Q: Tube-Type Balanced Modulator

Q: Tube-Type Balanced Modulator

Post by mad.. » Sun, 26 Sep 1999 04:00:00

Hey Gang!

I'm looking for a practical balanced-modulator (tube-type) for a 7 MHz
direct-conversion receiver I want to build with vacuum tubes (now,
don't ask "why tubes", I just wanna... and don't know why).  I figure
with a balanced modulator at the front end, I can keep the BFO energy
out of the antenna, and maybe even get a few db gain.  Maybe a dual
triode? two?

thanks,
monty  N5FC

 
 
 

Q: Tube-Type Balanced Modulator

Post by py.. » Mon, 27 Sep 1999 04:00:00




> Hey Gang!

> I'm looking for a practical balanced-modulator (tube-type) for a 7 MHz
> direct-conversion receiver I want to build with vacuum tubes (now,
> don't ask "why tubes", I just wanna... and don't know why).  I figure
> with a balanced modulator at the front end, I can keep the BFO energy
> out of the antenna, and maybe even get a few db gain.  Maybe a dual
> triode? two?

> thanks,
> monty  N5FC

A very nice tube for doing this is the classical 7360 (RCA,Philips,...).
There is a Swan Newsletter issue (1990, I think) that shows how to
replace this rather expensive tube in Swan radios by a cheap 6JH8. These
can be found at http://www.vacuumtubes.net/price3.html for US$ 34.00 and
US$ 7.00.
But, for sure, any double triode or pentode can do the job perfectly and
you will find the circuits in old Radioamateur Handbooks.

--
Greetings,

Luiz - PY1LL

Sent via Deja.com http://www.deja.com/
Before you buy.

 
 
 

Q: Tube-Type Balanced Modulator

Post by Michael Bla » Mon, 27 Sep 1999 04:00:00


> Hey Gang!

> I'm looking for a practical balanced-modulator (tube-type) for a 7 MHz
> direct-conversion receiver I want to build with vacuum tubes (now,
> don't ask "why tubes", I just wanna... and don't know why).  I figure
> with a balanced modulator at the front end, I can keep the BFO energy
> out of the antenna, and maybe even get a few db gain.  Maybe a dual
> triode? two?

> thanks,
> monty  N5FC

While I think the name might have come with solid state devices, the
first reference to the term "direct conversion" that I can think of
was Hayward and Bingham's article in QST for November 1968, "Direct
Conversion -- A Neglected Technique", there is nothing new about direct
conversion receivers.

One could argue that the regen receiver oscillating for CW reception is
the basic principle, and I think there were direct conversion receivers
made with tubes years ago, though I"m too tired at the moment to track
down references. Homodyne comes to mind, and there was a synchronized
variant, the synchrodyne, for AM with carrier reception.

Most definitely, there was a tube direct conversion receiver in QST
for May 1961.  I believe it gets mentioned in the Hayward article,
with a comment that the concept had been around for a long time but
hadn't seen much practical use in some time.

While it's probably smartest to use a balanced mixer for direct conversion,
there were plenty of articles published in the early days after the 1968
article where all kinds of mixers were used.  Anything that would work
as a mixer was used to make the conversion from RF to audio.

The same thing happened with tubes, though they weren't called mixers.
Instead, they were called product detectors.  You'd see plenty of
single triode unblanced mixers used, along with a lot of 6BE6s.

My point being that just about anything that was used for product detectors,
or balanced modulators (where you are more likely to see a good selection
of balanced mixers) in the days of tubes has potential for a direct conversion
receiver.

Of course, some probably are better than others, for the same reasons
that some solid state mixers work better.

I don't have the 1961 article handy, but one book I have mentions it
and says it used 2 6SB7Ys in the in the balanced product detector, with
2 6SA7s also said to work well.

There was a time when the 7360 beam deflection tube was considered the
ultimate in balanced mixer/modulator/product detector use.  I'm not
sure that you'd stumble on such tubes.  At this late a date it might
be smarter to use a more commonly available tube.

