First, my thank you's are in order to all who have answered my posts
concerning this amplifier...I have not yet fired it up, but I'm getting
there! (Taking it easy and following the good advice I've received).
Anyway, I've browsed the Heathkit manual and their instructions for
tuning the amp seem rather complicated....they tend to focus on tuning
for output and very specific plate and grid currents. Would it be safe
for me to instead use the following procedure (which is likely to get
me to the same point, but is easier to remember....it's the technique
we used t for the old club amplifier):

1) Turn on amplifier (of course) and allow it to warm up.
2) Set exciter for 80 watts output on cw (amp is supposed to take 100
watts, but I want to be on the safe side).
3) Set pulsed tuner aid so that I am running about a 25% duty cycle
(average power into amp will be 80 watts peak, but only 20 watts
average).
4) Set amp tune and plate controls to suggested starting points.
5) Switch amp out of bypass.
6) Tune amp "Load" for max power out, adjust "Tune" to dip plate
current, check grid and plate currents.
7) Increase pulsed exciter power gradually while repeating step 6.
7) Repeat step 7 until desired power out is achieved (keeping in mind
that I need to stay well within allowed grid and plate currents).


In a nutshell, that's how I remember tuning our club amp (although it
was near 20 years ago when I last tuned one.) Does this sound about
right? It seems much faster than the steps outlined by Heathkit and
safer too...also, would there be any problems with my signal if I keep
the exciter power fairly low...say at around 50 to 80 watts rather than
the 100 watts specified? (Granted, my output power will be lower, but
that is fine...especially while I'm still just testing the amp and if
any RFI will be generated by the amp.)
Thanks a bunch!
Craig KB8FGC

On Tue, 27 Jun 2006, wrote:

First, my thank you's are in order to all who have answered my posts
concerning this amplifier...I have not yet fired it up, but I'm getting
there! (Taking it easy and following the good advice I've received).
Anyway, I've browsed the Heathkit manual and their instructions for
tuning the amp seem rather complicated....they tend to focus on tuning
for output and very specific plate and grid currents. Would it be safe
for me to instead use the following procedure (which is likely to get
me to the same point, but is easier to remember....it's the technique
we used t for the old club amplifier):

1) Turn on amplifier (of course) and allow it to warm up.
2) Set exciter for 80 watts output on cw (amp is supposed to take 100
watts, but I want to be on the safe side).
3) Set pulsed tuner aid so that I am running about a 25% duty cycle
(average power into amp will be 80 watts peak, but only 20 watts
average).

I might even forget the pulser, and just use pure CW and start at 20 watts
of pure CW until you get the feel of "amp on" vs. "amp off" and the
effect of tuning.

4) Set amp tune and plate controls to suggested starting points.
5) Switch amp out of bypass.
6) Tune amp "Load" for max power out, adjust "Tune" to dip plate
current, check grid and plate currents.

I would recommend setting the loading control far CCW to start (i.e. low),
and tune the plate for maximum RF output. You may or may not see much of
a "dip" in plate current as you go through resonance (depending on what
"class" the amp is really running in), but you should see RF output go
from zero to something high.

7) Increase pulsed exciter power gradually while repeating step 6.
7) Repeat step 7 until desired power out is achieved (keeping in mind
that I need to stay well within allowed grid and plate currents).

Another issue you left out but you need to watch is what the SWR is
between the amplifier and its load. Quite a few of us (including me) use
an antenna tuner between our rigs and the transmission line. You almost
don't care what the SWR is between the tuner and the antenna, but on the
coax between the rig and the antenna tuner, you better be low (i.e. SWR
2:1 or lower, depending on the rig) instead of high (i.e. 3:1 or more)
because that reflected power will end up being dissipated in the
tube/heatsink. And, another thing: once I was a little off resonance on my
SB-230 and after transmitting for 1-2 minutes, the overtemp relay kicked
in and put the amp into bypass until the heatsink cooled off (this will
take a few more minutes, maybe less if you put a small fan on it) at which
time the bypass kicked off and I had power again (leave all the switches
on). So, you have to watch your plate resonance. If you raise loading,
always recheck plate resonance.


