[vecher]

Quick question.. I have a .04 Cap that will be replaced. What would you use as replacement.. a .033 or a .047

I used the .047 to replace the .05's So I am thinking to use the .033 to replace the .04..

Any preferences?

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[gregb]

.047 will be fine

Gregb

[vecher]

OK, Recap done. Powered up OK.. But all I get is a hum ..The hum changes volume with the volume control..

The eye tube wasn't working.. So I replaced it. It now lights up but not all the way?

Any way. I guess the next thing is to check voltages.. I powered it up on Variac. At 110 Volts I get about 600 MA.. So that's good.

What should I check next after voltages?

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[vecher]

Ok, I found the problem.. Voltages on the 6A8 were not correct traced back to the Phono switch..There is a Phono switch that needs to be put in Radio position. After I did that radio works great. Picks up station with just a short wire on antenna..Both AM and shortwave..

However there is a problem with the eye tube. Very little response. Saw some post about it and Buzz had similar problems with his.. So i will look at them..

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[vecher]

All, Ok I guess I do not really understand how this works in this Radio.. Can someone tell me what I am supposed to be getting on each pin with and without a signal? The tube works but on even the strongest signal ( I have a AM station about 2 miles from me. at 1440 KHZ) I only get about 1/4 way closed.. I have looked at some descriptions of this problem But don't really understand...

Some say check the voltage at R1 but I cannot find the resistor unless its inside the IF can?

I did align the radio and it picks up many stations..

So I guess I need someone who has worked on this radio and the Eye tube problems..

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[Radioroslyn]

The short answer is check all of the resistors around the eye tube circuit and the 6K7 IF amp tube. How it works is it's looking at the SG voltage on the 6K7. Where you get a strong signal the AVC circuit kick in and drops the gain of the mixer and IF amp this in turn causes the SG volt to increase because of less current flow. This closes the eye. Also have a look at the AVC voltage could be a weak tube or high value resistor. This tube is a bit different than the normal 6E5,6U5, and 6G5 as these a have there own triode driver in the tube.

Terry

[vecher]

Terry, Ok thanks.. Where is the best place to measure the AVC Voltage?

It should go more Neg with a stronger signal.. Right?

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[Radioroslyn]

Across c-22 is good. Use a hi impedance meter like a vtvm as you don't want to load the circuit down
Yes the more -avc voltage more the eye is going to close..

Terry

[vecher]

Terry Any clue as to how you get to these? Looks like they are inside the IF can..

How do you take off the top of the IF can without having to remove it? There is a couple of screws that could be removed ??

Here is a picture..

[Image: http://i292.photobucket.com/albums/mm38/...ztknaq.jpg]

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[Radioroslyn]

Ok so measure it at R-28.

Terry

[vecher]

Ok, Here is what I get..

AVC Line = -10 Volts Pin 3 of eye tube 123.2 Volts

[Image: http://i292.photobucket.com/albums/mm38/...afy7zq.jpg]

AVC line = -5.8 Pin 3 of eye tube 101.4 Volts

[Image: http://i292.photobucket.com/albums/mm38/...wdtxta.jpg]


AVC line = -15.0 Pin 3 of eye tube 146.0 Volts

[Image: http://i292.photobucket.com/albums/mm38/...whfu5p.jpg]

And finally No signal..

AVC line = -.40 Pin 3 of eye tube 78.7 Volts

[Image: http://i292.photobucket.com/albums/mm38/...ugfopn.jpg]

Do not Know if its working correctly. I would think it should close more??

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[Radioroslyn]

If I'm reading the specs for the eye tube correctly it appears that it needs 0v on the pin 3 to be completely open. This can't happen else you wouldn't have any SG voltage on the IF amp. Seems like a design issue.

Terry

[vecher]

Terry, Ok What I understand is The Grids of the 6af6 take anywhere between 80-160 Volts to close. With I assume 160 volts fully closed. Which kind of makes since .. with No signal pin 3 reads 78.7 volts. Or fully open since it takes 80 volts to start to close. But I cannot seem to get anywhere near 160 volts. The strongest signal I can find is only 146 volts.. Maybe there is a way to make this more sensitive?

Ps I did notice that on the plate I was getting 273 volts The range for the tube is 125-250 volts..

My B+ is higher to. according to paper work it should be 382 volts I get 392 Volts..

My field coil should be 1050 Ohms Mine measured 808 Ohms Thats probably why the B+ is a little higher..

Should I try to lower the voltage to the plate of the 6AF6 ? Maybe that would make it work better?

Comments??

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[Radioroslyn]

Let me rephrase what I posted before. The problem as I see it is that your eye tube's grid need to be at 0 volt to be fully closed and 160v fully open. That is a range of 160v. What you have is a range of 82v (78-160v). You are starting out with the tube 1/2 open to start out.

You can't drop the SG voltage on the 6K7 to 0 because no matter how much voltage you put on the CG I don't think you can cause the SG to pull enough current to drop the SG voltage down to any thing close to 0. Even if you could then you would have an IF amp that would have very poor gain.

Originally this tube was designed to be used with it's companion the 6AE6 to ampfile the avc voltage and control the grid voltage for the 6AF6, but SC decided not use it nor have an avc amp circuit so there would be enough voltage swing to cause the full operation of the eye opening and closing
https://frank.pocnet.net/sheets/127/6/6AE6G.pdf

By dropping the plate voltage all that will do is give you a dimmer glow from the tube not changing the angle of deflection.

Terry

[vecher]

Ok, Now I understand. So I guess its what it is. No big deal. I just thought it should be better than what I am getting..

Thanks for the explanation.

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