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Airgap for filament transformer ?
Airgap for filament transformer ?
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Old 29th April 2009, 02:51 PM   #11
Funker is offline Funker  Germany
diyAudio Member
Join Date: Feb 2009
Location: Hamburg, Germany
Hi Johann,
all other member explained already before what the possible reason for the unwanted xfmr heat up .

To find what the troble occur from , disconnect the HV secondary from the rectifer tube. Insert an Ammeter in the heater xfmr primary an turn the amp on. Take a little time until the rectifiers filament is warm up. Remeber the primary current . Now turn the amp off and replace the HV secondaries to the rectifier tube. Turn the amp on and check the primary current of the heater xfmr once more. If there is a different of both measured currents, you will have probably a problem with a core load due dc bias. I do not think there is an isolation leak , because that would blow the HV fuse and ruin your retifier tube immediately .

good luck !

regards from Hamburg

Ground your devices before they ground you
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Old 29th April 2009, 05:41 PM   #12
myster_maze is offline myster_maze  Greece
diyAudio Member
Join Date: Oct 2008
Did you measure the two secondaries of the filament transformer separately?
If they're not exactly identical ie 2.5V, this may cause a small DC current that saturates the core.
This happens if the two windings are not in parallel but in series. You can measure the resistance of each winding, too.
If one is higher than the other...
....there's no other way than taking the B+ from the end of the winding and not from the CT.
An air-gapped core will help but it's not THE solution.
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