Re: Intermittent no trace / sweep.
"( I mentioned I have a shop manual so why do I get advise to download it ?)"
I knew that.
"BTW I have been using this particular scope professionally for few years"
I did not know that. From what I had to go on you could have been a first time scope owner of someone who worked for Tektronix for 20 years. I try to avoid making assumptions because as the old saying goes...
What I do wonder now is how the controls are set up on that scope. On most, if the selector is set to normal sweep the delay controls have no effect. But then I didn't get to the point of finding out.
Under the circumstances all I could do is start from the beginning.
Glad to hear you got it figured out. "We" have some spare knobs from a 422 and a few 7XXX series plugins if they fit and you have trouble finding something that will. My luck is usually not as good, the plastic usually cracks on me and then it won't grab no matter how much you "tighten" the screw.
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Yes, the driver in my description is voltage, and
the current changes with voltage. Sorry for the
confusion.
-Chuck Harris
Raymond Domp Frank wrote:
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Chuck,
A real curve trace of a tunnel diode would show the trace rising to
the trigger voltage, and then reappearing at the near zero triggered
voltage. It would be discontinuous. There is no there there.
Didn't you mean to say "trigger current" and "triggered current"?
Raymond
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Re: 500-series fan motor disassembly.
Hi there, Just going again into this problem so trying to bring back to life this thread, hoping that someone with experience on this would like to share a good mechanical tip to disassemble the bushings' press-fit retainers. Thanks in advance, Sebastian. PS: Now, also posting this in Tekscopes2 list. On Sat, March 31, 2018 10:13 pm, Sebastian Garcia wrote: Thank you, Shaun.
OK, press-fit retainers; it seems I was missing the correct
English terms.
I'm missing the recommended mechanical tools and technique to properly
dis-assembly it.
Mounting can probably be performed well with a soft plastic hammer.
Perhaps clean up assembly, check the shaft/bushing fit and go from
there.
If I understand correctly, you are suggesting to avoid dis-assemble it.
From a preliminary inspection, I don't think it's an option in my case.
Search the archive for Stan Griffiths' posts, mentioning good reasons to
completely disassemble it.
Sebastian.
On Sat, March 31, 2018 9:40 pm, Shaun M wrote:
Sebastian,
Yes, I see the issue now. Your motor has cast endbells and press fit
retainers. One issue I have found with press fit assemblies is even
granting you can disassemble them without apparent damage, they often do
not reassemble properly.
Perhaps clean up assembly, check the shaft/bushing fit and go from
there.
Shaun Merrigan
On Sat, March 31, 2018 7:13 pm, Sebastian Garcia wrote: I uploaded some pictures:
/g/TekScopes/album?id=42033
As a reminder for anyone reading this (the posts from the web interface
removed the thread history), I'm looking for advice on removing the metal
end caps/retainers of the bushings assemblies.
Sebastian.
On Sat, March 31, 2018 6:44 pm, Sebastian Garcia wrote:
OK, now I see, in your assembly you have access to the tabs.
I will take a couple of pictures and share them in brief.
Thanks you,
Sebastian.
On Sat, March 31, 2018 6:37 pm, Shaun M wrote:
Sebastian,
As I recall, the tabs which hold the retainer to the endbell were
relatively easy to bend starting with a small flat blade screwdriver
followed by needle nose pliers. I bent them only far enough to remove
the
retainer. You can see in the mages that I did not straighten them out.
Shaun Merrigan On Sat, March 31, 2018 6:09 pm, Sebastian Garcia wrote: Hi Shaun,
Thank you; your pics are helpful, of course.
My motors looks a bit different but it seems the bushings assemblies are
similar.
How did you remove the metal end cap / retainer?
Best regards,
Sebastian.
On Sat, March 31, 2018 5:42 pm, Shaun M wrote:
Sebastian,
I disassembled and rebuilt (new bushings, check shaft diameter and wear,
balance blade assy, etc) the fan motor in my Tek 556 which includes many
images of the motor:
You may find it helpful.
Shaun Merrigan
On Sat, March 31, 2018 4:41 pm, Sebastian Garcia wrote: Hi there,
In this corner, just proceeding to clean some 500-series scopes' fan
motors.
There is very good advice in the list's archives, particularly from Stan
Griffiths.
My question: What is a recommended way to remove the metal end caps of
the bushing assembly?
Of course, will also need advice for a way to later put then again in
place.
Regards,
Sebastian.
