7360 or 6JH8 for first mixer?

[Tio Pedro]

Has anyone tried a 6JH8 in place of a 7360 for the
first mixer in a homebrew RX? How did they compare?

Pete

[raypsi]

Post by Tio Pedro
Has anyone tried a 6JH8 in place of a 7360 for the
first mixer in a homebrew RX?  How did they compare?
Pete

Well Eico uses a 7360 as a balanced modulator in my Eico 753. When it
comes time to replace it I'm going with the TV set version, 6LE8 used
as a chroma demodulator. I see the 6JH8 has an extra grid. I know you
can use it but you are going to have to play with that extra grid it
may not just go to ground, like most suppressor grids.

[Tio Pedro]

"raypsi" <***@gmail.com> wrote in message news:68e2ffeb- Well Eico
uses a 7360 as a balanced modulator in my Eico 753. When it
comes time to replace it I'm going with the TV set version, 6LE8 used
as a chroma demodulator. I see the 6JH8 has an extra grid. I know you
can use it but you are going to have to play with that extra grid it
may not just go to ground, like most suppressor grids.



Transmitters don't worry about noise figure or dynamic range...
I'm more worried about how the different gated beam tubes will
work in receiver applications.
Regarding your proposed mod, check this
website:http://members.shaw.ca/pacifictv/cartridg.htm
The 6JH8 can be used in lieu of the 7360 by following the
pin layouts shown on that page, as was done by Swan.

Pete

[Michael Black]

Post by Tio Pedro
Transmitters don't worry about noise figure or dynamic range...
I'm more worried about how the different gated beam tubes will
work in receiver applications.

I caught that point in your original post.

There were plenty of articles about using the other but cheaper
tubes similar to the 7360. But I'm not certain any I saw used
them as a first mixer. One could go back and check. And if
that's the case, either everyone just copied Squires 1963 article,
or there actually was a good reason to not use the cheaper variants
for the first mixer.

MIchael VE2BVW

[Tio Pedro]

Post by Michael Black
There were plenty of articles about using the other but cheaper
tubes similar to the 7360. But I'm not certain any I saw used
them as a first mixer. One could go back and check. And if
that's the case, either everyone just copied Squires 1963 article,
or there actually was a good reason to not use the cheaper variants
for the first mixer.
MIchael VE2BVW

Hi Micheal

Most of the magic seems to be being able to generate push-pull LO
injection for the deflection plates, that along with the P-P output tank
balance, is critical for max. signal rejection at the mixer output. I do
have
a 1600kHz daytimer next town over (1st IF is1600 kc.)

I was thinking of using a trifiliar wound balun, driven by a cathode
follower
buffer of off the first LO, to provide the 3 volt RMS injection to the
deflection
plates. That should provide balanced drive voltages to each deflection
electrode? Squires never provided a lot of
detail on his coils or how they were made. A balun might provide a modern
solution for balanced P-P injection from otherwise single ended LO sources.

Pete

[raypsi]

Post by raypsi

Post by Tio Pedro
Has anyone tried a 6JH8 in place of a 7360 for the
first mixer in a homebrew RX? How did they compare?
Pete

Well Eico uses a 7360 as a balanced modulator in my Eico 753. When it
comes time to replace it I'm going with the TV set version, 6LE8 used
as a chroma demodulator. I see the 6JH8 has an extra grid. I know you
can use it but you are going to have to play with that extra grid it
may not just go to ground, like most suppressor grids.

[J***@gmail.com]

Post by Tio Pedro
Has anyone tried a 6JH8 in place of a 7360 for the
first mixer in a homebrew RX? �How did they compare?
Pete

Back in the 1960's, Pat Hawker, G3VA reported (Amateur Radio
Techniques, Pat Hawker G3VA, 3rd ed, RSGB, p83) that Brian Booth,
G3SYC (SK ca. 2003), had used the 6JH8 beam deflection valve instead
of the 7360. Brian compared the two devices:
i) 6JH8 has a good deal more linear transfer characterisitic
ii) 6JH8 operates with the deflector plates at 0 volts, ie unnecessary
to bias to plus 25 Volts as per the 7360
iii) roughly similar transconductance 4400micromhos vs 5400micromhos
for the 7360
iv) 6JH8 has double the anode dissipation (3 watts)
v) then as now the 6JH8 is significantly cheaper.

The final comment was that Brian had used the 6JH8 as a receiver
mixer and also successfully as a mixer in transmitter circuits.

HTH and 73

John KC0G

[Tio Pedro]

Post by Tio Pedro
Has anyone tried a 6JH8 in place of a 7360 for the
first mixer in a homebrew RX? ?How did they compare?
Pete

Back in the 1960's, Pat Hawker, G3VA reported (Amateur Radio
Techniques, Pat Hawker G3VA, 3rd ed, RSGB, p83) that Brian Booth,
G3SYC (SK ca. 2003), had used the 6JH8 beam deflection valve instead
of the 7360. Brian compared the two devices:
i) 6JH8 has a good deal more linear transfer characterisitic
ii) 6JH8 operates with the deflector plates at 0 volts, ie unnecessary
to bias to plus 25 Volts as per the 7360
iii) roughly similar transconductance 4400micromhos vs 5400micromhos
for the 7360
iv) 6JH8 has double the anode dissipation (3 watts)
v) then as now the 6JH8 is significantly cheaper.

The final comment was that Brian had used the 6JH8 as a receiver
mixer and also successfully as a mixer in transmitter circuits.

HTH and 73

John KC0G

Great info, thanks! But I wonder how he achieved DC balance with
the deflectors set for 0 volts?

Pete