[Milsurplus] Receiver operating voltages.

[Kenneth G. Gordon]

On 20 Sep 2015 at 15:21, Hue Miller wrote: 

> Most of those old conversion articles seemed to think you had to adhere
> strictly to the rated dynamotor output voltage, when a lot less would do. 

I have mentioned the following several times on various lists: some years ago there was 
published in some amateur radio magazine, an article by someone who experimented with 
reduced voltages in his Drake receiver, I think it was an R4. He kept reducing plate voltage 
from its normal 250 VDC while testing sensitivity. He found that the receiver still exhibited 
excellent sensitivity at plate voltages as low as 12VDC. The main problem was reduction in 
AF power output. 
He finally increased the plate voltage to 50 VDC and left it there. 
He found that there was very substantial reduction in internally-generated noise, and heat 
was much reduced also. 
The RAX receivers all used plate voltages much less than 250 VDC. As I remember it, it 
was 160 VDC. 
In my experimentation with ARC-5 receivers, I found that, in my opinion, the optimum 
voltage is about 170 to 175 VDC, although at that plate voltage input, one really SHOULD 
move the screen voltage connection to the "hot" end of the two resistors, making the screen 
voltage about equal to the plate voltage. 
ARC-5 receivers are commonly operated at 24 VDC by some. Again, increasing the screen 
voltage makes a huge difference in how well the receivers operate. At 24 VDC the receivers 
take somewhat longer to warm up, and their audio output levels are quite low, but all else 
seems to remain as before. 
As I remember it, 250 VDC as the nominal plate voltage for receivers was established 
sometime in the late 1920s or early 1930s by home entertainment receiver manufacturers to 
assure adequate AF output volume. 

> I was surprised to read even in a couple National Radio Co. manuals about
> running their receivers on D.C. 'battery supplies. They mentioned B+ value
> of 135 volts - I think this was the HRO-50 and the NC-183. 

The manual for the RAK/RAL points out that 90 VDC is quite adequte when running off 
batteries. The normal plate voltage for those receivers is 180 VDC.

> I recently saw a H.V. B+ regulator circuit that used a HV FET in a quite
> simple circuit. IIR, this was in E.R. magazine in an article on updating the
> Heathkit HP-23 supply. That looked really promising for v.t. receiver
> supplies. -Hue  

Thanks for the reminder. I had forgotten about that. 
Ken W7EKB