[ARC5] 10-Meter 274N RX - The 20-27 RAT-1

[Geoff]

----- Original Message ----- 
From: "Mike Everette" <radiocompass at yahoo.com>
To: "arc5 mail list" <arc5 at mailman.qth.net>; "john rose" 
<brokenthumb at live.com>
Sent: Saturday, February 09, 2013 10:08 AM
Subject: Re: [ARC5] 10-Meter 274N RX - The 20-27 RAT-1


The 717A, I am pretty sure, is "an octal based 6AK5."

** As I keep repeating here and elsewhere.


It's a good tube; but the 6AB7 might actually be a better choice.

** Higher Gm but might not be adequate on 10M, it was pretty much topped out 
in a SX-28 followed by a 6SK7. I went with a pair of 6SG7's and saw a slight 
improvement. The SX-28A used a pair of 6AB7's mod per a Hallicrafters 
bulletin.


Without looking up tube characteristics, I am also pretty sure that the 6AK5 
is a sharp-cutoff-type which doesn't respond to AVC action as well as a 
remote-cutoff would.  The 717A is, I think, also sharp-cutoff.  The 6AB7 is 
remote-cutoff.

** Yep


Now, I'm not saying that progress is unnecessary; far from it.... but note:

For those who are of the opinion that older, longer-lead tubes are inferior, 
consider receivers like the National HRO (original) with its 6C6 and 6D6 
tubes, which remains one of the quietest and most sensitive of tube 
receivers.

** Mine has the 2.5V versions, 58 and 57's and is run on 180V where the 
noise is less and sensitivity on 10M better but its not up to later tubed 
HRO's on instruments.

 Perhaps an even better example is the RCA AR-88, which is so hot even with 
old octal types that it can, and will, hear the world WELL with only a few 
feet of antenna.... even on ten meters.

** Hearing is one thing, being able to state an actual SNR is something 
else.

Been there, done that, and have shirts with both National and RCA logos to 
prove it.  And my receivers are un-hacked; they run full-stock.

** Id say the NC-183 will at least equal the AR-88 and if you change the 
mixer to a 6SB7Y it is a big improvement, no hacks required. Ive even copied 
several 6M AM stations during openings.

** The USN RCA built RBB and RBC are also very superb performers. I was so 
impressed with them in the Navy that I added them to the collection here


Many receivers died horrible deaths back in the day on account of 
ill-advised "hacking" on the part of hams who followed the advice of 
ill-conceived articles in magazines like SeekU.... ripping out not only the 
first RF stage, but entire front ends in a quest for that extra 
tenth-of-a-microvolt, often resulting in a howling, squalling tangle of 
untameable feedback that caused the whole project to be shoved off the bench 
and kicked under the table -- or chucked into the dempsty-dumpsty.

** Mostly bottom feeder commercial sets or underwhelming military built for 
specific tasks...not higher end ham communications. The better mid to late 
30's ham sets would blow the BC-312/348 away.

Carl


73

Mike
W4DSE


--- On Sat, 2/9/13, john rose <brokenthumb at live.com> wrote:

> From: john rose <brokenthumb at live.com>
> Subject: Re: [ARC5] 10-Meter 274N RX - The 20-27 RAT-1
> To: "arc5 mail list" <arc5 at mailman.qth.net>
> Date: Saturday, February 9, 2013, 2:28 AM
>
> Fair Radio. Part# 717A-UN $15.00 each
>
> ----------------------------------------
> > From: kgordon2006 at frontier.com
> > To: arc5 at mailman.qth.net
> > Date: Fri, 8 Feb 2013 21:08:38 -0800
> > Subject: Re: [ARC5] 10-Meter 274N RX - The 20-27 RAT-1
> >
> > On 8 Feb 2013 at 21:42, Geoff wrote:
> >
> > > For G&G try a 6AB7 and 6AC7 if you can work
> out a quick way to solve
> > > the filament issue and compare to the mushroom.
> > >
> > > Carl
> >
> > Actually, the 'shroom' is a pretty good tube....ifn you
> can find one for a
> > reasonable sum now.
> >
> > I have looked for 717As on eBay and have had
> difficulty.
> >
> > Ken W7EKB
> >
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