[ARC5] ARC5 Digest, Vol 129, Issue 40
Paddy Ryan
pei7cn at eircom.net
Fri Oct 17 08:39:54 EDT 2014
Other bands on the ARC5s:
I must admit that I am not brave enough to touch the coils or remove plates
from the variable but I have tinkered with a few home brew tube converters
on all the ARC5 receivers. My current project is a 40m converter using a
single 12SA7 into a BC-453 with a 6800 xtal and it works a treat.The circuit
is from the 1960 Mobile Handbook. I have also used a 14B8 loctal in the
same circuit. From the 1957 Command Sets CQ book I have built the single
tube one on page 127 using a single 12AU7. It also works a treat and the
second harmonic of the 6800kc xtal can be made to work on 14mhz giving 20m
on the BC-453 but with loads of harmonics from other freqs. The advantage of
using the 453 is the great bandspread range and it is very stable being such
an LF receiver. It can also be made to work on 75m with a 3300khz xtal and
this will also work on 40m on the second harmonic.
The 453 can of course be made to work on any of the SW BCBs with one tube ,
a suitable xtal and some changes to the input circuit.
73 de Pat/EI7CN
-----Original Message-----
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Sent: Thursday, October 16, 2014 9:59 PM
To: arc5 at mailman.qth.net
Subject: ARC5 Digest, Vol 129, Issue 40
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Today's Topics:
1. Miniature Tube Rebuild of ARC-5 BC-453 Receiver
(Phillip Carpenter)
2. Re: Miniature Tube Rebuild of ARC-5 BC-453 Receiver
(Kenneth G. Gordon)
3. Re: ARC-5s at 10 meters (was 400784741321) (Kenneth G. Gordon)
4. Hacked ARC-5s at 10 meters - more (Kenneth G. Gordon)
5. Re: Four pin VT-25/52 to nine pin miniature adapter prototype
(mstangelo at comcast.net)
6. Re: 400784741321 (john rose)
----------------------------------------------------------------------
Message: 1
Date: Thu, 16 Oct 2014 13:48:50 -0400
From: Phillip Carpenter <carpenterpa at tds.net>
To: ARC-5 Mail List <arc5 at mailman.qth.net>, Ken Gordon
<kgordon2006 at frontier.com>
Subject: [ARC5] Miniature Tube Rebuild of ARC-5 BC-453 Receiver
Message-ID: <07BA54ED-52EA-4771-91D6-79355F987319 at tds.net>
Content-Type: text/plain; charset=us-ascii
I picked up a BC-453 that was completely rebuilt by some Ham back in the
1960s. It works but needs tweaking and realignment. The Ham rebuilt the
radio using mostly original parts but used the miniature tube versions of
the octal tubes and added a built in power supply and AF amplifier with
speaker.
The receiver's tube complement includes: 6C4, 6BE6, 3-6BH6s, 12AX7, and
6AQ5. Zener diodes are used in the power supply with a Triad R-10A power
transformer.
The receiver is neatly built. Does anyone know of any articles of a Ham
doing an ARC-5 receiver conversion to miniature tubes?
I'm in the process of tracing out the circuit but it would be helpful if
anyone can shed more light on this repackaged Command Set receiver or knew
the Ham who built it.
Phillip, W4RTX
Sent from my iPhone
------------------------------
Message: 2
Date: Thu, 16 Oct 2014 12:01:04 -0700
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: ARC5 <arc5 at mailman.qth.net>
Subject: Re: [ARC5] Miniature Tube Rebuild of ARC-5 BC-453 Receiver
Message-ID: <544015F0.7278.2CFCA3D3 at kgordon2006.frontier.com>
Content-Type: text/plain; charset=US-ASCII
On 16 Oct 2014 at 13:48, Phillip Carpenter wrote:
> I picked up a BC-453 that was completely rebuilt by some Ham back in the
> 1960s.
> It works but needs tweaking and realignment. The Ham rebuilt the radio
> using
> mostly original parts but used the miniature tube versions of the octal
> tubes
> and added a built in power supply and AF amplifier with speaker.
>
> The receiver's tube complement includes: 6C4, 6BE6, 3-6BH6s, 12AX7, and
> 6AQ5.
