Swamping transmitter input to amp
 

Hi all,
I am attempting to amplify a newly acquired multi elmac transmitter with a henry 2kw. The power of the elmac is too high and i have tried swamping it with a 50ohm dummy load in parallel with the amp. This helped but the input is still a little too high. Any suggestions? Is there a combination of resistors that can be used? Thanks. ND4jS. J

Swamping transmitter input to amp
 

On 03/23/2012 04:01 AM, ND4jS wrote:
Hi all,
I am attempting to amplify a newly acquired multi elmac transmitter with
a henry 2kw. The power of the elmac is too high and i have tried
swamping it with a 50ohm dummy load in parallel with the amp. This
helped but the input is still a little too high. Any suggestions? Is
there a combination of resistors that can be used? Thanks. ND4jS. J




Please note modern power resistors look a lot like transistors, and
frequently require heat sinks.

http://www.radio-electronics.com/inf...tor-values.php

Swamping transmitter input to amp
 

On Fri, 23 Mar 2012 11:01:10 +0000, ND4jS wrote:

Hi all,
I am attempting to amplify a newly acquired multi elmac transmitter with
a henry 2kw. The power of the elmac is too high and i have tried
swamping it with a 50ohm dummy load in parallel with the amp. This
helped but the input is still a little too high. Any suggestions? Is
there a combination of resistors that can be used? Thanks. ND4jS. J

1: Google "Attenuator", or look in your ARRL Handbook. You don't want to
just put a resistor in series or in parallel -- you want an L pad or
(much better) a pi- or T-circuit attenuator. Note that you probably need
a Honkin' Big Resistor or three -- whatever power reduction you achieve
from the exciter to the amp has to get burnt up in the attenuator; it
needs to be able to handle and dissipate the resulting heat.

2: Have you tried just turning down the drive (if you're operating SSB)
or retuning for a lighter load (if you're operating CW)? Either one is
easy to do, and doesn't require any equipment beyond what you have
already.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

Swamping transmitter input to amp
 

ND4jS wrote:
I am attempting to amplify a newly acquired multi elmac transmitter with
a henry 2kw. The power of the elmac is too high and i have tried
swamping it with a 50ohm dummy load in parallel with the amp. This
helped but the input is still a little too high. Any suggestions?

Hi,

Assuming the linear requires 80W input to produce 1500W,
you need 20W carrier input to the linear in AM mode.
I would replace the 6146 with a 2E26 (same base pin-outs)
and lower the screen voltage in the exciter
for 20W carrier output. Then, no need for an attenuator
and the exciter will run cool. Monitor the ALC output
voltage from the linear and adjust your modulation
for just below a trace of ALC on voice peaks.

The final tuning and loading adjustment of the linear
should be at full modulated input, not with just the 20W
carrier and no modulation, or the linear will not
be set up for full output. If you don't have an audio
oscillator to drive the Elmac, you might want to use
an 80W CW input level from another exciter,
and note the tune and load settings of the linear
for max output. Then keep those settings with the Elmac
exciter as input to the linear.

73,
Ed Knobloch

Swamping transmitter input to amp
 

On Sat, 24 Mar 2012 15:12:55 -0400, Edward Knobloch
wrote:

ND4jS wrote:
I am attempting to amplify a newly acquired multi elmac transmitter with
a henry 2kw. The power of the elmac is too high and i have tried
swamping it with a 50ohm dummy load in parallel with the amp. This
helped but the input is still a little too high. Any suggestions?

Hi,

Assuming the linear requires 80W input to produce 1500W,
you need 20W carrier input to the linear in AM mode.
I would replace the 6146 with a 2E26 (same base pin-outs)
and lower the screen voltage in the exciter
for 20W carrier output. Then, no need for an attenuator
and the exciter will run cool. Monitor the ALC output
voltage from the linear and adjust your modulation
for just below a trace of ALC on voice peaks.

The final tuning and loading adjustment of the linear
should be at full modulated input, not with just the 20W
carrier and no modulation, or the linear will not
be set up for full output. If you don't have an audio
oscillator to drive the Elmac, you might want to use
an 80W CW input level from another exciter,
and note the tune and load settings of the linear
for max output. Then keep those settings with the Elmac
exciter as input to the linear.

73,
Ed Knobloch

Ummm why not just lower the screen voltage on the existing 6146 ?

peter

Swamping transmitter input to amp
 

ND4jS wrote:
I am attempting to amplify a newly acquired multi elmac transmitter with
a henry 2kw. The power of the elmac is too high and i have tried
swamping it with a 50ohm dummy load in parallel with the amp. This
helped but the input is still a little too high. Any suggestions?

On Sat, 24 Mar 2012, Edward Knobloch wrote:
Assuming the linear requires 80W input to produce 1500W,
you need 20W carrier input to the linear in AM mode.
I would replace the 6146 with a 2E26 (same base pin-outs)
and lower the screen voltage in the exciter
for 20W carrier output. Then, no need for an attenuator
and the exciter will run cool. snip


On 3/24/2012 5:56 PM, Peter wrote:
Ummm why not just lower the screen voltage on the existing 6146 ?


Hi,

I think changing to a 2E26 instead of just cranking down the screen
voltage of the original 6146 for 20W output will result
in cleaner modulation. Starving the 6146 that much
for screen voltage may produce a varying load
to the modulator with plate (and screen) modulation applied.

Also, less risk of over-driving and possibly damaging
the tubes in the linear if the 2E26 is installed.
(A 2E26 costs about $4 new.) Cheap insurance.

73,
Ed Knobloch