[Boatanchors] Globe (WRL) V-10 VFO - Problem with voltage regulation

[Garey Barrell]

30 mA is the MAXIMUM current that an 0A2 can 'sink'.  The idea with shunt regulators (VR tubes, Zeners, etc.) is to set 
the MINIMUM current so that the regulator fires (~5-10mA).  In this case we want to sink about 10 mA in the KEY DOWN 
position, and then when the key is UP, the VR will have to sink the ~10 drawn by the oscillator when keyed, making a 
total of 20 mA, well within the 30 mA MAXIMUM.

The 'delta' current is what the VR tube has to control.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>

K9FFK wrote:
> Jerry:
> The  0A2 current range is 5 - 30 mA at 150 Vdc.
> At +175 V you would want an 833 ohm resistor to start (no load). (25V drop, 30 mA)
> Even that may be too high.
> A 47K resistor will only allow 3 mA regulator current...below minimum spec!
>
> Try subbing an 0B2 if you want.
> Or use a 560 ohm, 1W.
>
> I think that 47K is a typo..should maybe have been 470.
>
> Dick, K9FFK
>
>
> On 11/8/2013 4:10 PM, D C _Mac_ Macdonald wrote:
>> Try the regulator to give you 105V regulated with the specified dropping resistor.  I'd bet the VFO would run just 
>> fine with the lowered B+ voltage.  IIRC that's the 0B2.
>>
>> 73 - Mac, K2GKK in OKC
>>
>>
>> Sent from my iPhone
>>
>> On Nov 8, 2013, at 15:51, "Jerry" <jsternmd at att.net> wrote
>>
>> I found a V-10 in great shape but someone had cut the line cord close to the
>> chassis which made me worry that there were some potentially serious issues
>> with the VFO.  The inside looks new, however before applying power, I
>> checked to make sure the power transformer was not shorted.  The xfrmr works
>> fine supplying filament 6.2vac and separate 175vac to a half wave selenium
>> (65ma) that I replaced with 1n5408 plus a 200ohm dropping resistor.  I also
>> replaced the two 30uF lytics and left the large (~10mH) choke between the
>> two filter caps as it was not shorted either.  Thes B+ supplies the plates
>> to 6BH8 and 6CB6 using a 0A2 voltage regulator.  I cannot get the 0A2 to
>> strike at 175vdc from the filtered supply.  I replaced the 0A2 twice with
>> known tubes and still not striking.   The dropping resistor between the B+
>> and 0A2 is 47K, 1W per the schematic but in the VFO I found a 560 ohm 1 watt
>> instead.  I cannot tell if this was done by the previous owners to get the
>> 0A2 to strike earlier or if this was a factory mod not documented on my
>> schematic.   Can anyone offer advice?
>>
>> 73 Jerry
>> K1JOS