To KM1H and all,
I'm not knocking the Measurement 59! I have one at home, and we have 3
working units at work. My boss wanted me to toss them out a month ago, so I
shoved them deeper in the cabinet out of sight. Having a vector Z meter, I
don't use them much except where I don't want to contact the circuit
(massive, will break the tip on the probe) or I want extreme portability,
like while standing on a ladder probing the plate bypass on a large cavity
(10 feet tall) amplifier. The 59 is extremely handy.
Remember the book SOS at Midnight, where Tommy whats his face send SOS
using a GDO while trapped in the bad guys QTH tied up? What a great use of
a GDO.
> BTW, before the EPA clowns
>got involved I could time just about any engine by ear..from full race
>flathead Fords to 427 Chevy's.....guess I blinked real fast.
When I was a teen, my neighbor (passed away now) was an ESSO station owner
and mechanic. He did a complete tune up to my 1960 chevy 283 V8 engine,
with one hand on the valve cover feeling the vibration. Set the dwell, the
timing, the carb jets, the idle speed. I was astounded, and never saw
another mechanic do this, they always resorted to that big Sun Engine
analyzer thing. I'm drifting from the subject of this group...
> ( 470 to 1000pf are the most
>likely values). This should be added in parallel with a nice .005 to .01
>so the HF frequencies are adequately bypassed. The biggest problem is
>finding a .01 at over 3500VDC so paralleling .0047's is often necessary.
Good point about paralleling a VHF bypass cap. I found 470 pf with 3/8 inch
leads was perfect short for 100 MHz once. Used this across a lot of
control, DC, interlock circuits in the broadcast TX, in lieu of the more
expensive feedthru stud capacitors.
>I also noted your use of real fat choke forms John. While OK for your
>frequencies they really pile on the winding C rapidly.
Yes, they do. Had to make them large to get the length to hold off the HV,
the gradient across the turns. Didn' t want interturn arcing. I don't trust
the enamel alone, in case of knicks while winding. However, they make
double insulated enamel magnet wire now (not really enamel but
poly-something).
The extra big diameter (3 inch) was just for a test, to prove that it was
not the way to go. Once years back I did a bunch of plate RFC's for a
dielectric heater at 27 Mhz, and even experimented with Nichrome wire for
the coil. The thin long RFC had the lower Q at resonance. Fat coils had
higher Q peak as measured.
Nichrome was lower Q also. But I dropped the Nichrome when the DC current
alone made it glow like a heater in our rig (about 5 Amperes DC plate
current!).
>Also back in the 80's there was a HRM article mentioning the use of a
>ferrite rod inside a choke form...the reference was a 5KW commercial
>application with no series resonances 2-30MHz. Later on B&W used that
>concept on their BBC-5K choke.
>I wonder if anyone here has tried that? My one and only attempt resulted
>in smoke but that was over 10 years ago.
I would be afraid of saturation of the ferrite, and possibly overheating
it, causing the mag losses to increase to where it will pass the Curie
point and shatter. But there is probably the right stuff out there to do
it, if someone tried to engineer it correctly.
John
K5PRO
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