[ARC5] SCR-274N update

[Mike Hanz]

Mike may be correct about the commutator, but what he *meant* to say about the brushes was to get out some wet/dry sandpaper.  Emery cloth will result in some very nasty failure modes, as it contains conductive particles.  I've purged my abrasive stocks of both emery cloth and steel wool long ago.  With alternatives like wet/dry and 3M Scotch-brite pads, there is no reason to keep that old dangerous stuff around...dangerous for anyone working with electronic equipment, at any rate...

73,
Mike KC4TOS

On Oct 5, 2013, at 8:16 AM, Mike Everette <radiocompass at yahoo.com> wrote:

> If you have access to another dynamotor, give it a try.  You may have a commutator issue.  Have you looked at the dyno output with a scope to see if there's anything strange?  I mention this because the transmitters aboard the USS North Carolina at Wilmington, NC were plagued by rotten CW notes for a long time; they don't operate from dynamotors but do run off motor generators.  The moto-jenny on one finally went down and had to be repaired (NOT cheap) but hopefully that will solve the issue.  There was some sort of glitch riding on the output which resulted in a very diSTINKtive T7 (or worse) note!
> 
> Could also be that the brushes on the dyno are worn and need to be re-seated.  Get out the manual, and some emery cloth.  Real fun job.  Haven't done one in years, since the days of the Motie-Rollie and RCA (Requires Constant Attention) trunk mounted land mobile radios that weighed as much as I did.  The dyno was a real Brontosaurus, half the weight of the radio. Try wrestling one of those ARRRa-See-Aye Carfones out from behind the seat in the cab of a semi truck tractor.  UNGAWAAA!  Putting it back was even more fun.
> 
> 73
> 
> Mike
> W4DSE
> 
> 
> 
> 
> ________________________________
> From: Paddy Ryan <pei7cn at eircom.net>
> To: arc5 at mailman.qth.net 
> Sent: Friday, October 4, 2013 4:24 AM
> Subject: Re: [ARC5] ARC5 Digest, Vol 117, Issue 4
> 
> 
> in all the cases of the drift/chirp how are you keying? are you using the 
> relay or keying the cathode direct..the point about the dyno hum on the rx 
> is very interesting..73 de Pat/EI7CN
> 
> -----Original Message----- 
> From: arc5-request at mailman.qth.net
> Sent: Thursday, October 03, 2013 5:00 PM
> To: arc5 at mailman.qth.net
> Subject: ARC5 Digest, Vol 117, Issue 4
> 
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> Today's Topics:
> 
>    1. Re: SCR-274N Update (Fuqua, Bill L)
>    2. OT:  Security Guards (J. Forster)
>    3. Re: OT:  Security Guards (Fuqua, Bill L)
>    4. Re: OT:  Security Guards (D C _Mac_ Macdonald)
>    5. Re: OT:  Security Guards (Fuqua, Bill L)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Wed, 2 Oct 2013 18:21:04 +0000
> From: "Fuqua, Bill L" <wlfuqu00 at uky.edu>
> To: ARC5 <arc5 at mailman.qth.net>
> Subject: Re: [ARC5] SCR-274N Update
> Message-ID:
> <B7E8B5B4A202074084E2515A7B10A7F32D660B84 at ex10mb01.ad.uky.edu>
> Content-Type: text/plain; charset="Windows-1252"
> 
>   Modified ARC-5 transmitters had been used for very sable VFO's for Central 
> Electronics Exciters
> with no issues. They were operated at much lower voltage and power. I used 
> them for many years but not
> lately. The problem may be more complex than capacitor contacts. The 
> important issue with operating class C is
> that it is maintains an impedance that the modulator can handle for AM 
> operation.
> 
> 73
> Bill wa4lav
> 
> 
> ________________________________________
> From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on behalf 
> of Ian Wilson [ianmwilson73 at gmail.com]
> Sent: Tuesday, October 01, 2013 7:18 PM
> To: ARC5
> Subject: Re: [ARC5] SCR-274N Update
> 
> I had a slightly hacked 7Mc ARC-5 transmitter that had all sorts
> of problems with the oscillator. It would warble, the frequency would
> jump, etc. At one stage I removed and cleaned the main tuning
> capacitor. This made things magically OK for a while. Then the
> problem returned. I still suspect a dirty contact somewhere in
> the tuning capacitor area (or perhaps the padder capacitor). This
> (a high-resistance path in the oscillator) could cause the sort of
> problem you are seeing with low output.
> 
> Have you checked the grid current on the problem TX? If the
> drive from the oscillator is low, the tubes won't be in Class C,
> and the matching network might not stretch to the impedance that
> the plates want to see.