In a nutshell, that's how I remember tuning our club amp (although it
was near 20 years ago when I last tuned one.) Does this sound about
right? It seems much faster than the steps outlined by Heathkit and
safer too...also, would there be any problems with my signal if I keep
the exciter power fairly low...say at around 50 to 80 watts rather than
the 100 watts specified?

Not a bad idea until you get a feel for how the amplifier behaves in
tuning, how your lights dim on voice peaks, whether your circuit
breakers/fuses blow when you talk up the amp (have a flashlight handy at
night?), etc.

(Granted, my output power will be lower, but
that is fine...especially while I'm still just testing the amp and if
any RFI will be generated by the amp.)
Thanks a bunch!
Craig KB8FGC

Craig,
If it were me I would follow the Heath Kit instructions. I built that
amplifier in 1976, still have it. I have run it at 500 ma for many years
with it still putting out max power. I have had to replace the power supply
filter capacitors, other than than been a good 600 watts output amplifier.
While it might take a little longer to tune up, once you know what the
setting should be for a given frequency, you then can preset those and save
yourself alot of time.
Larry/W4LM

wrote in message
oups.com...
First, my thank you's are in order to all who have answered my posts
concerning this amplifier...I have not yet fired it up, but I'm getting
there! (Taking it easy and following the good advice I've received).
Anyway, I've browsed the Heathkit manual and their instructions for
tuning the amp seem rather complicated....they tend to focus on tuning
for output and very specific plate and grid currents. Would it be safe
for me to instead use the following procedure (which is likely to get
me to the same point, but is easier to remember....it's the technique
we used t for the old club amplifier):

1) Turn on amplifier (of course) and allow it to warm up.
2) Set exciter for 80 watts output on cw (amp is supposed to take 100
watts, but I want to be on the safe side).
3) Set pulsed tuner aid so that I am running about a 25% duty cycle
(average power into amp will be 80 watts peak, but only 20 watts
average).
4) Set amp tune and plate controls to suggested starting points.
5) Switch amp out of bypass.
6) Tune amp "Load" for max power out, adjust "Tune" to dip plate
current, check grid and plate currents.
7) Increase pulsed exciter power gradually while repeating step 6.
7) Repeat step 7 until desired power out is achieved (keeping in mind
that I need to stay well within allowed grid and plate currents).


In a nutshell, that's how I remember tuning our club amp (although it
was near 20 years ago when I last tuned one.) Does this sound about
right? It seems much faster than the steps outlined by Heathkit and
safer too...also, would there be any problems with my signal if I keep
the exciter power fairly low...say at around 50 to 80 watts rather than
the 100 watts specified? (Granted, my output power will be lower, but
that is fine...especially while I'm still just testing the amp and if
any RFI will be generated by the amp.)
Thanks a bunch!
Craig KB8FGC

Craig...At one time I had 4 SB230's
Now I have one on hf, and one converted to 6 meters.
Either tune by the book, or tune for maximum output....either way, just do
it fast.
The only big mistake to your steps I can see is not to start at 80
watts....that is close to full drive.
I would say to start at around 20 watts.
Make SURE the SWR that the amp sees is reasonable. ...less than 1.8:1 or
so....If you have a tuner in that path, make sure it can handle the
power....nothing MFJ!!!

