[ARC5] Receiver AC Power Supplies

[Mike Everette via ARC5]

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