Admiral 14R12 Restoration - Page 12 - Videokarma.org TV - Video

Crist Rigott · #**166** 10-20-2016, 11:41 AM

Quote:

Originally Posted by bandersen

This IF design uses over coupled IF transformers rather than stagger tuned. One stage is peaked to 25.3 and the other to 23.1. That's an economical design that flattens out the response somewhat but not as good as a real stagger tuned with multiple stages each peaked to a different frequency.

Did you follow all the setup directions including replacing the converted tube (6J6) with one that has pin 1 clipped off ? As mentioned above, it's important to use as low a signal level as possible

Bob,
I just saw this when I posted just above.

Yes, I followed the procedure and uses a known good 6J6 with pin #1 clipped off.

I'll redo the procedure and pay very close attention to having the signal generator turned down as low as possible.

One quick question. In the Sams it says that the dummy antenna terminals should be "Direct" connected. What is a dummy antenna? I'm thinking it really doesn't matter because there are no signals being transmitted anyway. I could be wrong though.

bandersen · #**167** 10-20-2016, 11:44 AM

Dummy antenna is your hook up to the RF signal generator. Often you put a cap in series with the positive lead and ground the other. I'm thinking that by direct they mean you don't use a cap. It would be helpful to see the whole Sams section in question. You should be injecting your signal to an ungrounded shield over the converter tube.

old_coot88 · #**168** 10-20-2016, 12:56 PM

Quote:

Originally Posted by bandersen

You should be injecting your signal to an ungrounded shield over the converter tube.

You can also do it with a turn or two of wire taped around the conv. tube. I always liked to disable the oscillator by bumping the tuner up between detents.

Crist Rigott · #**169** 10-20-2016, 01:15 PM

Quote:

Originally Posted by bandersen

Dummy antenna is your hook up to the RF signal generator. Often you put a cap in series with the positive lead and ground the other. I'm thinking that by direct they mean you don't use a cap. It would be helpful to see the whole Sams section in question. You should be injecting your signal to an ungrounded shield over the converter tube.

Bob,
I did show the whole SAMS alignment section a few posts above.

Yes, I'm injecting the signal through an ungrounded shield over the converter tube and through a .01uf cap.

Crist Rigott · #**170** 10-20-2016, 01:33 PM

Something else I might mention. I have my meter set on the -DC volts and I am adjusting for maximum needle going up the scale. Is this correct?

bandersen · #**171** 10-20-2016, 01:33 PM

Quote:

Originally Posted by Crist Rigott

Bob,
I did show the whole SAMS alignment section a few posts above.

Yes, I'm injecting the signal through an ungrounded shield over the converter tube and through a .01uf cap.

Oh sorry, I didn't realize that was the Sams. Direct coupling for the dummy antenna means don't use a capacitor.

Quote:

Originally Posted by Crist Rigott

Something else I might mention. I have my meter set on the -DC volts and I am adjusting for maximum needle going up the scale. Is this correct?

Yes, if the meter is showing a peaking response. By that I mean there is definitely a peak as you adjust the slug. I've worked on many sets where the maximum was a negative voltage. Annoying that they never mention that in the alignment instructions.

Crist Rigott · #**172** 10-20-2016, 01:59 PM

Quote:

Originally Posted by bandersen

Oh sorry, I didn't realize that was the Sams. Direct coupling for the dummy antenna means don't use a capacitor.

Yes, if the meter is showing a peaking response. By that I mean there is definitely a peak as you adjust the slug. I've worked on many sets where the maximum was a negative voltage. Annoying that they never mention that in the alignment instructions.

Bob,

Yes, it seems on the -DC volts is where I get a definite peak. +DC volts setting there wasn't any real peak. IIRC, the needle would go go up but never down.

I've adjusted the Video IF using my VTVM and a signal generator turned almost all the way down. Next I'll hook up the Eico 369 and O'scope to see the response curve.

Crist Rigott · #**173** 10-20-2016, 02:53 PM

Here is what I have. The waveform looks pretty much like the ones I have already gotten.

Total width is 28.6 to 21
Central trough is at 25.6
Left "peak" is at 26.5
Right "peak" is at 24.5

Vertical graduations is at .2 volts
Horizontal graduations is at 5 volts

I've included a picture of the controls on the Eico 369.

It seems that the frequency isn't where it supposed to be as in the trough should be 24.3.

Also midway on the "high" slope is 27.25 instead of 25.75.

It kinda looks like the waveform is about 1.5 high?

BTW, I'm using the marker to determine the freq of the waveform which is connected to my freq. counter.

Any ideas? I'm not going to do anything till I hear back as to what is going on.

As always, your help it is appreciated.

bandersen · #**174** 10-20-2016, 03:00 PM

I suspect you RCA RF generator is off. Using a modern frequency counter with an old RF generator can give weird results. How about doing the alignment visually ?

I find that adjusting the scope / sweep gen settings so that each division is 1MHz to be very helpful.

Crist Rigott · #**175** 10-20-2016, 03:16 PM

Quote:

Originally Posted by bandersen

I suspect you RCA RF generator is off. Using a modern frequency counter with an old RF generator can give weird results. How about doing the alignment visually ?

I find that adjusting the scope / sweep gen settings so that each division is 1MHz to be very helpful.

Good point. But I failed to mention that I'm using a totally rebuilt Eico 322 generator and the freq. counter is attached to another BNC which I've added. Sorry for the confusion.

I'll tweak the coils to see if I can align it visually.

How do you set the scope up so each division is 1mhz?

Thanks.

bandersen · #**176** 10-20-2016, 03:18 PM

have you looked at the output of the Eico 322 on your scope ? Is it a pure sign wave or is it "lumpy"? Make sure modulation is turned off too.

Adjust the display width on your scope or sweep width while observing markers 1 Mhz apart.

Crist Rigott · #**177** 10-20-2016, 03:19 PM

Quote:

Originally Posted by bandersen

Adjust the display width on your scope or sweep width while observing markers 1 Mhz apart

Of course! Duh!

Crist Rigott · #**178** 10-20-2016, 03:48 PM

OK, I did a visual alignment. In reality, it didn't take much to get the waveform shown.

The PIP is at 24.3 which is where the trough should be. I looked around and tweaked some more but I couldn't shift the trough to freq. of 24.3. BTW, each H division is 1MHz.

I would think it is important to have that trough at 24.3, right? I'm just guessing that the 24.3 is midway between 25.3 and 23.1, hence the trough. Any ideas as to how to shift that trough? Or do I need to?

When I say shift the trough, I really mean the whole waveform.

bandersen · #**179** 10-20-2016, 04:34 PM

Yes, it's important. It can be very frustrating when doing it visually when things are way off because you have four slugs to adjust.

Have you calibrated the 369 marker generator ? I think it's possible to use the 369 as a fixed frequency RF generator. Maybe use it for the alignment instead of the Eico 322.

Crist Rigott · #**180** 10-20-2016, 06:28 PM

Quote:

Originally Posted by bandersen

Yes, it's important. It can be very frustrating when doing it visually when things are way off because you have four slugs to adjust.

Have you calibrated the 369 marker generator ? I think it's possible to use the 369 as a fixed frequency RF generator. Maybe use it for the alignment instead of the Eico 322.

Yes, I calibrated the 369. I know my freq. counter is cal'd also.

I think I can use it for alignment. But I'm not sure of where to get the signal out from the generator. Also I'm wondering how to attenuate the signal so I can use the least possible.

I'll look into it.