Daily GLOWBUGS
Digest: V1 #105
via AB4EL Web Digests @ SunSITE
Purpose: building and operating vacuum tube-based QRP rigs
Subject: glowbugs V1 #105
glowbugs Saturday, September 6 1997 Volume 01 : Number 105
Date: Thu, 04 Sep 1997 22:07:32 EDT
From: kb9iua@juno.com (Kevin L Anderson)
Subject: Dumb Question # XJ74B -- Grid-Block Keying ??
When I look through articles and plans from past Handbooks,
QSTs, etc., the low-power transmitters all seem to be
cathode keyed. How come? Why doesn't there seem to be
plans for low-power transmitters using grid-block keying?
For some reason I have it in my dumb head that cathode
keying, and the voltages across the key and resulting on-off
nature of the RF generation to be a bad thing compared
to my understanding of grid-block keying. Please correct
my understanding if I'm wrong.
Someday I have plans of extracting out the TX portion of
my HW-16s schematic and see if I couldn't build a grid-block
keyed transmitter.
Thanks. Cheers/73. Kevin, KB9IUA
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Kevin Anderson, KB9IUA, Rock Island IL USA
kb9iua@juno.com or Kevin.L.Anderson@usace.army.mil
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Date: Wed, 03 Sep 1997 00:13:43 -0400
From: Steve Ellington <n4lq@iglou.com>
Subject: Re: Dumb Question # XJ74B -- Grid-Block Keying ??
Grid block keying is of course better but requires more components to
produce the
negative grid voltage. Maybe the Handbook was just trying to keep things
simple.
Back in the old days, no one paid much attention to keying but now days,
just try getting on the air with a mushy signal and you will be flooded
with OO reports! I know cuz I did!
73 Steve N4LQ
Date: Fri, 05 Sep 1997 05:46:06 GMT
From: wrt@eskimo.com (Bill Turner)
Subject: Re: Dumb Question # XJ74B -- Grid-Block Keying ??
On Wed, 03 Sep 1997 00:13:43 -0400, Steve Ellington <n4lq@iglou.com>
wrote:
>Grid block keying is of course better but requires more components to
>produce the
>negative grid voltage. Maybe the Handbook was just trying to keep things
>simple.
>Back in the old days, no one paid much attention to keying but now days,
>just try getting on the air with a mushy signal and you will be flooded
>with OO reports! I know cuz I did!
>73 Steve N4LQ
>
_____________________________________________________________________
Steve is quite right, of course. Another factor back in the '50s when
I got started was that the typical 6146 output stage didn't have a
separate negative voltage source for the control grid bias. The grid
bias was derived from rectified grid current, so there wasn't any DC
source to switch on and off. The natural thing to do was cathode
keying. Some moderately elaborate LCR networks were developed to
shape the keyed waveform, and with a little care the signals weren't
too bad. Ahhhh... the good 'ol days!
73, Bill W7TI
Date: Fri, 5 Sep 1997 08:30:20 -0500 (EST)
From: "Roberta J. Barmore" <rbarmore@indy.net>
Subject: Re: Dumb Question # XJ74B -- Grid-Block Keying ??
Hi, Steve, Kevin, et al!
On Wed, 3 Sep 1997, Steve Ellington wrote:
> Grid block keying is of course better but requires more components to
> produce the negative grid voltage. Maybe the Handbook was just trying
> to keep things simple.
Yes, especially the small "Novice" rigs. The cost of another rectifier
tube, a bit of filtering, and a voltage divider could well have put the
cost of parts for a starter transmitter beyond the budget of a young
ham--and made explaining how it worked all the more complicated, too.
It may be unclear to folks *why* grid-block keying is "better." After
all, no matter how we do it, we're slamming the tube off and on. *It*
doesn't know the difference between being shut down by being biased off or
having the plate supply interrupted!
Ahhh, but the *key* does. Cathode keying (or for the adventurous,
keying in the B+) runs the *entire* plate current (plus screen, in the
case of cathode keying) through the key! Grid-block keying, we quite
often hang a largeish "pull-up" (or "pull-down," since it is a negtive
voltage) resistor to the source of bias, and just short it to ground with
the key; the current involved can be *tiny!*
This buys us some good things: key-clicks will be inherently less
(smaller current, smaller spark!) and filtering/shaping can be done with
simple R/C circuits. So there's your "better." ...If you can tolerate
some backwave, it's possible to not quite cut off the tube; gets ugly
fast, especially if you're running without any doublers (or Xwhatever)
between osc and PA, but makes the transition between "(almost) off" and
"on" smoother. This was a 1930s trick to key an eco (VFO) cleanly.
