"Kenneth Scharf" wrote in message
...

The reason that the 6146 tube generally requires neutralization and the
807 does not is because of the higher gain of the 6146. The 6146 will
draw greater plate current at a lower screen voltage (with the same
plate voltage) than the 807. It is the higher 'gain' of the screen
grid that matters here (since a screen grid tube acts as two triodes in
cascade as far as power gain is concerned). The 6146 is actually
better shielded than the 807 and has less lead inductance which helps
stability. In order to avoid neutralization the 807 requires extra
shielding to keep the grid from 'seeing' the plate. Sub mounting the
tube socket below the chassis so the bottom of the plate is even with
the level of the chassis will do the trick. James Millen sold tube
shields for the 807 which were aluminum cans open at both ends with
spade lugs to mount to the chassis. With the 807 sockets mounted to
the chassis and the shields mounted on the chassis, the tops of the
cans would be just below the level of the bottom of the 807 plates.
Recall the AN-ARC5 transmitters? They sub mounted the 1625 tubes so
the plates were just at the level of the chassis, same idea.


Neutralization becomes more of an issue the higher you go in frequency.
Most simple entry level transmitters using a single 6146 in the 1950's
and 1960's were not neutralized as the 6146 was only used "straight
through" on 80 or 40 meters. On higher bands it was used as a frequency
multiplier/power stage. The Eico 730, the Elmac AF67, the Heath DX-20,
DX-35, and DX-40, and the Knight T60 used no neutralization. The Eico
723, the Heath DX-60 and the Drake 2NT. however, did. If used on 80 and
40-meters only, I seriously doubt if Frank will need neutralization with
his 5933 as long as the driver tank is located below the chassis and the
final tank circuit is above the chassis. A shield around the base of the
5933 is a good idea, of course.

In the 1936 issue of QST, an article entitled "Operating Notes on the
Transmitting-Type Beam Power Tube" noted:
"Careful tests show that with shielding of this nature the tube has
no tendency to oscillate at frequencies up to and including the 7-Mc.
band; it functions as a true screen-grid amplifier. On 14 Mc. it
will self-oscillate after a fashion, but usually with negligible power
output.
When separately excited, however, it settles down nicely and behaves
like any normal amplifier, showing no tendency to go off on its
own — this, too, when driven by the fourth harmonic of a Tri-tet
oscillator operating at a very low power level. On the whole, therefore,
we have found no occasion for attempting to neutralize the tube,
which is fortunate, because it is always a rather messy job to neutralize
a tube with such low grid-plate capacity."

73, Barry WA4VZQ

"
Nordic Breeds WA4VZQ" wrote in message
... "Kenneth Scharf"
wrote in message
...

The reason that the 6146 tube generally requires neutralization and the
807 does not is because of the higher gain of the 6146. The 6146 will
draw greater plate current at a lower screen voltage (with the same plate
voltage) than the 807. It is the higher 'gain' of the screen grid that
matters here (since a screen grid tube acts as two triodes in cascade as
far as power gain is concerned). The 6146 is actually better shielded
than the 807 and has less lead inductance which helps stability. In
order to avoid neutralization the 807 requires extra shielding to keep
the grid from 'seeing' the plate. Sub mounting the tube socket below the
chassis so the bottom of the plate is even with the level of the chassis
will do the trick. James Millen sold tube shields for the 807 which were
aluminum cans open at both ends with spade lugs to mount to the chassis.
With the 807 sockets mounted to the chassis and the shields mounted on
the chassis, the tops of the cans would be just below the level of the
bottom of the 807 plates.
Recall the AN-ARC5 transmitters? They sub mounted the 1625 tubes so the
plates were just at the level of the chassis, same idea.


Neutralization becomes more of an issue the higher you go in frequency.
Most simple entry level transmitters using a single 6146 in the 1950's and
1960's were not neutralized as the 6146 was only used "straight through"
on 80 or 40 meters. On higher bands it was used as a frequency
multiplier/power stage. The Eico 730, the Elmac AF67, the Heath DX-20,
DX-35, and DX-40, and the Knight T60 used no neutralization. The Eico
723, the Heath DX-60 and the Drake 2NT. however, did. If used on 80 and
40-meters only, I seriously doubt if Frank will need neutralization with
his 5933 as long as the driver tank is located below the chassis and the
final tank circuit is above the chassis. A shield around the base of the
5933 is a good idea, of course.