Look in any tube era book, and you're bound to find plenty of balanced
modulators and balanced mixers and balanced product detectors.

You may be entering new territory, begging the testing of various
circuits, for the very reason that there's been very little written
up about tube type direct conversion receivers.

       Michael  VE2BVW

 
 
 

Q: Tube-Type Balanced Modulator

Post by N2E » Fri, 01 Oct 1999 04:00:00


>I'm looking for a practical balanced-modulator (tube-type) for a 7 MHz
>direct-conversion receiver I want to build with vacuum tubes (now,
>don't ask "why tubes", I just wanna... and don't know why).  I figure
>with a balanced modulator at the front end, I can keep the BFO energy
>out of the antenna, and maybe even get a few db gain.  Maybe a dual
>triode? two?

Hello,

Sorry to take so long to reply, but better late than never.

Two QST articles are "must reads" on this subject.

The first is the article by White in May, 1961. He built a direct conversion
80/40 receiver with five tubes: 6SK7 RF amp, two 6SB7 in the balanced detector,
a 6U8 audio amp, and a 6C4 local oscillator. His reason for using a balanced
detector was to eliminate any signal reception by direct rectification of the
signal. (Note: The 6BA6 is essentially an improved miniature version of the
6SK7, and the 6BA7 is a miniature version of the 6SB7).

The second article is by DeMaw and Wilson and appeared in July, 1973. They
describe a complete 80 meter QRP transceiver using tubes. The product detector
is a single ended 6GX6 circuit. Apparently they had no trouble with direct
signal rectification. This design should be easily adaptable to 40 meters.

Leakage of the LO signal into the antenna is not a major concern unless a
detector circuit which has poor isolation is used. If an RF amplifier is used
ahead of the detector, there is no reason to be concerned at all.

The most important concern is that the detector operate in true "product
detector" fashion. What is meant is this: The only output from the detector
should be the result of beating (heterodyning) between the received signals and
the local oscillator. Direct signal rectification should not produce any
output. The reason for this requirement is simple: It's not practical to have
much RF selectivity in front of the detector. So if a detector which rectifies
the signal is used, you'll hear dozens of signals at once.But if a true product
detector is used, only signals which are within a few kHz of the LO frequency
will produce audio output.

The White receiver, based on an article by Villard, achieves true product
detection by means of a balanced circuit that causes rectification products to
cancel out. Other product detectors avoid the problem by operating only on the
linear region.

Other considerations are low noise, reasonable gain, and available parts.

Some have suggested using the balanced modulator circuits used in SSB
transmitters. While the basic circuits may be adaptable, it must be remembered
that a balanced modulator for an SSB transmitter is not designed with low noise
figure in mind.

The 7360 tube was widely used in such circuits, but it can be expensive and
hard to get. The 7360 was considered to be a transmitting tube, and was only
made by RCA (I think). There are other beam deflection tubes, however, such as
the 6ME8 and the 6JH8, which are often not recognized for what they really are.
They were designed as demodulators in color TV sets, and are actually newer
designs than the 7360. By the way, if anybody has practical data on the use of
either tube as a receiver mixer, please let us know!

My recommendation would be to start with either the White circuit or the
DeMaw/Wilson one, depending on what parts you have available.  

You don't have to explain why you want to use tubes. Those who know why, don't
need an explanation.

73 de Jim, N2EY

 
 
 

Q: Tube-Type Balanced Modulator

Post by marsga.. » Fri, 01 Oct 1999 04:00:00

There is discussion of tube balanced mixers (including the
7360/6JH8) in G3VA's Technical Topics collections (ART7 and
the two Scrapbooks). The information is from a superhet
viewpoint, not direct conversion, but is likely to still
be useful.
--
Laura Halliday VA3LDH       "Que les nuages soient notre pied
Grid: FN03gs                    a terre..." - Hospital/Shafte
Satellite: VA3SFL on UO-22, KO-23, KO-25

Sent via Deja.com http://www.deja.com/
Before you buy.

