[Boatanchors] Lowering Receiver B+, Again.

[Brian Clarke]

Simple solution, Bob, Rob and Dave.

Replace the 80 rectifier tube with a full-wave solid state rectifier (= two
diodes, eg, 1N4006). Leave the tube socket in place and wire the diodes
directly to the socket terminals = easy to reverse. Put the 80 away
somewhere safe; some audiophool will pay big $$$ for it in time. Put 100 Ohm
resistors in series with each diode - to emulate the Voltage drop of the 80
tube under load. Feed the raw rectified output to a choke-input filter. Now,
instead of 340 Vdc with awful regulation, you get 218 Vdc with good
regulation.

With this solution, the heater Voltages will still be within the OEM
specification range; no need to add extra iron. However, if your mains
Voltage is higher than the set was designed for, then go for Bob's bucking
transformer solution. This will take your choke-input-filtered output to
around 200 Vdc.

73 de Brian, VK2GCE

On Friday, 23 December 2016 1:34 PM, Bob Groh said:

Hummmm.  These are a few, somewhat off the cuff comments on the subject:

First, I would use a bucking transformer - probably 12V or so.  This will
have the benefit of dropping the voltages - all of them including the
filaments.

Second I would replace your rectifier with a solid state bridge - but - I
would drive it only off 1/2 of the secondary HV winding. This would reduce
the HV by about 1/2 or there abouts. Got to think a bit more about that -
unfortunately I would really like a solution that takes some current from
each side of the CT.  But somehow got to get a solid state rectifier in
there - saves a bunch of filament power (5V at 2A or so).
At any rate, not a complete solution but I'll give it some more thought.
Certainly ties in with my work with restoring old receivers. More later.

73
bob Groh, WA2CKY

On Thu, Dec 22, 2016 at 10:44 AM, Rob Atkinson <ranchorobbo at gmail.com>
wrote:

> get a small 5 to 10 Hy choke and convert it to choke input supply.
> make sure it can handle the current demand.
>
> 73
>
> Rob
> K5UJ
>
>
> >
> > As originally designed, the output of the full-wave
> > B+ rectifier (type 80 tube) at the capacitor-input
> > filter is a needless 340V