Why a damper isolation transformer?

[Findm-Keepm]

I understand that Damper tubes can develop a H-K short, and cause problems. But both Triad and Thordarson (26F70) made isolation transformers to isolate the damper filament from the rest of the chassis, and alleviate the H-K short issues.

But why use a transformer, when replacemnt of the tube would likely solve the problem without modification or added expense?

Perhaps some chassis were more prone, or the H-K short could cause many more problems? They were first made in the 50s, so probably not a color-TV specific problem....

Any ideas?

[wa2ise]

Originally Posted by Findm-Keepm

...or the H-K short could cause many more problems? They were first made in the 50s, so probably not a color-TV specific problem....

Any ideas?

Early damper diodes (like 6W4) probably didn't have quite enough H-K insulation, as compared to later ones. Look at a late version, you'd see a spiral of whitish coated wire? between the heater and the cathode.

The isolation transformer was probably a solution to avoid having to replace the tube every few months, which consumers would not like at all...

[init4fun]

Since the heater power for the majority of the tubes was grounded to the chassis on one side of it's line , connecting the damper's heater with one side grounded was said to put too much potential between the now grounded heater and the operating at much higher voltage cathode . This caused many HK shorts in damper tubes and you'll find some sets with a separate damper heater winding incorporated into the main transformer for this very reason . The aftermarket transformer was used as a repair for sets without such a separate winding that were repeatedly shorting damper tubes .

[dieseljeep]

Originally Posted by wa2ise

Early damper diodes (like 6W4) probably didn't have quite enough H-K insulation, as compared to later ones. Look at a late version, you'd see a spiral of whitish coated wire? between the heater and the cathode.

The isolation transformer was probably a solution to avoid having to replace the tube every few months, which consumers would not like at all...

I never used 6W4's in sets, newer or older. The only tubes I carried was 6AX4 and 6AU4 and the series counterparts.
You couldn't use the Raytheon Japanese 6CJ3/6DW4 in Zenith color sets. The heater current wasn't right. The regulator and damper tube heaters were in series. In those sets, you had to use a GE or Zenith branded 6CJ3/6DW4.

[Electronic M]

Even some later sets like to eat dampers. Case in point I have a Silvertone CTC-15 clone that if the osc. coil is adjusted too far off of synch lock will short it's damper REAL fast. It had a good damper but all lytics were bad and killing the B+ when I got it. Damper tested good before test where it gave shrunken raster than faded out so I spun my wheels for months trying to get HV with a blown damper (after the recap). It ate 2-3 replacement dampers while trying to go through the H osc. adjustments. And since then it has killed at least 1 more in operation (that one did not short, but it also fooled me by testing good unless you held the test button for 8-30 sec and allowed it to slump into the bad range.).