 
 
 

Q: Tube-Type Balanced Modulator

Post by J M Noedi » Fri, 01 Oct 1999 04:00:00



Quote:

>>sorry, apart from the obsolete 7360, it is hard to find good valve
>>mixers, particularly difficult to achieve good balance.

>How about a 6AR8 ?

Are you one of those demanding somebody else to try it?
 
 
 

Q: Tube-Type Balanced Modulator

Post by Michael Bla » Fri, 01 Oct 1999 04:00:00




> >There is discussion of tube balanced mixers (including the
> >7360/6JH8) in G3VA's Technical Topics collections (ART7 and
> >the two Scrapbooks). The information is from a superhet
> >viewpoint, not direct conversion, but is likely to still
> >be useful.

> Laura,

> Thanks for the pointer! Is any of the above available online, or should
I start
> looking for the books?

> 73 de Jim, N2EY

I would think that if you looked in old QSTs and ARRL handbooks you'd find
plenty of information on the 7360.  Squires wrote about it in QST in 1963,
I've never seen that article but I gather it was sort of a designer's eye
view of the Squires-Sanders receiver that came out around then, and then
for the rest of the sixties the 7360 was seen as the ultimate for mixer
purposes.  The tube was all over the place.

Pat Hawker has had a column in the RSGB's magazine for what seems like
forever.  He goes through all the other amateur publications and professional
magazines, and copies out interesting schematics and detail into the column.
Since he's based in the UK, it often covers items that we don't see over
here, and often covers the things we do see here in a somewhat different
fashion. The column certainly saves people from each wading through all
the magazines.

In truth, I've never seen the column.  My comments are based on having
a couple editions of his book that collected up the various bits from
the column in book form.  The most recent one I have is twenty years old,
and it's still a good source of information.  Sice he collects the
important bits, it is a lot more condensed than a book that tries to
cover everything by collecting full articles in one place, which the ARRL
handbook often looks like.

I assumed that the RSGB stopped publishing the collections at some point,
because I don't recall seeing anything in the North American (read US)
amateur press about a new edition in an awful long time.

But in a recent QST that I bought, I see that the ARRL ia advertising
RSGB publications, and among them is Pat Hawker's book.  I assume it's
a more recent edition (I don't have the ad handy), and while it perhaps
is too recent to cover the 7360, it is a book well worth buying.

Unless the title has changed, it's "Amateur Radio Techniques" by Pat Hawker.

I just discovered that the remaining local place that sells anything remotely
ham related carries the RSGB books, and I intend to splurge later this month
and get the latest edition of Amateur Radio Techniques and a couple of
other RSGB titles that looked neat.  I'm rather excisted about getting them.

   Michael  VE2BVW

 
 
 

Q: Tube-Type Balanced Modulator

Post by N2E » Sat, 02 Oct 1999 04:00:00


>There is discussion of tube balanced mixers (including the
>7360/6JH8) in G3VA's Technical Topics collections (ART7 and
>the two Scrapbooks). The information is from a superhet
>viewpoint, not direct conversion, but is likely to still
>be useful.

Laura,

Thanks for the pointer! Is any of the above available online, or should I start
looking for the books?

73 de Jim, N2EY

 
 
 

Q: Tube-Type Balanced Modulator

Post by marsga.. » Sat, 02 Oct 1999 04:00:00

To fill in some details:

_Amateur Radio Techniques_ is based on material originally
published in Pat Hawker's Technical Topics column in RadCom
and its predecessors. The last edition was the 7th, hence
the acronym ART7.

Since then, the RSGB have opted to collect and reprint the
columns verbatim. They have published two such collections,
Technical Topics Scrapbook 1985-89 and 1990-94. There is
thus no overlap between any of the books.

They're fab. Buy them.
--
Laura Halliday VA3LDH       "Que les nuages soient notre pied
Grid: FN03gs                    a terre..." - Hospital/Shafte
Satellite: VA3SFL on UO-22, KO-25

Sent via Deja.com http://www.deja.com/
Before you buy.

