Hallicrafters T-506 Late Production Set

[M3-SRT8]

Like a dummy, I only ordered two 470pF 15kV axial caps. I need four.

Can I substitute ceramic disc caps? Two are in the HV Cage, two underneath near the bleeder resistors. The parts list calls for 500pF 6kV.

[M3-SRT8]

Another question: I hear the HV RF Coil is a soft spot on these TVs.

Should I:

1. Clean and bake it at 180 degrees?

2. Space the top lid by .25"

3. Add a muffin fan?

Love to see a pic of the HV Cage with the fan installed.

Thanks.

[Tom Albrecht]

Originally Posted by M3-SRT8

Another question: I hear the HV RF Coil is a soft spot on these TVs.

Should I:

1. Clean and bake it at 180 degrees?

2. Space the top lid by .25"

3. Add a muffin fan?

Love to see a pic of the HV Cage with the fan installed.

Thanks.

My experience with a Hallicrafters set that had a problematic coil was as follows:

1. Clean, bake, and coat with fresh varnish: Temporarily fixes the problem, but not long term. (although others have reported better results)

2. Lift the lid by 1/4 inch: not sufficient to help.

3. Add muffin fan and lift the lid: works well. I had a very small muffin fan that fit inside the cage. About 30 mm square, 10 mm or so thick. Didn't like the noise it made.

4. Best fix: replace the coil with a different one (I used a donor from a Teletone junker)

Not all Hallicrafters sets have this problem. You might be lucky and have one of the good ones.

[kvflyer]

I have this to look forward to! I have one in queue. I also like the stainless steel paint that was used on the metal cabinet, but have not found it locally.

[M3-SRT8]

[QUOTE=Tom Albrecht;3212247]My experience with a Hallicrafters set that had a problematic coil was as follows:

1. Clean, bake, and coat with fresh varnish: Temporarily fixes the problem, but not long term. (although others have reported better results)

2. Lift the lid by 1/4 inch: not sufficient to help.

3. Add muffin fan and lift the lid: works well. I had a very small muffin fan that fit inside the cage. About 30 mm square, 10 mm or so thick. Didn't like the noise it made.

4. Best fix: replace the coil with a different one (I used a donor from a Teletone junker)

Not all Hallicrafters sets have this problem. You might be lucky and have one of the good ones.[Quote]

Would doing the 1st 2 suggestions help? I mean before I power it up.

[M3-SRT8]

The bottom of my HV Coil assembly has a resistor on Pins 5 and 6. It doesn't show up on the schematics that I'm looking at (late production 6AU6 T-54) and I can barely read the bands. I THINK it's Green-Black-Yellow. 500 kohms. Half watt.

It tests OL on my Fluke. The 6C4 oscillator is such a critical tube so I want to get it right. My HV Coil board has two .25uF 600V and one .001 6kV.

Any ideas, Gents?

[M3-SRT8]

Originally Posted by M3-SRT8

The bottom of my HV Coil assembly has a resistor on Pins 5 and 6. It doesn't show up on the schematics that I'm looking at (late production 6AU6 T-54) and I can barely read the bands. I THINK it's Green-Black-Yellow. 500 kohms. Half watt.

It tests OL on my Fluke. The 6C4 oscillator is such a critical tube so I want to get it right. My HV Coil board has two .25uF 600V and one .001 6kV.

Any ideas, Gents?

It's a cap. Measures 2.7 pF. Specs at 4.7pF. Duh.

[Tom Albrecht]

Originally Posted by M3-SRT8

Like a dummy, I only ordered two 470pF 15kV axial caps. I need four.

Can I substitute ceramic disc caps? Two are in the HV Cage, two underneath near the bleeder resistors. The parts list calls for 500pF 6kV.

You can give the ceramic caps a try, but they might not work well. I did a study of this a few years ago and was able to show how the applied DC voltage across high voltage ceramic caps actually changes their capacitance. This causes severe distortion of the scanned raster.

That problem, however, is mainly with vertical deflection. In your set, those use much larger value capacitors like .01 uF (or I believe even .05 uF in the Hallicrafters). Your 470 pF caps are probably for horizontal deflection or HV filtering, which have less of a problem with this.

What I found with ceramic capacitors is that if you simply use a significantly higher capacitance value than the original tubular capacitor, ceramic will work. So for example, if you see problems using 470 pF ceramic capacitors, then using something like 2000 pF (.002 uF) or more will probably work just fine. Maybe even .001 uF would do the trick.

For some of my previous work on this subject, see: http://www.videokarma.org/showthread...=260749&page=2

I have a more complete write up of it somewhere else, but I can't find a link to it right now.

[M3-SRT8]

Originally Posted by Tom Albrecht

You can give the ceramic caps a try, but they might not work well. I did a study of this a few years ago and was able to show how the applied DC voltage across high voltage ceramic caps actually changes their capacitance. This causes severe distortion of the scanned raster.

That problem, however, is mainly with vertical deflection. In your set, those use much larger value capacitors like .01 uF (or I believe even .05 uF in the Hallicrafters). Your 470 pF caps are probably for horizontal deflection or HV filtering, which have less of a problem with this.

What I found with ceramic capacitors is that if you simply use a significantly higher capacitance value than the original tubular capacitor, ceramic will work. So for example, if you see problems using 470 pF ceramic capacitors, then using something like 2000 pF (.002 uF) or more will probably work just fine. Maybe even .001 uF would do the trick.

For some of my previous work on this subject, see: http://www.videokarma.org/showthread...=260749&page=2

I have a more complete write up of it somewhere else, but I can't find a link to it right now.

I ordered up more of the proper caps.