Ive been building a 6M amp using a 4CX250B. I was looking through the
schematic of other amps to get an idea of what is needed for a plate
choke. In the Sep 1984 QST page 12 I found a plate choke described as
1-5/8 inches of # 22 enameled wire close wound on a 3/8 inch Teflon
rod. COULD THIS BE CORRECT??. That sounds like about two turns of wire
to me.

I believe what they meant to say was 'close wind the wire until the
coil is 1-5/8 inches long'.

I also do not have the Teflon(tm) rod that was also part of the
discription. Would ceramic work as well?

BTW I have no plans of building a cathode driven amp as dhown in the
article. I was just stealing plans for the choke.


Jimmie

I'd think an old Ohmmite Z-50 would be ideal. Wonder
what the value in uH was?

Pete

On Mar 22, 4:25*pm, "Unca Pete" wrote:
I'd think an old Ohmmite Z-50 would be ideal. Wonder
what the value in uH was?

Pete

I thought about a Z-50. I have one I use on a 6 Meter amp using a pair
of 6146Bs. I didnt know if it would work with the 4cx250s or not.

6.8 uh rings a bell but Im not sure.

Id rather wind my own if it will keep me from having to pull out the
credit card and pay more shipping than what the thing cost.


Jimme

"JIMMIE" wrote in message
...
On Mar 22, 4:25 pm, "Unca Pete" wrote:
I'd think an old Ohmmite Z-50 would be ideal. Wonder
what the value in uH was?

Pete

I thought about a Z-50. I have one I use on a 6 Meter amp using a pair
of 6146Bs. I didnt know if it would work with the 4cx250s or not.

6.8 uh rings a bell but Im not sure.

Id rather wind my own if it will keep me from having to pull out the
credit card and pay more shipping than what the thing cost.


Jimme
&&&&&&&&&&&&&&&&&&&&&

One book calls for an 8.2 uH choke.
One design is for using # 28 wire spaced 1 wire diameter on a 1/2 inch form
and 1 3/4 inches long.
Another calls for 30 turs of # 20 wire spaced 1 wire diameter on a 3/4 inch
diameter form that is 3 3/4 inches long. I think the wire stops about 1/2
inch from each end on that form.
If the z50 would handle the current it should be ideal.

On Mar 22, 11:20*pm, "Ralph Mowery"
wrote:
"JIMMIE" wrote in message

...
On Mar 22, 4:25 pm, "Unca Pete" wrote:

I'd think an old Ohmmite Z-50 would be ideal. Wonder
what the value in uH was?

Pete

I thought about a Z-50. I have one I use on a 6 Meter amp using a pair
of 6146Bs. I didnt know if it would work with the 4cx250s or not.

6.8 uh rings a bell but Im not sure.

Id rather wind my own if it will keep me from having to pull out the
credit card and pay more shipping than what the thing cost.

Jimme
&&&&&&&&&&&&&&&&&&&&&

One book calls for an 8.2 uH choke.
One design is for using # 28 wire spaced 1 wire diameter on a 1/2 inch form
and 1 3/4 inches long.
Another calls for 30 turs of # 20 wire spaced 1 wire diameter on a 3/4 inch
diameter form that is 3 3/4 inches long. *I think the wire stops about 1/2
inch from each end on that form.
If the z50 would handle the current it should be ideal.

Thanks for the info 32 turns is what I calculated. I was guessing on
the wire size/ spacing.

Jimmie

On Mar 22, 11:20*pm, "Ralph Mowery"
wrote:
"JIMMIE" wrote in message

...
On Mar 22, 4:25 pm, "Unca Pete" wrote:

I'd think an old Ohmmite Z-50 would be ideal. Wonder
what the value in uH was?

Pete

I thought about a Z-50. I have one I use on a 6 Meter amp using a pair
of 6146Bs. I didnt know if it would work with the 4cx250s or not.

6.8 uh rings a bell but Im not sure.

Id rather wind my own if it will keep me from having to pull out the
credit card and pay more shipping than what the thing cost.

Jimme
&&&&&&&&&&&&&&&&&&&&&

One book calls for an 8.2 uH choke.
One design is for using # 28 wire spaced 1 wire diameter on a 1/2 inch form
and 1 3/4 inches long.
Another calls for 30 turs of # 20 wire spaced 1 wire diameter on a 3/4 inch
diameter form that is 3 3/4 inches long. *I think the wire stops about 1/2
inch from each end on that form.
If the z50 would handle the current it should be ideal.

