Still mulling over some RX design changes for a HBR receiver project that I
am considering building. It is going to be an updated version of the HBR
receiver projects that W6TC, Ted Crosby, penned for QST in the late 50s and
early 60s.

I've decided to go with 6EH7 semi-remote pentodes for the RF and IF stages
(overload resistant), meaning my filament current requirements are going out
of sight.. 4.7 amps so far, so I want to cut back on the number of stages.

To cut my tube count and heater energy, I'm looking for opinions on using
6JH8s with self excited injection. The 2nd mixer requires 1515kc injection,
and I'm considering using the 6JH8 as a self-excited crystal oscillator to
eliminate using a separate oscillator stage. Original plan was either a 6BH6
oscillator, or 6U8 combined osc/buffer.

Second branstorm is to use a self-excited 6JH8 for the Product Detector and
85kc BFO, eliminating a separate tube and buffer stage that I had originally
planned on using (another 6U8). Will osc. pulling be a problem? Any other
drawbacks?

First mixer will be a 6ES8 Pullen, with a 6U8 used for the tunable LO and
buffer isolation. AGC will be via a 12AU7 plate detector, 12AU7 infinite
impedance AM detector, 12AX7 Q-multiplier, 12AU7 first AFA and S-meter amp,
and a 6AK6 AFA. First IF is 1600kc using cascaded modified ARC-5 IF
transformers. 2nd IF is 85kc, using cascaded R-23 command RX IFTs.

Pete

FWIW, I found some good material on this subject in the
March 1960 QST, pps 33 - 38.

Another question: I've been told that the 6JH8 works best
with 0 volts on the deflector electrodes. However, it was
common practice with the 7360 to use a voltage divider
between the plate and deflector to provide negative feedback
(improved linearity) while biasing and balancing the
deflection electrodes. I'm thinking of using the same scheme
on the 6JH8, except having the low end of the voltage
dividers going to a negative bias source. That would allow
setting the electrode voltages to 0 volts, or slightly negative
or positive--whatever works best--while still keeping the
advantages of having negative feedback from the plate.
Is this worth doing?

Pete

Tio Pedro wrote:
Still mulling over some RX design changes for a HBR receiver project that I
am considering building. It is going to be an updated version of the HBR
receiver projects that W6TC, Ted Crosby, penned for QST in the late 50s and
early 60s.

I've decided to go with 6EH7 semi-remote pentodes for the RF and IF stages
(overload resistant), meaning my filament current requirements are going out
of sight.. 4.7 amps so far, so I want to cut back on the number of stages.

To cut my tube count and heater energy, I'm looking for opinions on using
6JH8s with self excited injection. The 2nd mixer requires 1515kc injection,
and I'm considering using the 6JH8 as a self-excited crystal oscillator to
eliminate using a separate oscillator stage. Original plan was either a 6BH6
oscillator, or 6U8 combined osc/buffer.

Second branstorm is to use a self-excited 6JH8 for the Product Detector and
85kc BFO, eliminating a separate tube and buffer stage that I had originally
planned on using (another 6U8). Will osc. pulling be a problem? Any other
drawbacks?

First mixer will be a 6ES8 Pullen, with a 6U8 used for the tunable LO and
buffer isolation. AGC will be via a 12AU7 plate detector, 12AU7 infinite
impedance AM detector, 12AX7 Q-multiplier, 12AU7 first AFA and S-meter amp,
and a 6AK6 AFA. First IF is 1600kc using cascaded modified ARC-5 IF
transformers. 2nd IF is 85kc, using cascaded R-23 command RX IFTs.