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Replacement of nuvistors with JFET's (specifically, MPF102 JFETs) in the
422 scope vertical amplifiers has been accomplished by "Kurt" and was
documented several years ago in his blog. I believe this is also
described at www.w140.com, under the "422" scope webpage. However, the
plate voltage in the 422 scopes is about +25 volts. The plate voltage
of the nuvistors in the vertical preamps of the 453 scopes (early S/N's)
is about +75 volts, so I suspect this would likely zap a MPF102. There
might be other JFETs that have adequate drain-to-source voltage rating
to serve as replacement for the nuvistors in the 453 (early S/N) scopes.
Mike Dinolfo N4MWP
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On 04/28/2018 05:24 PM, 搁别苍é别 wrote: I believe the replacement is MPF102, pin for pin. less filament of course.
搁别苍é别
On 2018-04-27 08:46 PM, Dale H. Cook wrote:
At 06:50 PM 4/27/2018, Jeff Urban wrote:
Now that I think about it I bet some of these triodes could be
replaced with depletion mode N channel FETs. Tek replaced the front-end, sweep generator, and trigger generator
Nuvistors (all 8393) with FETs in the 453 beginning with serial 20,000.
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
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I believe the replacement is MPF102, pin for pin. less filament of course.
搁别苍é别
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On 2018-04-27 08:46 PM, Dale H. Cook wrote: At 06:50 PM 4/27/2018, Jeff Urban wrote:
Now that I think about it I bet some of these triodes could be replaced with depletion mode N channel FETs. Tek replaced the front-end, sweep generator, and trigger generator Nuvistors (all 8393) with FETs in the 453 beginning with serial 20,000.
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
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Still have to follow up and make more measurements. Its the fuse on the 20V supply to the HV assembly. Tek calls it the HV fuse even though its in a low voltage line. Probably less than an amp flows. I can see the arc. I thought at first it was along the 1meg resistor that feeds the HV to the CRT but its on a lead underneath that, probably on one of the caps on either side of the 1Meg resistor. Its a sort of corrona to the air. Very odd. Its this arc that's drawing all the current. Making measurements here is difficult both because of the narrow range where the arc is not happening and because of the somewhat cramped space.
The base voltage on Q930 is wrong. Supposed to be -4.4 volts but I get about +11 volts. This is with the fuse out so voltages are probably pretty upset. It would turn the transistor on hard. Maybe an illusion. Anyway, I will make some more measurements and make sure the other supplies are working. I know the +75V supply is OK but first thing should always be to check the PS.
Don't think its an insulation failure.
I need to study the handbook and schematic further to see what I want to measure. Very strange problem although I suspect someone else has encountered it before.
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On 4/28/2018 9:32 AM, b c via Groups.Io wrote: Okay yeah looks like the data collected do line up with each other and
your CRT HV seems to be working at least to a point.
This is F937 (2A) that you're seeing burn? I would call this the "HV"
fuse, though there are many other voltages that are quite high. How
many amperes is flowing through the fuse you're working with when the
CRT starts glowing at that circa 90V line voltage you found?
Perhaps it's just insulation failure, these scopes are quite old now.
This could cause higher current drain and burn the fuse. Are you
saying the high tension second anode lead is leaking charge? Can you
stick some plastic in its path to prevent the arcing discharge?
--
Richard Knoppow
dickburk@...
WB6KBL
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Hello, I see there is another Tektronix 547 in the Massachusetts area for those still looking. Marty.
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On Friday, April 27, 2018, 3:09:27 PM EDT, Roy Morgan <k1lky68@...> wrote: Chuck and other Simple Green interested folks, The FAA may well have put out a notice, but I have not seen it (a pointer to it would be appreciated), BUT: The Army did put a notice in it’s aircraft maintenance magazine, quite some years ago now (quite possibly before the more suitable Simple Green formulas were introduced). The Army instructions were (summarized): - DO NOT use Simple Green on aircraft - DO use Army-approved cleaners and procedures. The article did not go into detail about what the stuff does to aircraft, but was clear that it should not be used. (I can later send a copy to interested folks.) Further, Bill Carns, much respected and long-experienced leader in the Collins community cautions about using harsh cleaners on radios.? It seems to me that basing decisions about cleaners on 3 to 5 years absence of “problems” may be a bit short sighted.? The Tek 545B that I expect to bring back to operation has been in moderate to poor storage conditions for a decade or so, and was made a lot of decades ago.? I expect that I”ll be depending on it as my main scope for another decade or two.? (Do 90-year-olds still work on radios?? I hope to.) In the past, I have used 50-50 409 and household ammonia as a magical cleaner for radios.? That may well have been unwise! I had a bit of hope to get the 547 from New Hampshire, but was not surprised the first responder took it.? So — I am modestly in the market for another one.? I am in central NY and can travel some distance to avoid shipping. (I lost a 547 and a whole lot of other treasures in a disaster.) Roy Morgan k1lky68@... On Apr 23, 2018, at 5:51 PM, Chuck Harris <cfharris@...> wrote:
FAA put out a notice against the use of Simple Green for
cleaning aluminum airplanes a number of years ago.? The
problem is it wicks into joints, and under rivets, where
it sits and corrodes.
