[ARC5] Fw: Reducing BC-459A chirp: 12A6 replacement for 1626

John Watkins jpwatkins9 at yahoo.com
Fri Jul 23 22:36:21 EDT 2010 

Henery,

If you have any left, I could use a 12A6 for my Arc-5 project.  Let me know the cost and do you take Paypal?

Should go to:

John Watkins
POB 1080
Seguin, Texas
78156-1080

Thanks,

John  WD5ENU/A45XV

--- On Fri, 7/23/10, Henry Mei'l's <meils at get2net.dk> wrote:

> From: Henry Mei'l's <meils at get2net.dk>
> Subject: [ARC5] Fw:  Reducing BC-459A chirp: 12A6 replacement for 1626
> To: arc5 at mailman.qth.net
> Date: Friday, July 23, 2010, 9:23 PM
> Some corrections:
> 
> 1. 'non-resistive load' - should read 'non-reactive load'
> 2. It seems that I have 40 (not 25) 12A6's, so I can send a
> few, free of 
> charge.
>     ( I'm doing an inventory-list  of my
> compenents and gear.)
> (3. My TVI-free ARC-5's were run at about 25 to 40 Watts,
> input.)
> .
> Henry, Cph.
> 
> 
> ----- Original Message ----- 
> From: "Henry Mei'l's" <meils at get2net.dk>
> To: "Discussion of AN/ARC-5 military radio equipment." 
> <arc5 at mailman.qth.net>
> Sent: Thursday, July 22, 2010 8:45 PM
> Subject: Re: [ARC5] Reducing BC-459A chirp: 12A6
> replacement for 1626
> 
> 
> >I didn't mention it, but the novice who wrote the blurb
> got the idea from a 
> >W7KOG.  Also, wasn't a novice supposed to be
> running xtal control then?
> >
> > Actually, I had situations where my TCS had RF in all
> kinds of strange 
> > places, such as the plates of the modulator tubes (in
> CW mode). I don't 
> > remember precisely, but I think I was loading into a
> non-resistive dummy 
> > load with short leads, getting a good plate dip and
> appropriate RF current 
> > in the ant. ammeter - RF was indicated by a neon bulb
> - this was back 
> > around 1961. - Dont remember if this was before or
> after my pi-net output 
> > mod.
> >
> > We didn't have TVI problems with my 80 & 40 meter
> ARC-5's back in the 
> > 50's - even when I was loading into the supporting
> metal headset of my 6' 
> > x 6' metal venetian blinds (!)- It worked for NY area
> QSO's and more). We 
> > were using a indoor TV ant. no more than  10-15'
> from my rig and antenna..
> >
> > Thanks Bill, I'm looking forward to receiving the
> tubes --BTW I've got 
> > about twenty five 12A6's some NOS, so if any one needs
> some, let me know.
> >
> > Henry, Cph.
> >
> >: "Mike Hanz" <aaf-radio-1 at aafradio.org>
> >> To: "Discussion of AN/ARC-5 military radio
> equipment."
> >> <arc5 at mailman.qth.net>
> >> Sent: Thursday, July 22, 2010 10:39 AM
> >> Subject: Re: [ARC5] Reducing BC-459A chirp: 12A6
> replacement for 1626
> >>
> >>
> >>> Antenna matching was certainly one of the
> major factors for TVI.  Also
> >>> remember that hams never did appreciate a two
> tube 807-ish transmitter
> >>> that only put out 15 watts RF.
> :-P   They pushed those poor little sets
> >>> to extremes with far higher voltages and
> currents than they were ever
> >>> designed to take, either from a power
> standpoint or a heat dissipation
> >>> perspective.  Then they wondered how come
> why for they put out so much
> >>> TVI and the tubes never lasted very
> long.  Of course, at 50 cents a
> >>> tube, who cared at the time?  I have a
> couple here that were modified
> >>> with screen wire over all the louver slots and
> other unmentionable
> >>> indignities, all because the modifier couldn't
> keep the tubes from going
> >>> into all sorts of nonlinear perturbations at
> the power levels he was
> >>> demanding.  But, so what, they would
> say...a NIB T-15/ARC-5 is only
> >>> $5.95, and after I hack it up for 160 and use
> it for a while, I can just
> >>> toss it into the parts bin.  Lots more
> where that came from... :'(
> >>>
> >>>  - Mike
> >>>
> >>> On 7/22/2010 1:15 PM, J. Forster wrote:
> >>>> On the TVI thing, IMO it was more a lack