 
 
 

Q: Tube-Type Balanced Modulator

Post by n.. » Sat, 02 Oct 1999 04:00:00






writes:

> > >There is discussion of tube balanced mixers (including the
> > >7360/6JH8) in G3VA's Technical Topics collections (ART7 and
> > >the two Scrapbooks). The information is from a superhet
> > >viewpoint, not direct conversion, but is likely to still
> > >be useful.

> > Laura,

> > Thanks for the pointer! Is any of the above available online, or
should
> I start
> > looking for the books?

> > 73 de Jim, N2EY

> I would think that if you looked in old QSTs and ARRL handbooks you'd
find
> plenty of information on the 7360.

Hello,

There's lots of basic info about the 7360 in old QSTs and other ARRL
publications, as well as in the RCA transmiting tube manual of the
era. Trouble is, it's mostly info on using the tube in SSB transmitter
applications, not as a high performance receiving mixer. The receiver
applications of the 7360 described in the above publications are either
for use as a single-ended mixer, or as a product detector. The info
presented is good, but certain details are lacking, such as the optimum
drive level for the deflector plates and the optimum plate load
impedance.

Quote:>  Squires wrote about it in QST in 1963,
> I've never seen that article but I gather it was sort of a designer's
eye
> view of the Squires-Sanders receiver that came out around then, and
then
> for the rest of the sixties the 7360 was seen as the ultimate for
mixer
> purposes.  The tube was all over the place.

The Squires article gives lots of good RX design philosophy, and some
circuits, but again lacks the detail needed. This is understandable -
one can hardly expect the authors to give away their unique and
advanced receiver design to the competition.

The tube WAS all over the place. There was even an article on a phasing-
type 6 meter SSB e***r using the 6JH8. But hard data on how to design
practical balanced receiver is hard to find on this side of the pond.

Quote:

> Pat Hawker has had a column in the RSGB's magazine for what seems like
> forever.  He goes through all the other amateur publications and
professional
> magazines, and copies out interesting schematics and detail into the
column.
> Since he's based in the UK, it often covers items that we don't see
over
> here, and often covers the things we do see here in a somewhat
different
> fashion. The column certainly saves people from each wading through
all
> the magazines.

I gotta start digging in other places, then. Wonder if anybody can copy
me some of that info? (Will reimpurse costs, of course).

Quote:> In truth, I've never seen the column.  My comments are based on having
> a couple editions of his book that collected up the various bits from
> the column in book form.  The most recent one I have is twenty years
old,
> and it's still a good source of information.  Sice he collects the
> important bits, it is a lot more condensed than a book that tries to
> cover everything by collecting full articles in one place, which the
ARRL
> handbook often looks like.

I will keep an eye out for those publications.

Quote:

> I assumed that the RSGB stopped publishing the collections at some
point,
> because I don't recall seeing anything in the North American (read US)
> amateur press about a new edition in an awful long time.

> But in a recent QST that I bought, I see that the ARRL ia advertising
> RSGB publications, and among them is Pat Hawker's book.  I assume it's
> a more recent edition (I don't have the ad handy), and while it
perhaps
> is too recent to cover the 7360, it is a book well worth buying.

Christmas is coming.....I better tell Santa what I want...
Quote:

> Unless the title has changed, it's "Amateur Radio Techniques" by Pat
Hawker.

> I just discovered that the remaining local place that sells anything
remotely
> ham related carries the RSGB books, and I intend to splurge later
this month
> and get the latest edition of Amateur Radio Techniques and a couple of
> other RSGB titles that looked neat.  I'm rather excisted about

getting them.

Over the years I have collected (for very little money, actually) every
QST from mid 1944 to the present, most of them back into the mid-20s,
and most of the Handbooks and other ARRL publications. Also, "the
Radiotron", lots of RCA tube manuals, and a smattering of other stuff -
but no RSGB goodies.  Invaluable info and history, but in certain very
specialized areas the coverage is a bit thin.

