[ARC5] ARC5 Digest, Vol 154, Issue 9

[Paddy Ryan]

thank you..it is always very useful to hear of these unusual faults and the 
journey to find them..I have a BC-455 here that was completely (I mean 
completely) re-wired by a previous owner with grey plastic covered light 
duty solid wire..the only wire in the set is all this grey stuff underneath 
the chassis and it was also re-capped too(completely)..to my utter dismay it 
was not working and I immediately suspected a mistake in the re-wiring( rash 
judgement)..I spent a week re-checking that wiring but could not find a 
single error..as the set was not oscillating as a last resort I took off the 
cover of the variable cap and starting checking the connections to the 
coils..all the original wiring was intact and had not been disturbed..on 
checking continuity from the solid wire of the variable to the osc coil 
terminal I could not get continuity..although the wire was right at the 
terminal I noticed that the terminal had never been soldered..it was 
completely clean and the wire was a hair's breath away from it..a dab of the 
iron and away we went..I also had a similar fault with a non functioning BFO 
in another receiver ( inside the bfo can a connection to one of the trimmers 
was left unsoldered and un-connected)..just keep looking I suppose..73 de 
Pat/EI7CN

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Sent: Friday, November 18, 2016 9:38 PM
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Subject: ARC5 Digest, Vol 154, Issue 9

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Today's Topics:

   1. BC-454-B, tough problem (Ian Wilson)
   2. Re: BC-454-B, tough problem (Kenneth G. Gordon)
   3. Re: BC-454-B, tough problem - oops... (Kenneth G. Gordon)
   4. Re: "Quiet" ARC-5 Keying (Ian Wilson)
   5. Re: "Quiet" ARC-5 Keying (Kenneth G. Gordon)


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Message: 1
Date: Fri, 18 Nov 2016 13:04:10 -0800
From: Ian Wilson <ianmwilson73 at gmail.com>
To: ARC5 <arc5 at mailman.qth.net>
Subject: [ARC5] BC-454-B, tough problem
Message-ID:
<CAEz8jcQOeEBoO8EGUdA1atj_VBnDWGb-vtjUoiGPaQ+JOaiYDA at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

I've been resurrecting a BC-454; everything worked FB except for the local
oscillator stage (triode part of the 12K8 triode-hexode).

The triode plate voltage appeared to be absent. This part of the circuitry
is a little obscure, since there is a 200k plate series resistor that is
contained
in the RF oscillator subunit of the plug-in coil thingy. Also, the plate
supply
for this stage is routed through the capacitor cover.

OK, I now know more about the LO stage than I ever wanted to. Removing
the capacitor cover (which involves approximately every screw plus removal
of 2 of the IFTs and most of the tubes) and disconnecting the bare wire
going to
the variable cap showed 8 ohms to ground. A strange number. The almost-short
turned out to be one of (there are two!) the air-variable trimmer
capacitors that
are in parallel with the oscillator tuning part of the 3-gang capacitor.

I can't see the moving parts of this trimmer, but turning it a few times
must
have broken up the whisker (guessing that's what it was). I left the trimmer
off its previous position. All working now.

All the coil cans contain more than just inductors. Worth studying during
these
dark hours while awaiting Armageddon, perhaps.

73, ian K3IMW
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Message: 2
Date: Fri, 18 Nov 2016 13:14:00 -0800
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: Ian Wilson <ianmwilson73 at gmail.com>
Cc: ARC5 at mailman.qth.net
Subject: Re: [ARC5] BC-454-B, tough problem
Message-ID: <582F6F18.9951.140ED0B at kgordon2006.frontier.com>
Content-Type: text/plain; charset=US-ASCII

On 18 Nov 2016 at 13:04, Ian Wilson wrote:

> I've been resurrecting a BC-454; everything worked FB except for the local
> oscillator stage (triode part of the 12K8 triode-hexode).

Hmmm....innersting...

> The triode plate voltage appeared to be absent.

Well, as I remember it, it is pretty low to begin with: something like 35 
VDC at most.

> This part of the circuitry
> is a little obscure, since there is a 200k plate series resistor that is 
> contained
> in the RF oscillator subunit of the plug-in coil thingy. Also, the plate 
> supply
> for this stage is routed through the capacitor cover.
>
> OK, I now know more about the LO stage than I ever wanted to. Removing
> the capacitor cover (which involves approximately every screw plus removal
> of 2 of the IFTs and most of the tubes)

Yup. Good thing everything is held in by 3-48 screws, eh?

> and disconnecting the bare wire going to
> the variable cap showed 8 ohms to ground. A strange number. The 
> almost-short
> turned out to be one of (there are two!) the air-variable trimmer 
> capacitors that
> are in parallel with the oscillator tuning part of the 3-gang capacitor.

