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

Sat Jan 29 02:15:35 EST 2011

Hello all,
At the yahoo group "ARC-5radio" (a group at www.groups.yahoo.com, previously mentioned) you can see notes I wrote concerning running the ARA and ARC-5 receiving sets on 60v B+ line.

My experience with this is that very few changes are required to operate from 60v, BUT the oscillators in some sets struggle at low plate currents.  Specifically if the plate voltage is measured and compared with the spec in the 30MB military manual THE VOLTAGE IS AT SPEC, but (there is always at "but") this means that the plate current is low (from memory down from perhaps 750uA to much less).

To compensate I bridge the local oscillator plate dropping resistor (which is maybe 150 to 300k in some sets) with a 33k resistor.  That restores the plate current to about 750uA and at the same time increases the plate voltage to a higher than spec figure (maybe 30 or 40 volts).  The spec figure is in the order of 15 volts, according to the manual.

I also bridge the top 7k power resistor in the screen divider (this is the two 7k power resistors in the middle of the chassis - easily seen).  A nasty person may lift the bottom of the potentometer (not a variable pot, just two power resistors in series) from ground.

MAKE A NOTE OF THE MOD AND PUT THE NOTE IN THE VALVE BOX OR TIE THE NOTE TO THE CHASSIS WITH STRING.

My experience is that the sets work on 60V, but the gain is reduced in the mixer and the BFO without the mod described.  If I had known this I would have built a 90 or 120V PSU; I prefer to leave the sets un-modified.  

Hope this info helps all.

Les

PS Dennis, I really appreciated getting the circuit for your HF converter, and I'll write to you about it in due course.  Before this I used a different cct, (JFET, similar to a cct seen in the ARRL handbook) and got similarly "useful" results feeding 80 meters into the R-23 nav set.  At least as sensitive as a modern Jap all transistor rx.  Very stable, and very selective.  The set stopped drifting after about 30 seconds.   Made me think about building a regen "back end" that tuned the same 190 .. 520 kHz as the R-23.  - Les

> ----- Original Message -----
> From: Dennis Monticelli <dennis.monticelli at gmail.com>
> To: Jess Lewis <kr4oj at bellsouth.net>
> Cc: arc5 at mailman.qth.net
> Subject: Re: [ARC5] Power Supplies for the ARC-5 Rx.
> Date: Fri, 28 Jan 2011 21:13:37 -0800
> 
> 
> Hi Jess,
> 
> I share your affection.
> 
> Why not just use a stack of 9V batteries for B+?  Putting more than about
> 70V on the receiver does not improve performance much and the caps will
> thank you for it.  You can power the filaments off any convenient LV power
> supply.  This is usually the way I power them.
> 
> On Fri, Jan 28, 2011 at 10:56 AM, Jess Lewis <kr4oj at bellsouth.net> wrote:
> 
> > ?Hello,
> > I just joined this list. I have several old ARC-5 Receivers (various freqs)
> > and a couple of the transmitters. Most from E-Bay, in the past year or so. 2
> > of each are "un-hacked" :o)) and I also have a couple of the Dynamotors for
> > the receivers.
> >
> > I have loved the old units, since I first became aware of them, from CQ
> > magazine, back in the 50's. Got my ham license in 1965, and always meant to
> > convert a few & get on the air. But, alas, I found a deal on some used
> > Heathkit stuff, went that way, and never got back to the ARC5s except a
> > Q5'er, using the BC453 & a converter (not really a "Q5er", but a pretty good
> > rx for 40 meters.)
> >
> > I would like to try and put some of the stuff on the air, without hacking
> > up the unit, anymore than I have to, mainly for cosmetic and nostalgia
> > purposes. I know that several , probably most of the caps, will need
> > replacing, and Ken Gordon (W7EKB), sent me some good ideas about opening
> > various potted units, replacing the internal caps, then re-potting.
> >
> > My ACTUAL question (and reason for posting) is about power supplies for the
> > receivers. Recently, I saw on E-Bay, several neat little power supplies,
> > built on the original Dynamotor frames, and would plug into the original
> > Dynamotor socket. Several have sold already, actually for an unbelievable
> > price :^)).
> > I understand that the original power supply units were built and offered
> > for sale, by Fair Radio Sales, in Lima, Ohio.  They, of course, no longer
> > have any. Does anyone know of a possible source for these PS units?  Even a
> > source for the transformer?  I have the dynamotor base and most of the parts
> > to fab one up, if I could only find the transformer.
> > Any help or suggestions are welcome.
> >
> > Thanks for listening.
> > 73,
> > Jess  KR4OJ
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