My experience with 6146's (and one time with a 5933) was that from 40
meters on up, they could be easily be made to self oscillate if they were
lightly loaded. (talking final amplifier stages), and this is where a poor
man's neutralization procedure took place)
When lightly loaded, or better yet with no drive at all, swinging both
the input and output tuning condensers (sometimes referred to as
"capacitors") would induce an oscillation on the
intended band of operation. A single piece of wire used as a negative
feedback condenser could be wiggled about to find a place that tamed things
down.
Only problem with this was that the rough neutralization achieved was
frequency (or band) dependent. Usually it would be "good enough" if
neutralized on the highest band to be used.
Parasitic oscillation was a whole different problem, and didn't seem to
care much if the stage was neutralized or not!!!!!!

Lynn, W7LTQ

"Edmund H. Ramm" wrote in message
...
In "Nordic Breeds WA4VZQ"
writes:

[...]
Neutralization becomes more of an issue the higher you go in
frequency.
Most simple entry level transmitters using a single 6146 in the 1950's
and 1960's were not neutralized as the 6146 was only used "straight
through" on 80 or 40 meters. On higher bands it was used as a
frequency
multiplier/power stage. The Eico 730, the Elmac AF67, the Heath
DX-20,
DX-35, and DX-40, and the Knight T60 used no neutralization.

Nor does the E.F. Johnson Viking Ranger. But it's CW-only variant,
named "Navigator" IIRC, does.

The Eico 723, the Heath DX-60 and the Drake 2NT. however, did.

The Drake 2-NT has a 6HF5 line output valve in the PA stage.

Several of the transmitters I named also used TV sweep tubes. In
general, all of the higher power TV sweep tubes have a higher perveance
than does a 6146. In the case of the 6HF5, the transconductance (plate
amps/grid volts) is 1.6 times that of the 6146. My point was that with
reasonable layout, neutralization would not be required. All of these
transmitters multiplied in the final above 40 meters. If the plate is
tuned to a harmonic while the grid is tuned to the fundamental, there is
far less need to neutralize.

73, Barry WA4VZQ

"Nordic Breeds WA4VZQ" wrote in message
...
"Edmund H. Ramm" wrote in message
...
In "Nordic Breeds WA4VZQ"
writes:

[...]
Neutralization becomes more of an issue the higher you go in frequency.
Most simple entry level transmitters using a single 6146 in the 1950's
and 1960's were not neutralized as the 6146 was only used "straight
through" on 80 or 40 meters. On higher bands it was used as a frequency
multiplier/power stage. The Eico 730, the Elmac AF67, the Heath DX-20,
DX-35, and DX-40, and the Knight T60 used no neutralization.

Nor does the E.F. Johnson Viking Ranger. But it's CW-only variant,
named "Navigator" IIRC, does.

The Eico 723, the Heath DX-60 and the Drake 2NT. however, did.

The Drake 2-NT has a 6HF5 line output valve in the PA stage.

Several of the transmitters I named also used TV sweep tubes. In general,
all of the higher power TV sweep tubes have a higher perveance than does a
6146. In the case of the 6HF5, the transconductance (plate amps/grid
volts) is 1.6 times that of the 6146. My point was that with reasonable
layout, neutralization would not be required. All of these transmitters
multiplied in the final above 40 meters. If the plate is tuned to a
harmonic while the grid is tuned to the fundamental, there is far less
need to neutralize.

73, Barry WA4VZQ

You are surely correct there, Barry. I guess my homebuilt rigs never
multiplied in the final stage. I did try multiplying with a 211 (VT-4C)
triode in the final (read BC-375), but the power output instrument (75 watt
light bulb) was not impressed. (it did, of course have elegant Hammarland
neutralizing condensers in the plug-in tuning units)

Old Chief Lynn, W7LTQ

"Edmund H. Ramm" wrote in message
...

Several of the transmitters I named also used TV sweep tubes.
[...]

Yes, all several two of them: Eico-723 and Heathkit DX-20, apart
from the Drake 2-NT already pointed out by me. Which means they don't
belong in a discussion about true transmitting valves (807 and 6146),
and their respective merits regarding neutralisation.

BTW, the above mentioned Eico-730 is a modulator.

73, Eddi ._._.


I think I am detecting a hint of sour grapes here, Eddi. My post was a
reply to Ken Scharf's post saying the 6146 would be more stable than the
807 because of its higher perveance and lower lead inductance. The TV
sweep tubes generally have considerably higher perveance than the 6146.
As for lead inductance, some TV sweep tubes had exceptionally long leads
to reduce "blivets" (a.k.a. snivets, VHF parasitics sometimes associated
with Barkhausen oscillation); these were unsuitable for use in
transmitters above 7 MHz or so. One lot of 6HF5's ran the cathode lead
from the top of the tube to the base; these barely worked on HF [Bill Orr
W6SAI, "Full Blast" Operation of TV Sweep Tubes, Ham Radio, April 1968].