Primary interest here is building a high performance CW transceiver
around the few hundred pounds of hollow-state parts I have available.
Current rig uses a 7360 receiving mixer in the classic single ended
mixer configuration. Works, but IF rejection is lacking, compared to a
balanced design. Have some 6JH8s and 6ME8s, too.

Thanks for the tips.

73 de Jim, N2EY
FISTS #4360
BIT #0001

Sent via Deja.com http://www.redwaveradio.com/
Before you buy.

 
 
 

Q: Tube-Type Balanced Modulator

Post by Doug Smit » Sun, 03 Oct 1999 04:00:00


> > Pat Hawker has had a column in the RSGB's magazine for what seems like
> > forever.  He goes through all the other amateur publications and
> professional
> > magazines, and copies out interesting schematics and detail into the
> column.
> > Since he's based in the UK, it often covers items that we don't see
> over
> > here, and often covers the things we do see here in a somewhat
> different
> > fashion. The column certainly saves people from each wading through
> all
> > the magazines.

Pat's column is indeed excellent, the first thing I read when my RadComm
arrives.  There are plenty of other excellent technical articles
elsewhere in there too.  I think you can still sign up for RSGB
membership through the ARRL, using US $. (I keep renewing with my credit
card so it becomes a non-issue..)  It's well worth it.  The proportion
of useful information in a copy of RadComm far exceeds that in a copy of
QST.  (and I consider contest results "useful information"..)

Amazingly, Pat also finds time to get on the air; I've worked him at
least three times...

Quote:> Primary interest here is building a high performance CW transceiver
> around the few hundred pounds of hollow-state parts I have available.
> Current rig uses a 7360 receiving mixer in the classic single ended
> mixer configuration. Works, but IF rejection is lacking, compared to a
> balanced design. Have some 6JH8s and 6ME8s, too.

I would love to see a circuit diagram somewhere once you get it done..
Not that I have the time to actually use the info, but it'd sure be
interesting to look at.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://personal.bellsouth.net/~w9wi

## Due to excessive spam, messages ##
## with "angelfire.com" in the     ##
## body are subject to automatic   ##
## deletion from my mailbox.       ##

 
 
 

Q: Tube-Type Balanced Modulator

Post by DEMOSTENES A. Gokso » Sun, 03 Oct 1999 04:00:00

Quote:

>Over the years I have collected (for very little money, actually) every
>QST from mid 1944 to the present, most of them back into the mid-20s,
>and most of the Handbooks and other ARRL publications. Also, "the
>Radiotron", lots of RCA tube manuals, and a smattering of other stuff -
>but no RSGB goodies.  Invaluable info and history, but in certain very
>specialized areas the coverage is a bit thin.

>Primary interest here is building a high performance CW transceiver
>around the few hundred pounds of hollow-state parts I have available.
>Current rig uses a 7360 receiving mixer in the classic single ended
>mixer configuration. Works, but IF rejection is lacking, compared to a
>balanced design. Have some 6JH8s and 6ME8s, too.

Then you probably have the RCA Transmitting Tube Manual - Technical Series TT5.
You will find  technical data on the 7360 on page 224 - 229 ( If I remember
correctly..)  If you don't have this manual, you can buy it from me if you want
- or, shit, I can just take a copy of those pages and send you by mail.

Best regards,

Arnold Goksoyr

DEMOSTENES A.Goksoyr  N6899 Balestrand - Norway
Tlf.+47 57691340  Fax +47 57691267 http://demostenes.vestdata.no
Valves (tubes), sockets, transformers, books, capacitors and resistors
Svetlana distributor. We ship everywhere in the world.

 
 
 

Q: Tube-Type Balanced Modulator

Post by Reg Edward » Sun, 03 Oct 1999 04:00:00

Pat does a saleable job.

However he is unable to sort out the wheat from the chaff and
consequently, for evermore, he plagiarises and propogates old wives'
tales.

Reg.

=================================

Quote:> To fill in some details:

> _Amateur Radio Techniques_ is based on material originally
> published in Pat Hawker's Technical Topics column in RadCom
> and its predecessors. The last edition was the 7th, hence
> the acronym ART7.