Yes. One you adjust when aligning the rig, the other hidden near the front 
is to be set and
forgotten.

> I can't see the moving parts of this trimmer, but turning it a few times 
> must
> have broken up the whisker (guessing that's what it was). I left the 
> trimmer
> off its previous position. All working now.

Well, you may wish to set it where the manual says to. Otherwise alignment 
may suffer a bit.

> All the coil cans contain more than just inductors. Worth studying during 
> these
> dark hours while awaiting Armageddon, perhaps.

Indeed.

In one of my hacked up R-25s (1.5 to 3.0 MHz), I found a no-solder joint in 
the oscillator
coil-can. It had been painted with that red lacquer that indicated that it 
had been checked
when the receiver was built, but whoever it was missed the no-solder joint. 
Soldering that
brought the receiver back to life.

I find it interesting to find 70+ year old construction errors... :-)

Also, in at least one case, I found that the slugs in the coil-cans were all 
loose after 70+
years. I flooded each can with melted bees-wax and that cured several 
instability issues.

Ken W7EKB

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Message: 3
Date: Fri, 18 Nov 2016 13:17:31 -0800
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: ARC5 at mailman.qth.net
Subject: Re: [ARC5] BC-454-B, tough problem - oops...
Message-ID: <582F6FEB.9963.1442562 at kgordon2006.frontier.com>
Content-Type: text/plain; charset=US-ASCII

On 18 Nov 2016 at 13:14, Kenneth G. Gordon wrote:

> Also, in at least one case, I found that the slugs in the coil-cans were 
> all loose after 70+
> years. I flooded each can with melted bees-wax and that cured several 
> instability issues.

Geeze no! Not the can: I flooded the coil FORM with beeswax. There was 
already some
there, but it had hardened and was no longer effective.

Ken W7EKB

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Message: 4
Date: Fri, 18 Nov 2016 13:31:24 -0800
From: Ian Wilson <ianmwilson73 at gmail.com>
To: David Stinson <arc5 at ix.netcom.com>
Cc: ARC-5 <arc5 at mailman.qth.net>
Subject: Re: [ARC5] "Quiet" ARC-5 Keying
Message-ID:
<CAEz8jcQ1WSMQ0P5bFk7Ci1QcB6WskDq5b+j2HjfUJOedDtAjfg at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

[Replying to a very old thread here].

I finally seem to have some time to get some of my ARC-5 gear on the air
again.
One thing I would like to do is to try out keying
  a) using the Selector relay in the TX (with contacts adjusted so PA turns
on first),
  b) using a HV MOSFET in the B+ supply (external to the TX).

I have a few FQP2N80 that look good to me (800V, 85W). Does anyone have an
actual circuit (different devices, no doubt) that I could start from?

73, ian K3IMW


On Fri, Aug 26, 2011 at 2:06 PM, David Stinson <arc5 at ix.netcom.com> wrote:

> If you really want to keep the keying "quiet," key all the B+
> (meaning just the 550 volt line into the "correct" voltage divider
>  per the manual and a past post)   as Mike suggests,
> but do it with a Hi-Voltage MOSFET.
> Here's a new one that can handle 900 volts at 20 amps!
> http://search.digikey.com/scripts/DkSearch/dksus.dll?
> Detail&name=497-8772-5-ND
> FETs for switching high voltages and currents are common now.
> I invite The Smart People here, who have helped me many times,
> to tell you all about it.
>
> 73 Dave S.
>
> P.S. Ian; was I supposed to send you some information?
> Please forgive as I tend to forget things lately... very
> troublesome...
>
> ______________________________________________________________
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Message: 5
Date: Fri, 18 Nov 2016 13:38:20 -0800
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: Ian Wilson <ianmwilson73 at gmail.com>
Cc: ARC5 at mailman.qth.net
Subject: Re: [ARC5] "Quiet" ARC-5 Keying
Message-ID: <582F74CC.23296.15733CD at kgordon2006.frontier.com>
Content-Type: text/plain; charset=ISO-8859-1

On 18 Nov 2016 at 13:31, Ian Wilson wrote:

> [Replying to a very old thread here].
>
> I finally seem to have some time to get some of my ARC-5 gear on the air 
> again.
> One thing I would like to do is to try out keying
> ? a) using the Selector relay in the TX (with contacts adjusted so PA 
> turns on first),
> ? b) using a HV MOSFET in the B+ supply (external to the TX).
>
> I have a few FQP2N80 that look good to me (800V, 85W). Does anyone have an
> actual circuit (different devices, no doubt) that I could start from?

Well, keep us informed of what you come up with.

Ken W7EKB

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