[ARC5] An "Extra Class" Question:

arc5 at ix.netcom.com arc5 at ix.netcom.com
Thu Feb 7 14:18:00 EST 2013 

The output tranformer secondary of a plate modulator delivers 300 V RMS at 100% modulation.  What device at what specs can be connected across this secondary to prevent modulation excursions beyond the specified level?

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------Original Message------
From: Geoff <geoffrey at jeremy.mv.com>
To: "Paddy Ryan" <pei7cn at eircom.net>,<arc5 at mailman.qth.net>,"Geoff" <geoffrey at jeremy.mv.com>
Date: Thursday, February 7, 2013 1:49:51 PM GMT-5
Subject: Re: [ARC5] ARC5 Digest, Vol 109, Issue 55More on the BC1206

Im surprise a WW2 radio enthusiast doesnt know how to remove a Loktal!
There is a litle indexing nub on the base and if you rock the tube in that 
direction while pulling up the "lok" will release.

Carl


----- Original Message ----- 
From: "Paddy Ryan" <pei7cn at eircom.net>
To: <arc5 at mailman.qth.net>
Sent: Thursday, February 07, 2013 12:57 PM
Subject: Re: [ARC5] ARC5 Digest, Vol 109, Issue 55More on the BC1206


> 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
>
> -----Original Message----- 
> From: arc5-request at mailman.qth.net
> Sent: Thursday, February 07, 2013 4:06 PM
> To: arc5 at mailman.qth.net
> 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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