[ARC5] ARC-2 Information
Rich Post
kb8tad at gmail.com
Sun Sep 6 23:23:53 EDT 2020
Hallicrafters used the floating B- design starting with the S-38C. The
S-38, S-38A, and S-38B all had one side of the power line switched to the
chassis, thus a hot chassis either when switched on, or off by way of the
cold tube filaments. All had insulators and a capacitor between the
chassis and the metal cabinet. The ground terminal connection was by way
of a capacitor from the ground screw to chassis and the backing covered the
chassis exposed metal until it was bruised and the stray ground wire
touched it. The S-38B was the first to be UL approved. It used a "cheater
cord" style of interlock requiring the removal of the back to access the
chassis. Its back was a bit more substantial than the earlier ones. The
short-lived SR-75 was based on the S-38B. I have restored both the SR-75
and the S-38B upon which it was based by installing isolation transformers
in the space left after removal of the fat cardboard electrolytic.
The Echophone EC-1 and a couple of relatives, as the forerunners of the
S-38 series, had the same hot-chassis arrangement and the flimsiest of
cardboard backs.
If you decide to restore one of these without the iso tran, at least make
sure the insulators between the chassis and cabinet are intact and replace
the cap between the two with a "Y" cap. Another solution is to replace the
power cord and plug with an ALCI from a hair appliance.
73 de Rich KB8TAD
On Sun, Sep 6, 2020 at 10:47 PM <hwhall at compuserve.com> wrote:
> "What we've got here is... failure to communicate." LOL I think there's
> a misunderstanding re the terminology.
>
> On at least some AA5 sets there was indeed a separate internal ground buss
> or common, separate from the chassis itself. And there was a capacitor that
> went from that buss to the chassis. E.g., the Hallicrafters S-38E and
> others. A paralleled resistor & capacitor conntected buss & chassis. The
> schematic shows two different grounding symbols as a result.
>
> Wayne
> WB4OGM
>
> -----Original Message-----
> From: Tom Lee <tomlee at ee.stanford.edu>
> To: arc5 at mailman.qth.net
> Sent: Sun, Sep 6, 2020 7:15 pm
> Subject: Re: [ARC5] ARC-2 Information
>
> Hue,
>
> Sorry, but you're simply wrong about this. I am speaking from direct
> experience. Only two wires power up the classic AA5. No such thing as a
> distinction between ground and a chassis. You are confusing later safety
> practice with decades of history that preceded three-wire power cords.
>
> See, for example,
> http://www.angelfire.com/electronic/funwithtubes/AA5-1.html.
>
> Or the wikipedia entry on the AA5.
>
> --Tom
>
> --
> Prof. Thomas H. Lee
> Allen Ctr., Rm. 205
> 350 Jane Stanford Way
> Stanford University
> Stanford, CA 94305-4070
> http://www-smirc.stanford.edu
>
> On 9/6/2020 19:06, Hubert Miller wrote:
> > I don't think so. From the 1940s at least, there was a "ground" and a
> chassis, with some capacitor like 0.05 mFd connecting the two.
> > The Regressive Edu-Kit really surprised me. I have the manual and the
> kit, and I don't recall a word of warning that your headphone wire
> > could with a flip of coin, be AC hot. When I first saw the Edu-Kit
> manual, I saw the 3 wire line cord and first thought it was wired for
> safety,
> > but one wire was just a resistance.
> > BTW, around 1985 I wrote an electronics magazine and asked if they
> should still be running Edu-Kits' ads with the testimonials from 1947
> > customers. I also questioned the usefulness of the 1985 Edu-Kit
> suggestion that printed circuits were the up & coming thing.
> > The magazine editor wrote me back ( this was in the Paper Age ) that
> Edu-Kits always paid their bill.
> > I should have kept that letter with my Edu-Kit manual.
> > I should also have kept the letter from Tom Kneitel telling me I didn't
> know enough to criticize and that he owned a Trans-Am and a boat
> > and so there you go.
> > -Hue Miller
> >
> >> I can attest to that! Having worked for several years in a TV/radio
> service shop in the early 1970s, I can verify that AA5s of that era always
> had the chassis hardwired to one side of the AC line. The nominal filament
> voltages added up to 121V for a reason. Classic problem was replacement of
> a frayed cord or bad plug by the consumer, who had a
> > 50-50 chance of tying the chassis to the hot side of the line. Murphy
> guaranteed that I would only see that 50%.
> >
> > The Progressive/Regressive Edukits not only did the same thing, but with
> resistance wire to drop much of the line voltage to drive the filaments.
> > My next door neighbor replaced the cord with a regular piece of zip
> cord. The result was much unhappiness.
> >
> > -- Tom
> >
> > --
> > Prof. Thomas H. Lee
> > Allen Ctr., Rm. 205
> > 350 Jane Stanford Way
> > Stanford University
> > Stanford, CA 94305-4070
> >
> https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww-smirc.stanford.edu%2F&data=02%7C01%7C%7Caee3a473249242a856c308d852d065ac%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637350402290408248&sdata=LgIJyeWWq%2BxrzaQA%2FPUHPfAP8CWohFAfn2plKNksZDI%3D&reserved=0
> >
> > On 9/6/2020 18:38, Scott Robinson wrote:
> >> Actually, quite a few AC-DC radios DID have their chassis wired to
> >> one side of the line Some mid-30s examples are a horror--easily
> >> touched live parts. Late _mid-fifties and on (Zenith, in particular),
> >> did a very good job isolating the chassis in their AM-FM table radios.
> >>
> >> Since most small TVs had metal cases, I bet they are isolated.
> >>
> >> Scott Robinson
> >>
> >> PS-I hate AC-DC radios.
> >>
> >> On 9/6/20 6:08 PM, Hubert Miller wrote:
> >>> Except: Scott, the machines with one side of the AC line connected
> >>> directly to chassis were bottom end, such as the buzzbox welders
> >>> advertised in magazines and kit radios for young people. (
> >>> "Regressive Edu-Kit" was one ) TVs and radios did not have the
> >>> chassis connected DIRECTLY to AC line.
> >>> ONE ham rig did, I think SBE-13. I have one somewhere. Had a safety
> >>> indicator lamp on front panel.
> >>> -Hue Miller
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