[Hammarlund] HQ-170A VHF VR tube??

[Roy Morgan]

At 09:45 AM 1/27/04 -0600, Craig Roberts wrote:
>  ... R53, the 10 watt resistor going to the OB2, should be 2K, not 3K. 
> ...if its just the 170A, then 3K is fine."
>
>Hmmm.  It's all very confusing, really.  My receiver is indeed an HQ-170A 
>VHF.  However, if I use a 2K dropping resistor at R53, I get 143 volts on 
>the regulator tube socket --

The right way to pick the dropping resistor is by the *current* in the 
regulator, not by the voltage across it.  If the dropping resistor is too 
low, low enough to raise the regulator voltage by much at all, then there 
is WAY too much current in that tube.  Any 105 volt regulator that runs at 
143 volts is being seriously punished, or is past the end of its life.

Here is what I suggest:

1) Learn the current range for the regulator you want or have.

2) Arrange a way to measure the current in the tube. I suggest a 1- or 
10-ohm resistor permanently wired in at the tube socket to ground.  Measure 
the voltage across it with a DMM (for one ohm, you get one millivolt per 
milliamp of current.)  A neat alternative is one of those socket extenders 
that has removable links for each pin.  Not everyone is lucky enough to 
have one of those.

3) Adjust the dropping resistor so the thing stays in its regulation range 
*both* with varied load and over the range of line voltages you 
expect.  The load can vary, for instance, if the BFO is fed by the 
regulator (I'm not familiar with this radio so this is only an example.)

4) Set the range of  currents through the regulator at the lower end in 
stead of the higher end of the rated range for long tube life.


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
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