I have been a bit overwhelmed by my offer to machine teflon cocoons for
the aboveamp conversion. Anyone who has already requested them-I have a
list will- get them.
However, we are beginning our long awaited move to the N.C. mountains,
so time on the lathe is at a premium. My apologies to those whom I
cannot get to. Perhaps after I am settled in, we can try this again.. Of
course, first things first, the tower, EME dishes etc!!

Dale W4OP parinc@bellsouth.net 

Greetings to all,
I have a question abt the AM-6154 amp, as used on 144mc.
Is it absolutely neccesary to use the Teflon plate choke mod on 2m, or is
this only requiered for 220mc on up? If required, does anyone have the
Teflon neccesary for this?
Dave  N9HF
kerld@uwwvax.uww.edu


Hi Dave,

I made several of these for some friends a few months back, and can set up
the lathe to make another- no charge, just cover my mailing. Not sure I
still have the drawing though. If you do not have a drawing I'll mail the ham I
made the other ones for. Let me know.

Dale W4OP
for PAR Electronics, Inc.
parinc@bellsouth.net

Hi, Jim;

Your request for help was passed on to myself by still another guy who
picked it up from the W6YX reflector, to which I don't subscribe.

At 01:41 PM 1999-08-20 -0400, you wrote:
>Hi MIke,
>Have field-striped the VHF amp and as mentioned 
>last night, found the input coupling capacitor 
>shorted. That is, the rotor shorted (actually dragging)
>to the stator.

Very unusual; I don't think I've ever seen a possibility of the rotor of
the input coupling cap being so misaligned! But in fact, the rotor itself
is press-fit on the end of the black shaft. You may or may not be able to
press it back into place snug against the shoulder of the black shaft that
locates the shaft on the inside of the grid compartment.

>Would you be so kind as to post a message on 
>the VHF reflector requesting "the rotor portion 
>of the input coupling capacitor, C2, of the
>6154 VHF Amp. If that is not available, would 
>consider the grid line assembly which consist 
>of the C2, input coupling capacitor, C1, the 
>input tuning capacitor and the TNC RF input 
>connector. Don't really need C1, so if that
>were removed, it would be OK."

I presume that you were able to get the Bristol set screws in the end of
the grid line loose so you could pull the long grid line out? That's quite
a feat; few of those setscrews ever come loose again, and I've worn out a
lot of drill bits trying to drill them out.

Why do you need to replace the TNC input connector, too? Is the wiper that
connects the rotor of C2 to the center pin of the connector in good shape?
C1 is the capacitor that most often gets "screwed up" as some folks attempt
to remove plates to reduce the sharpness of grid tuning (which is
exarcerbated by the backlash of the whole grid tuning shaft assembly). I've
been able to find several small replacement capacitors that just barely fit
in the place of C1, but most do not; the ceramic insulator is just a tad
too large.

I do have several spare input coupling cap rotors on the black shafts as I
remove them for 432 MHz conversions. The black shaft is semi-flexible; in
one amp, I could not get the setscrews in the end of the grid line loose so
I could not remove the grid line pedestal inductor. But the pedestal was
already loose (the reason it had to be replaced) and I was able to rotate
it slightly while rotating the rotor of the cap, and carefully bending the
black shaft itself, while working the rotor and shaft past the pedestal.
Once the rotor was out, the pedestal could be unscrewed. Actually, I
believe I had to rotate the rotor to allow the pedestal to be rotated one
turn which allowed rotating the rotor into still another position which
allowed the pedestal to completely clear as it was unscrewed from the grid
line. Once I got the rotor out, the black shaft was again straight even
though I had to bend it slightly to get the rotor to clear the pedestal.

Then I made another interesting discovery: by drilling the shaft hole in
the side of the grid box to 1/4", it was possible to replace the original
single-plate input coupling capacitor with a multiplate Johnson trimmer
similar to the type used for C1. This allowed building a whole new input
coupling circuit that was able to tune both 144 and 222 MHz. The gear on
the end of the black shaft fits these trimmer caps perfectly. The threaded
mounting shaft of the capacitors is just barely long enough to allow the
outside nut to be tightened securely. What I did in this case was to
replace the original grid line (which had been cut in an abortive 432
modification by the former owner) with a center-tapped inductor loaded by
the tube grid on one side and tuned by the original grid tuning capacitor
C2 on the other end (basically a half-wave LC tank). I used the original
grid bias choke, soldered to the middle of the new inductor, to feed grid
bias to the coil and thence the grid. In this case, I had more than 10
watts drive available so installed a couple of 1K/2W carbon comp resistors
from the grid to a button mica feedthrough cap installed on pieces of brass
shim stock soldered to the shell of the socket to load the grid (ordinary
grid swamping technique). The input was link-coupled with the inductance of
the loop tuned out by the new C1 mounted where the black shaft used to be.
As it turned out, the new cap wasn't really needed as I eventually had to
short it for best input VSWR, which is something less than 1 watt reflected
for 15 watts forward on either 144 or 222 MHz.

