C-lator hum

[martin manning]

The 6.3V windings are 750 mA each, so one would be enough for two 12AX7's, but there are of course many other things it could be used for.

[ynor]

In comparison, there's "only" 400 mA on the 1x stock one.

Screenshot_20240405_223217_OneDrive.jpg

[ynor]

Well, it was fun as long as it lasted. I cut the leads and tidied it up. Thought it looked good. Only thing changed was connecting the HV wire and heaters wires from the other side of the board, and moving the first ground to the middle of the chassis. Tried to power it up. First thing I see is there's no pilot light. Did some measuring and find that there is no voltage in the heaters. Unsoldered the heater wires and measure 0 V between them. Also tried the other 6.3V secondary. No voltage there as well.

Some other voltages have changed, see next post. HV has increased from 129 to 135 V. But B+ is higher and it seems the dropping string doesn't work as B+1 and B+2 is very high! What causes the heaters secondaries on the transformer to fail and also messes with the dropping string??

20240406_100916.jpg

[ynor]

Failure.png

[bepone]

disconnect pt and try all trafo voltages " in the air", after you change some burned fuses or so

[ynor]

Thanks. Will try. No fuses burned yet.

[martin manning]

With cold cathodes there will be no high voltage current draw to drop the voltage along the string. Seems like you had it connected properly. The question is how did you lose both 6.3V windings. Any funny smells or other evidence?

[bepone]

heaters missing chk-connect heaters wires

[ynor]

With cold cathodes there will be no high voltage current draw to drop the voltage along the string. Seems like you had it connected properly. The question is how did you lose both 6.3V windings. Any funny smells or other evidence?

No nothing. No fuses burnt, no smells, no fires (!). Seems to me the transformer malfunctioned. Or could it be damaged by some kind of mistake during rewiring that caused it to malfunction after start up?

[ynor]

heaters missing chk-connect heaters wires

I did. Also unsoldered them and measured "in the air": 0 VAC.

[ynor]

Close ups

20240406_100954.jpg

20240406_100950.jpg

[martin manning]

Did you ever put the cover on? I would think if you did, and the mounting bolt contacted both the top and bottom, the primary would over heat and there would be smoke. Strange that both 6.3V are dead when you only had one of them connected. Check the resistance of those windings to see if they are open.

[ynor]

Yes I had the cover on before I fired it up. But I am 100 % sure that the mounting bolt was not in contact with the lid.

I'll measure the resistance between both 6.3V windings. How should I interpret the results?

[martin manning]

You should see very low resistance, an ohm or two, indicating they are have not gone open.

[bepone]

almost impossible that the heater wires are burned.. they are thickest ones.. 0% chance..chk better what is there