Key down your rig while watching the amps' RF output and spin the plate knob
quickly each way to find a 'kick' or peak in output. At 20 watts drive, I'd
expect 150 or so watts out. Stop transmitting, and wait 5 or 10 seconds. Now
is the part that you only learn from experiance....it'd be nice if you were
doing it with a TS520's 6146 final....instead of an unobtanium
8873....But....
you need to transmit, and tune the load control while simultaneously
juggling the plate control. All the while looking at the wattmeter for more
output. At some point, rotating the load and peaking with the plate will
NOT end up in more output. That is where you stop.
Now you can increase power from the rig to whatever you want...but the load
and plate will have to be 'touched up' again with the increased drive.
Pulsers are kind of a waste. Someone who has used an amp for a while should
be able to tune it up in 2 or 3 three second transmissions. If you are
playing with knobs while key down for 15 to 20 seconds, you shouldn't own an
amp!!
....Dave


wrote in message
oups.com...
First, my thank you's are in order to all who have answered my posts
concerning this amplifier...I have not yet fired it up, but I'm getting
there! (Taking it easy and following the good advice I've received).
Anyway, I've browsed the Heathkit manual and their instructions for
tuning the amp seem rather complicated....they tend to focus on tuning
for output and very specific plate and grid currents. Would it be safe
for me to instead use the following procedure (which is likely to get
me to the same point, but is easier to remember....it's the technique
we used t for the old club amplifier):

1) Turn on amplifier (of course) and allow it to warm up.
2) Set exciter for 80 watts output on cw (amp is supposed to take 100
watts, but I want to be on the safe side).
3) Set pulsed tuner aid so that I am running about a 25% duty cycle
(average power into amp will be 80 watts peak, but only 20 watts
average).
4) Set amp tune and plate controls to suggested starting points.
5) Switch amp out of bypass.
6) Tune amp "Load" for max power out, adjust "Tune" to dip plate
current, check grid and plate currents.
7) Increase pulsed exciter power gradually while repeating step 6.
7) Repeat step 7 until desired power out is achieved (keeping in mind
that I need to stay well within allowed grid and plate currents).


In a nutshell, that's how I remember tuning our club amp (although it
was near 20 years ago when I last tuned one.) Does this sound about
right? It seems much faster than the steps outlined by Heathkit and
safer too...also, would there be any problems with my signal if I keep
the exciter power fairly low...say at around 50 to 80 watts rather than
the 100 watts specified? (Granted, my output power will be lower, but
that is fine...especially while I'm still just testing the amp and if
any RFI will be generated by the amp.)
Thanks a bunch!
Craig KB8FGC

Straydog wrote:



because that reflected power will end up being dissipated in the
tube/heatsink.

Another "Old Wives Tale"! Tubes are only "matched" to the point where
the desired output is obtained. Reflected power will see the amp as a
mismatch and will again be reflected back towards the antenna.

73, Roger

--
Remove tilde (~) to reply

Remember the USS Liberty (AGTR-5)
http://ussliberty.org/

I'd like to add one item to Dave's post below for caheaton's benefit:

If you don't have a 50-52 ohm dummy load (pure resistance, dry or oil,
whatever, but with capability to handle 100-200 watts of dissipation for
at least as long as you will be spinning those knobs), please get one.
And, learn how that amplifier tunes up going into a known, low SWR dummy
load (your SWR meter is between the transceiver and the amp). Your antenna
tunner (which is between the amp and the antenna feedline) shoud be tuned
up for low SWR _BEFORE_ you turn on the amp. After you know the SWR is
low, then turn on the amp and drive it with, say, that 20 watts of
carrier, or with the microphone gain turned down. Once you are statisfied
that the SWR is low with/without the amp in the circuit, then you can
crank up either the carrier (alone) for touch-up tuning, or crank up the
audio gain (and watch the room lights flicker, etc).

And, I'll go along with the recommendation below to do the tune up pretty
fast.

===== no change to below, included for reference and context =====

On Wed, 28 Jun 2006, Dave Edwards wrote:

Craig...At one time I had 4 SB230's
Now I have one on hf, and one converted to 6 meters.
Either tune by the book, or tune for maximum output....either way, just do
it fast.
The only big mistake to your steps I can see is not to start at 80
watts....that is close to full drive.
I would say to start at around 20 watts.
Make SURE the SWR that the amp sees is reasonable. ...less than 1.8:1 or
so....If you have a tuner in that path, make sure it can handle the
power....nothing MFJ!!!

