The Pacemaker was the first single sideband transmitter built by the E.F. Johnson
company. It was manuafactured for only a two year time span, from 1956 to 1958.
Follow along on the work we did to this transmitter.
This is the top of the chassis as we original received it. Not too dirty, but it had some missing tubes and a replacement high voltage choke (center right in the picture) that was much too small.
Follow along on the work we did to this transmitter.
This is the top of the chassis as we original received it. Not too dirty, but it had some missing tubes and a replacement high voltage choke (center right in the picture) that was much too small.
Click on any picture to enlarge it
Top of chassis prior to restoration
Top of chasis after restoration
Bottom of chassis prior to restoration
Bottom of chassis after restoration
Filament and HV fuse addition
Original manual (full download)
Annotated schematic
Redrawn schematic of audio portion
Here's the chassis after restoration. Note the replacement high voltage choke.
The blue capacitors are a prior owner's attempt at "recapping" the transmitter.
These were more or less just tacked in using hot melt glue and point to point wiring
to the capacitor leads.
We pulled every capacitor added by the prior owner, using more appropriate
capacitors soldered to the original terminal strips and tie points. We also tested
every resistor and found several substantially out of specification. These were
replaced as well.
We always add a fuse to the high voltage transformer's centertap. This is a
precaution against any future short of a filter capacitor that tends to burn up the
transformer before the line fuse can blow. In this project, we also added a fuse to the
6.3V filament winding, as seen here.
We were fortunate in being able to borrow a nice clean original manual for the
transmitter. While we had it, we made a high quality scan. We've made the scan
available for download by clicking the image to the left.
Though the Pacemaker had a brief life, Johnson did make a few improvements to
the circuit. We were able to identify a few by comparing three versions of the
schematic. We've indicated the differences that we identified in the marginal notes
we added to this schematic.
Schematics are often hard to follow if you need to study a particular circuit, and the
Pacemake is no exception. The Pacemaker is a phasing sideband rig, so the audio
circuit is critical to its performance. We found it necessary to redraw the audio
portion of the original schematic to better follow the circuit. It can be downloaded
by clicking the image.
E.F.Johnson Pacemaker transmitter
Johnson paint formula:
The following is the Sherwin Williams formula for the older maroon and gray paint scheme. Both use the 32 oz Ultradeep base, either acrylic 6403-25981 or oil 6403-25775:
Johnson Maroon: B1 black=22, R3 magenta=6, R4 new red=8
Johnson Gray: W1 white=19, B1 black=25, N1 raw umber=14, R2 maroon=1
The following is the Sherwin Williams formula for the older maroon and gray paint scheme. Both use the 32 oz Ultradeep base, either acrylic 6403-25981 or oil 6403-25775:
Johnson Maroon: B1 black=22, R3 magenta=6, R4 new red=8
Johnson Gray: W1 white=19, B1 black=25, N1 raw umber=14, R2 maroon=1