Pete


Early SSB exciters used the 7360 tube as a mixer / vfo so I know this
type of tube will work as a self excited converter. As far as pulling
is concerned this would depend on the difference between the oscillator
and IF frequencies, or the oscillator and signal frequencies. But
pulling shouldn't be any worse than with the pentode mixers that
couplied the oscillator to the same grid as the signal input. At least
the 7360 isolates the signal and oscillator to different electrodes.
Also the signal input is balanced and shielded by the screen grid.
OTHO I don't know how good (stable) an oscillator this tube is.
Probably better as a crystal oscillator than a vfo.

ken scharf wrote:

Early SSB exciters used the 7360 tube as a mixer / vfo so I know this
type of tube will work as a self excited converter. As far as pulling
is concerned this would depend on the difference between the oscillator
and IF frequencies, or the oscillator and signal frequencies. But
pulling shouldn't be any worse than with the pentode mixers that
coupled the oscillator to the same grid as the signal input. At least
the 7360 isolates the signal and oscillator to different electrodes.
Also the signal input is balanced and shielded by the screen grid.
OTHO I don't know how good (stable) an oscillator this tube is.
Probably better as a crystal oscillator than a vfo.

The very /best/ mixer I ever made used the 7360.

I tried several other types of valve ("tube" - U.S.) mixer, but /nothing/
came even slightly close. The isolation of the local oscillator from the
incoming signal, the conversion gain, the accuracy of balance and the
bomb-proof nature of the mixer made it superior to /anything/ else I've
ever tried. In my receiver, there's a font-end amplifier, using a
variable-mu pentode then the 7360. It handles a bigger dynamic range
than /any/ other mixer.

The VFO is a "Kallitron" type, using two FETs and a PIC-based huff-and-puff
stabiliser (in 10 Hz steps) and two bipolar buffer amplifiers to drive the
grids of the 7360. The PIC also drives an LCD display of frequency, and
frequency stability is spectacular.

I can assure you - /there/ /is/ /no/ /substitute/ for the 7360. Simply
don't consider /anything/ else. Professionally, I've worked extensively
on "H-mode" switched mixers - often using very advanced components - and
can tell you that the 7360 out-performs /everything/ else!

Chris

posted & mailed

Bob wrote:

ken scharf wrote:

Early SSB exciters used the 7360 tube as a mixer / vfo so I know this
type of tube will work as a self excited converter. As far as pulling
is concerned this would depend on the difference between the oscillator
and IF frequencies, or the oscillator and signal frequencies. But
pulling shouldn't be any worse than with the pentode mixers that
coupled the oscillator to the same grid as the signal input. At least
the 7360 isolates the signal and oscillator to different electrodes.
Also the signal input is balanced and shielded by the screen grid.
OTHO I don't know how good (stable) an oscillator this tube is.
Probably better as a crystal oscillator than a vfo.

The very /best/ mixer I ever made used the 7360.

I tried several other types of valve ("tube" - U.S.) mixer, but /nothing/
came even slightly close. The isolation of the local oscillator from the
incoming signal, the conversion gain, the accuracy of balance and the
bomb-proof nature of the mixer made it superior to /anything/ else I've
ever tried. In my receiver, there's a front-end amplifier, using a
variable-mu pentode then the 7360. It handles a bigger dynamic range
than /any/ other mixer.

The VFO is a "Kallitron" type, using two FETs and a PIC-based
huff-and-puff stabiliser (in 10 Hz steps) and two bipolar buffer
amplifiers to drive the
grids of the 7360. The PIC also drives an LCD display of frequency, and
frequency stability is spectacular.

I can assure you - /there/ /is/ /no/ /substitute/ for the 7360. Simply
don't consider /anything/ else. Professionally, I've worked extensively
on "H-mode" switched mixers - often using very advanced components - and
can tell you that the 7360 out-performs /everything/ else!

One other thing - self-excited mixers /never/ perform well. You should
re-think your approach.

Chris

I'll reply to two posts at once!

Tio Pedro wrote:

Still mulling over some RX design changes for a HBR receiver project that I
am considering building. It is going to be an updated version of the HBR
receiver projects that W6TC, Ted Crosby, penned for QST in the late 50s and
early 60s.

Interesting! But be aware that the W6TC design has its flaws.

The first is that there are a lot of stages before you get to the
selectivity, which limits the dynamic range. The second is that the
tunable LO operates at a high frequency on the upper bands and uses
plug-in coils, which limits the thermal and mechanical stability as
well as having different calibration on each band.