Yes, the Eico 730 was a typographical error. It should have been Eico
720. The DX-20 used a 6DQ6A which has only slightly more
transconductance than the 6146. The Knight T-60 also used a 6DQ6. The
AF67 used a 6146 with no neutralization. (Another rig I did not mention
was the Eico 753 which used a pair of 6DQ6's _without_ neutralization but
in AB1 linear mode. Of course, in AB1 it could not frequency multiply in
the final.) The 6146 has only a slight increase in gain over the 807.

As to whether receiving and TV sweep tubes should be included in the
discussion, 6L6 tubes have been used by hams in transmitters since the
1930's. In fact, the 1614 was a 6L6 designed for RF service. RCA even
notes that curves for the 807 apply to the 1614 within its maximum
ratings.

The original poster, Radio Vintage, wanted a simple 2 or 3 tube 80/40
meter transmitter with VFO. For circuit ideas, I believe that the large
number of articles using TV sweep tubes should not be ignored. The
discussion was not specifically about neutralization. I suggested
doubling in the final as a means to simplify the design in that
neutralization would likely be unnecessary.

73, Barry WA4VZQ

On 01/27/2011 06:35 PM, Nordic Breeds WA4VZQ wrote:
"Edmund H. wrote in message
...

Several of the transmitters I named also used TV sweep tubes.
[...]

Yes, all several two of them: Eico-723 and Heathkit DX-20, apart
from the Drake 2-NT already pointed out by me. Which means they don't
belong in a discussion about true transmitting valves (807 and 6146),
and their respective merits regarding neutralisation.

BTW, the above mentioned Eico-730 is a modulator.

73, Eddi ._._.


I think I am detecting a hint of sour grapes here, Eddi. My post was a
reply to Ken Scharf's post saying the 6146 would be more stable than the
807 because of its higher perveance and lower lead inductance. The TV
sweep tubes generally have considerably higher perveance than the 6146.
As for lead inductance, some TV sweep tubes had exceptionally long leads
to reduce "blivets" (a.k.a. snivets, VHF parasitics sometimes associated
with Barkhausen oscillation); these were unsuitable for use in
transmitters above 7 MHz or so. One lot of 6HF5's ran the cathode lead
from the top of the tube to the base; these barely worked on HF [Bill Orr
W6SAI, "Full Blast" Operation of TV Sweep Tubes, Ham Radio, April 1968].

Yes, the Eico 730 was a typographical error. It should have been Eico
720. The DX-20 used a 6DQ6A which has only slightly more
transconductance than the 6146. The Knight T-60 also used a 6DQ6. The
AF67 used a 6146 with no neutralization. (Another rig I did not mention
was the Eico 753 which used a pair of 6DQ6's _without_ neutralization but
in AB1 linear mode. Of course, in AB1 it could not frequency multiply in
the final.) The 6146 has only a slight increase in gain over the 807.

As to whether receiving and TV sweep tubes should be included in the
discussion, 6L6 tubes have been used by hams in transmitters since the
1930's. In fact, the 1614 was a 6L6 designed for RF service. RCA even
notes that curves for the 807 apply to the 1614 within its maximum
ratings.

The original poster, Radio Vintage, wanted a simple 2 or 3 tube 80/40
meter transmitter with VFO. For circuit ideas, I believe that the large
number of articles using TV sweep tubes should not be ignored. The
discussion was not specifically about neutralization. I suggested
doubling in the final as a means to simplify the design in that
neutralization would likely be unnecessary.

73, Barry WA4VZQ


When the 6146 was used as a class C final neutralization was optional
(except maybe on 10 meters). As a linear amplifier neutralization will
lower the IMD and is a good idea for a clean signal. Most SSB
transmitters with 6146's in the final were neutralized.

BTW on 2 meters the 6146 is ABOVE it's self neutralization frequency and
HF neutralization circuits don't work. Sometimes a tuned trap in the
screen did the trick, sometimes INCREASING the plate/grid feed back with
a gimick capacitor was used. Also grounding the metal base with spring
fingers instead of the base pin at the socket might be required.

If TWO 6146's were used in push pull on VHF a conventional cross over
neutralization scheme with gimick capacitors vs the tube plates worked
out well.