Hallicrafters T-506 Late Production Set

[old_coot88]

Any chance of posting a schematic?

[jr_tech]

There must be an open connection somewhere in the heater string if the tubes are not lighting... a bad selenium rectifier will not be a cause of the tubes not lighting.
Perhaps continuity check the heater strings from ground, working back to the power cord end... there must be an open circuit in the heater strings.
CRT heater ok? Fuse ok?

jr

[M3-SRT8]

How do I check the CRT heater? Fuse is ok.

[init4fun]

Originally Posted by M3-SRT8

How do I check the CRT heater? Fuse is ok.

An Ohm meter on pins 1 and 12 (the pins on either side of the ridge on the locating pin on the CRT's connector) should read very low ohms , high ohms (or infinity) mean the heater is open .

[jr_tech]

CRT heater is pins 1 and 14 (the pins next to the key-way, on either side). It should ohm out pretty low, around 2 to 3 ohms.

jr

[M3-SRT8]

Originally Posted by jr_tech

CRT heater is pins 1 and 14 (the pins next to the key-way, on either side). It should ohm out pretty low, around 2 to 3 ohms.

jr

CRT Heater reads 1.9 ohms.

[M3-SRT8]

Okay. did a test of the AC string. Everything checks out except the following pins measured no continuity to ground. Per Sam's T-54:

V4 6AU6 Pin 4

V5 6AU6 Pins 3 & 4

V6 6AU6 Pins 3 & 4

I'm hoping this is an ah-ha! moment. All the wiring in this area looks fine. I'm thinking (hoping?) one of you guys can take a look at a schematic armed with this info and say "check ceramic cap on V4" or words to that effect.

I say this because I don't want to go into this area half-cocked and mess something up. Especially after this real pretty recap.

Thanks.

[jr_tech]

The isolation of the pins from ground described suggests two open circuits:

1. between pin 3 & 4 of V4, perhaps open heater, dirty pins, broken or poorly tensioned socket pins.

2. between pin 3 of V8 and pin 4 of V6, perhaps broken wire, cold solder joints.

It is also possible that your probe was not making good connection to these pins due to flux left after changing capacitors.

jr

[M3-SRT8]

Originally Posted by jr_tech

The isolation of the pins from ground described suggests two open circuits:

1. between pin 3 & 4 of V4, perhaps open heater, dirty pins, broken or poorly tensioned socket pins.

2. between pin 3 of V8 and pin 4 of V6, perhaps broken wire, cold solder joints.

It is also possible that your probe was not making good connection to these pins due to flux left after changing capacitors.

jr

I was very careful with the probe. No caps were replaced in that area (V4 - V6) because they're all ceramics.

I'll check the suggested areas later today.

Thanks.

[M3-SRT8]

Resoldered the AC Pins on V1 through V7. Plugged it in, brought it up gradually with the Variac and all the tubes except the 1B3 lit. No raster with brightness all the way up. I assume full clockwise is full brightness.

Well. I'll be back at it after dinner.

Thanks!

[M3-SRT8]

Brought it up again with the variac. With the Selenium Rectifier installed:

At 115 V AC:

6X5GT Pin 8: Spec 390V Test 255V

25Z6GT Pin 8: Spec 260 Test 110V

Is the Sel. Rectifier toast?

[jr_tech]

If you have about 125V on pin 5 of the 25Z6 (V20) the selenium is operating ok.

jr

[M3-SRT8]

I installed the diode, with a couple of 25 ohm 10 watt resistors.

Bingo. At household 121 VAC, full Raster came on. Sound on. Pin 8 on 6X5GT reads 390V. Exactly as per spec.

Raster is a bit dull, but I haven't put a signal on nor have I adjusted the 6C4 oscillator.

Should I run it a bit to wake everything up?

[Notimetolooz]

Good news.
Shows why replace the seleniums with silicon is recommended.
There shouldn't be any problem with running it like this for a little.
Could uncover other problems, don't leave it unattended.

[M3-SRT8]

Originally Posted by Notimetolooz

Good news.
Shows why replace the seleniums with silicon is recommended.
There shouldn't be any problem with running it like this for a little.
Could uncover other problems, don't leave it unattended.

Thanks, No Time Toloose.

https://getyarn.io/yarn-clip/6504048...c-95bf796a5a7e