[HBR] Power Supplies used in HBR 14 and HBR 16

[Tim Shoppa]

K5UOS writes:

> I have a question concerning the HBR power supplies and how the choke
> and transformer requirements were determined. I believe I generally know
> the answer but would appreciate a clear reason for doing what I have
> done in the past....overkill. 

> My question: The sum of the plate and gride currents for the tubes used
> in the HBR 16 exceeds the currents listed in the tubes specs. The tube
> specs show the sum of the typical plate currents alone to be approx
> 157ma. The HBR 16 only uses 150 ma choke(s). The transformer requirement
> in the HBR 16 is for 120ma.

> How do you scientifically choose the ratings for the transformer and
> choke assuming the recommended plate voltage is used?

> After the fact I can measure but what rule of thumb would help up front?

Up front, you can look at how each stage is biased, use the characteristic
curves to get the appropriate currents, and add those up.

If you look in a tube spec sheet, you will find "max plate currents": those
will never be used in a receiver except at a couple stages. You also find
plate currents for different classes of operation in different service. But
even those don't describe exactly how the tube will be used in a different
circuit, and they often list currents at near max plate voltage, and in
real life currents will tend to be lower.

Tim.


There was a mention of HBR receivers in January 2008 QST. 

Don K5UOS


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