[ARC5] 6volt tubes in the receivers

Fri Oct 19 04:14:32 EDT 2012

My six volt one has the filaments in parallel..wait for it..the 12A6 is 
replaced by a 6J5..and there is a 'new' 6F6 and an output transformer fitted 
in the dynamotor space..I am not the guilty party but I guess the hacker 
wanted the best of both worlds,hi!..I have taken out the 6F6 and did a bit 
of re-hacking..73 de Pat/EI7CN

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Sent: Thursday, October 18, 2012 11:54 PM
To: arc5 at mailman.qth.net
Subject: ARC5 Digest, Vol 105, Issue 90

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Today's Topics:

   1. Re: 6V sub for 12A6 - 6C5 (Kenneth G. Gordon)
   2. Re: 6V sub for 12A6 - 6C5 (gordon white)
   3. Re: On Hacking (Kenneth G. Gordon)
   4. Re: Replacing the 12v tubes with 6volt types (WA5CAB at cs.com)

----------------------------------------------------------------------

Message: 1
Date: Thu, 18 Oct 2012 13:21:28 -0700
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
Subject: Re: [ARC5] 6V sub for 12A6 - 6C5
To: ARC-5 Mail List <arc5 at mailman.qth.net>
Message-ID: <508064C8.9933.1B91B159 at kgordon2006.frontier.com>
Content-Type: text/plain; charset=US-ASCII

On 18 Oct 2012 at 11:25, gordon white wrote:

> Yes, probably a 6K6. In one of my receivers the tubes are all 6 volt
> types with a 6C5 in the audio socket, which makes no sense

Actually, yes it does: for both tubes, the plate is pin 3, the grid is pin 
5, the
cathode is pin 8, the filaments are pins 2 and 7, and the internal shield is 
pin
1.

Therefore, a 6C5 COULD have been used in place of a 12A6. What you
would end up with is a triode audio output stage instead of a pentode stage.
Screen connections would have been ignored and would have no effect on
either the receiver or the tube.

I would be very interested to learn how the audio output would change with
that substitution.

Perhaps the original owner only had a 6C5. I think that substitution is very
clever. Obviously, the original owner did some careful checking before he
plugged it in.

Ken W7EKB

------------------------------

Message: 2
Date: Thu, 18 Oct 2012 16:25:50 -0400
From: gordon white <gewhite at crosslink.net>
Subject: Re: [ARC5] 6V sub for 12A6 - 6C5
To: kgordon2006 at frontier.com
Cc: ARC-5 Mail List <arc5 at mailman.qth.net>
Message-ID: <508065CE.9070004 at crosslink.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Actually, the original owner was the A.R.C. morgue. I really do not
think I touched that receiver.

  - Gordon

------------------------------

Message: 3
Date: Thu, 18 Oct 2012 14:21:11 -0700
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
Subject: Re: [ARC5] On Hacking
To: ARC-5 Mail List <arc5 at mailman.qth.net>
Message-ID: <508072C7.18184.1BC85FA3 at kgordon2006.frontier.com>
Content-Type: text/plain; charset=US-ASCII

On 17 Oct 2012 at 23:41, Todd, KA1KAQ wrote:

> Thinking back to the first time I heard a signal coming out of the
> BC-455B I mauled (power & audio only) in '79-80 with the help of one
> of my college profs, I'm still in awe of the amount of performance put
> forth by that little pile of next-to-nothing in a shoebox amount of
> space.

I can still remember the total awe that hit me when I first heard one in
operation, and then was able to use it.

> The clarity of signals and ease of tuning was/is outstanding.
> Pound for pound, and time frame adjusted, it has to be one of the best
> basic receivers of all time. Was discussing this recently I think with
> you, Ken, or someone on here.

Yes. We did. I said at the time what I still insist is true: those were and 
still
are the finest single-band receivers ever built.

As Robert Downs and I were chatting about, the ARC build and design
quality were fully equal to Collins'.

> Can't wait to fire up one of the RAX-1 receivers and see what it
> produces. They' just look cool.

I agree. When I first saw those, I was not particularly impressed. It was 
only
after I found schematics and a write on them that I began to appreciate
them.

vy 73,

Ken W7EKB

------------------------------

Message: 4
Date: Thu, 18 Oct 2012 18:54:01 -0400 (EDT)
From: WA5CAB at cs.com
Subject: Re: [ARC5] Replacing the 12v tubes with 6volt types
To: Arc5 at mailman.qth.net
Message-ID: <53949.76ebd0ab.3db1e289 at cs.com>
Content-Type: text/plain; charset="US-ASCII"

I'm surprised, considering how long this sub-thread has continued, that no
one has mentioned the obvious.  The first criteria for s 6 volt tube to
replace the 12A6 is that it draw the same filament current as a 6SR7, which 
is
what it will be in series with.

6SR7     300 mA
6C5       300 mA
6F6       700 mA
6K6       400 mA
6L6       900 mA
6V6       450mA
6W6      1200 mA

There are several later double-letter octal beam tetrodes and power
pentodes but they all have heater currents of 450 mA or more.

Maybe that's why A.R.C. apparently plugged a 6C5 into a receiver,
presumably to get a quickey 14 volt receiver for some reason.  :-)

Of the available choices, the 6K6 comes closest to working right.  To a
first approximation (ignoring the fact that tube heater resistance is pretty
current sensitive), the series string current would be 343 mA.  There would 
be
7.2 volts across the 6SR7 and 5.4 volts across the 6K6 (with 12.6 VAC/VDC
applied).  Actually, because of the resistance variations with 
delta-current,
it would be a little worse than that.  But I've done it for a few hours
(until I got the 28 volt system working in my International Scout) and it 
works
OK.  If I hadn't been building a 28 volt add-on system, I would have tacked
a resistor across the 12SR7 socket to balance the drop.

With a 6F6, the imbalance is so great that using the rated currents to
calculate heater resistance would be 'way off but using them, you get 8.8 
volts
across the 6SR7 and I would bet in practice, you would get closer to 10
volts.  The 6F6 would certainly run cool enough to pull out while hot with 
your
bare fingers.  :-)

In a message dated 10/18/2012 15:12:47 PM Central Daylight Time,
kgordon2006 at frontier.com writes:
> 12A6 has a 7AC base.
>
> So does the 6V6....and the 6K6 and 6F6 and...
>

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

------------------------------

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