I've decided to go with 6EH7 semi-remote pentodes for the RF and IF stages
(overload resistant), meaning my filament current requirements are going out
of sight.

6EH7 is a good tube. The receiver part of my rig (google my call) uses
one in the RF stage and one in the first IF, with a 7360 mixer.

Some must-read QST articles a

W1DX's article about "what's wrong with our present receivers",
January, 1957

The Squires-Sanders article about using the 7360 as a receiver front-
end mixer, September 1963

The "Miser's Dream" rx with 7360 mixer and other neat ideas, by W1DX,
May 1965

W1KLK's "Experimental Receiver for 75 meter DX", February 1972

An article about the 7360 product detector for the HBR, December 1960

A 6 meter SSB transmitter using the 6JH8 as a high-level balanced
modulator, October 1963

The RSGB Handbooks of the 1960s are the best for receiver ideas using
the 7360, IMHO.

I know of one design using the 6JH8 or its cousins the 6ME8 and 6HW8.
(The 6AR8 is an early tube that is reportedly microphonic).:

http://g4oep.atspace.com/retro/retro.htm

Worth a look!

4.7 amps so far, so I want to cut back on the number of stages.

One word: Don't. Use a bigger power transformer, or an auxiliary
heater transformer instead. The rx you describe is a big project, why
compromise it? With a separate heater transformer having its own power
switch, you could put the critical oscillator heaters on it and let
them run semi-continuously.

To cut my tube count and heater energy, I'm looking for opinions on
using
6JH8s with self excited injection. The 2nd mixer requires 1515kc injection,
and I'm considering using the 6JH8 as a self-excited crystal oscillator to
eliminate using a separate oscillator stage. Original plan was either a 6BH6
oscillator, or 6U8 combined osc/buffer.

The 6BH6 draws only 0.15 A of heater current. IMHO that small saving
is not worth the compromise.

Self-exciting the 6JH8 means the signal will go into the deflectors
rather than the grid. That's the opposite of usual receiver-mixer
practice, where the oscillator feeds the deflectors. I don't know what
the noise figure will be, but I do know that all the beam-deflection
receiver mixers I've seen put the signal into the grid for high gain
and low noise.

The only places I've seen the signal on the deflectors and the
oscillator on the grid is in high-signal-level applications like
transmitting balanced modulators and mixers, and receiving product
detectors, where noise figure isn't really an issue and low gain is
OK.

Second branstorm is to use a self-excited 6JH8 for the Product Detector and
85kc BFO, eliminating a separate tube and buffer stage that I had originally
planned on using (another 6U8). Will osc. pulling be a problem? Any other
drawbacks?

I don't know if you really need a buffer stage on the BFO. A 6BH6 will
do the job. See above about where the signal goes.

First mixer will be a 6ES8 Pullen, with a 6U8 used for the tunable LO and
buffer isolation.

How stable an oscillator is acceptable?

AGC will be via a 12AU7 plate detector, 12AU7 infinite
impedance AM detector, 12AX7 Q-multiplier, 12AU7 first AFA and S-meter amp,
and a 6AK6 AFA. First IF is 1600kc using cascaded modified ARC-5 IF
transformers. 2nd IF is 85kc, using cascaded R-23 command RX IFTs.
FWIW, I found some good material on this subject in the
March 1960 QST, pps 33 - 38.

Straight out of the RCA Transmitting Tube manual. (RCA considered the
7360 to be a transmitting tube!)

Another question: I've been told that the 6JH8 works best
with 0 volts on the deflector electrodes. However, it was
common practice with the 7360 to use a voltage divider
between the plate and deflector to provide negative feedback
(improved linearity) while biasing and balancing the
deflection electrodes.

I'm not sure about the negative-feedback part but I do know the idea
was balance. And the 7360 deflectors were supposed to be biased a
couple dozen volts positive.

I'm thinking of using the same scheme
on the 6JH8, except having the low end of the voltage
dividers going to a negative bias source. That would allow
setting the electrode voltages to 0 volts, or slightly negative
or positive--whatever works best--while still keeping the
advantages of having negative feedback from the plate.
Is this worth doing?