Key down your rig while watching the amps' RF output and spin the plate knob
quickly each way to find a 'kick' or peak in output. At 20 watts drive, I'd
expect 150 or so watts out. Stop transmitting, and wait 5 or 10 seconds. Now
is the part that you only learn from experiance....it'd be nice if you were
doing it with a TS520's 6146 final....instead of an unobtanium
8873....But....
you need to transmit, and tune the load control while simultaneously
juggling the plate control. All the while looking at the wattmeter for more
output. At some point, rotating the load and peaking with the plate will
NOT end up in more output. That is where you stop.
Now you can increase power from the rig to whatever you want...but the load
and plate will have to be 'touched up' again with the increased drive.
Pulsers are kind of a waste. Someone who has used an amp for a while should
be able to tune it up in 2 or 3 three second transmissions. If you are
playing with knobs while key down for 15 to 20 seconds, you shouldn't own an
amp!!
...Dave


wrote in message
oups.com...
First, my thank you's are in order to all who have answered my posts
concerning this amplifier...I have not yet fired it up, but I'm getting
there! (Taking it easy and following the good advice I've received).
Anyway, I've browsed the Heathkit manual and their instructions for
tuning the amp seem rather complicated....they tend to focus on tuning
for output and very specific plate and grid currents. Would it be safe
for me to instead use the following procedure (which is likely to get
me to the same point, but is easier to remember....it's the technique
we used t for the old club amplifier):

1) Turn on amplifier (of course) and allow it to warm up.
2) Set exciter for 80 watts output on cw (amp is supposed to take 100
watts, but I want to be on the safe side).
3) Set pulsed tuner aid so that I am running about a 25% duty cycle
(average power into amp will be 80 watts peak, but only 20 watts
average).
4) Set amp tune and plate controls to suggested starting points.
5) Switch amp out of bypass.
6) Tune amp "Load" for max power out, adjust "Tune" to dip plate
current, check grid and plate currents.
7) Increase pulsed exciter power gradually while repeating step 6.
7) Repeat step 7 until desired power out is achieved (keeping in mind
that I need to stay well within allowed grid and plate currents).


In a nutshell, that's how I remember tuning our club amp (although it
was near 20 years ago when I last tuned one.) Does this sound about
right? It seems much faster than the steps outlined by Heathkit and
safer too...also, would there be any problems with my signal if I keep
the exciter power fairly low...say at around 50 to 80 watts rather than
the 100 watts specified? (Granted, my output power will be lower, but
that is fine...especially while I'm still just testing the amp and if
any RFI will be generated by the amp.)
Thanks a bunch!
Craig KB8FGC

On Wed, 28 Jun 2006, Roger D Johnson wrote:

Straydog wrote:



because that reflected power will end up being dissipated in the
tube/heatsink.

Another "Old Wives Tale"! Tubes are only "matched" to the point where
the desired output is obtained.

All depends on your definition of matched.

Reflected power will see the amp as a
mismatch and will again be reflected back towards the antenna.

I think that is only partly true. Yes, there will be reflectd power going
back out to the antenna, but there was an article in QST back a number of
years ago. Yes, the mismatch also results in higher plate dissipation,
too. I will correct myself about reflected power being disipated in tube,
but the mismatch will increase the plate dissipation. The other issue is
being off plate resonance. I had my SB-230 trip the overtemp relay when I
moved frequency and did not retune the final.

You also need to allow for loss in the transmission line. Not all of what
gets reflected at the mismatches ends up at the other end of the
transmission line. SWR (i.e. reflected power generated at the
antenna/feedline) would not be a problem if the transmission line
were long and lossy.

