[Milsurplus] Fwd: Re: Lowering Receiver B+, Again.

[Kenneth G. Gordon]

I'm with Bruce on this one, David:

1) Full-wave rectification.

2) CHOKE input (get rid of the input capacitor). You MAY have to increase the capacitance 
of the remaining capacitor(s) to keep ripple at a low level, though.

3) Bucking transformer on the input.

Reducing the filament voltage is not going to effect operation and will contribute to longevity 
of the tubes.

You might also consider inserting a resistor in the B+ feed, since the current draw in 
receivers is normally pretty constant.

On another note: reducing receiver operating voltages appears to have almost no effect on 
operation of the receiver at all.

I have mentioned this a time or two before, but I think repeating it may contribute to the 
ongoing discussion:

Many years ago, I read an article in one of our ham magazines in which the author 
recounted his experiences with reducing the operating voltages in a Drake 2B receiver. To 
make a long story shorter, he reduced the operating voltages in steps to something like 
12VDC from the normal 250 VDC, and found that other than it taking a bit longer for his 
receiver to warm up, and the reduction in audio output power,  nothing else was effected.

He finally raised it back up to about 50 volts, mainly in the interests of adequate audio 
output power, and left it there.

The main effect in the operations which he noted was very noticeable reduction in noise, so 
much so that signals seemed to "pop out" at him when he tuned across them.

In my own experiments, I have determined that the optimum (in my opinion) for operating 
voltages for our ARC-5 receivers is about 170 VDC, although at that voltage, one must 
move the screen voltage feed to the "hot" end of the divider string.

BTW, the HFO in the ARC-5s at the normal 250 VDC input is operating at a voltage of 35 
VDC. It seems to have plenty of injection to the mixer at a voltage of as low as 12 VDC, so I 
really don't think reduction in operating voltage is going to effect your RME in that regard 
either.

In any case, in my opinion, 340 VDC is MUCH too high for a receiver!!! It is not necessary.

Ken W7EKB

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