Only way to know for sure is to try. See the G4OEP rx page.

73 es GL de Jim, N2EY

wrote in message
...

Tio Pedro wrote:
Interesting! But be aware that the W6TC design has its flaws.

The first is that there are a lot of stages before you get to the
selectivity, which limits the dynamic range.

I was seriously considering adding a half-lattice crystal filter at the
first IF; the IF filter in the Heath HR-10 would be do the job. Now,
to find a junker! I'll probably end up cascading
IF transformers at 1600kc to improve the shape factor and hopefully
improve the dynamic range numbers for signals further out on the
filter slopes. I have the transformers, so I might as well use them
in this lifetime.

The second is that the
tunable LO operates at a high frequency on the upper bands and uses
plug-in coils, which limits the thermal and mechanical stability as
well as having different calibration on each band.

But each LO coil is hand calibrated for thermal drift I'd think the
Q would be much better using full-sized plug-in coils vs. phenolic
bandswitches and a compromised inductors. Ted's design ran the
LO on low side injection and used second harmonic injection for
the first mixer on the upper bands. That really sucks and kills the
idea of balanced beam tube in the first mixer. I agree, the design
is dated, and the advent of cheap IF filters killed the design. The
harmonic mixing scheme really bothers me.

6EH7 is a good tube. The receiver part of my rig (google my call) uses
one in the RF stage and one in the first IF, with a 7360 mixer.

Been, there, done that Getting to see a lot of nice RXs searching
the web!

One word: Don't. Use a bigger power transformer, or an auxiliary
heater transformer instead. The rx you describe is a big project, why
compromise it? With a separate heater transformer having its own power
switch, you could put the critical oscillator heaters on it and let
them run semi-continuously.


As you noted, the design is inherently limited..

Self-exciting the 6JH8 means the signal will go into the deflectors
rather than the grid. That's the opposite of usual receiver-mixer
practice, where the oscillator feeds the deflectors. I don't know what
the noise figure will be, but I do know that all the beam-deflection
receiver mixers I've seen put the signal into the grid for high gain
and low noise.

Check SSB Exciter Circuits Using a New Beam Deflection Tube,
by K2FF in the March 1960 QST. It is one of the better presentations
that appeared in QST. He also shows a self-excited product detector
circuit as one example. I'd think the advantage in the PD with
G1 injection might be improved BFO blowby rejection,
which could otherwise affect the AGC system?


I don't know if you really need a buffer stage on the BFO. A 6BH6 will
do the job. See above about where the signal goes.

The buffer could be used for a CF or phase inverter, if I wanted to
use BFO injection on both deflectors. I know only one needs to be
driven in practice.

First mixer will be a 6ES8 Pullen, with a 6U8 used for the tunable LO and
buffer isolation.

How stable an oscillator is acceptable?

Buffer stage is recommended practice with the Pullen Mixer. It's easier
to use the pentode/triode, and ending not needing to use the stage, than
to add it later..

I'm not sure about the negative-feedback part but I do know the idea
was balance. And the 7360 deflectors were supposed to be biased a
couple dozen volts positive.

The negative feedback is mentioned in the QST article; it applies to
the product detector circuit where the deflector bias is taken directly from
the plates of the tube.

73 es GL de Jim, N2EY

Thanks for the comments..

Pete

Bob wrote:
ken scharf wrote:

Early SSB exciters used the 7360 tube as a mixer / vfo so I know this
type of tube will work as a self excited converter. As far as pulling
is concerned this would depend on the difference between the oscillator
and IF frequencies, or the oscillator and signal frequencies. But
pulling shouldn't be any worse than with the pentode mixers that
coupled the oscillator to the same grid as the signal input. At least
the 7360 isolates the signal and oscillator to different electrodes.
Also the signal input is balanced and shielded by the screen grid.
OTHO I don't know how good (stable) an oscillator this tube is.
Probably better as a crystal oscillator than a vfo.

The very /best/ mixer I ever made used the 7360.