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Regarding the tunnel diode branch from this thread - it is indeed possible to see the complete I-V curve of a tunnel diode in low frequency or DC conditions. Normal curve tracers can't do it because their series R is too high, so it appears discontinuous. Specially made, very low resistance test fixtures can suppress the instability caused by the TD's negative R, allowing display of the actual I-V - even that magical negative R region.
You can find such a test circuit in either (or maybe both - I forget) the GE or RCA TD manuals from the 1960s. The circuit displays the I-V on a scope, just like a curve tracer, but it's dedicated to only this function. I had once thought about building one of these, for curiosity, but for general go-no-go testing of TDs, it's not really necessary to see that part anyway. You can trust that the TD is doing its thing if you can see the endpoints, on a regular curve tracer, or in-circuit.
Ed
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Re: Intermittent no trace / sweep.
Roy, I got the screw however could not get it in and in the process stripped the thread...
But no big deal, just talk to old man who has "100's" of scopes and he stated that the problem is bad switch wafer. I actually believe that there was newer a screw holding this "flywheel thingy".
So I am still trying to fix this instead of getting a "new" one.
Now for my real question to the group / forum ( what is the difference ?) -
I like to hear form somebody who
actually replaced ( removed and put back ) the "A&B seep generator " board on 464 A7 board in Tek manual.
Cheers
Vaclav
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Isn't it normal for the trace to be distorted with the beam finder? The beam finder applies a fairly hard clipping to X and Y amplifiers to keep the spot on screen.
When you say there is something arcing in the HV box can you see the arc? The high voltage capacitors (C906, C976, C952, C954, C953, C961) are all likely points of failure in a scope of this age. I had to replace two of the 2.5kV rated capacitors in a 454 but they only showed any sign of leakage with a 1kV insulation tester so low voltage testing will not reliably find high voltage faults.
Roger
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Re: TM504A differences from TM504
Hi Hawker,
The TM504A is apparently quite rare. It doesn't show up in any of the catalogs. In the 1993 catalog the TM504 is listed along with several other mainframes but by 1994 the only TMxxx plugins are the TM5003, TM5006A, TM502A, TM503B, and TM506A.
There is nothing active in any of the TM500 mainframes so I am puzzled by your comment about an oscillation and feedback in the power supply. This sounds like it has a switching power supply which would make it VERY DIFFERENT from a TM504 and more like the TM5003 or TM5006.
Dennis Tillman W7PF
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-----Original Message-----
Hawker on Thursday, April 26, 2018 7:22 AM, said
I'm finally getting around to fixing, updating and working on my 500 plug
in collection.
I have a, apparently, rare TM504A chassis that was modified by a previous
owner so not all modules work in all slots and sources do not talk to
destinations. It also has an oscillation in the power supply that I need to
fix (Classic issue with how they did the feedback on the power supply). It
is finally time for me to understand the back programing header and how to
use it so that say my freq counter can read the oscillator or the volt
meter read the power supply though the back plane while still being able to
swap out modules.
I have been unable to find a manual or schematic for this unit, but there
are plenty for the TM504. Is there any real difference other than the
addition of a fan and switch location? Is the TM504 service manual good
enough or if not where can I hunt down a TM504A one?
I sure wish there was a modern version of the 500 modules. I have some
great modules with no current product options. I use the filter/pre-amp all
the time at work and once I updated the op amps it works better than the
current version by another vendor. But these things sure are getting old
and I wonder if it is worth my time to keep them working for bench work any
longer. For now I'll keep trying.
Thanx,
Hawker -- Dennis Tillman W7PF TekScopes Moderator
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Okay yeah looks like the data collected do line up with each other and
your CRT HV seems to be working at least to a point.
This is F937 (2A) that you're seeing burn? I would call this the "HV"
fuse, though there are many other voltages that are quite high. How
many amperes is flowing through the fuse you're working with when the
CRT starts glowing at that circa 90V line voltage you found?
Perhaps it's just insulation failure, these scopes are quite old now.
