To:               baack@maine.edu
From:             Steve Harrison 
Subject:          Re:Meter Readings about the amp.


>I am sitting here doing a comparison of meter readings.
>( now I realize that they were modded by two different people, and 
>you might not be able to speak about the 144 amp as well as you could 
>the 432MHz amp. )

Well, actually, almost all the 144 readings will be at least a little bit
low because of a couple of diodes wired across the meter which cause the
meter to read low. Move the diodes where they are supposed to be, and the
144 meter would read a lot closer to the 432 readings. Lessee here..


>* = keydown
>? = idle

By idling, I believe you mean in receive mode. Idling is actually usually
what we call the mode when in transmit but with no RF drive.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


>VScreen readings:
>
>432 ? =02
>432* =40 ( minus 2 to 38 with talking / whistling on ssb)

This is correct. When the amp is not keyed, it will read the -02 you say
(actually, it should be zero; but the meter needle is probably not zeroed
now). When keyed but idling (no RF input), it will read about 40 as you
say. Then when putting out full power with the 451 driving it, it will stay
at 40 or drop very slightly to 38 as you say.


>144?=38
>144*=37 ( minus 2 to 35 with whistle)

The discrepancy here is that the 144 amp is wired so it always has screen
voltage, even in receive mode. Nothing wrong with that, really; I just like
to remove screen voltage on receive.


>Vgrid:
>432?=pinned off the scale
>432*=38 ( drops to 36 with whistle)

This is correct except that, again, idling would be with no RF drive.


>144?=38
>144*=38 ( fluctuates UP to 38.5 maybe )

This is correct; the meter reading goes up a bit because the guy who
modified the 144 amp probably didn't modify the grid bias regulator
circuit. The effect is small but results is a higher tendency to generate a
mite bit of splatter because the voltage is not completely stable.
Here, we will see the largest difference between the two amps because of
the diodes. If they were moved inside the 144 amp, the meter would likely
read at least as high and probably higher than the 432 amp for the same
output power.


>Cur-plate:
>
>432?= 3
>432*=10 ( then up to 46 with whistle)

>144?=0
>144*=10 (up to 24)

>V-plate:
>
>432?=23
>432*=21.5 (the whistle test to 18)
>
>144?=25
>144*=23 ( down to 19 on whistle)

The slight difference here is probably because the resistors in one or the
other amplifier are aging and changing value. I didn't have precise values
to put in the 432 amp to make the meter really accurate, and it's probably
reading slightly low as you note.
Here, the 432 amp actually has no signal at all for either RVS or FOR,
which are the REVERSE and FORWARD power readings for the directional
couplers in each amp. If you remember, I showed you how those are rated at
only 75 watts, and mentioned that they usually will die with the 400+ watts
they are subjected to in modified amateur service. Apparently, the 144 amp
still has the coupler installed. At some time, it will probably fail and
you will read completely different meter readings.

Meanwhile, however, the 144 amp RVS and FOR meter readings are useful
because they indicate the same as the Bird power meter, except that the
actual scale reading is probably not real accurate. But maybe it is; I
*think* I might have adjusted the 144 amp's reading to be the same as the
Bird when you had it down here. The readings for the 432 amp, on the other
hand, are completely meaningless. They are varying slightly with the
whistle blow because the power supply for the meter amplifiers is probably
varying voltage very slightly.


>RVS:
>
>432?= -0
>432*= -0
>
>144?=-0
>144*= -0 ( up to 16 on whistle blow)
>
>FWD
>
>432?=0
>432*=0 ( needle flickers but no reading on scale)
>
>144?=3
>144*=3( up to 45 on whilstle blow)

>SO what do you make of these readings?
>
>ANything you can tell me.. what normal is where they should be, 
>what to look out for ( if v-plate reads.. WATCH OUT)

About the only real problems will be these; and if you see these, the fuse
will probably blow next:

1. If Cur-Plate is pinned, STOP TRANSMITTING; it should drop to about 10.
If so, you are either overdriving the amplifier or the antenna SWR has gone
awry. If NOT, SHUT OFF HIGH VOLTAGE; you've probably lost the grid bias
power supply. With high voltage off, check Vgrid; in receive mode, it
should pin the meter; in transmit, it should read around 30 to 50 or so,
definitely no lower than about 30. If it does, something's not right with
the grid bias power supply.

2. You didn't mention the new Igrid meter position I added to the 432 amp.
Some people have added this position, but not too many as it's a
somewhat-involved modification.

