[ARC5] Receiver AC Power Supplies

[Jim Falls]

Borrowed from Dave AB5S: light the filaments and provide low B+. Significantly less warm-up drift, they run much cooler overall, and less stress on those PITA, hard to reach bypass caps. I'm a convert. 

Cheers!
Jim K6FWT
CBLA #37

> On Dec 14, 2014, at 19:51, Mike Everette via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> Back to National stuff for a moment (hope I may be forgiven the off topic references) -- it's been said, time and again, that the WW2-and-older HRO receivers actually work best with about 180 volts of B plus, rather than the 240 volts that usually comes from the National power supplies. The sensitivity is improved because the internal noise is reduced; and the stability is enhanced (even though, as-they-come, the HRO is pretty darn good).  I have found this to be very true, and the only thing that might be considered a negative is slightly reduced audio output.  However, I have no problem with that; when the radio is driving an 8-inch speaker (as was supplied by National), it stiff has enough audio to more than fill up my 10x12 shack space.
> I don't doubt that the ARC-5 type receivers work better at a lower voltage.  Probably most tube radios would perform better at lower voltages than "normal."  
> 
> I do know (from experience) that the RME-45 series receivers will DEFINITELY do much better with about 220-240 volts of B plus, instead of the 320 volts or so in the "stock" model.  Much less drift, for one thing. If the radio has its original transformer -- can you believe this, 720 volts, center-tapped! -- all you need to do is change the power supply to a choke-input filter.  The transformer will thank you because it runs much cooler.  
> 
> And, Jeep, the RME receivers have much the same enhancement of sensitivity you find in the Command Set, when raising the front end screen voltage.
> Probably most tube type receivers would benefit from lower B plus.
> 73
> MikeWA4DLF
> 
>      From: DSP3 <jeepp at comcast.net>
> To: Mike Everette <radiocompass at yahoo.com>; "arc5 at mailman.qth.net" <arc5 at mailman.qth.net> 
> Sent: Saturday, December 13, 2014 10:20 AM
> Subject: Re: [ARC5] Receiver AC Power Supplies
> 
> 
> On 12/13/2014 10:09 AM, Mike Everette wrote:
> 
>  This is slightly off topic, but what you mentioned about the National receivers reminds me of something I've observed with my NC-173. 
>  Using a metered Sencore variac/isolation transformer, I have seen a "sweet spot" at about 105 to 107 volts AC input where the receiver sensitivity peaks  noticeably.  Above that voltage, even at 110 volts, it falls off a bit. 
>  I haven't monitored any internal supply voltages to see what may be happening; however, this is readily apparent just from listening to the audio and incoming  signals.. 
>  73 
>  Mike WA4DLF
> 
> 
> 
> Tell you what Mike... I've not seen (but not tried, either) on the National but I have noticed that exact phenomena on ARC-5/274-N receivers at about 160v or so B+.  Curious???
> 
> 
> 
> Jeep - K3HVG
> 
> 
> 
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