I am wanting to power a Heathkit VF-1 VFO from the Globe Scout 65B. The transformer is considered 'husky'. However, no low voltage exists in the Globe. Seeing the Globe HV goes thru two series capacitors. why not increase the original capacitance from the pitiful 2x 16uF in series to two 70uF caps and tap the center of the series caps. It should be 250 volts at the capacitor tap. The VF-1 only uses a few milliamps B+, should not unbalance the series capacitors to any appreciable amount. 6 volt @ .3 amp is no extra load of concern on the filament either, less than 2 watts! I will use a LED VFO dial light to keep filament current load down. BTW- changed rather high voltage stressed 5U4 to a 5R4. New 120 volt line voltage vs old 115 volt will make up the extra 5R4 voltage drop. What do you think?
BTW- noticed a 50000 ohm bleeder resistor across the two HV caps. I have a 50K with adjustable tap that can connect to the center of two capacitors to assist in equalizing voltage on each cap if that would work.
I am always wary when it comes to dramatically increasing the filter cap value on a vintage power supply because the parts have aged to begin with and ham radio manufacturers often used parts that didn't have a lot of "overhead" for lack of a better term. I'd replace the caps but try to stick with something close to the original value but I don't know if the filter has a choke in it or not. With only 8 µF total, surely it is choke input. the 50K bleeder is probably fine if it is still okay. Here are the downsides: on CW, poor regulation because the load is on and off and with only 8 µF the supply v. will be all over the place. Even with 35 µF you'll have a v. swing on CW. That will affect the VFO, which by the way, I'd run with a dropping resistor. If the VF1 has a gas regulator tube in it, that may help. If it were up to me, I'd restore the rig's power supply to its schematic values and run the VF1 off a separate power supply. Then it is independent of the wild B+ swing on the transmitter if you operate CW. BTW use decent electrolyitics or an 8 mfd oil cap if it will fit. Don't use old caps from a hamfest or China.
The Heathkit VF-1 makes regulated power from an 0A2 tube thus the varying B+ voltage is not an issue. I only use new capacitors. The Globe B+ is choke input.
[sarcasm] ya... 0A2 regulator... works well... [/sarcasm] I'll mention one semiconductor device: TL783 (I put together a separate power supply in a separate box to keep my VF-1 pristine and to keep the current demands of my DX40 transformer to a minimum.)
BTW- posted this question at Antique Radio forum and got many replies. They stated do not use the capacitor series center tap. Use a dropping resistor. I will replace 50K 10 watt bleeder with a 50K 25 watt bleeder with a tap. Thanks all.
I have a VF-1 that I use with a Globe Scout 680. The 680 is virtually identical to the 65B except for the bands covered. The VF-1 is a good match for the Globe Scout. I know that you would like to power the VF-1 from the GS, but I highly recommend building a dedicated power supply for the VF-1. It's easy and relatively cheap. And you will reduce the tendency to chirp on CW or to drift on by not being tied to the transmitter's power supply.
The Heath VF-1 should never be powered from the transmitter. That is a sure way to get chirps! Also, for best operation, including stability, the 6AU6 tube needs to be replaced with a 6AH6 and the 0A2 needs to be replaced with an 0B2 (this is the screen regulator). Then, use the 0A2 removed from the VF-1 in an external power supply to provide 150-volts regulated to power the VF-1. This works great and the screen voltage is reduced to 108-volts which also helps with the stability. Both tubes can be replaced with no actual modifications necessary to the VF-1. The Heath HG-10 / HG-10B VFO actually needs to be powered from a regulated 150 VDC supply. Hidden in the manual is a suggestion that this be done. Glen, K9STH
