[AMRadio] Sommerkamp FR100B Receiver

Wed Nov 23 19:17:20 EST 2011

Mark,

I spent the better part of last spring restoring one.  It took six (6) 
FR-100B receivers in various condition, collected over a 15 year period to 
get just one unit restored to the point of being "as new."  There are 
relatively few caps to change and most are available from Antique Electronic 
Supply.

For those not familiar with the FR-100B, it's the receiver used in the 
now-famous JA1MP QSL card showing Yaesu founder, Sako Hasagawa at the 
controls of an early "F" line (ca. 1965). The card was issued in the 
mid-'90s to commemorate the release of the FT-1000MP.  Hasagawa and Wolfgang 
Sommerkamp teamed up in the '60s to market and re-brand the Yaesu product 
line in Europe.  The only difference between the two brands of FR-100B is 
the front panel moniker.

There are several electrical variations of the receiver -- some 
significantly different and you'll need to acquire the right schematic. For 
example, the early FR-100B breaks the C.T. of the HV transformer secondary 
to put the Rx in standby.  It's horrendous.  Shortly afterwards, Yaesu 
developed a better AGC bus and re-established the C.T. connection.  Another 
difference is that the VFO mechanics  are different among variants.  The 
FR-100B uses a 6BM8 and a NE-2 neon bulb to form a 100v regulator.  Never 
seen that before but regulation is excellent once all the faults are 
cleared.

There are many similarities between the FR-100B and Collins 75S.  Clearly, 
Hasagawa had copied many of the same S/Line design concepts into the F line. 
The FR-100B uses a Kokusai 455 kHz mechanical filter.  If the receiver seems 
extremely dead, be prepared to completely restore the filter.  It requires 
disassembly of the filter module and clearing out decomposed foam from the 
ceramic tuning discs.  The rotted foam forms a mechanical 'short" across the 
discs.  It's about a three hour job to do it right.  But after cleaning? 
Wow, what huge difference.  I never would have believed that a ca. 1960s 
tube Rx would have too much gain and sensitivity on 10m.  This one does when 
the filter is working properly.

The AF stages will need modification.  But it's easy  Hasagawa decided to 
route the headphones from 1/2 of a 12AT7 through a 0.05uF disc cap through a 
normally-closed (NC) headphone jack, then feed the NC pin to a 6AQ5 class-A 
power amp.  Modern 8-32 ohm headphones don't do well being coupled by 0.05 
uF of capacitance.  I used the same technique used in the Drake R-4B. 
Namely, re-wiring the jack after the 6AQ5.  Now, tons of gain into low-Z 
phones.

The FR-100B user experience in the '60s must have been very much like owning 
a 75S.  The front panel consists of thick sheet of anodized aluminum, 
engraved and filled.  I absolutely love that look and I've copied it into my 
own panel designs.  The Rx is very roomy like a 75S and alignment is 
straight-forward.  Also, the BFO crystals have a tendency to drift a bit 
such that the audio passband on one sideband may sound "thinner" than the 
other.  Unfortunately, the xtal circuit will not allow crystal bending. 
Boy, I tried several methods and in the end its best to order a set of BFO 
crystals through JAN, ICM, etc, if necessary

Just be aware that the odds are not in your favor of the receiver being 
functional.  It will be almost imperative to clean the mechanical filter. 
I've only found perhaps one in ten that was working without significant IF 
path loss.  I don't want to scare you off about my collection of 6 
receivers.  I wanted to create a museum piece using the best parts from the 
carcasses I had collected.  The cabinets are being carefully painted this 
week and I hope to soon show the FR-100B and FL-200B on my QRZ.com page.

I think the FR-100B is historically significant.  For better or worse, it 
was the product that laid the foundation toward the obliteration of U.S. 
manufacturers.  From the FR-100B came the FR-50, then the FTdx series, 
FT-101...and the rest is history.

Paul, W9AC

----- Original Message ----- 
From: "mark depaepe " <n5yey at live.com>
To: <amradio at mailman.qth.net>
Sent: Wednesday, November 23, 2011 4:26 PM
Subject: [AMRadio] Sommerkamp FR100B Receiver

> Hello all,
>
> I recently picked up a Sommerkamp FR100B receiver. It has been in storage 
> for years so it will need some work to get it into a usable condition. 
> Does anyone have a schematic or service manual or know where I can find 
> one?
> I have never seen one of these radios before. Does anyone have any 
> experience with this receiver?  Is it worth repairing?
>
> 73
> Mark
> Sent from my Verizon Wireless BlackBerry
>
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