As it is now, the 451 doesn't have enough drive to make Igrid read
anything; in fact, it should NOT read anything other than zero when driven
hard. Any meter reading in SSB would mean the amp is being overdriven and
it will be splattering (actually, the meter can read just a little bit; but
nothing higher than, maybe, 5 or 10). IF you had more driver power, such as
15 to 20 watts, you would be able to drive the amp into drawing grid
current and the meter could well peg. It would also be splattering
something fierce!

3. I also added Iscr, which is for reading screen current. Normally, your
432 amp can't be driven by the 451 to cause Iscr to read far from zero. But
if your antenna SWR were to go high, it's possible that Iscr would also
read high or negative against the lower peg. If you do not have an output
meter to watch and you are concerned about your antenna due to icing or
other possible erratic conditions, you can watch Iscr for sudden
fluctuations. Iscr is a very sensitive indicator of how the amplifier is
tuned or the output load (antenna SWR).

If you had 15 to 20 watts of drive, you would see considerable variation in
the Iscr reading with voice peaks. That would be normal although those
peaks should not reach either end of the meter scale; normally, even when
driven hard, Iscr will tend to remain around zero or slightly positive.

A secondary backup to the Iscr reading is the screen voltage, V-screen.
Normally, this will read around 40 on the meter. Under high drive, improper
plate tuning, or high antenna SWR, V-screen may drop significantly from 40
to as low as 20. If it drops more than about 5 meter divisions, you are
DEFINITELY either overdriving the amplifier, or it is not tuned up
correctly. The tube will last a lot longer when you do not drive or tune
the amplifier so that V-screen varies that much; and you also will not
generate nearly as much splatter. ANY variation in V-screen will cause some
splatter to be generated; but in these amplifiers, there will be a slight
drop in the meter reading due to power supply voltage drops even when the
amplifier is not being driven.

From:             Steve Harrison 
Subject:          6154/6155 Plate Tuning

I've received five replies on the plate tuning so far. Three of them are in
the 60 to 69 range, but two are way off..one is at 112 and the other is at
125! It may be that those two have the cavity "plunger" set for UHF instead
of VHF. This "plunger" is on the front of the cavity (not the front panel of
the cavity, but the cavity itself where the gears are), and is a short shaft
that sticks out the front by about 3/4" to 1"; it has a slip-lock tab on it
to keep it from slipping out of place, and there is a long pin through the
end by which one can grab it to change the plunger location. In the side of
the large cavity itself, there is a stamped notation that says 

                           VHF -->
                           <--UHF



which shows you which position the plunger should be in for either band,
116-150 MHz or 225-400 MHz. I do not know whether the cavity will resonate
on 2 meters when it is in the UHF position, but I suspect that it might. You
can pull the slip tab back and then grasp the shaft to pull it out; it takes
some muscle, but it will pull loose. It will come out about another 3/4" or
so. To put it back in, just push the shaft in until it seats and you can get
the lock tab back into the groove on the shaft. You won't hurt anything at
all by pulling it out and pushing it back in.

Anyway, you should find your output power peaking somewhere within the range
of numbers listed above.

I'm a new reader/subscriber to this reflector, and the owner of a AM6154.
 The last few weeks, have been very helpful, providing several new ideas,
and
hints on operation.  

1.  My over all intent is to raise the power output of this amp.  500 Watts
would be good,  1000 would be better, and I would like to try for the max
consistant, with putting out a  clean stable " amateur " signal.   Thank you
Dick for your patient explantion of the difference between 350 watts and 500
watts,  but your too late, I already climbed the tower to replace my
feedline
to gain 1.5 db, reworked my preamp to gain 1.5 db N/F,  Had I known  how
worhless 1.5 db was I wouldn't have bothered.  Does the term " weak signal "
ring a bell ?

2.  Abuse of the power ratings of tubes is in the finest tradition of
amateur
radio.  The best example I can think of is the multitude of  3-500 HF amps
able to run 1000 watts out  As of a few years ago the spectral purity of
these amps met amateur standards. Strict adherence to databook ratings is a
must for engineers designing for sale to customers.  We are explorers and
experimenters  working with limited budgets and resources.  Yes I think
either a 350, or 400 watt tube should be able to provide 500 watts or more
of
clean output, in amateur SSB or CW service. When I plan for tube service I
thought I
should work with "dissapation "  I want to radiate 500 watts not disapate it
as tube heat.  So if I have an efficient final tank well matched to the
tube,
and a suitable low SWR load should't I radiate most of the power ?    If the
Tank on the AM6154/5  is not well matched to the characistics of the 8930
how
can I improve it ?