> Zener diodes are used in the power supply with a Triad R-10A power
> transformer.
>
> The receiver is neatly built.
Yes, it sure is. Thank you for the photo. I have never seen such a
modification
> Does anyone know of any articles of a Ham doing an
> ARC-5 receiver conversion to miniature tubes?
No, although there is an article, "The ARC-5 Repackaged" in one of the
Surplus destruction manuals in which someone repackaged a BC-453 onto a
3" high rack-panel. But he used the octal tubes.
> I'm in the process of tracing out the circuit but it would be helpful if
> anyone
> can shed more light on this repackaged Command Set receiver or knew the
> Ham who
> built it.
I would have no idea. Perhaps someone else here?
It was very well done, IMHO.
Ken W7EKB
------------------------------
Message: 3
Date: Thu, 16 Oct 2014 12:09:29 -0700
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: ARC5 <arc5 at mailman.qth.net>
Subject: Re: [ARC5] ARC-5s at 10 meters (was 400784741321)
Message-ID: <544017E9.12483.2D0456C6 at kgordon2006.frontier.com>
Content-Type: text/plain; charset=US-ASCII
On 16 Oct 2014 at 7:27, Ian Wilson wrote:
> I would be surprised if the Q of a solenoid in the HF region increases
> with frequency - for Cu, the skin depth between 1MHz and 10MHz
> decreases by a factor of more than 3; so, as a first-order approximation,
> the Q at 28MHz would be close to the Q at 8MHz (the increase in wL
> is more or less cancelled by the increase in r).
Thanks, Ian. However, I suspect that Neil didn't mean that the "Q" increased
with frequency, but simply that the increase in frequency didn't affect the
circuit "Q". Your and his explanation coincide.
>
> In practice I suspect that the Q drops off faster than this because of
> the effects of distributed capacitance (which in effect requires more
> turns to achieve the desired inductance at higher frequencies, hence
> yet more loss).
Yes. I had thought of that too, and had wondered about it.
> The combination of tube gain falling off above about 10MHz together
> with losses in coil switching is presumably responsible for the "deaf
> as a post" performance for some classic boatanchor receivers above
> 20m....
Which brings up an interesting point: after I had finally gotten my hacked
BC-454 to work properly at 10 meters, I was very surprised to find that the
sensitivity at 10 meters was quite adequate. Although I will have to go back
to review my notes, I recall that around a 1 microvolt signal was being
easily
copied there.
There was, of course, considerable noise, most probably from that horrid
12K8 mixer, but the signal was easily discernible, and this was with the
original 12SK7s in it.
Ken W7EKB
------------------------------
Message: 4
Date: Thu, 16 Oct 2014 12:16:00 -0700
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: ARC5 <arc5 at mailman.qth.net>
Subject: [ARC5] Hacked ARC-5s at 10 meters - more
Message-ID: <54401970.27705.2D0A4E3D at kgordon2006.frontier.com>
Content-Type: text/plain; charset=US-ASCII
All this discussion brings up in my mind another question: it has been
suggested that when the 12SK7s are replaced with 12SG7s, the overall
internally generated noise level drops significantly.
I have tried this, and found it to be true for frequencies at 6 MHz and
above,
but that it really didn't do much at MF or even on 80 meters.
As I have repeatedly said, as far as I'm concerned, the primary source of
receiver noise is that damned 12K8 mixer, which Terman's lists as the very
noisiest mixer tube in his list at an ENR of 280,000 ohms.
However, in reviewing the characteristics of the 12SK7 and the 12SG7, there
are noticeable differences.
For one thing, when I use a 12SG7 in the RF amp, in most cases, I can no
longer peak the antenna trimmer: it is swung way over at one limit and
obviously needs to go further.
Does anyone know what minor changes in biasing, let's say, that one would
do to correct this?