I found a circuit that uses a 50 ohm % watt wirewound resistor for a
plate RFC on a 4cx250.
I may have to try that.


Jimmie

JIMMIE wrote:
On Mar 22, 4:25 pm, "Unca Pete" wrote:
I'd think an old Ohmmite Z-50 would be ideal. Wonder
what the value in uH was?

Pete

I thought about a Z-50. I have one I use on a 6 Meter amp using a pair
of 6146Bs. I didnt know if it would work with the 4cx250s or not.

6.8 uh rings a bell but Im not sure.

Id rather wind my own if it will keep me from having to pull out the
credit card and pay more shipping than what the thing cost.


Jimme
Any choke that is not self resonant at 50MHz and has enough inductance
to give an impedance at least 10 times the plate load resistance will
work. It, of course, must be able to handle the required voltage and
current. The form can be ceramic, Teflon, or any material that does not
absorb RF at 50 MHz. An air wound choke will work too, but would have to
be wound with thick enough wire to be self supporting, and it might be
hard to meet the other requirements with this type of construction.

On Mar 28, 11:45*am, ken scharf
wrote:
JIMMIE wrote:
On Mar 22, 4:25 pm, "Unca Pete" wrote:
I'd think an old Ohmmite Z-50 would be ideal. Wonder
what the value in uH was?

Pete

I thought about a Z-50. I have one I use on a 6 Meter amp using a pair
of 6146Bs. I didnt know if it would work with the 4cx250s or not.

6.8 uh rings a bell but Im not sure.

Id rather wind my own if it will keep me from having to pull out the
credit card and pay more shipping than what the thing cost.

Jimme

Any choke that is not self resonant at 50MHz and has enough inductance
to give an impedance at least 10 times the plate load resistance will
work. *It, of course, must be able to handle the required voltage and
current. *The form can be ceramic, Teflon, or any material that does not
absorb RF at 50 MHz. An air wound choke will work too, but would have to
be wound with thick enough wire to be self supporting, and it might be
hard to meet the other requirements with this type of construction.- Hide quoted text -

- Show quoted text -

OK I made a coil per the instructions I mentioned and placed it in
parallell with a 50 ohm resistor and connected it to my antenna
analyzer. There is a big spike in the SWR at about 75 Mhz. I assume
this is the self resonant frequency of the coil. Is this far enough
away from 50Mhz to use as a plate choke?

JIMMIE wrote:
On Mar 28, 11:45 am, ken scharf
wrote:
JIMMIE wrote:
On Mar 22, 4:25 pm, "Unca Pete" wrote:
I'd think an old Ohmmite Z-50 would be ideal. Wonder
what the value in uH was?
Pete
I thought about a Z-50. I have one I use on a 6 Meter amp using a pair
of 6146Bs. I didnt know if it would work with the 4cx250s or not.
6.8 uh rings a bell but Im not sure.
Id rather wind my own if it will keep me from having to pull out the
credit card and pay more shipping than what the thing cost.
Jimme
Any choke that is not self resonant at 50MHz and has enough inductance
to give an impedance at least 10 times the plate load resistance will
work. It, of course, must be able to handle the required voltage and
current. The form can be ceramic, Teflon, or any material that does not
absorb RF at 50 MHz. An air wound choke will work too, but would have to
be wound with thick enough wire to be self supporting, and it might be
hard to meet the other requirements with this type of construction.- Hide quoted text -

- Show quoted text -

OK I made a coil per the instructions I mentioned and placed it in
parallell with a 50 ohm resistor and connected it to my antenna
analyzer. There is a big spike in the SWR at about 75 Mhz. I assume
this is the self resonant frequency of the coil. Is this far enough
away from 50Mhz to use as a plate choke?
That's half an octave away. Good enough.
I would install the choke in the circuit and without applying power or
drive put a gird dip meter to the choke and double check for resonance
again. IF resonance at 50 mhz is detected, swing the tank capacitors to
make sure you are just detecting resonance in the tank circuit coupled
through the choke. If that is what you see, it's OK.