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

[Garey Barrell]

Charles -

OK.  According to the measurements Jerry made a few months ago, the 6BH8 draws about 9 mA when 'keyed'.  I would design 
at least 10 mA for 0A2 current, so we need a resistor to drop 185-150 or 35 VDC.  At 15 mA that would be 2200 ohms, = 16 
mA.  Key up, the 0A2 would have to shunt the additional 9 mA for a total of 25 mA.  Both are well within the 0A2 rating 
of 5 - 30 mA.

You 1600 ohms would result in 22 mA key down, and 31 mA key up through the 0A2, which is slightly above it's limit.

2000 ohms would be 18 mA key down, and 27 mA key up, a little better, and within the tubes limits.

Needs to be a 1W resistor, minimum.

These numbers assume the B+ is actually 185 VDC.

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>

Charles Ring wrote:
> My schematic, which I thought was from BAMA, shows R4 as 4.7K though the decimal point almost bleeds into the 7 and is 
> easily missed. I see that  the V-10 manual now on BAMA is from you and indeed its schematic shows 47K. My  V-10 had 
> 4.7K and showed a drop in 0A2 plate voltage when keyed of several volts. I paralleled another resistor to bring the 
> total resistance down to 1600 ohms and there is almost no visible voltage drop on my analog meter. This might be the 
> answer to my chirp problem.
>
> 73 de W3NU
>
>
>
>
> On 11/18/2013 2210, Garey Barrell wrote:
>> Charles -
>>
>> As long as it doesn't completely go out, it's ok.  It's a shunt regulator, which means that when the key is up and 
>> the oscillator isn't drawing any current, the 0A2 has to draw enough current through R4 to keep it's plate at 150 
>> VDC.  Then when the key is down and the oscillator draws ~10 mA the 0A2 draws less current, keeping the voltage at 
>> 150 VDC.  The 0A2 should regulate anywhere from 5 to 30 mA.  The resistor should be such that the 0A2 draws about 20 
>> mA key up, for a total of ~30 mA.
>>
>> If the filter capacitors are leaky, the B+ becomes low, and when the key is down there isn't enough unregulated 
>> voltage to keep the 0A2 'lit'.  Another possibility is that R4 has gone up in value, again limiting the available 
>> current flow.
>>
>> A voltmeter on the Plate of the 0A2 should read close to 150 VDC with very little (volt or so) difference between key 
>> up and key down.
>>
>> By the way, the schematic is wrong, R4 is 4.7k NOT 47k.
>>
>> 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>
>>
>> Charles Ring wrote:
>>> My V-10 has a chirp which at 20 meters is really awful. Really fit only for use during the Classic Exchange.
>>>
>>> A new question: when the VFO is keyed, should the brightness of the 0A2 stay the same? Mine almost goes out.
>>>
>>>
>>
>>
>
>