>Also found three screen grid bypass capacitors bad, 
>one broken and two scorched pretty badly so have 
>replaced  them. Amazing what one finds when all the 
>other stuff is taken off the bottom of the tube socket.

I've often found the small mica caps on the screen terminal to appear to be
scorced, but they were always good. I suspect that the caps came from the
manufacturer that way as I've previously seen them, brand-new from the
vendor, with the center portions of the caps already slightly blackened.

If you look at the ITT schematics for the VHF and UHF RF drawers, you will
notice that they appear to specify different sockets for each frequency
range (the schematics also mention the capacitance of each socket but I
don't have them immediately at hand and don't remember the capacitances). I
have not yet been able to check the vendor's capacitance specification for
the sockets as I just noticed this a few weeks ago and the remaining VHF
and UHF drawers that I have here all have the same socket, a Johnson
124-110. I suspect that in the VHF amplifiers, they may have simply added
the capacitors so the lower-capacitance sockets used in the UHF amps could
also be used on VHF. I don't feel this is a very satisfactory compromise,
however. It causes a lot of additional inductance due to the screen lead
inside the socket and the mica capacitors which may make the amplifiers
less than completely stable at VHF. In fact, I have had one RF drawer
oscillate to the point that I finally had to add neutralization. I suspect
that if I installed the higher-capacitance socket in that drawer, the
neutralization may not be necessary.

>There was a lot of dirt there too. This tube 
>looks pretty clean. 

I believe that at least during the last years of removal from service and
before selling to the surplus dealers, many of these units went through at
least a cursory refurbishment at some FAA repair depot which including
installing new tubes. I've encountered some mainframes that had updates
added to the grid bias and DC-to-AC inverter modules along with date stamps
on the module frames as late as 1991, plus tube date codes as late as 1993.

>It is labeled Eimac, FEZA 3140.

Is that stamped in red ink or a engraved number? The engraved numbers were
internal Eimac lot ID numbers; the tube type should be stamped in red.
There should also be a date code such as 2491, which would mean the tube
was manufactured in the 24th week of 1991. Actually, however, I've not
encountered any of these amps lately with Eimac tubes; almost all have had
the Amperex DX393 installed which seems to work as well as the Eimac. And
the tubes have all appeared to be brand new.

73, Steve K0XP

To:             	wb5apd@STC.NET
From:           	Steve Harrison 
Subject:        	Re: (Fwd) am-6155
Copies to:      	baack@maine.edu

At 07:31 AM 2/22/99 -0500, Bob Dodson wrote:
> I have a totally stock (un-modified) am-6155 here. Can I put a variac on
>it and bring all voltages up slowly to condition tube and PS.

Hi Bob, the answer is no, you cannot use a variac to "condition" one of these 
amplifiers because they
have internal relays (including a time-delay) that require full 120VAC to
turn on.

>Should it be in tune or operate or does it matter. Want to make sure it
has cut off
>bias etc before I try this. What do I need to do to bring this stock amp
>up.

In stock condition, the amplifier will not work as it requires
interconnection with the accompanying exciter; some relatively-minor
modifications must be performed in order to use these amplifiers in
stand-alone amateur use. The grid circuit will not resonate within any
amateur band without some modification, and there is no built-in switching
for cut-off bias, nor any provision for antenna transfer switching.

A request for power connectors:

From:             Arthur Moe 
To:               kosrd@juno.com

I have found a small quantity of power plugs for the AM-6155/6154 or
other equipment using the small twist lock.

$5.50 shipped.

Art
KB7WW

Jeff K Sherman wrote:
> 
> Hello All,
>   Does anyone have a AM-6155 Power Cord that can be parted with ???
> If so, I need one.


 General repair

You may want to contact Richard Staron, VE3FAC, at 
regarding the AM series amps.  Rick, a long time friend and an excellent
builder, has done extensive mods on those amps for 144/222/432 Mhz.  He
MAY have changed e-mail addresses so get back to me if the e-address is
no good. 

