[Central-Electronics] CE 458 VFO Output Level

[Paul Christensen]

Bob,

Good info from you and others...

The VFO output voltage was measured at the octal accessory connector with a DSO.  As expected, the 80-20M position produces the most output but it's still only 3V p-p.

Jim Candela supplied some good info and I have a known, working 458 on the way.  Having a working unit as a reference greatly accelerates repair time.  Time is my #1 enemy.

Although I knew that the 40m output is tripled, I didn't realize that band had little SSB activity in the '50s.  But come to think of it, my OM, W9EAC (SK) once told me that during the '30s and '40s, 40m was limited to CW only.   So, not sure when 40m phone privileges were granted by the FCC.

I recently made the mistake of trying to null the carrier when using a 40m crystal.  The deception occurs because the 20A loads up perfectly, and as expected with a 40m crystal.  Bob Sullivan provided the sage advice that a multiple is required to beat with the 9 MHz oscillator for SSB. 

I now have over 100 pages of CE material that includes abridged manual pages, schematics, block diagrams, notes, and mod instructions.  It's quite a mess.  Unless someone has already put this material into cohesive order, I can take this on as a project when I retire.    Adding to the confusion, I see several evolutionary changes to the 20A over its production life.

I'm amazed at the complexity, but also the simplicity of the 20A-458 pair.  After reviewing CE's published 458 conversion mods and the alignment procedure, all but a few of today's ops wouldn’t be able to manage it.   

Paul, W9AC



-----Original Message-----
From: central-electronics-bounces at mailman.qth.net <central-electronics-bounces at mailman.qth.net> On Behalf Of Robert Nickels
Sent: Wednesday, May 22, 2019 11:13 PM
To: central-electronics at mailman.qth.net
Subject: Re: [Central-Electronics] CE 458 VFO Output Level

On 5/22/2019 6:48 AM, Paul Christensen wrote:
> Can anyone confirm what reasonable levels to expect from the 458 VFO?

Paul -

Indirectly at least...when feeding the 20A with an external VFO I found the note of "8 volts peak RF" on the schematic to be pretty much right for 80 and 20 meters.  That would be 16 volts peak-to-peak or about 5.6 volts RMS for full output.   The output of the 20A is definitely proportional to the VFO voltage and while I didn't try 40 and other bands extensively I did find that more VFO signal was required for 40 than for 80 and 20 meters.   I suspect this was not an issue because early SSB was primarily on 80 and 20 meters, and because most hams used the 20A to drive a linear which may have had sufficient gain that full output from the excite may not have been required.

I'm not sure how you're measuring it, but .5 volts is definitely too low, and 3 volts peak would still be insufficient to produce full output on the best bands (80/20).  If you have a way to put an 8 volt peak signal at the right frequency for 40 meters into the 20A that would provide a point of comparison.

73, Bob W9RAN

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