I am in the early stages of building an 811/813 rig and need lots of help.

First of all, I can't seem to find plans or schematic for such a beast
but there must be hundreds of them out there.

I have the power supply, a Ranger to drive it, a cabinet and a few RF
parts but no modulator.

Would appreciate any help I can get.

JACK K9ACT


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http://www.amwindow.org/tech/htm/813/813.htm



Jack Schmidling wrote:
I am in the early stages of building an 811/813 rig and need lots of help.

First of all, I can't seem to find plans or schematic for such a beast
but there must be hundreds of them out there.

I have the power supply, a Ranger to drive it, a cabinet and a few RF
parts but no modulator.

Would appreciate any help I can get.

JACK K9ACT


--
PHOTO OF THE WEEK: http://schmidling.com/pow.htm
Astronomy, Beer, Cheese, Fiber,Gems, Sausage,Silver http://schmidling.com

"Jack Schmidling" wrote in message
...
I am in the early stages of building an 811/813 rig and need lots of help.

First of all, I can't seem to find plans or schematic for such a beast but
there must be hundreds of them out there.

I have the power supply, a Ranger to drive it, a cabinet and a few RF
parts but no modulator.

Would appreciate any help I can get.

JACK K9ACT


--
PHOTO OF THE WEEK: http://schmidling.com/pow.htm
Astronomy, Beer, Cheese, Fiber,Gems, Sausage,Silver http://schmidling.com

Jack,
The 1960 ARRL handbook has a single 813 amp and a GG amplifier with a pair
of
811s. The 17th edition (circa 1967) of Bill Orr's Radio Handbook features
designs for 813s and a specific design for a class-B modulator using a pair
of 811s.

After the 1960s, people turned to Linear amplifiers and switched to SSB from
AM.
Ed, N5EI
Ed, N5EI

Nomad wrote:
http://www.amwindow.org/tech/htm/813/813.htm

Been looking at that but not sure how to accommodate 811's for mods.

Also, I do not understand the purpose of the Heising choke in it.

Anyone know?

js


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The Heising choke removes the dc from the output side of the modulation
transformer. The DC saturates the core and reduces fidelity.

This circuit is not common in ham gear because of the additional expense,
weight and cost - but it was common in broadcast circles.

I would make one change to the 813/811 circuit. If you load the grid down
with fixed resistors, you can remove the need for neutralization. You would
load the grid side of the circuit enough so that full power from the exciter
(a Ranger I recall)) would just drive the amplifier.

More sensitive tubes can get away with using a 50 ohm resistor and no tuning
on the input. That would probably not result in sufficient drive (I have
not worked with the numbers). However, you could use something like a 300
ohm resistor to load the grid then use a 4:1 step up broadband transformer.
One less control. One less potential for overdriving the amp. No
neutralization.

73, Colin K7FM

COLIN LAMB wrote:

More sensitive tubes can get away with using a 50 ohm resistor and no tuning
on the input. That would probably not result in sufficient drive (I have
not worked with the numbers). However, you could use something like a 300
ohm resistor to load the grid then use a 4:1 step up broadband transformer.
One less control.

My thoughts exactly but what is a 4:1 broadband transformer, other than
the obvious?

I was talking to someone today about not tuning the input and he said it
can't be done.

js

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However, you could use something like a 300
ohm resistor to load the grid then use a 4:1 step up broadband transformer.

My thoughts exactly but what is a 4:1 broadband transformer, other than the
obvious?

I was talking to someone today about not tuning the input and he said it can't
be done.


One can certainly use a 50 ohm load for the exciter and a broadband transformer
with an impedance ratio sufficiently high so as to get the required RF voltage
on the 813 grid, but:

- if the required turn ratio is high, chances are that neutralization will
anyway be required, because the plate-to-grid RF voltage feedback (due to
plate-to-grid capacitance) will not see the grid as a sufficiently low impedance
point any more.

- it may not be easy to realize a broadband transformer properly working on the
whole 160meters - 10m- range and also showing a high reactance value at any
frequency across that range. In particular on the lower frequencies (e.g. 40 to
160 meters) its reactance may not be high enough to show the exciter a
purely-resistive 50-ohm load. A resonating parallel capacitor (different for
each band) may then be needed if one does not like the SWR meter to show some
reflected power.

73

Tony I0JX