3.  More specific questions :

A:  What are the specific limitations of the AM supply ?  Not enough
capactance for  SSB  dynamic regulation ?   How much would be enough ?  Not
enough Transformer  for good regulation ? 
   
B: Post a circuit for us non- engineers to copy to
monitor screen and control grid current  ?   I'm  looking in the various
handbooks for a circuit to give a visual alarm when I exceed proper drive
levels.  I don't think the heavily damped meter on the AM is fast enough to
show a good warning.  A circuit was posted here to show screen regulation, I
intend to try that.  I have also sent away for the info on the beefed up
grid
supply.  How about a switch circuit to run the thing in Class C on CW.
 Higher effencicy in C right ?   

C:  Specificly what does the "output filter " contribute ?  I was
planning to remove mine.  It is a 400 MHz low pass,  what specific spectral
products need to be filtered ?  I don't see low pass filters on any of the
Handbook designs. Nor any of the solid state products availible. 

D:  What is the proper way to tune the Input coupling, and output coupling ?
 How tight you are coupled would seem to have an effect on Linerty.  Tuning
for smoke at the moment.

Terry  K8NNU

From: Km1h@juno.com
  To: Wayne Heinen
Subj: RE: AM-6155

I feel that your last 2 posts were the best I have ever read on the
AM6154/6155 issue Dick. It was most refreshing!

When the AM series were first introduced to the ham bands QRO SSB/CW
activity was at an absolute low because you either had the kilobucks to
buy a Henry, etc or you had to build your own. Then as now the actual
ability of most hams to build anything of quality from scratch is very
limited. 

The AM offered Joe Sixpack a chance to boost his 10W to a new level at
minimal expense. Very quickly, all sorts of mods appeared in print to
improve performance on 3 ham bands. Some articles were great...others are
typical ham garbage. The good ones came to the conclusion that 300-350W
out was about the maximum in accordance with good engineering practice
(those last 3 words appear in FCC rules).

Now fast forward to 1995-97. We have an ever increasing number of
VHF/UHF ops that haven't a clue how to even spell "engineering" much less
conform to any quality standard. Not all these new ops came from the CB
ranks but they do share one common quality....that is to get absolute max
power and watch the meters bounce as high as possible. Not a clue as to
what is going up the coax except "lots of watts man". License class is no
guarantee  of ability any longer either. 
Again...not a clue if the bias or screen supply is losing regulation or
even what class of operation the tube is in. All they know is that they
can work that new grid on tropo or whatever and the h..l with any of the
locals. 

Next, add to this mix a few that for whatever reason have risen to levels
of prominence in the weak signal community and command a following of
like minded individuals. Even worse the newcomers think these guys are
gods.  Their sole reasoning, purpose  or emotion is Me.me.me and instant
gratification. In the real world they are called Prima Donnas. Many also
tend to claim various calling frequencies as their own personal preserve
but thats a different issue..............

The Svetlana 4CX400A is a nice tube and deserves serious consideration in
the AM and new construction. It IS NOT an excuse to get 500W out of an
 -xxxx. Its sole benefits are slightly improved efficiency and thermal
stability due to the Russian's continuing level of tube development back
when we were still enemies. That tube IS capable of a clean 600W output
but NOT under the AM power supply restrictions. Just take a serious look
at the AM PS dynamics and you will realize that 350-400W SSB PEP is about
the limit...period... for a nice clean signal. Above that the signal
really starts to deterioate and at 500W the IMD  AND spur levels remind
me of a CB sweep tube amp.   

73.....Carl  KM1H  in FN42 NH 

From: Lanej@provide.net
  To: Wayne Heinen
Subj: 4CX400 CONVERSION OF AM-6155

Here are the results of my implementation of the 4CX400 in the 144Mhz
conversion of the ) AM-6155.  

1)  10 watts yields 500 (supplies set for 240V)
2)  -44 volts bias yields 100 mA plate idling current
3)  Observed efficiency:  65%
3)  Bias voltage divider changes:  R14   15K, R16  4.7K 
4)  Paralell C2 with C1 on bias board.  (These caps may need to be replaced
on many amps due to their age.  I suspect bias instability may be due to
these caps failing in some cases.)

E-mail direct for more details -- John Lane, W8KX