> of understanding of the set
> >>>> design than anything.
> >>>>
> >>>> Most vehicular sets (plane and ground
> vehicle) were designed to work 
> >>>> with
> >>>> electrically short (capacitive) antennas,
> hence the roll-a-ductor or
> >>>> variometer. When run into a long wire or
> beam or 50 Ohm system, the
> >>>> output
> >>>> was not resonated. Hence the TVI got out.
> >>>>
> >>>> -John
> >>>>
> >>>> =============
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>> Hi Henry,
> >>>>>
> >>>>> I cannot believe that filament voltage
> rises due to RF pickup other 
> >>>>> than
> >>>>> the
> >>>>> meter used getting fooled due to the
> high RF flying around.  Now 
> >>>>> having
> >>>>> said
> >>>>> that, byapssing of all filament lines
> with additional caps was
> >>>>> commonplace
> >>>>> to reduce TVI.  Hams did this at
> the same time they rewired the 
> >>>>> filament
> >>>>> circuitry for 12V.  I found that
> my T-22 (after a minimal reversible 
> >>>>> mod
> >>>>> to
> >>>>> the output tank) did not generate
> excessive harmonics at the output 
> >>>>> and
> >>>>> I discovered that the cabinet offered
> sufficient shielding also.  This
> >>>>> is
> >>>>> in
> >>>>> contrast to all the articles written
> in the past about how to deal 
> >>>>> with
> >>>>> TVI
> >>>>> in ARC-5's by adding all kinds of
> shielding and tank conversion to PI,
> >>>>> etc.
> >>>>> The major contributor to the TVI
> problem turned out to be leakage of
> >>>>> harmonic energy via the key and power
> lines.  So I filtered all those
> >>>>> lines,
> >>>>> did a final RF sniffer test and all
> was OK.
> >>>>>
> >>>>> Regarding chirp reduction, I didn't
> understand exactly what WN7RKY was
> >>>>> talking about from the brief excerpts
> you provided.  Which tubes were
> >>>>> involved?  Sounds like a novice
> ham did a little experimenting and 
> >>>>> found
> >>>>> a
> >>>>> way in his radio to reduce the chirp
> by playing with the screen feed.
> >>>>> My
> >>>>> own tests and experiments led me to
> conclude there are basically two
> >>>>> approaches to addressing the
> chirp.   Either you regulate all supplies
> >>>>> (starting with the PA screens) or you
> delay keying the PA until after
> >>>>> the
> >>>>> OSC settles.  The latter can be
> accomplished either by keying both and
> >>>>> then
> >>>>> using a cap to delay the PA keying
> relay or you can just run the osc
> >>>>> continuously during transmit
> periods.  I actually do all the above :-)
> >>>>>
> >>>>> BTW, your tube shipment is all boxed
> up securely and now I need to get
> >>>>> some
> >>>>> custom declaration paperwork from the
> post office.
> >>>>>
> >>>>> Dennis AE6C
> >>>>> On Thu, Jul 22, 2010 at 5:02 AM, Henry
> Mei'l's<meils at get2net.dk>
> 
> >>>>> wrote:
> >>>>>
> >>>>>
> >>>>>> Found this in on page 64 of
> Hints&  Kinks, Vol. 5 (1955)(WN7RKY).
> >>>>>> Screen
> >>>>>> grid voltage derives (from osc.
> anode voltage?) via a 20k series
> >>>>>> resistor,
> >>>>>> bypassed witrh a 0.001uF cap. This
> is supposed to reduce chirp.
> >>>>>>
> >>>>>> (This mod is almost invisible mod
> and shouldn't cause too much
> >>>>>> consternation among the purists
> among us -- and it's easy to retro 
> >>>>>> ;0)
> >>>>>>
> >>>>>> Any one tried the this tube switch
> ?
> >>>>>>
> >>>>>> (BTW: On page 40, there is also
> mention of RF causing 1625 filament
> >>>>>> voltages to rise to 18-22 volts,
> cured by grounding to a copper strip
> >>>>>> running across the chassis and
> feeding filament voltage via RF-lossy
> >>>>>> microphone cable with bypass caps
> at both ends. This is probably old
> >>>>>> hat;
> >>>>>> just thought I'd mention it,
> anyway.)
> >>>>>>
> >>>>>> 73
> >>>>>>
> >>>>>> Henry OZ1UF, Cph.
> >>>>>>
> ______________________________________________________________
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