> 
> 73, ian K3IMW
> 
> 
> 
> On Tue, Oct 1, 2013 at 3:44 PM, Mark K3MSB <mark.k3msb at gmail.com> wrote:
> 
>> Hi Gang
>> 
>> Got to have some radio time yesterday and did some experimentation to try
>> and characterize my ARC-5 ?issues? related in the previous email.
>> 
>> To save typing:
>> 
>> 40M TX/RX is BC-459-A / BC-455-B
>> 
>> 80M TX/RX is BC-696-A / BC-454-B
>> 
>> Receiver drift tests were to allow 30 minutes warm-up then measure drift
>> after 30 minutes.
>> 
>> 40M RX:  1.92 KHz / hr.  Dynamotor used.  RX works well.
>> 
>> 80M RX:  This is the receiver with the nasty hum on the audio.   Drift was
>> 0.98 KHz / hr with the dynamotor.   The tone from my ICOM was T7 or T8. 
>> I
>> then removed the dynamotor and used my HP-23 for the B+ (250).  Drift was
>> less than ? KHz / hr, and the ICOM tone was a nice T9.      I tried
>> swapping the dynamotor with the 40M RX last week and the hum on the audio
>> persisted, so the hum looks to be an RX problem related to the
>> dynamotor.  Perhaps
>> L15.   All capacitors, except C5, were replaced (forgot that one?)
>> 
>> 
>> 
>> Transmitter testing:  30 minute warm-up then test after 30 minute
>> intervals.
>> 
>> 80M TX:  almost no drift, nice tone heard on ICOM RX.  TX works well.
>> 
>> Plate: 555V, Screen 308V,  Osc 225V,  Power out: 30W @190 mA Ip
>> 
>> Here?s an on-air recording my friend made:
>> 
>> http://www.k3msb.com/scr274n/k3msb_80m_on_air.wav
>> 
>> 
>> 
>> 40M TX: (The problem child?.)
>> 
>> Plate: 550V, Screen  296V,  Osc 198V,  Power out 20W @ about the same Ip.
>> 
>> Drift:  sometimes none, sometimes about 1 KHz over a 60 second interval.
>> 
>> Tone was rough (T7 or T8) on my ICOM as well as received by my friend:
>> 
>> Here?s an on the air recording:
>> 
>> 
>> 
>> http://www.k3msb.com/scr274n/k3msb_40m_on_air.wav
>> 
>> 
>> 
>> I swapped the Oscillator and PA tubes from my 80M TX and put them into the
>> 40M TX, and the results were slightly better, but only very, very 
>> slightly:
>> 
>> 
>> 
>> http://www.k3msb.com/scr274n/k3msb_40m_new_tubes_on_air.wav
>> 
>> 
>> I then returned the original tubes into the 40M TX.
>> 
>> As a final test, I removed the PA tubes and listened only to the 
>> Oscillator
>> signal on my ICOM?the oscillator was rough!!  So, it looks like a bad
>> component in the BC-459A oscillator circuit.   All caps were replaced in
>> the transmitter.  No resistors were replaced; some were slightly out of
>> spec but not by much.
>> 
>> A final observation ? regardless of the series capacitor I use on 40 or 
>> 80,
>> the TX coupling control is always at max for maximum power, which seems
>> strange.  I?m going through a 4:1 UNUN after the series cap.
>> 
>> 73 Mark K3MSB
>> 
>> 
>> 
>> 
>> 
>> 
>> On Thu, Sep 26, 2013 at 7:54 PM, Bill Cromwell <wrcromwell at gmail.com>
>> wrote:
>> 
>>> On 09/26/2013 01:29 PM, Mark K3MSB wrote:
>>> 
>>>> Both the 40 and 80M transmitters have a slight chirp which doesn?t
>> bother
>>>> me in the least.
>>>> 
>>>> The stability and tone on the 80M transmitter are fine, but the 40M
>>>> transmitter drifts and the tone is about T8, maybe T7.  The drift is
>>>> noticeable as I sometimes have to slightly retune during a 
>>>> transmission.
>>>> 
>>>> The power supply for both transmitters is the same.  It?s a hefty 28V
>>>> power
>>>> transformer with a full wave bridge rectifier and a 38000 uF cap (with
>>>> bleeder) as the filter.  The HV/OSC/Screen supply is completely
>> separate.
>>>> 
>>>> 73 Mark K3MSB
>>>> 
>>>>   Hi Mark,
>>> 
>>> A slight amount of chirp gives a signal some "character". On a busy
>>> contest weekend when the bands are filled wall to wall with sterile,
>>> computer generated code a fist and some "character" stands out better
>> than
>>> any sliver-slicing filter. Large amounts of 'drift' that take a
>> transmitter
>>> out of the distant receiver's passband (and onto a different QSO in
>>> progress) is a problem. Good to get rid of *that*.
