[ARC5] ARC5 Digest, Vol 109, Issue 55More on the BC1206

Thu Feb 7 12:57:47 EST 2013

Interesting..I have a few of these..mostly with the 28D7..some of them are 
'microphonic'..I hate those loctals anyway..how are you supposed to take 
them out..a screwdriver between the bottom of the tube and the socket can 
damage or even break the tube ..some of them are not microphonic and work 
perfectly..I have re-capped them all (much easier than the ARC5s) and found 
no bad resistors but the cloth wiring is in terrible condition..I even have 
one unused one in its own box (serial no matching) but it is till fairly 
dirty and the wiring is no better than the 'used' ones ..maybe they were 
never used either and just post war surplus kept in poor condition..I notice 
that one or two of the loctals make contact badly and need a little tip to 
correct..I think also that when they heat up there is some expansion and 
this may cause bad contact..their construction is poor compared to the 
ARC5s..the 512 one I have I cannot get working..to be fair they work way 
down from 28v and the single supply is very handy..I am very tempted to take 
out those loctals and replace them with octals and the ARC5 tube layout or 
similar..it would require a bit of planning before execution but would be an 
interesting exercise..infact now that I think of it you could try it one by 
one and thinking even further make up an octal to loctal adaptor before 
touching anything on the chassis,hi!..I must check out the 28D7 mounting as 
mentioned..another idea I have is to add a bfo and use an outboard converter 
to put it on other bands..that 200 khz range is very tempting and the 
bandspread might be ok..the sensitivity is pretty good..73 de Pat/EI7CN

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Subject: ARC5 Digest, Vol 109, Issue 55

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Today's Topics:

   1. Re: 10 meter BC-454 (john rose)
   2. More on the BC-1206 (Robert  Eleazer)
   3. More on the BC-1206 (Jack Antonio)

----------------------------------------------------------------------

Message: 1
Date: Thu, 7 Feb 2013 00:28:31 -0800
From: john rose <brokenthumb at live.com>
To: arc5 mail list <arc5 at mailman.qth.net>
Subject: Re: [ARC5] 10 meter BC-454
Message-ID: <BAY167-W105B0C22B22CA5A2CCE1FCFDA060 at phx.gbl>
Content-Type: text/plain; charset="iso-8859-1"

CQ magazine January 1967 has an article by Gordon White "Command Set 
Receivers for All Frequencies- The Easy Way"

Max capacity of c4 part #4609 is 41 mickymikes.
L1 6 1/8 turns #24 tin
L2 14 turns #34 SSE (silk wound enameled)
L3 6 1/8 turns #24 tin
L4 2 1/2 turns #32e (enameled)
L5 5 18 turns #24 tin
All wound at 17 tpi
----------------------------------------
> From: WA5CAB at cs.com
> Date: Thu, 7 Feb 2013 00:41:20 -0500
> To: Arc5 at mailman.qth.net
> Subject: Re: [ARC5] 10 meter BC-454
>>
> Unfortunately, the RAT and RAV manuals do not give the capacitance range
> for the tuning capacitor main sections or the turns in the coils for the 
> 46109
> (20-27 MC) which would have been a good starting point.
>
> Say again the number of turns in L1, L3 and L5. I take it that you
> confirmed that the slugs were still in all of the coil sets.
>

------------------------------

Message: 2
Date: Thu, 7 Feb 2013 09:45:11 -0500
From: "Robert  Eleazer" <releazer at earthlink.net>
To: <arc5 at mailman.qth.net>
Subject: [ARC5] More on the BC-1206
Message-ID: <3622EB6D838D4DECB6A31166ACE6F464 at DH26DQ31>
Content-Type: text/plain; charset="iso-8859-1"

Continuing with fiddlin' with my BC-1206's I now I have two that work.  The 
BC-1206-A, the one with the 28D7, worked after some tube wiggling.  Further 
examination revealed a design flaw.

The tube sockets are held in place by pan head machine screws.  This is no 
problem with the octal tubes (ever notice the raised portion between the 
plug and the skirt on metal tubes?  It provides good clearance for the screw 
heads).  But for the 28D7, a Loctal tube, the combination of the lack of 
space between the skirt and the plug and the itty bitty short tube pins, 
leads to the tube not quite fitting in the socket tight enough to make good 
contact.  I am going to replace those screws with special low profile pop 
rivets.

As for the question of why they used two tubes in some cases and used the 
ones they chose - the only installations I know of for the BC-1206 were in 
fighter type aircraft.  The set did not work through an audio source switch 
but was wired into the same circuit as the SCR-522.  It was possible to hear 
the 522 and 1206 simultaneously.  Pilots even had to be cautioned to not try 
to talk to someone using the 1206.

These were mostly single seat fighter aircraft, so there was only one set of 
headphones to drive.  I don't know if the 1206 got any audio assist from the 
522 audio.  The only multi-seat aircraft that I have found used the 1206 is 
the P-61, and in that case the radio was mounted in what must have been a 
highly awkward position behind the pilot's right shoulder, facing forward. 
Even in the P-61 there was no reason for the radar operator or the gunner to 
hear the BC-1206, so I doubt they could.

The BC-1206 was very obviously suitable for the type of use in light 
aircraft that Dave is so enamored of (Dave: will send you pictures of my 
Lear set).  But I do not know if it was ever used for that purpose.

Wayne

------------------------------

Message: 3
Date: Thu, 07 Feb 2013 11:06:10 -0500
From: Jack Antonio <scr287 at att.net>
To: arc5 at mailman.qth.net
Subject: [ARC5] More on the BC-1206
Message-ID: <5113D0F2.9030701 at att.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

The main problem I ran into in getting my BC-1206-C running was
with shorted mica compression trimmers in the IF cans.

Had to remove the IF cans, uncompress the trimmers and gently blow
out the crud.  I have heard of metal migration in mica caps,
(such as the mica capacitors in Hallicrafters IF cans)
so I'm assuming this is what happened here.  Also, the tabs on the
loktal tube sockets were very prone to breaking off with
only a very minimal amount of movement, unsoldering
was a painstaking process.

>On 2/7/2013 9:45 AM, Robert Eleazer wrote:

> These were mostly single seat fighter aircraft, so there
  was only one set of headphones to drive.  I don't know if
  the 1206 got any audio assist from the 522 audio.

One of the AN/ARC-3 manuals (AN 16-30ARC3-3 rev 13 June 1949),
describes the interconnection of either a BC-1206 or MN-26. The
audio is connected to pin 14 ("Audio input(aux)") of the R-77 receiver.

The manual says there is to be a placard to state the VHF set must be
on to use the receiver. It also states that in the event
of failure of the VHF radio, to plug the headset directly into
the receiver.

I have other ARC-3 manuals that do not mention the use of the aux
audio input, and it appears that an external range or compass receiver
is directly connected to the headset line, essentially in parallel with
the VHF radio. (This is all referring to fighter or single place
installations.)

I'd like to see documentation showing the interconnection of a -1206
to an SCR-522, to add to my files.

Jack Antonio WA7DIA/4

------------------------------

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End of ARC5 Digest, Vol 109, Issue 55
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