking for an AUDIO SIGNAL GENERATOR. The instructions are asking for 1500 cycles of audio to be injected into the MIC input recepticle. It is also asking to sweep the audio down to 300cycles.

This is an old term I am not sure what type of equiptment I need to buy for this purpose.

What type of AUDIO SIGNAL are they talking about?

Is this an analog frequency generatior for the audio range?  

Could I buy some old used piece of equiptment off
e-bay for $30.00 that would do the job?
Does an old heath kit oscilliscope perform this function?

Could I use the sound card on my computer for this purpose?

Any advice at all would be great!!
Erik AC0FA

Posts: 4380

« Reply #1 on: January 06, 2007, 10:58:03 AM »

Hi Erik,
Well you must have gotten it to work!  Hooray!
The alignment procedure is a bit odd compared with most transceivers I've seen.  But the audio generator is a simple sinewave oscillator that covers at least 300 Hz to 1500 Hz, of course most cover a great deal more.  You set it to 1500 Hz and do an adjustment and then set it to 300 Hz and do another (the "sweep it to" phrase is just incorrect English for "reset").
You don't need a VTVM as a modern DVM serves the same function and you can use a hamband receiver (probably with the antenna disconnected) for a "field strength meter."  An oscilloscope is not needed for the aligment and is not a substitute for the equipment listed.
Were I you I would run through the procedure a few times without making the adjustments as the alignment may not be far off.  At least you will get an idea of how good or bad the present condition is compared to optimum and what you are supposed to be looking for.  
Concerning buying a cheap audio generator, that should be no problem.  I bought an old Heathkit for about $10 that would do the job just fine.  The calibration may not be perfect but all the alignment is doing is adjusting the balanced modulator for correct audio alignment so your voice won't sound either tinny or bassy.
Have fun Allen

Posts: 69

« Reply #2 on: January 06, 2007, 12:15:05 PM »

Faced with the same situation here. My audio generator quit and I needed to finish the job quickly. I used a PC program which was already here in the shack. It seems like there are some good free ones down this page.

Posts: 298

« Reply #3 on: January 06, 2007, 02:55:16 PM »

Well it is working better.

I got 5 watts out on 14.200 mhz it previously went away when I had trouble with the choke on the 6gk6.
All resistors are the correct value and the tin can capacitors are good/replaced.

Haven't tackled the big 80mf 500V on the top side. That one is card board. And looks like it has been changed.

I jumpered pin 5 to pin 1 which is still connected to pin 8 thru the external jumper.

Recieve went away and there is a buzz in the audio and no tx.

When I cut the 1-5 jumper there is recieve and the buzz went away. I got 5 watts out and blew a fuse which was only 5 amps for some reason.

I replacd it with a 8 amp ceramic slow blow. I am re-checking the connetions at the accessory socket terminal pin 1 and 8 have coax with an extremely thin conductor.

Erik AC0FA            

Posts: 298

« Reply #4 on: January 25, 2007, 09:14:40 AM »

I am getting closer to take off with this rig.
It was over heated and abused. Something took out the transistor and one of the resistors in the crystal oscillator.  

After basically replacing all the resistors and capacitors any previous alignment the rig had went right out the window.

I hooked up the frequency counter and set the crystal oscillator trimmers to 5500kc and 5503.3kc pretty much just tightened down.

The rig works much better with the crystal oscillator functioning.

The VFO is working but was off frequency about 600hz.

After bringing that into spec I hooked up the Oscilloscope to the vfo amp, mixer and driver tubes and peaked adjustment coils on the scope.

I got a really nice tripple saw tooth wave at the input to the driver. That would be the sum and differential frequencies injected from the carrier oscillator and vfo amplifier resulting in the third  
diferential frequency.

The carrier balance has started working again.
I double checked all the coils with the frequency counter and they are right on.

Pretty soon I will re-install the finals and do a  final tune.  

The rig did not respond well to doing a voltage check with a DMM.

It would seem that the negative bias was grounded time and time again. Some of the resistors popped in the finals. But they were easily replaced. I will remember to use a VTVM for that escapade.

I Read the manual and found it hard to believe someone could do a alignment with just a vtvm and a field strength meter.

May be that was just a sales pitch because that was all the equiptment ham's had in 1973.  Oscilloscopes cost more than a new cadillac back then.    

Oh well, live and learn.
Erik AC0FA

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