Ken W7EKB
Kenneth G. Gordon W7EKB
"Courage is being scared to death but saddling up anyway."--- John Wayne
------------------------------
Message: 5
Date: Thu, 16 Oct 2014 19:25:17 +0000 (UTC)
From: mstangelo at comcast.net
To: Ben Hall <kd5byb at gmail.com>
Cc: ARC-5 <arc5 at mailman.qth.net>
Subject: Re: [ARC5] Four pin VT-25/52 to nine pin miniature adapter
prototype
Message-ID:
<336210093.6971915.1413487517561.JavaMail.root at comcast.net>
Content-Type: text/plain; charset=utf-8
Nice!
Where did you find the 4 pin plug?
Mike N2MS
----- Original Message -----
From: Ben Hall <kd5byb at gmail.com>
To: ARC-5 <arc5 at mailman.qth.net>
Sent: Thu, 16 Oct 2014 00:57:01 -0000 (UTC)
Subject: [ARC5] Four pin VT-25/52 to nine pin miniature adapter prototype
Good evening all,
Assembled a quick prototype this evening:
<http://www.kd5byb.net/BC230/proto1.jpg>
Once the superglue is dry, I'll do a fit check in my BC-230. :)
Thanks much and 73,
ben, kd5byb
------------------------------
Message: 6
Date: Thu, 16 Oct 2014 19:48:46 +0000
From: john rose <brokenthumb at live.com>
To: AKLDGUY . <neilb0627 at gmail.com>
Cc: arc5 <arc5 at mailman.qth.net>
Subject: Re: [ARC5] 400784741321
Message-ID: <BLU404-EAS110E6BE429DDB3DFA3A0ADCDAAB0 at phx.gbl>
Content-Type: text/plain; charset="utf-8"
Your assumption that ARC used the condenser (part #6558) from the 6 to 9.1
(#46106) rig is incorrect. The RAV (#46109) which tunes 20 to 27 mcs uses a
unique condenser (#4609). While Ken was telling us about his struggle with
the 3 to 6 rig, some pix of this unique item were posted (constructed of
?unobtainium?). Ken was working with a BC454 which uses another condenser
(#4601).
BTW the IF of the 20/27 rig is 4200 kcs and Mr. White very nicely outlined
why this is so in the article Command Set Receivers for all Frequencies. Has
anyone here seen any of these for sale lately?
From: AKLDGUY .
Sent: ?Thursday?, ?October? ?16?, ?2014 ?3?:?04? ?AM
To: kgordon2006 at frontier.com, arc5
> I completely rewound all three inductors in the receiver following the
article
> that Gordon White wrote some time ago entitled, "Command Receivers for
> All Frequencies", in which article Gordon described and listed the turns
on
> the coils that ARC came up with for THEIR early HF receivers up to 27 MHz.
>
> I used ARC's 27 MHz data, in fact, as the starting point for my coils.
OK, you rewound the coils on the basis of A.R.C.'s data.
Q is the reactance of either the inductor or capacitance at resonance,
divided
by the series resistance, which in this case is in the coil if we ignore
other very
small losses.
In my suggested modification (no modification of the coil) the Q is more
than
tripled by going from 7-9 to 28-30 MHz because the coil reactance more than
triples. The higher Q at the higher frequency means the selectivity curve
is the
same as at the lower frequency. The curve will be the same number of dB down
at the same frequency offset at both 9 MHz and 30 MHz.
There would therefore seem to be no good reason for taking turns off the
coils.
Why did A.R.C. use reduced turns? Probably because they were faced with a
too large value of tuning gang (no smaller gang available), so they used a
large
amount of **parallel** capacitance across the gang to reduce its tuning
range
and reduced the number of turns to compensate.
> Now I WILL say that your method would most certainly eliminate the
> necessity for removing any plates from the capacitors, but I STILL say,
that
> the inductances would have to be "adjusted" also in order to maintain
circuit
> "Q".
Yes, my method does eliminate the need to remove plates, but the selectivity
self-adjusts by virtue of the rise in Q as described above. A Q of 100 at 9
MHz
(easily possible) becomes a Q of more than 300 at 30 MHz, and the
selectivity
(percentage change) at both bands is the same.
I'd suggest that anyone contemplating modifying a 6-9.1 Mc/s receiver for
10m
try my suggestion first. You have nothing to lose. It's simple and
reversible. Use
very good quality capacitors and let them cool before evaluating.
73 de Neil ZL1ANM
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