[Central-Electronics] The CE 20A and BC-458 VFO

[David Olean]

Hello CEers

I am new to this e mail list. I have been a ham for a long time and used 
a Central Electronics 10A on 144 MHz back in 1965, I loved that rig. It 
was great rig that my brother and I could afford and it sure made DXing 
on 144 MHz a lot easier. We were both early proponents of SSB meteor 
scatter on VHF.  On 50 MHz, SSB was instrumental in popularizing 
ionospheric scatter for ham use in1965 as well. So fast forward a few 
decades and I found a derelict 20A at a flea market, and restored it in 
2017 to use as a January 1st SKN rig. I was disappointed in that the CW 
keying was almost perfect. I was hoping to get a little bit of chirp or 
whoop on the signal.  I used a DDS VFO.

I have since scrounged up a Central Electronics 458 VFO and have been 
working on it with pretty good results.  My unit has the 458-10  option 
but I am unable to find a schematic of this add-on kit on the internet.  
Can anyone point me to a good schematic?  I tried to reverse engineer 
it, but my shaky hands make schematic drawing somewhat problematic. My 
first pass was illegible!  It looks like the kit had a 48.4 MHz Butler 
oscillator that mixed with an 11-10 MHz signal from the 458 VFO to 
generate a 37.4-38.4 MHz signal for ten meter SSB operation.  I did get 
the 458-10 to work, but I sure would like a schematic of the ten meter 
kit for my records.

I was a bit disappointed at how the ten meter assembly attached to the 
chassis in the BC-458. It used one screw on the VFO can to hold it 
down.  Coax cables were flopping around near the 1626 VFO tube and the 
1625 buffer amp, causing frequency shifts depending on where the cable 
was! The VFO can that covered the VFO coil did not have all the screws 
for holding it down. This made for a distinct frequency "burble" on 5 
MHz.  I found a few more screws to fix that!  I re engineered the 
458-10  chassis, fitting a 1/8" aluminum plate to the bottom so that I 
could drill and tap some mounting holes and make a more secure mounting 
arrangement. The plate also was countersunk to make flush the mounting 
screws and the BC458 capacitor screws, so the kit assembly was securely 
flush and adequately fastened to the BC-458 chassis. It is now much 
better looking and seems quite rugged.

One problem I noted was that the 10-11 MHz signal from the BC-458 was 
routed thru an RG-58 coax with the ground attached to the 458 chassis, 
but the center conductor was connected to the ten meter sub assembly 
which was not well grounded to the unit.  All this made for instability 
of the VFO. If anything moved, the frequency would jump a bit.  In 
addition to securely fastening the 10 meter sub assembly down tight, I 
added a ground lug on it to eliminate any ground inductance for the 10 
MHz coax cable.

Anyway, I am rambling on here, but I wonder if anyone has a decent 
schematic for that ten meter CE option for the VFO?  It is referred to 
as a 458-10, and was available as a kit or factory wired.

73

Dave K1WHS