Stan Timms, VA3ST (ex-VE3DIR), has also done a lot of work on the 222
and 432 Mhz amps.  Unfortunately he does not have e-mail and his
telephone number is unlisted.  I have it but would need his permission
to give it out.  His address should be OK in the usual ham databases. 
It's in Fonthill, Ontario.  He has particular experience in getting the
432 amp stablized.  The usual mods leave it pretty flaky as far as
tuning goes. (I stick to 8877's!)

Good luck!
-- 
73,

Peter Shilton			         Address:	215 Windecker Road
VE3AX (ex-VE3VD, VE3EMS)		          	R.R. #1
FN02cw						        Cayuga, Ontario, CANADA
Mail to: VE3AX@iCOM.ca			                NŻA 1EŻ






 
From:             Steve Harrison 
Subject:          Re: AM 6154/55  HELP!!! I LOST THE TUBE!
Date sent:        Mon, 28 Jul 97 12:29:08 EST5EDT


>(Without a meter, I have no *true* way of telling that the tube is 
>bad) But my elmer has a tube tester, and we are going to take a look 
>at it later this week... snif... snif..

Sure, you do...the front panel meter will tell you if the tube is gone! If
it still draws plate current when you talk, then the tube is OK. If there
seems to be nearly no output (everyone says you're super-weak), then you
probably blew something inside the RF drawer. If this is the case, I can
tell you what to look at. It will not be any fun, though...disassembly of
the RF drawer cavity assembly is a pain at the least and a REAL pain at
worst.

So,
1. Does the plate current meter wiggle? The tube's likely good.
2. If it does not wiggle when you talk, does it at least rise up to about
the same current that it did before when you don't talk? This should be
between 50 and 100 milliamperes on the meter (the plate current meter is 500
mils full scale). The tube's probably good and something broke, blew or came
unsoldered in the tube grid compartment.
3. Does the air exhaust still get hot in transmit (not merely warm, and it
will be warm just sitting there in receive mode..but HOT)? If so, the tube
is probably still pulling current; and if it's doing that, then it's
probably still good.

If the plate current meter does not rise in #2 above, look at the grid bias
voltage; when in receive mode, the meter should be pinned which represents
over -100 volts cutoff bias. In transmit mode, the meter should drop down to
some lower voltage, usually between -60 and -80 volts, and the tube's plate
current should increase as the voltage is adjusted less negative.

Also, look at the plate voltage; it should be over 2000 VDC in receive mode
(usually around 2500 or slightly more, maybe even 2700) and drop to perhaps
as low as 1900 when the tube draws as much as 400 mils or more.

>SO, I called RF parts. (For a new tube)
>They quoted the 8930 at $200.00 and they would have to order it.
>They also said that they had a Penta (sp??) DX-393 equivalent for 
>$129.00 (in stock)






DO NOT ORDER A NEW TUBE!!! At least, not yet. There is an even better tube
available for either $120 or $140 that will give more output power than the
8930...ah so, I see your next question; I've already answered the first
part. Yes, you do have to make one mod, but it's physical. The stock tube's
anode is slightly larger in diameter than the 4CX400A by about 80 thousands
of an inch, just enough that the 400A will not make good contact to the
finger stock without bending it out. So the mod is simply to bend the finger
stock CAREFULLY toward the center of the socket. Do this a few fingers at a
time and just bend them a little bit at a time until you figure out how much
to bend them to make contact with the 400A's anode. You can hold the 400A
upside down to see how much you are bending the fingerstock. The fingerstock
material is beryllium-copper and fairly brittle; that is, if you bend it too
much, the fingers will snap off. Breaking off a couple of fingers here and
there won't hurt you, particularly on 2m..but try not to do it!


>A) How complicated is it to change these tubes? 
It's a mere swap and bend the fingerstock.

>B) Which one should I go with? (Is the Penta any good??)
 Don't even consider Penta at all. Go for the 4CX400A because it will do just as well as
the 8930 at much less cost.

Has your Elmer had much experience with tuning tube amplifiers? These beasts
do not tune very similarly to lower-frequency HF-type amps at all. They
really have to have a power meter on the output to get tuned well, you
really cannot do it by simply watching the plate current or other front
panel meter indications. If you didn't blow the tube, then I strongly
suggest you break a leg trying to at least borrow a Bird or something;
alternatively, we can design a simple little RF detector that you can
install to give you a front panel indication of RF output. This would use
the cables inside the RF drawer that originally were attached to the output
power sensor (BTW, you never did tell me whether that device is still inside
your amplifier).