This could cause higher current drain and burn the fuse. Are you
saying the high tension second anode lead is leaking charge? Can you
stick some plastic in its path to prevent the arcing discharge?
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On Fri, 2018-04-27 at 14:01 -0700, Richard Knoppow wrote: ????Some progress. First to answer your questions; D940 appears?
to be good.
? I do not have either a ring tester or a bulb tester. What I use?
is a metered Variac and put a Triplett 630A across the fuse?
holder to measure the current. Its set on the 12A range and I can?
see clearly when the current??begins to rise with line voltage. I?
tried disconnecting the CRT at its socket and also disconnected?
the HV lead to the helix at the HV compartment. Made no?
difference but thank you for the suggestion.
????So far, here is what I've found. When the line voltage begins?
to get to normal something in the HV compartment begins to arc. I?
found its a lead from the HV transformer to the filter for the?
"helix". Since there was HV I decided to see if I was getting any?
sort of trace. At around 90V line voltage (I have to note this?
again) I could get a trace with the beam finder. The trace was?
distorted and that makes me think I've been chasing my tail on?
the HV. I now think the problem is in one of the lower voltage?
supplies. I have errands to run today so will get to this?
tomorrow. It would be great if I had a second decent scope but I?
don't so will have to trace this down via a voltmeter. In any?
case I think the presence of a trace of sorts indicates the HV is?
OK and the CRT is OK. I now need to study the other power?
supplies to find the problem. I can run the scope at full line?
voltage with the HV fuse removed. The distorted trace should give?
me some clue as to what has failed. My guess is a filter cap?
somewhere since the thing overheated.
?????Any suggestions would be welcome. In any case I now have?
some confidence that I can fix the thing.
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FG504 and failed Q270 (SPS2927)
My FG504 had suddenly died when I tried to use it yesterday (no output basically). After a lot of probing around I discovered that Q270 on the A3 Loop board had failed. It's specified as 151-0438-00, a selected SPS2927. I'm sure this one has come up before but I can't find a spec or alternative device.... can anyone suggest a suitable device please. I've put in a BC212L just to prove the fault diagnosis but it would be nice to get the right part.
In the course of trouble-shooting I wasn't sure where to start. The manual describes the complete workings but doesn't say how/where the triangle waveform actually starts off in life! I eventually realised the whole thing was a closed loop (A3 LOOP Board should have been a clue :-)), which doesn't help diagnosis..... had to go probing all transistor terminals looking for trouble. Can anyone explain the signal generation process in a simple fashion?
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Chuck, A real curve trace of a tunnel diode would show the trace rising to
the trigger voltage, and then reappearing at the near zero triggered
voltage. It would be discontinuous. There is no there there.
Didn't you mean to say "trigger current" and "triggered current"? Raymond
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You seem to understand electronics pretty well... You might want
to look up one of the two transistor circuits that behave like a
tunnel diode, build one, and study it. It's probably better to
just consider it magic.
It probably didn't help the tunnel diode's understandability to
name it after the physics property that makes it work. I think
a better name would have been a "trigger diode".
It also doesn't help that the curves that are typically published
are more a manifestation of the curve tracer's very slow speed
capabilities than they are of what the tunnel diode is really doing.
More on that later...
Imagine a part that as you increased the voltage across the part,
the current rises, and rises, and rises, then at a trigger voltage,
the current instantly drops to a near zero lower value... like you
burned out a fuse.
As you let the voltage continue inching its way up, the current stays
low, until it reaches a threshold where it once again starts to rise
endlessly and rapidly, like a conducting diode.
Here's where the typical I/V curves fail you: The current drop at the
tunnel diode's trigger voltage is so fast that you never would be
able to see it on any curve tracer without a ton of intrinsic capacitance
(inside of the curve tracer) slowing it down.
A real curve trace of a tunnel diode would show the trace rising to
the trigger voltage, and then reappearing at the near zero triggered
voltage. It would be discontinuous. There is no there there.
Thanks to magic, the I/V curve is reversible. So, there is really
two trigger voltages: one going up, and one going down.
Through a variety of tricky tricks, you can exploit those sudden
changes in current to produce very pretty trigger pulses. And use
those pretty trigger pulses to trip flip-flops, and multivibrators.
-Chuck Harris
Jeff Urban wrote:
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Now if they only find something for those tunnel diodes. Actually they don't seem to go bad but I had scopes with tunnel diode triggering and they will just about sync to noise, seriously. I have trouble understanding how the hell they work. I have been inundated with formulae and I/V curves but still it just doesn't register.
