Hi All,

I just purchased an air castle model 6758, checked out a majority of the caps and resistors, then hooked up 6 volt batt. and powered up. The power supply vibrator hums quite loud, but no power to any of the tubes, i have the schematic for it but it is difficult to read. I have 6 volts on the power tube (19) but nothing else. I could use a little help on where to start looking, any advise would be aprecieated. thanks.
Joe

Did you check and/or replace the two electrolytic capacitors in the power supply? Most likely they will be bad. This power supply is a synchronous type. There are extra contacts in the vibrator that act to rectify the high voltage secondary voltage eliminating a rectifier tube.

Clifton

:Hi All,
:
:I just purchased an air castle model 6758, checked out a majority of the caps and resistors, then hooked up 6 volt batt. and powered up. The power supply vibrator hums quite loud, but no power to any of the tubes, i have the schematic for it but it is difficult to read. I have 6 volts on the power tube (19) but nothing else. I could use a little help on where to start looking, any advise would be aprecieated. thanks.
:Joe

:Did you check and/or replace the two electrolytic capacitors in the power supply? Most likely they will be bad. This power supply is a synchronous type. There are extra contacts in the vibrator that act to rectify the high voltage secondary voltage eliminating a rectifier tube.
:
:Clifton

Hi Clifton, yes I did replace the two 8 mfd electrlytic caps, they tested bad. But the was no difference in power up. Does the vibrator usually hum loud or should it be quiet? That was my focus was the power supply unit.
:
::Hi All,
::
::I just purchased an air castle model 6758, checked out a majority of the caps and resistors, then hooked up 6 volt batt. and powered up. The power supply vibrator hums quite loud, but no power to any of the tubes, i have the schematic for it but it is difficult to read. I have 6 volts on the power tube (19) but nothing else. I could use a little help on where to start looking, any advise would be aprecieated. thanks.
::Joe

"Divide and conquer."

I think that I'd totally disconnect the B+ bus at the second filter cap, apply power, and see if the B+ voltage comes up OK at that cap. If it does, you likely have a shorted bypass cap pulling B+ to ground.

These vibrator sets have an audible hum when working correctly, but a very loud hum might be an indication that the set's B+ bus is drawing excessive current.

:"Divide and conquer."
:
:I think that I'd totally disconnect the B+ bus at the second filter cap, apply power, and see if the B+ voltage comes up OK at that cap. If it does, you likely have a shorted bypass cap pulling B+ to ground.

:CV I have a guess I stupid question, where would I locate the bypass cap. And the b+ voltage? The schematic isn't to easy to follow on this radio.

:These vibrator sets have an audible hum when working correctly, but a very loud hum might be an indication that the set's B+ bus is drawing excessive current.

The B+ bus originates at the left electrolytic capacitor- can't make it out on the schematic but it might be C18 or C19.

Both C2 and C5 are RF bypass caps, however, they are isolated from the B+ bus by high-value resistors so even if they were dead-shorted they can't be the cause of B+ overcurrent- if in fact the B+ is even really shorted to ground. You first need to find out if it is or not by disconnecting everything on the B+ bus fed by C18 (or C19).

If you still have no B+ at the cap after disconnecting everything fed by it, you have a serious problem- possibly a shorted power transformer. If B+ comes up at the cap you will need to figure out exactly what on the bus is pulling it down. Easy to do- just methodically disconnect each item hanging on the bus until the voltage pops back up. But first things first.

And we did double-check the polarity of C18 and C19 and make sure their working voltage rating was sufficient for the power supply voltage(s).

Clifton

:The B+ bus originates at the left electrolytic capacitor- can't make it out on the schematic but it might be C18 or C19.
:
:Both C2 and C5 are RF bypass caps, however, they are isolated from the B+ bus by high-value resistors so even if they were dead-shorted they can't be the cause of B+ overcurrent- if in fact the B+ is even really shorted to ground. You first need to find out if it is or not by disconnecting everything on the B+ bus fed by C18 (or C19).
:
:If you still have no B+ at the cap after disconnecting everything fed by it, you have a serious problem- possibly a shorted power transformer. If B+ comes up at the cap you will need to figure out exactly what on the bus is pulling it down. Easy to do- just methodically disconnect each item hanging on the bus until the voltage pops back up. But first things first.

Hey Joe
You have 6 volts at the power tube? That would be heater voltage. All the tubes would have 6 volts at their respective heater pins. Make sure all the sockets are clean and the tubes are warming up.
CV and Clifton are steering you towards checking the B+ which is the high voltage output from the vibrator. If you have no B+, you need to replace or repair the noisy vibrator.

::The B+ bus originates at the left electrolytic capacitor- can't make it out on the schematic but it might be C18 or C19.
::
::Both C2 and C5 are RF bypass caps, however, they are isolated from the B+ bus by high-value resistors so even if they were dead-shorted they can't be the cause of B+ overcurrent- if in fact the B+ is even really shorted to ground. You first need to find out if it is or not by disconnecting everything on the B+ bus fed by C18 (or C19).
::
::If you still have no B+ at the cap after disconnecting everything fed by it, you have a serious problem- possibly a shorted power transformer. If B+ comes up at the cap you will need to figure out exactly what on the bus is pulling it down. Easy to do- just methodically disconnect each item hanging on the bus until the voltage pops back up. But first things first.

:Hey Joe
:You have 6 volts at the power tube? That would be heater voltage. All the tubes would have 6 volts at their respective heater pins. Make sure all the sockets are clean and the tubes are warming up.
:CV and Clifton are steering you towards checking the B+ which is the high voltage output from the vibrator. If you have no B+, you need to
replace or repair the noisy vibrator.

I removed the power supply and isolated t to 6volt source. I checked voltages at both filter caps. C19 I believe had 170 volts DC. C 18 had 5 volts DC. Across the transfomer I had 170 volts DC. The vibrator had 165 across two pins I'm guessing 4 and 5. And 5 volts across 2 and 3. Not sure on pin numbers. There is only wires going to radio chassis two of them are for power switch and ground. The other comes of the one side of the transformer, that wire only has a 5 volt output. No high voltage is going to chassis. Hope this info helps.
Joe.
:
:
:::The B+ bus originates at the left electrolytic capacitor- can't make it out on the schematic but it might be C18 or C19.
:::
:::Both C2 and C5 are RF bypass caps, however, they are isolated from the B+ bus by high-value resistors so even if they were dead-shorted they can't be the cause of B+ overcurrent- if in fact the B+ is even really shorted to ground. You first need to find out if it is or not by disconnecting everything on the B+ bus fed by C18 (or C19).
:::
:::If you still have no B+ at the cap after disconnecting everything fed by it, you have a serious problem- possibly a shorted power transformer. If B+ comes up at the cap you will need to figure out exactly what on the bus is pulling it down. Easy to do- just methodically disconnect each item hanging on the bus until the voltage pops back up. But first things first.

I'm assuming that C19 is the rightmost electrolytic, the one being fed by the power transformer. That would leave C18 as the leftmost elecrolytic, the one that normally feeds the B+ bus.

Now, assuming EVERYTHING is disconnected from the B+ bus and that only the filter choke that feeds C18 from C19 is connected to C18, that pretty much isolates the problem to a shorted C18 or a filter choke that has its winding internally shorted to the choke's metal core.

Try removing the connection from the choke that feeds C18. If you now get 170 VDC or more on both sides of the choke, you have a shorted C18. If the C18 side of the choke is still low voltage, the choke is bad.

Don't operate the unit for more than a few seconds at a time, since driving into a near short is extremely stressful to the power transformer and vibrator.