[TowerTalk] Johnson Matchbox Question

[Joe Subich, W4TV]

On 2022-03-13 3:24 PM, Mickey Baker wrote:
> The KW Matchbox that I have is a simple device with a single inductor
> with 8 taps that all connect back to a 2 gang band switch.
Those taps/2 gang band switch would be on the secondary coil.

Manual and schematic for the Johnson Matchbox is here:

<https://bama.edebris.com/download/johnson/matchbox/matchbox.pdf>

Unfortunately, the schematic does not give tapping info for the
primary/link coil but if the ratio of tap point to size of the
coil shown is reasonably accurate 1.25 of 5 turns looks about
right.  It's likely/common that the T/R relay has been removed
(and along with it the receiver antenna feed/muting contacts).

73,

    ... Joe, W4TV


On 2022-03-13 3:24 PM, Mickey Baker wrote:
> The KW Matchbox that I have is a simple device with a single inductor with
> 8 taps that all connect back to a 2 gang band switch.  I can’t speak to any
> mods made.
> 
> W0QE has a comprehensive video:
> https://youtu.be/OvRI1m4bBjQ
> 
> Mickey N4MB
> 
> On Sun, Mar 13, 2022 at 1:27 PM Tom Hellem <tom.hellem at gmail.com> wrote:
> 
>> I have a Johnson KW Matchbox that doesn't seem to be working quite right.
>> It's very hard to accomplish a perfect match at times even though the load
>> is well within the claimed capability of the tuner. The RF input from the
>> TX is injected into an approx. 5 turn coil which surrounds a smaller
>> diameter coil of many more turns. Looking at the 5 turn coil I can see that
>> some previous owner had tried tapping different points on it for injecting
>> the RF.
>> Question- how critical is the tap point on this coil for proper operation
>> of the tuner?
>> The 5 turn coil is grounded on one end and open on the other, and is
>> currently tapped approx. 1-1/4 turns from the grounded end.
>> Does anybody know where Johnson tapped this coil when they built the tuner?
>>
>> Any input gratefully accepted.
>>
>> Tom
>> K0SN