73, Steve Ko0U/1

  






HI RON & BERT
have lost all info from years back on AM6155-65 conversion's
But one of the thing's some guy's found was dirty plate?tank cavity
assembly's absorbing RF output ????? simular to bert's problem---
this is a help of problem only as it appears to be additional needed
remedities per other return help info indicates. I use lacqure thinner
to swabb out/clean electronic's! cheap ???
also be sure to only use KAPTON insulator on plate bypass as some have 
used teflon with poor results?? being porous and requires thicker
material than kapton, dilerict/voltage rating is much better per mil
thickness!!!!! see recent reflector posting for source of kapton??

WA3TTS,  Michael K. Sapp,  had a very good file on various conversion and
remidity's for these unit's in early/mid 80's,
any one know where mike is????
 Was in Pittsburg, PA area last i knew??
73 best Tom W2DRZ






 

  To: Wayne Heinen
Subj: RE: AM-6155 PROBLEM

Ron Klimas WZ1V wrote:

> 
> At 10:40 PM 1/28/97 -0500, you wrote:
> 
> >Hello Bert,
> >I think I have the cure for your problem. I just got an AM6155 from Fair
> >Radio sales. I got it going just in time for the Jan. Contest.
> >I ran across the same problem with the oscillation you are talking about
> >and found the problem on the base of the 8930 socket. If you have the
> >diagram, it is shown in figure 6-26 the A7 Schematic Diagram and is
> >listed on the diagram as E1. It looks like a spark gap on the diagram
> >and physically it looks like a gas discharge tube that is mounted on the
> >tube socket. I just clipped mine loose where it was connected to pin one
> >of the tube and my problems were over.
 
Yes, I clipped one out of a 432 AM6155 that had the same problem - solved
it.
I also have an AM6154 and never had this problem with it.
The only mods that I did to both of my amps were to:
1. strap one of the 100K resistors
2. added a ground wire from the ground end of the 2 10 Ohm resistors
to  the chassie

> >>WHAT's number 2 do?

 3. added the 2 caps to the input
4. did the rewireing to supply voltage for the metering
5. did the rewire on the bias supply
6. change r3 on the meter board

All these mods were from N3AHI dated 10/28/83

I get good signal/audio reports on both my amps and both have output of
500 watts or better.
Hope this helps
73 de Tony KD4K







RE>AM6155 MODS

1. I agree with Dave that teflon can be used in place of the Kapton.  We
had so many problems with the kapton blowing out in our area, that I
started recommending that people replace the kapton with teflon before
they ever fired the amp up.  Yes it did affect the tuning some but did
not move it out of range on 144 or 220.

2. With regards to efficiency measurements and overheating.  The plate
current metering on many of these units will not read accurately without
changing the position of the meter protection diodes.

 If you find CR4 and CR6 installed on the Buffer amp/multi electrical Ins
A5 board remove them and install directly across the meter terminals.  On
many units CR4  will be on the pc board and CR6 will be found installed
on the S1 meter switch.  If so you can leave CR6 on the switch and just
move CR4 from the board to directly across the meter.

What happens is that at amateur power levels the voltage drop across the
meter movement and metering resistor R17 4.32 K ohms is enough to create
some leakage current in diode CR4 and causes the meter to read low.  I
measured a 40 percent error in the plate current reading as a result of
the microamps leaking through the diodes.

Placing them directly across the meter still affords some protection of
the meter while  lowering the voltage drop across the diodes enough to
stop the leakage current.  The original circuit had the diodes in
parallel with the series combination of the meter movement and R17
creating enough voltage drop to start turning on the diode.

After this you can accurately determine if you are exceeding the plate
dissipation rating of the tube when you get 500 watts out.  If you hold
the plate dissipation below the tube rating it will usually eliminate
overheating problems.

A side effect of moving the diodes is that in the heater voltage meter
position the meter will no longer read 24.  Experimenting with increasing
the value of R18 can return the reading to a nominal 24 if desired. 

John Lock  KF0M







From: Ns4w@mail.tds.net

  To: Wayne Heinen
Subj: RE: AM-6155 PROBLEM:  THE SO

Well, I seem to have my AM-6155 instability problem fixed !  There were
a large number of responses and offers of assistance generated from 
my original post, and what a great thread!  Many solutions were postulated,
and I tried several.

The winner was Chuck, W8MQW, who correctly diagnosed a problem with the
control 
grid bias supply , and suggested a circuit to stiffen it up.  I used the
output of 
E10 to drive a NTE240 transistor, with the collector connected to TP4, and
the emitter to the control grid.  A 22k resistor was placed from the
emitter to ground at E12.

Stable 350 watts out now.

