[Boatanchors] Lowering Receiver B+, Again.

[Reflectors]

How about a zener diode in series with the B+?

Darrell


> On Dec 22, 2016, at 8:16 AM, David Stinson <arc5 at ix.netcom.com> wrote:
> 
> We've probably covered this particular issue in discussions about lowering B+ in receivers to help preserve them, but I can't find it in my archives
> and don't remember, so I beg your patience with my aged and leaky head.
> 
> I've recently restored a nice RME-45.  Here is a photo of it next to the WWII "Liberty Ship" MacKay:
> https://goo.gl/photos/zwz8CeYmGb9EVR1k8
> 
> As originally designed, the output of the full-wave
> B+ rectifier (type 80 tube) at the capacitor-input
> filter is a needless 340V and better than 320V gets distributed.  I've already had an insulaton failure at an RCA "accessory" jack which shorted B+ to ground:
> https://goo.gl/photos/So8HJtFZKEeY7mQ29
> (I will be Q-doping the old, oxidizing wire insulation in the future.)
> 
> There are nearly irreplaceable band switches which
> could suffer the same fate.   So lowering the B+
> to this set is a priority.  While trouble-shooting,
> I determined that the radio would play
> acceptably on AM with as little as 90V for B+.
> I did not test for BFO operation or higher-band LO
> operation at that level- need to do more testing.
> I don't "chase DX" with boatanchors and hold  "preservation over performance," so reasonable
> reductions in performance are acceptable to me.
> 
> I know several non-destructive techniques to reduce the B+.
> A "bucking" transformer will not do the job as one which took the B+ down enough would also take the filaments below an acceptable voltage. As a temporary measure, I removed one leg of the
> HV transformer winding from a plate of the 80
> rectifier, converting it into a half-wave rectifier.
> This reduced the B+ at the filter input to 260V,
> giving some temporary "breathing room."
> Performance did not suffer, nor is there any
> notable increase in AC hum in the audio.
> 
> Here is my question:
> What, if any, are the pitfalls of converting the
> full-wave rectifier into a half-wave rectifier?
> Overall current draw is reduced in proportion
> to the voltage reduction.  No evident increase
> in transformer heat dissipation.  What are the
> possible long-term issues with this?
>