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Re: TM504A differences from TM504
Did you find info on TM504A? It could not have been produced for very long. In my "newest" 1983 Tek catalog, Tek are offering the TM500 (not A) and they had then brought out the TM5003 and TM5006.
The user customization of the frames was an asset for flexibility but can cause damage with surplus TM500 equipment. People don't check for customization including movable tabs in the card edge connector to block module ingress. Any "new to you" TM500/5000 needs to be checked for a few things. Past users may have made mods so that the frame is not "plug and play" and this can cause you to inadvertently damage module or frame. Worthwhile as you said, to understand the customization possibilities and options.
I am still a big TM500/5000 fan. There wasn't anything like it back then. Working units have uses today. Basic physics measurements are accurately and inexpensively made with TM500/5000 if you don't need computer interface. Easy to repair. Lots of info and parts.
Not sure what would be today's "equivalent" system with the breadth of modules and cases. It was a very flexible system although bulky by today's standard and no computer interface unless you had certain newer modules and frames with GPIB.
George
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Re: Hello from new old member
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Now if they only find something for those tunnel diodes. Actually they don't seem to go bad but I had scopes with tunnel diode triggering and they will just about sync to noise, seriously. I have trouble understanding how the hell they work. I have been inundated with formulae and I/V curves but still it just doesn't register.
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Re: Help with 24x5B processor board A5 and option 5 timer trigger
I plan to replace the MUX (U2530) this weekend and wonder if I can put solder mask on the guard traces between signal pins?? I would use Circuit Works CW2500 epoxy which is good to 350 C.? I cant think of any downside and it would help avoid solder shorts.? The guard traces are very close to the signal pins and shorts mean rework with solder braid.? 14 pins at this pitch are sure to get one that needs touch up.?
I haven't decided yet whether I will do hand soldering or hot air.? I purchased a griddle at Walmart for $18.00 to act as a preheater and calibrated it with my IR temperature meter.? Its easy to hold the temperature around 170 C.? I will use a hand held fan to cool the board after soldering and before lifting it off the griddle so I don't temperature shock the board.? But I may loose my nerve and just hand solder the new part.? Either way, I think solder mask over the guard traces would help keep the solder from overflowing.
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On ?Monday?, ?April? ?23?, ?2018? ?09?:?02?:?08? ?AM? ?CDT, Chuck Harris <cfharris@...> wrote: As I said, you must heat the bottom of the board to 100-150C.? This is well below the solder melt temperature, and cool enough that it won't damage parts.? Then when you use your hot air, you can keep its temperature throttled back to 300-350C, and you will only have to heat the joint for a couple of seconds. When you try to do all the heating and melting with just hot air at the top of the board, you have to way overheat the parts to get the solder to melt. The underboard heater doesn't have to be anything fancy, it could be a hot plate made to warm your coffee cup. I use a commercial product, which cost about $100, and has temperature control.? Search: quartz under board heater. I also use a beaker stirrer that has a temperature controlled heater.? With that I can even reflow smaller boards. A teflon coated frying pan, or griddle, would work too.. you will have to do something to throttle the heat down, and the sides get in the way. If you must use a soldering iron, use something with a chisel tip, and lots of flux.? You can wipe the tip over the leads. -Chuck Harris machineguy59 via Groups.Io wrote: ? Thank you.? I have the right jumpers in the right place.? I also found a J103 on the schematic and put a jumper on it as shown on the schematic.? The scope now powers on without incident except the trace vertical positions, and intensity knobs do not change trace position or intensity.? I am using the screen bias adjustment as an intensity control.
I am resigned to the idea that my soldering technique cooked the new MUX (U2530) when I installed it.? That has never happened to me before.? So I am planning a new method to hand solder U2530 with a temperature controlled, 1 mm tip soldering iron.? Using 63/37 tin/lead solder and a temperature of 270 degrees.? I am considering high temperature epoxy to coat the guard traces between each pin of U2530.? Ordinarily, this would be overkill but I want to be certain the package is not damaged this time.? Comments?
? ? On ?Monday?, ?April? ?23?, ?2018? ?01?:?49?:?48? ?AM? ?CDT, satbeginner <castellcorunas@...> wrote:
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At 06:50 PM 4/27/2018, Jeff Urban wrote: Now that I think about it I bet some of these triodes could be replaced with depletion mode N channel FETs. Tek replaced the front-end, sweep generator, and trigger generator Nuvistors (all 8393) with FETs in the 453 beginning with serial 20,000. Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
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Jeff Urban
Mike Dinolfo
Raymond Domp Frank
GeorgeP
Dale H. Cook