Hallicrafters T-506 Late Production Set

[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.

[Tom Albrecht]

Originally Posted by M3-SRT8

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

Maybe, but probably not. I did the steps I reported in the sequence listed. I started to have success with #3.

[Notimetolooz]

Over in the ARF the subject of the H.V. transformer has recently come up.
https://antiqueradios.com/forums/vie...p?f=3&t=359879

[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.

[MadMan]

The way I always think about it is the stripe on the diode is the | from the schematic symbol ->|-

Which would also be the opposite of what Tom said, I believe he meant the + comes out of the stripe side. But the stripe side is the cathode (-) and the arrow side is the anode (+). So remember my mnemonic device so you don't get confused: in the symbol ->|- the arrow points in the conventional direction of electricity flow from + to - (not the actual direction in physics, which is backwards O_o [but don't think about that]) and the stripe on the diode is the vertical line |.


https://learn.sparkfun.com/tutorials...d-led-polarity

[M3-SRT8]

Originally Posted by MadMan

The way I always think about it is the stripe on the diode is the | from the schematic symbol ->|-

Which would also be the opposite of what Tom said, I believe he meant the + comes out of the stripe side. But the stripe side is the cathode (-) and the arrow side is the anode (+). So remember my mnemonic device so you don't get confused: in the symbol ->|- the arrow points in the conventional direction of electricity flow from + to - (not the actual direction in physics, which is backwards O_o [but don't think about that]) and the stripe on the diode is the vertical line |.


https://learn.sparkfun.com/tutorials...d-led-polarity

Thanks for jumping in. Soooo, the TAIL of the arrow attaches to the lead that was attached to the " + " lead of the Selenium Rectifier?

Huh? Oh, Boy.

[old_coot88]

Originally Posted by M3-SRT8

Thanks for jumping in. Soooo, the TAIL of the arrow attaches to the lead that was attached to the " + " lead of the Selenium Rectifier?

NEGATORY. Please see post#4. The banded end (stripe) on the Si diode is the cathode. The "+" marking on the selenium is the cathode, dumb as this seems. The only sensible interpretation is "the B plus voltage comes from here."

[Electronic M]

Originally Posted by M3-SRT8

Thanks for jumping in. Soooo, the TAIL of the arrow attaches to the lead that was attached to the " + " lead of the Selenium Rectifier?

Huh? Oh, Boy.

Nope. Look at a tube rectifier the B+ line comes from the cathode....He is right in that there does need to be a voltage potential across the diode as marked in his drawing to conduct. Think of the old selenium power supply and the load of the TV as 2 batteries in series plus on one connects to minus of the other. They marked the selenium not with it's own polarity but with the polarity of the other battery it connects to.

The stripe on a new diode is the B + end of the selenium.

The old selenium polarity notation is bassackwards from modern convention.

[M3-SRT8]

Oooookay.

I removed the diode and reattached the leads to the rectifier when I attempted to first power it up. Bringing it up on the Variac yielded nothing. No tubes lit.

I checked the switch continuity. It's fine. Checked the leads coming into the switch. They're ok.

Did a resistance check on 6X5GT. Strange readings:

Pin 1: Inf. Test Inf.

Pin 2: 2 ohms Test 1.6

Pin 3: 60k Test soars from 350k

Pin 4: Inf. Test Inf.

Pin 5: 60k Test soars from 460k

Pin 6: Inf. Test Inf.

Pin 7: 0 ohm Test 0.2

Pin 8: 70k Test soars past 1 meg

What's up with this?

Thanks

[M3-SRT8]

25Z6 Readings. Also way off:

Pin 1: 60k Test Inf

Pin 2: 25 ohms Test 144k

Pin 3: 160k Test 1.3 meg and climbing

Pin 4: 64 ohms Test 144k

Pin 5: 10k Test 11.43k

Pin 6: 46 ohms Test Inf

Pin 7 26 ohms Test 144k

Pin 8: 60k Test 1.1 meg and climbing

Weird. And the chassis is recapped, and I've checked everything twice, at least.

[jr_tech]

Series string set...did you check all of the heaters and assure that tube pins are clean and making connection? 18 ohm resistor ok? All bets are off on the resistance readings until you have heater strings intact.

Also, did you notice that the Sams shows c4a & b connected backwards? that cap actually has common plus ! Riders has it correct.

jr

[M3-SRT8]

I already cleaned all the tube sockets with contact cleaner and a pipe cleaner.

I replaced all the 'Lytics as they were wired ex-factory, same grounding points, replaced all wiring with new. Double checked it. Tested all components before install.

Tested the tubes before fire up.

Would a dead selenium rectifier prevent start up? When I was waiting for an answer on the diode polarity I hooked up the rectifier and attempted to fire it up that way.

[M3-SRT8]

Both 18 ohm resistors near the rectifier test fine.

I had checked all resistors on the chassis before fire up. Replaced only the four 4.7 meg resistors in the sweep section as they were beyond 20%.

[M3-SRT8]

I have C4A and C4B common plussed to the ground on the 25Z6, just like the factory.

Still checking...