>>> 
>>> 73,
>>> 
>>> Bill  KU8H
>>> 
>>> ______________________________**______________________________**__
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> ______________________________________________________________
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> 
> ------------------------------
> 
> Message: 2
> Date: Wed, 2 Oct 2013 17:55:04 -0700 (PDT)
> From: "J. Forster" <jfor at quikus.com>
> To: ArmyRadios at yahoogroups.com
> Cc: ARC5 at mailman.QTH.net, Milsurplus at mailman.QTH.net
> Subject: [ARC5] OT:  Security Guards
> Message-ID:
> <42043.12.226.214.5.1380761704.squirrel at popaccts.quikus.com>
> Content-Type: text/plain;charset=iso-8859-1
> 
> Rand Paul Tweeted out this afternoon that the Obama administration sent 7
> security guards to the WWII Memorial, to keep people out. This included
> Honor Flight Vets.
> 
> That's 4 more guards than President Obama sent to Benghazi to ptotect our
> Ambassador in Libya!
> 
> ----------
> 
> (For that don't know, the WWII Memorial is a set of statues on the
> National Mall completely out in the open plus a walkway to view them.
> 
> Honor Flight is a charity that brings WWII vets to see their Memorial)
> 
> -John
> 
> ==================
> 
> 
> 
> ------------------------------
> 
> Message: 3
> Date: Thu, 3 Oct 2013 01:32:25 +0000
> From: "Fuqua, Bill L" <wlfuqu00 at uky.edu>
> To: "jfor at quikus.com" <jfor at quikus.com>, "ArmyRadios at yahoogroups.com"
> <ArmyRadios at yahoogroups.com>
> Cc: "ARC5 at mailman.QTH.net" <ARC5 at mailman.QTH.net>,
> "Milsurplus at mailman.QTH.net" <Milsurplus at mailman.QTH.net>
> Subject: Re: [ARC5] OT:  Security Guards
> Message-ID:
> <B7E8B5B4A202074084E2515A7B10A7F32D661C58 at ex10mb01.ad.uky.edu>
> Content-Type: text/plain; charset="us-ascii"
> 
>   Lets stay away from politics.
> Also, it seems that the return address is bogus.
> 
> ________________________________________
> From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on behalf 
> of J. Forster [jfor at quikus.com]
> Sent: Wednesday, October 02, 2013 8:55 PM
> To: ArmyRadios at yahoogroups.com
> Cc: ARC5 at mailman.QTH.net; Milsurplus at mailman.QTH.net
> Subject: [ARC5] OT:  Security Guards
> 
> Rand Paul Tweeted out this afternoon that the Obama administration sent 7
> security guards to the WWII Memorial, to keep people out. This included
> Honor Flight Vets.
> 
> That's 4 more guards than President Obama sent to Benghazi to ptotect our
> Ambassador in Libya!
> 
> ----------
> 
> (For that don't know, the WWII Memorial is a set of statues on the
> National Mall completely out in the open plus a walkway to view them.
> 
> Honor Flight is a charity that brings WWII vets to see their Memorial)
> 
> -John
> 
> ==================
> 
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> 
> 
> ------------------------------
> 
> Message: 4
> Date: Wed, 2 Oct 2013 22:21:23 -0500
> From: D C _Mac_ Macdonald <k2gkk at hotmail.com>
> To: "Fuqua, Bill L" <wlfuqu00 at uky.edu>, "jfor at quikus.com"
> <jfor at quikus.com>, "ArmyRadios at yahoogroups.com"
> <armyradios at yahoogroups.com>
> Cc: ARC-5 Mail List <arc5 at mailman.qth.net>, Military Surplus Mail List
> <milsurplus at mailman.qth.net>
> Subject: Re: [ARC5] OT:  Security Guards
> Message-ID: <BLU178-W5012F1495528B7B303FA06F1170 at phx.gbl>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> Our petulant chicken in chief's folks had barricades put up around the 
> memorial !
> 
> And what return address is bogus???
> 
> 
> * * * * * * * * * * *
> * 73 - Mac, K2GKK/5 *
> * (Since 30 Nov 53) *
> * k2gkk at hotmail.com *
> * Oklahoma City, OK *
> * USAF & FAA (Ret.) *
> * * * * * * * * * * *
> 
> 
>> From: wlfuqu00 at uky.edu
>> To: jfor at quikus.com; ArmyRadios at yahoogroups.com
>> Date: Thu, 3 Oct 2013 01:32:25 +0000
>> CC: ARC5 at mailman.QTH.net; Milsurplus at mailman.QTH.net
>> Subject: Re: [ARC5] OT: Security Guards
>> 
>> Lets stay away from politics.