73, Roger

--
Remove tilde (~) to reply

Remember the USS Liberty (AGTR-5)
http://ussliberty.org/

Thanks again to the group for all the advice. Yes, I had planned on making
sure the antenna was tuned before hitting it with the amp (guess I should
have mentioned that). The tuner I bought should take the power
okay...recently purchased a used (but in great shape) Nye Viking MB-II. I
also have a Heathkit Cantenna dummy load (with oil) I purchased at the same
Hamfest, so I should be all set in that department. I've also run a
dedicated circit for the amp (240 volts) and while I was at it ran a
dedicated 120 volt circuit for the rest of my shack's equipment....so at
least the amp shouldn't be dimming the lights! :-)
Thanks again and please keep up the discussion....I'm absorbing all of this
collected wisdom and will blend it to form my own procedure....hopefully
none of this will be for naught!
73, Craig KB8FGC

straydog wrote:
A bunch of stuff about Art Maxwell...

Art, W4PON



Art, consider it this way, if you have high SWR, you are driving
a load that is the wrong impedance for your transmitter. Suppose
we were talking about an audio amplifier that was designed to drive
an 8 ohm speaker. If we drove a 1 ohm speaker, would you not expect
the audio amplifier to be over loaded? Perhaps a little hot around
the collar? If we drove a 1000 ohm speaker, the amplifier would have
trouble generating enough voltage to get any significant power out to
the load.

Art Maxwell wanted to drive a low VSWR load because he was using
coaxial cable, and as the VSWR increases, the cable sees higher
voltages and currents inside of it than it will see at a 1:1 VSWR.
These higher voltages and currents will cause cable heating, and
a loss of power to the antenna.

If one was using a high impedance ladder line type of transmission line,
it wouldn't much matter what the VSWR was, but not so for coax.

-Chuck Harris

On Thu, 29 Jun 2006, Chuck Harris wrote:

straydog wrote:
A bunch of stuff about Art Maxwell...

His name is Walter Maxwell and I did use his name correctly. I also wrote
a number of sentences about my experiences and I related all this to
Craig's questions.

Art, W4PON



Art, consider it this way, if you have high SWR, you are driving
a load that is the wrong impedance for your transmitter.

If you read Walter Maxwell's articles, you would see that by his
explanations the sentence you just wrote is wrong.

Suppose
we were talking about an audio amplifier that was designed to drive
an 8 ohm speaker.

I have measured the DC resistance of many 8 ohn speakers and they always
show less than one ohm of DC resistance.

If we drove a 1 ohm speaker, would you not expect
the audio amplifier to be over loaded?

Would you care to specify what you are driving that "1 ohm speaker" with?
DC, AC (complex waveform, sine waveform, square waveform)? Duty cycle? How
much voltage? Would you care to specify whether that speaker is heavily
coupled to the atmosphere or lightly coupled? If the speaker were in outer
space, what "X ohms" would you expect it to be?

Perhaps a little hot around
the collar? If we drove a 1000 ohm speaker, the amplifier would have
trouble generating enough voltage to get any significant power out to
the load.

Art Maxwell

I don't know any Art Maxwell, but the author that I talked about was
Walter Maxwell.

wanted to drive a low VSWR load because he was using
coaxial cable, and as the VSWR increases, the cable sees higher
voltages and currents inside of it than it will see at a 1:1 VSWR.

Walter Maxwell included a substantial amount of historical information
regarding the fact that amateurs used open wire feeders for decades before
coax came out and that all these guys didn't know anything about SWR but
when SWR was discovered, it was also discovered that all of these guys
were very effectively communicating under conditions of very high SWR and
the reason it didn't mean anything is tht open wire feeders have very low
losses, generally even much lower than good coax. I have seen attenuation
figures in the older editions of the Radio Handbook. Its true.

These higher voltages and currents will cause cable heating, and
a loss of power to the antenna.

I once ran a 100 watt output 440 mhz brick amplifier to a 440 mhz beam
with 1.2-1.1 SWR through a 50 foot length of RG-8/U on FM and the cable,
during the course of a 30 minute two way QSO became a good 20 degrees
warmer.

If one was using a high impedance ladder line type of transmission line,
it wouldn't much matter what the VSWR was, but not so for coax.

According to Walter Maxwell, it does not have to be high impedance
ladder/open wire. And, what does matter is that the transmission line,
regardless of its characteristic impedance, be low loss. I think he is
right.

-Chuck Harris