[SignalOne] Reverse Engineering the 4CX350F

[signalone@mailman.qth.net]

Bill asked for details on the mod.  I'll do it.  It will be a while
coming but I like to write and take notes. 

Here are some impressions until I have time to work on the S/1.

I have taken some pictures of the 4CX350F with a low-res digital
camera. The odd thing is that it looks like it belongs there.

The tube socket is on a duct that matches a rectangular opening in the
rear panel.  I can see the wiring on the socket through the opening.  

I believe that this same opening is used for the Beryllium block.

The tube sits too high and I can press down the RF shield to touch the
4CX350F cap.  Of course this would not happen if the transceiver were
in the cabinet.   This suggests that the 4CX350F is sitting much higher
than the 8072 used to. 

There are a half dozen wires coming out of the rectangular opening.
These terminate in a loctal (or is it octal) plug.

I'm guessing that there used to be a blower attached to the rear
opening and there was an outboard HV (and likely screen voltage) power
supply.  4CX350F?  350 watts of plate dissipation?  This monster might
have put out 500 watts. 

I guess the fellow made the mod for more power.  Isn't the 8873 tube in
the Heathkit SB-230 only 400 watts of dissipation? 

I bought an unknown condition 8072 on eBay.  I will be looking for
parts to restore the radio.  Probably the hardest parts to find will be
the Beryllium block, tube socket, and whatever the tube socket was
mounted on.  I'll need info on the circuit and the orientation and
layout of the components near the tube.

I think I saw a schematic diagram of the CX7A powersupply on the
Internet.  

As I gather parts, I'll verify that the internal power supply is
working.

Next I'll remove the 4CX350F.  This tube is a rough one, the fins are
not straight and the circumference is not circular.

I also have to repair and remove the external voltage regulator.

I will not remove the 4CX350F until I have a known good 8072 and all
the parts for installing it.  

The reason for that rule is that I don't want the radio to be in a
disassembled state for an extended period of time.  That's how radios
end up on eBay with all the knobs missing or half assembled.

Someone takes a radio to pieces, doesn't have an essential component,
and loses interest in it over time.  The parts drift away and another
mystery of Ham radio emerges.

-- More editorializing --

I don't know how this radio came my way or anything of its history.
I'm learning that Signal/One was an interesting sideline in the history
of radio.  

I'm trying to make sense of it and value.  I think that the S/1 is like
a Ferrari or AC Cobra.  Someone wanted to build the best and gave it
their best shot. 

I saw on the web that there were about 1,000 Signal/Ones built of all
types (not including the IC-781 derivatives).   Given that, these are
rare collectables, in the class of the Gold Dust Twins and the SX-88,
certainly more collectable than a KWM-380.

Search the web and eBay for "Catalin radio".  Why, why are people
collecting that junk?   I can't figure out why people who can't play
the guitar collect 1950's guitars from the "golden age of rock and
roll".  I don't understand why they bid them up to hundreds of
thousands of dollars.

They do it because someone told them that it is a collectable and, by
gosh, they believe it.  Well, it's not.  Perhaps Elvis's favorite
guitar is worth something but all the rest are just mass produced
guitars. 

They like to "look" at them????

The reason that the Signal/One cost so much in 1970-1975 is that there
was significant engineering put into it.  Ehrhorn wanted the best radio
he could build.

A side bar, I saw the story of the HW-32 (or maybe HW-22) that
Signal/One hand built for Thor Heyrdahl. I believe that the Smithsonian
has it. That is a collectable.  

Significant engineering and quality parts.  Well, maybe not all quality
parts but they did the best that they could with what they had.

There was a time that older Ferrari's fell in value to a few thousands
of dollars.  This is the life cycle of collectables.  I'm guessing that
old boatanchor radios have bottomed out.  I'm speculating that "pivot"
models like the 75A-4, the R-390, the Signal/One, top end models that
represent a new direction, will increase in value.