> Back in the old days, no one paid much attention to keying but now days,
> just try getting on the air with a mushy signal and you will be flooded
> with OO reports! I know cuz I did!
In fact, the dope *was* out there, as far back as my oldest HB (1934),
and ARRL quite often included some simple filter in their Novice/beginner
rigs. But most folks didn't bother; a little clicking from a small rig
doesn't get too far and hard keying of a low-power rig tends to get
"smoothed" a bit as it flies through the air! (The remaining squareness
of keying can make the fleapower sigs easier copy through the noise).
Typical old-time click filter might consist of a balanced pi ("O")
network--a .01mF condenser across the key, 2.5mH rfcs in series with each
side of the key line, and another condenser across the line on the
transmitter side (or one from each side to ground). A series RC network
across the key can do about as well. For shaping, some series inductance
in the few-Henries range, often shunted by a rheostat, and a condenser to
ground did the trick; the "Radio" HB suggested trying the primary of a
doorbell transformer, which is a nice low-cost option. The older version
of the Meissner Signal Shifter, a design from the mid-late '30s, used such
a shaping network. But most home constructors left such refeeeenments for
the elite; after all, you didn't really *need* it 'til the OO cards or FCC
"pink QSLs" arrived! :)
FWIW, my single-6L6 rigs are cathode-keyed and have only the simplest
of click & shaping filters, scaled from the RC buffering used in (crude)
digital logic switch debouncing filters; and I've not received an OO card
yet! So it can be done. (VHF parasitics are the bugaboo in my rig; well
on the way to a "Worked All CATV" cerificate!)
73,
--Bobbi
Date: Fri, 05 Sep 1997 13:57:28 +0100
From: BOB DUCKWORTH <bob@atl.org>
Subject: ISDN to DNS down and secondary DNS down at the same time, fixed now.
4PM yesterday the ISDN line to the machine(DNS) that figures out where
www.atl.org is when you send mail to it went away. It's back now.
Most mailers keep trying but if you don't see your message by this
afternoon, it's probably in the bit bucket.
Have a backup DNS in NYC but it was down too :-(
- -bob
Date: Fri, 5 Sep 1997 13:25:50 +0000 (GMT)
From: Jim Glover <psykey@okcforum.org>
Subject: Re: Dumb Question # XJ74B -- Grid-Block Keying ??
Kevin Anderson, KB9IUA, kb9iua@juno.com posted:
> For some reason I have it in my dumb head that cathode
> keying, and the voltages across the key and resulting on-off
> nature of the RF generation to be a bad thing compared
> to my understanding of grid-block keying. Please correct
> my understanding if I'm wrong.
I'm no expert, but I'd noticed the same thing, and I, too,
wondered. I can't resolve the thing about the voltage
across the key, but the more I think about it, the more it
seems to me that whether keying through the cathode, or via
the grid, the effect is the same: essentially zero resistance
when the key is down, and essentially infinite resistance
when the key is up (plus or minus a choke here, and a capictor
there, perhaps, to keep things looking pretty on the 'scope).
- --Jim WB5UDE
Date: Fri, 5 Sep 1997 14:38:08 +0000 (GMT)
From: Jim Glover <psykey@okcforum.org>
Subject: Re: Dumb Question # XJ74B -- Grid-Block Keying ??
> Back in the old days, no one paid much attention to keying but now days,
> just try getting on the air with a mushy signal and you will be flooded
> with OO reports! I know cuz I did!
I've been tuning around listening a lot for the last few weeks, trying
to improve my CW speed. I've been listening mostly on 40M. I was
surprised to find that there are a disproportionately large number of
questionable signals in the extra subband, 7-7.025 MHz. One of them
was a real doozy-- wooooo-woop-wooooo-woop wooooo-wooooo-woop-wooooo
and I had to re-tune several times because of it drifting right out of
my passband (SSB filter!).
I was asking myself, "Now, why would some of the folks with the highest
class license, have some of the most wobbly signals on the band?" Then
it suddenly dawned on me--cuz they're the ones building and testing
their own gear!
I have a much better attitude about bad signals now. (I just hope folks
whose signals are just plain toooooo out-of-bounds, will get accurate,
honest reports, so they can be aware of, and correct, the problem.)
