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

Henry Mei'l's meils at get2net.dk
Fri Jul 23 22:23:46 EDT 2010 

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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