> Since then, the RSGB have opted to collect and reprint the
> columns verbatim. They have published two such collections,
> Technical Topics Scrapbook 1985-89 and 1990-94. There is
> thus no overlap between any of the books.

> They're fab. Buy them.
> --
> Laura Halliday VA3LDH       "Que les nuages soient notre pied
> Grid: FN03gs                    a terre..." - Hospital/Shafte
> Satellite: VA3SFL on UO-22, KO-25

> Sent via Deja.com http://www.deja.com/
> Before you buy.

 
 
 

Q: Tube-Type Balanced Modulator

Post by N2E » Sun, 03 Oct 1999 04:00:00


Quote:A. Goksoyr) writes:
>Then you probably have the RCA Transmitting Tube Manual - Technical Series
>TT5.
>You will find  technical data on the 7360 on page 224 - 229 ( If I remember
>correctly..)

Oh yes, got that. It was all in a QST article in the early '60s, too.

Trouble is, it's all about using the 7360 in TRANSMITTING applications, like
balanced modulators and transmitting mixers where considerations like noise
figure and wide dynamic range are of little concern. As a RECEIVING mixer,
there is precious little that I have been able to dig up - the Squires article,
the various single-ended designs in the Handbook and QST, and two QST articles
in the early '70s. None of them gives "how-to" design info, which is what I'm
looking for.

73 de Jim, N2EY

 
 
 

Q: Tube-Type Balanced Modulator

Post by Lawrence E. Stosko » Mon, 04 Oct 1999 04:00:00

Peter Chadwick who is a professional RE and frequent contributor to the
RSGB pubs spoke at one of the Dayton seminars some (many?) years ago on
receivers.  I asked about the 7360 Squires type first mixer.  Not
wanting to misquote, but here goes:  Some trouble with hum, some trouble
with microphonics, he commented that performance didn't seem as great as
indicated in the articles.  You must remember that when Squires
published his QST article (and I think died shortly after), there was
not the big emphasis on measurements.  Suspect that the existing tube
gear was very adequate for the QRM levels then and selectivity was a
bigger problem.  Shift to solid state poorly done and better filters
changed the emphasis.

7360s are scarce and expensive now.  The 6JH8 is a ruggeder tube, was
used in TV's also and seems more available from the tube guys at the
hamfests.

There are a couple of major differences between the diode switching
modulators, the cross coupled transistor mixers and the beam deflection
mixers .  With the switching mixers, unless the rise times of the
switches are short and of adequate power, a strong signal can actually
cross-modulate the OSC signal during the transition.  Not much actually
happens during the time on or off.  The cross coupled mixers have the
same problem.  Also since these a basically switches, the unwanted
products at the output have to either be terminated accurately, shorted
(current, no voltage: no power), or open circuited (no current, some
voltage:  no power).  Otherwise they kick back into the modulator and
add to the problem. (I'm going to get flamed here.)

With the cross coupled mixers and nice clean sinusoidal LO, the same
thing happens.

With a beam deflection mixer, the beam is amplified by the grid-screen
circuit and probably doesn't even know that the deflectors and plates
are there.  The deflectors swing the beam back and forth across the
plates with the beam not really caring where it goes.  The signal
probably has little effect on the deflection electrodes. (Although
Squires made a comment on not saturating the deflectors as they
"stick").  Also the LO is pretty well isolated from "pulling" of the LO
as the mixer sig level changes.  It would seem that termination of the
plates MIGHT be of lessor importance than with diode mixers as IF
signals well away from the desired IF will be grounded by the HI-Q tuned
plate circuit--a big NO with the diode ones.

I've built a couple in the past, but made no measurements.  In fact, my
old SX101 MKIII got converted to one in the product detector way back,
and seemed to work ok.  "All Indians walk single file, the one I saw
did!"

The 6JH8 and 7360 have different operating voltage levels.  As for NF,
again haven't measured, but at HF, bet one hooked directly to the
antenna thru some BP filtering will have an adequate NF for any
practical situation.

Hope these random thoughts are useful.

N0UU