@JMFahey. I want to point out that the failure I described was not related to poor winding isolation as there was no arcing inside the transformer. But primary self resonance was somewhere in the upper audio band, maybe interwinding capacitance was high. Furthermore I presume a weak coupling primary-primary, i.e. a high stray inductance that enabled these peaks of some 2500V that destroyed the tubes.
The problem with protection diodes is, although they clamp primary minimum voltage to -1V - this does not guarantee that anode voltage of the other leg is limited to 2 x supply voltage. Limited coupling between both primary windings enables higher peak voltages. Interleaved windings reduce these effects, but may increase winding capacitance.
And transformers with high impedance - i.e. many turns - tend to exhibit a low primary self resonance.
Ideally, self-resonance should be above 20kHz - just my 2c
And transformers with high impedance - i.e. many turns - tend to exhibit a low primary self resonance.
Ideally, self-resonance should be above 20kHz - just my 2c
I take care of HVAC systems at work. At times a 20hp drive for the cafeteria goes out on over voltage and I have to reset it. The motor gets up to about 20% of rated speed and overcurrent is displayed on the drive. I always say to myself, 'Come on baby, come on...'. Always a sigh of relief when it hits 60 Hz and starts backing off. This is a big old motor running a big, slow moving fan (relative to the fan diameters now). I got to say they just don't make them like they used to.
If you're paranoid, add 68ohm (or thereabouts) across the 8ohm tap.
Yes, it steals some power (OMFG!) and limits some of the "flavour" from the speaker impedance swings but it will ensure you have a load
Friction. Oil.
At 20% speed the fan itself needs 4% of nominal power. If the VFD thinks it needs over-voltage (and isn't trying to do 0-60 in 5 seconds), something else is the drag.
Cliff type switching sockets switch the earth contact also.
Suitable resistor (50R) between switched tip tag and switched sleeve tag would provide idiot proofing, ie in circuit when unplugged, completely out of circuit when cable plugged in.
This of course will not protect against cable disconnection at the speaker end.
Dan.
Suitable resistor (50R) between switched tip tag and switched sleeve tag would provide idiot proofing, ie in circuit when unplugged, completely out of circuit when cable plugged in.
This of course will not protect against cable disconnection at the speaker end.
Dan.
The load resistor is wired between the switched tip contact, and the unswitched ground (earth) contact. So it is connected from amplifier output to ground if the plug is not inserted, or partially inserted.
You can of course also also return the ground end of the resistor to the power amp ground, instead of to the unswitched ground contact on the output jack.
In no case should the ground end of the dummy resistor be soldered to a switched contact.
-Gnobuddy
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