>> Also, it seems that the return address is bogus.
>> 
>> ________________________________________
>> From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on 
>> behalf of J. Forster [jfor at quikus.com]
>> Sent: Wednesday, October 02, 2013 8:55 PM
>> To: ArmyRadios at yahoogroups.com
>> Cc: ARC5 at mailman.QTH.net; Milsurplus at mailman.QTH.net
>> Subject: [ARC5] OT: Security Guards
>> 
>> Rand Paul Tweeted out this afternoon that the Obama administration sent 7
>> security guards to the WWII Memorial, to keep people out. This included
>> Honor Flight Vets.
>> 
>> That's 4 more guards than President Obama sent to Benghazi to ptotect our
>> Ambassador in Libya!
>> 
>> ----------
>> 
>> (For that don't know, the WWII Memorial is a set of statues on the
>> National Mall completely out in the open plus a walkway to view them.
>> 
>> Honor Flight is a charity that brings WWII vets to see their Memorial)
>> 
>> -John
> 
> 
> 
> ------------------------------
> 
> Message: 5
> Date: Thu, 3 Oct 2013 05:23:43 +0000
> From: "Fuqua, Bill L" <wlfuqu00 at uky.edu>
> To: D C _Mac_ Macdonald <k2gkk at hotmail.com>, "jfor at quikus.com"
> <jfor at quikus.com>, "ArmyRadios at yahoogroups.com"
> <armyradios at yahoogroups.com>
> Cc: ARC-5 Mail List <arc5 at mailman.qth.net>, Military Surplus Mail List
> <milsurplus at mailman.qth.net>
> Subject: Re: [ARC5] OT:  Security Guards
> Message-ID:
> <B7E8B5B4A202074084E2515A7B10A7F32D661C97 at ex10mb01.ad.uky.edu>
> Content-Type: text/plain; charset="us-ascii"
> 
> email to return address bounced.
> I suspect that just like the US population about half
> the readers of these list are from either party. Why post
> emails that insults half the readers. Even if it was 1/4 and 3/4
> why?
> 
> 
> 
> ________________________________________
> From: D C _Mac_ Macdonald [k2gkk at hotmail.com]
> Sent: Wednesday, October 02, 2013 11:21 PM
> To: Fuqua, Bill L; jfor at quikus.com; ArmyRadios at yahoogroups.com
> Cc: ARC-5 Mail List; Military Surplus Mail List
> Subject: RE: [ARC5] OT:  Security Guards
> 
> Our petulant chicken in chief's folks had barricades put up around the 
> memorial !
> And what return address is bogus???
> 
> * * * * * * * * * * *
> * 73 - Mac, K2GKK/5 *
> * (Since 30 Nov 53) *
> * k2gkk at hotmail.com<mailto:k2gkk at hotmail.com> *
> * Oklahoma City, OK *
> * USAF & FAA (Ret.) *
> * * * * * * * * * * *
> 
> 
>> From: wlfuqu00 at uky.edu
>> To: jfor at quikus.com; ArmyRadios at yahoogroups.com
>> Date: Thu, 3 Oct 2013 01:32:25 +0000
>> CC: ARC5 at mailman.QTH.net; Milsurplus at mailman.QTH.net
>> Subject: Re: [ARC5] OT: Security Guards
>> 
>> Lets stay away from politics.
>> Also, it seems that the return address is bogus.
>> 
>> ________________________________________
>> From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on 
>> behalf of J. Forster [jfor at quikus.com]
>> Sent: Wednesday, October 02, 2013 8:55 PM
>> To: ArmyRadios at yahoogroups.com
>> Cc: ARC5 at mailman.QTH.net; Milsurplus at mailman.QTH.net
>> Subject: [ARC5] OT: Security Guards
>> 
>> Rand Paul Tweeted out this afternoon that the Obama administration sent 7
>> security guards to the WWII Memorial, to keep people out. This included
>> Honor Flight Vets.
>> 
>> That's 4 more guards than President Obama sent to Benghazi to ptotect our
>> Ambassador in Libya!
>> 
>> ----------
>> 
>> (For that don't know, the WWII Memorial is a set of statues on the
>> National Mall completely out in the open plus a walkway to view them.
>> 
>> Honor Flight is a charity that brings WWII vets to see their Memorial)
>> 
>> -John
> 
> 
> 
> ------------------------------
> 
> _______________________________________________
> ARC5 mailing list
> ARC5 at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/arc5
> 
> 
> End of ARC5 Digest, Vol 117, Issue 4
> ************************************ 
> 
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