Steve, the W.W. Grainger catalog has a couple pages of centrifugal 
blowers. Last time I looked, a 3" squirrel cage at 3000 rpm would get 
enough pressure for a 4CX250B, e.g. 5/8" in water column. Its easy 
enough to test. Get some clear plastic tubing, form it into a vertical U 
shape, and run one open end to the pressurized chamber (not where the 
air blast blows directly into the end of the tube, you want a pressure 
check, not a velocity check). Put some water into the tubing so it 
stands a couple inches up both sides with the power off. A half drop of 
detergent makes the water stick less, and a drop of food coloring makes 
it easier to see. Tubing diameter is not critical so long as its not so 
small that the water crawls up it by surface tension. I use about 1/4"

I think I've seen 4" squirrel cages that would produce enough pressure 
at 2400 rpm. Maybe 5" at 1800 rpm. Its the peripheral speed that gets 
converted to pressure, if the scroll is right for pressure.

The squirrel cage blower is poorly applied when producing only a few CFM 
at the high pressure a 4CX250B needs. Actually a radial blade blower 
does much better. Granger carries those too, though maybe not SMALL 
enough. I built one once out of the bottom inch of a fruit juice can 
with essentially radial blades. Then I used the top to close off the 
other side. I cooled a 4CX250B nicely with a scroll made from a cereal 
box. Unfortunately the tape I assembled the scroll with has died of old 
age. I spun that impeller with a small 2 pole motor. So it probably ran 
2800 to 3000 rpm. To produce pressure, the scroll needs to grow a lot 
less than it does to produce volume, the condition of the standard 
squirrel cage.

However, as far as I can tell, unless the radial blade blower 
specifically made for pressure is used, the old addage of "if its not 
noisy its not big enough" applies to cooling and significant air cooled 
tube with the finned cooler.


The impeller from a shop vac would be appropriate for tube cooling. It 
probably wouldn't need to run at 12,000 RPM, probably just 3000 rpm.






From: Lanej@provide.net
  To: Wayne Heinen
Subj: AM-6155 TO 4CX400 :  MORE IN


I got quite a few requests for information so I'll just post what I have
here.
In general I followed the notes of N3AHI in the overall conversion except
as follows:
1)  I left the screen supply unmodified (per rational of K1WHS)

2)  I modified the metering circuit using 2 series, back to back pairs of
1N4148's across the meter.  I verified correct bias and screen voltages
with a Fluke 77.  This mod corrected the low plate current reading.

3)  Cleaned the plate blocking cap and coated surfaces with Dow-Corning #4
dielectric compound but did not use teflon replacement.

4)  So far I have not had a problem with bias instability so I haven't
played with any active regulation.  As previously noted I suspect these
problems are pathology, not genetics.

5)  The plate contact finger stock had to be slightly enlarged to fit the
smaller anode diameter of the 4CX400.
per WZ1V, also consult his  4CX400 222 Mhz conversion notes for the
AM-615X series.)

6)  I use the 1992 'Handbook input circuit for their 144 Mhz 8930 project.

7)  I notice the following sags at full output:  Ep:  2200 to 1900, Es: 390
to 350, Eb
 -44 to -42.

8)  I bias the tube a little closer to B conditions (90mA at idle) to
offset the slight sag at full out.

9) I could possibly get another 100 or so watts out if I ran the HV supply
with the taps set to 205 volts but I'm not sure the results are worth the
extra stress on the supply.  I'm leaving it at 240 for now.

10) Loading of the amp is very light.  This seems to give lowest screen
current and highest output power.  I'd be interested in knowing what others
have observed with this.

11) On the air reports indicate good quality but I haven't checked it on
the Tek 2710 yet.

12)  I see no reason why this shouldn't work on 432Mhz or on the '6154. 
Price for the 4CX400 is about $140 everywhere I checked.  Anyone know of
any deals out there? 
                                        -- W8KX







Subj: RE: AM6155 ON 144?
Chris,

Most of the conversions for 2M use the input cavity of the AM6154 which is
lower in frequency than the AM6155. 

I do have a copy of a mod by K1WHS that pads down the 6155 grid cavity so
that it will tune 2M. The other mods to the power supply, etc. are the same
for the 6154 or 6155.

Dave's mod to the 6155 requires a 27 pf, a 15 pf and a 240 pf mica
capacitors. He got 350 watts out which is in the ballpark of the other mods.
He writes that he could get more out but kept blowing the plate blocking
capacitor. He and others have reported this problem and recommend replacing
it with teflon. Dave reports converting  6155's and all worked well. 

I can send you a copy of the mod if you'd like. Send me your address and
I'll drop it in the mail.

                                                          
73, Harry, W3IIT                                hbrown@voicenet.com