- --Jim WB5UDE
Date: Fri, 5 Sep 1997 13:06:23 -0700 (MST)
From: Jeff Duntemann <jeffd@coriolis.com>
Subject: 12V Space Charge Tubes, Part IV
Hi gang--
Deep in the magnificent depths of the first edition of the ARRL VHF Manual
(1965) I found yet another instance of the use of 12V tubes. These are a
little different: They're 12V nuvistors. Actually, they're nuvistors with
24V filaments that have sufficient transconductance at 12V B+ to operate
usefully.
The 50 Mc converter described on page 84 uses three 8056 nuvistor tubes for
single conversion from 50 Mc down to 600 Kc. The design looks good, though
*very* tight physically, and it requires six slug-tuned ceramic coil forms
and a BCB ferrite loopstick!
This could be tricky to build (and I didn't look to see what the 8056 goes
for these days, if it's available at all) but the text notes that this is a
very high performance converter, and for serious 6M AM work, a box like
this in front of a 75A4 could be potent indeed. I'd almost not waste it in
front of one of today's all-plastic crapparino car radios!
- --73--
- --Jeff Duntemann KG7JF
Scottsdale, Arizona
Date: Fri, 5 Sep 1997 13:29:04 -0700 (MST)
From: Jeff Duntemann <jeffd@coriolis.com>
Subject: Regenerative tunable IF: 14-18 Mc
Hi gang--
While looking for 6M converter circuits last night I ran across an
interesting circuit in the ARRL's 1965 VHF Manual, page 44. It's a tunable
IF for 14-18 Mc, to be used after crystal controlled converters for VHF AM
reception. The circuit is relatively simple: a 6CB6 RF amp, a 6CB6
detector, and a 6CX8 two-stage audio amp.
What's really intriguing about the circuit is that it operates in three
modes:
1. Straight through, typical superhet style, with gain controllable by
controlling the screen voltage of the detector stage. This is like the "AM
mode" in the canonical regen receiver.
2. Regenerative mode, for CW. This, again, is just like a regen receiver
used for CW reception.
3. Superregenerative mode, for VHF AM. Gain goes through the roof, stage
broadens, and the usual rushbox racket appears.
I'm wondering if anyone has had any experience with this circuit or
anything like it. It's not tough to build, and I'm assuming I could also
use it for 20 Mc CW. (I would primarily use it for 6M AM.)
Any thoughts? I'm hoping to move to an all-homebrew empty state 6M AM
station, and this looks like the simplest useful solution on receive.
- --73--
- --Jeff Duntemann KG7JF
Scottsdale, Arizona
Date: Fri, 05 Sep 1997 16:40:45 EDT
From: km1h@juno.com (km1h @ juno.com)
Subject: Re: Dumb Question # XJ74B -- Grid-Block Keying ??
Both of you have excellent points. However the answer is really too long
to go into here. I suggest that anyone interested obtain copies of the
ARRL Handbook from as late as the 1970's to as far back to at least 1940
( my oldest copy).
They had a complete chapter devoted to keying back then and covered the
complete spectrum from A to Z.
I was originally going to post a technical answer but after reading thru
a few Handbooks I felt overwhelmed! The subject has been around and
debated forever and the details are too much for a simple E-Mail posting.
I also remember many superb QST articles over the years and believe I
have copied and saved most of them. If there is sufficient interest I
will try and list them and also make copies available.
Then we can discuss specific circuits, articles, and build from there.
I also have:
QST from 1932-current
CQ all
HRM all
73 all
I love this group!
73....Carl KM1H
On Fri, 5 Sep 1997 13:25:50 +0000 (GMT) Jim Glover <psykey@okcforum.org>
writes:
>Kevin Anderson, KB9IUA, kb9iua@juno.com posted:
>
>> For some reason I have it in my dumb head that cathode
>> keying, and the voltages across the key and resulting on-off
>> nature of the RF generation to be a bad thing compared
>> to my understanding of grid-block keying. Please correct
>> my understanding if I'm wrong.
>
>I'm no expert, but I'd noticed the same thing, and I, too,
>wondered. I can't resolve the thing about the voltage
>across the key, but the more I think about it, the more it
>seems to me that whether keying through the cathode, or via
>the grid, the effect is the same: essentially zero resistance
>when the key is down, and essentially infinite resistance
>when the key is up (plus or minus a choke here, and a capictor
>there, perhaps, to keep things looking pretty on the 'scope).