I tried several other types of valve ("tube" - U.S.) mixer, but /nothing/
came even slightly close. The isolation of the local oscillator from the
incoming signal, the conversion gain, the accuracy of balance and the
bomb-proof nature of the mixer made it superior to /anything/ else I've
ever tried. In my receiver, there's a font-end amplifier, using a
variable-mu pentode then the 7360. It handles a bigger dynamic range
than /any/ other mixer.

The VFO is a "Kallitron" type, using two FETs and a PIC-based huff-and-puff
stabiliser (in 10 Hz steps) and two bipolar buffer amplifiers to drive the
grids of the 7360. The PIC also drives an LCD display of frequency, and
frequency stability is spectacular.

I can assure you - /there/ /is/ /no/ /substitute/ for the 7360. Simply
don't consider /anything/ else. Professionally, I've worked extensively
on "H-mode" switched mixers - often using very advanced components - and
can tell you that the 7360 out-performs /everything/ else!

Chris

Sounds like you're building a receiver with only one tube in it (a 7360)
and everything else solid state. Then again the 7360 probably makes a
very good product detector too.

Bob wrote:
ken scharf wrote:

Early SSB exciters used the 7360 tube as a mixer / vfo so I know this
type of tube will work as a self excited converter. As far as pulling
is concerned this would depend on the difference between the oscillator
and IF frequencies, or the oscillator and signal frequencies. But
pulling shouldn't be any worse than with the pentode mixers that
coupled the oscillator to the same grid as the signal input. At least
the 7360 isolates the signal and oscillator to different electrodes.
Also the signal input is balanced and shielded by the screen grid.
OTHO I don't know how good (stable) an oscillator this tube is.
Probably better as a crystal oscillator than a vfo.

The very /best/ mixer I ever made used the 7360.

I tried several other types of valve ("tube" - U.S.) mixer, but /nothing/
came even slightly close. The isolation of the local oscillator from the
incoming signal, the conversion gain, the accuracy of balance and the
bomb-proof nature of the mixer made it superior to /anything/ else I've
ever tried. In my receiver, there's a font-end amplifier, using a
variable-mu pentode then the 7360. It handles a bigger dynamic range
than /any/ other mixer.

The VFO is a "Kallitron" type, using two FETs and a PIC-based huff-and-puff
stabiliser (in 10 Hz steps) and two bipolar buffer amplifiers to drive the
grids of the 7360. The PIC also drives an LCD display of frequency, and
frequency stability is spectacular.

I can assure you - /there/ /is/ /no/ /substitute/ for the 7360. Simply
don't consider /anything/ else. Professionally, I've worked extensively
on "H-mode" switched mixers - often using very advanced components - and
can tell you that the 7360 out-performs /everything/ else!

Chris

The very first ARRL HB I ever owned (1967) used the 7360 in the mixer
stage of a classic receiver (HB67) as well as another design (junior
misers dream). The first receiver was an 80 meter single conversion set
with a crystal controlled converter ahead of it. Similar commerical
designs were the HA350 and the 2B. The HB67 used a 6D10 compactron as
the first mixer/oscillator in the converter section. The MMD receiver
had the 7360 in the front end (NO RF stage) with a first IF of 3300 KHZ.
An RF Q multiplier was used instead of the RF stage. As you mentioned
the oscillator injected into the deflection plates in both cases

ken scharf wrote:

Sounds like you're building a receiver with only one tube in it (a 7360)
and everything else solid state. Then again the 7360 probably makes a
very good product detector too.

No - the RF amplifier stage is a variable mu pentode, and there are more
variable mu valves used in the IF, another 7360 for the product detector,
and the rest is solid state. The hybrid approach seemed best - for
example, the variable current drawn by the audio stages is /entirely/
isolated from the IF supply, the front end supply and the local oscillator
supply. At the moment, it's a single conversion superhet, with a 10.7 MHz
IF (because I have 10.7 MHz filters), though I'm considering making it dual
conversion, with a very high first IF, to improve the inherent image
problems.

C.