[ARC5] Power Supplies for the ARC-5 Rx...and others.

[Bob Macklin]

Consider that a 120VAC isolation transformer with a bridge rectifier and a 
capacitive input filter will give you about 170VDC.

You could use one of these with a 12V or 24V transformer for the filaments.

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"
----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: <Arc5 at mailman.qth.net>
Sent: Saturday, January 29, 2011 9:54 AM
Subject: Re: [ARC5] Power Supplies for the ARC-5 Rx...and others.


> On 29 Jan 2011 at 6:45, Military1944 at aol.com wrote:
>
>> In a message dated 29/01/2011 05:06:28 GMT Standard Time,
>> vk2bcu at operamail.com writes:
>>
>> I'm  dithering between a B+ supply value of 60 and 120 volts.  I don't
>> think  90 to 120 volts stresses the set much, and it may work a little
>> better at the  higher voltage.
>
> In my experimenting on this matter, I determined that the receivers worked
> best at a voltage of between 160 and 180 VDC.
>
> IMHO, 250 VDC is really too much, and not necessary even when the
> receivers were new.
>
> Now.... I have mentioned this next in the past, but will reiterate it here 
> for
> your benefit.
>
> There was an article in one of the ham magazines some time ago, possibly
> as much as 30 years ago, in which the author, using a Drake 2B lowered the
> plate voltage in steps, while carefully documenting the results of careful 
> tests
> during the procedure.
>
> He found that the Drake 2B continued to operate just fine down to as low 
> as
> 12 VDC B+, although the audio output power was severely reduced at that
> point.
>
> The most important of his findings was that internally generated noise was
> drastically reduced as he reduced the HV, and a small reduction in HV
> resulted in a much greater reduction in noise. In other words, the effect 
> was
> not linear.
>
> I distinctly remember some of his words: he said that at one point in his
> reduction series, he turned the receiver on, let it warm up and thought it 
> was
> dead, as he could hear nothing at all on the 20 meter band....until he 
> tuned
> in a signal, when that suddenly "popped up" to full clarity. The receiver 
> noise
> was simply at such a low level he THOUGHT it was dead. It most certainly
> was not.
>
> He finally raised the B+ back up to about 50 VDC and that is where he left 
> it.
>
> His contention (and others' I have read) was that receiver B+ was simply 
> too
> high, having been chosen to be 250 VDC mainly because "that is the way we
> always did it." and it had become an industry standard for no really good
> technical reason, except perhaps for audio amp stage power output, and 
> that
> with modern tubes and components, much lower voltages would be better.
>
> Both National and Collins used voltages around 180 VDC in some of their
> later receivers.
>
> Ken Gordon W7EKB
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