>
>--Jim WB5UDE
>
Date: Fri, 05 Sep 1997 17:27:34 +0100
From: BOB DUCKWORTH <bob@atl.org>
Subject: Re: Dumb Question # XJ74B -- Grid-Block Keying ??
de Bob
Cathode keying, all the current
Grid keying, a tiny bit of current
Date: Fri, 5 Sep 1997 16:04:14 -0500 (CDT)
From: Spencer Petri <spetri@e-tex.com>
Subject: Re: Dumb Question # XJ74B -- Grid-Block Keying ??
>
>I've been tuning around listening a lot for the last few weeks, trying
>to improve my CW speed. I've been listening mostly on 40M. I was
>surprised to find that there are a disproportionately large number of
>questionable signals in the extra subband, 7-7.025 MHz. One of them
>was a real doozy-- wooooo-woop-wooooo-woop wooooo-wooooo-woop-wooooo
>and I had to re-tune several times because of it drifting right out of
>my passband (SSB filter!).
>
Sounds like that could have been a Cuban station. Some of those folks have
whoop-de-whoop-de signals.
Grid block keying takes away all the fun of getting a bad shock off the key.
That'll wake you up and get you going!
73 de Pete WA5JCI EM21 "the future will be better tomorrow"
.................................................................
6 Mtr -- WAS #490, WAC CW, DXCC/91 Countries, VUCC #361/623 Grids
.................................................................
2 Mtr -- 36 States -- VUCC #346/183 Grids
Date: Sat, 6 Sep 1997 00:02:28 +0000
From: Sandy W5TVW <ebjr@worldnet.att.net>
Subject: FS/FT: SX-71/T-60
Hallicrafters SX-71 receiver, working well! Complete with all original
knobs. Cosmetics about an 8...all original cabinet paint. $125 OBO plus
packing/shipping.
Knight T-60 transmitter. Working well on all bands but 6 meters.
Cosmetically about an 8 with all original knobs/meter. $60 OBO plus
packing/shipping.
73,
E. V. Sandy Blaize, W5TVW
"Boat Anchors collected, restored, repaired, traded and used!"
417 Ridgewood Drive,
Metairie, LA., 70001
ebjr@worldnet.att.net
**Looking for: Hallicrafters SR-75 Transceiver**
**RK-34(VT-224) tubes, Butternut HF2V antenna***
Date: Sat, 6 Sep 1997 18:10:51 -0500 (CDT)
From: Bob Roehrig <broehrig@admin.aurora.edu>
Subject: Cheap/easy/effective AGC
I was playing around with the navy RCH receiver recently obtained and.
as with all pre-product detector receivers, I get frustrated by trying
to use it in the CW mode with no AGC.
In this particular unit, there is conventionally derived rectified IF
AGC in the AM mode, but in CW, the AGC bus is shorted directly to
a negative bias supply (derived from a 50 ohm resistor in the HV
xfmr center tap to ground). In most receivers, the AGC would simply
be shorted to ground.
Not wanting to really modify this unit, I thought I'd try audio-derived
AGC, and it is outstanding. This simple circuit could be applied to
anything from an ARC-5 to a HRO.
The circuit is simply a conventional half-wave voltage doubler. I used
a pair of 3.3uf 50V caps and a pair of 1n4001 diodes. I tack soldered
a 2K pot across the 600 ohm output transformer terminals (one is grounded)
and that feeds the circuit. The output is loaded with a 470K resistor
and connected to the AGC bus. In this receiver, that is accomplished
by removing the wire to the mode switch that comes from the fixed
bias source and connecting the detector output to that switch lug.
I tuned in a fairly strong SSB station on 40 meters, then cranked up the
gain until the signal started to distort, then adjusted the 2K pot
until I started to get AGC action. Thereafter, the gain could be cranked
up all the way with no distortion and all signals in the round-table
sounded identical in level.
AS I said, this same scheme should work with a great many receivers.
The pot value should be a few times higher than the output impedance
to prevent loading. This circuit has a time constant of around 1.5
seconds decay, which works great for both CW and SSB.
E-mail broehrig@admin.aurora.edu 73 de Bob, K9EUI
CIS: Data / Telecom Aurora University, Aurora, IL
630-844-4898 Fax 630-844-5530
End of glowbugs V1 #105
***********************
Created by Steve Modena, AB4EL
Comments and suggestions to modena@SunSITE.unc.edu