conversion for surplus receivers - part I
(part two = f13.htm)
2q AM/CW/SSB detector in Kw.E.a is the Audion-type.
The circuit diagrams shows that only the BFO unit is modified for SSB, but only a small circuit
is added, and it is easily converted back to the original state. It is however, an advantage to
decrease the IF level to the detector in CW/SSB mode further with an additional capacitor
across '348' 300pF capacitor
BFO circuit in Kw.E.a.
It is quite complex and not really easy to read the circuit diagram. Different version of circuits
shows different details, so some may be wrong, but it is difficult to say without closer inspection
into the receiver.
The same notes are also mentioned on page 22r
Lorenz 6P203 receiver; detectors
Note that the IF is splitted, with two different last IF stages, one for CW/SSB detector and
another for AGC, so it is no problem to receive CW/SSB with AGC on. The only modification
needed, was to change the anode resistor for BFO from 220k to 33k to increase the anode
current and increase the BFO injection. Used it on many evenings listening to 3800kc, and I
am surprised that the audio quality for ssb is so well. Audio output stage is a 6AU6/EF94. The
receiver has also a remarkable good audio cw filter with bandwidth down to 0.3kHz.
W5UOZ's product detector for HQ-129X (Hammarlund).(See CQ April 63) This was
an important note to read, and may have changed my opinion towards thinking about "choosing
the proper circuit for the specific receiver" .
Since the original BFO is an Electron-coupled type, I would use Hartley or Colpitts type oscillator!
To much equipment has been damaged by silly persons who decided to modifiy it but never
really found the solution to fulfil it. The receiver would be wrecked and never operated again.
In some cases such receivers are seen at auctions, but most are just put in the garbage. In the
actual application it is much attenuation in the output circuit. It is probably better to use a proper
audio low pass filter and risk to have more attenutation at the input, possibly adding a resistor in
series with the input since small coupling capacitors are only an indication of an amateur who
really doesn't know what he is doing, see the next circuit diagram for a similar stage, but
The best idea is keep the oscillator type, and use the suitable product detector which goes
with it. If the original BFO is a Hartley or Colpitt type, the best idea is to replace the BFO valve
with a 6AJ8/ECH81 or 6K8/ECH35.
Another well-proven circuit is used in Drake receivers, this is from the 2-B, it may well be used with
In some cases the BFO causes more problems than the lack of product detector. For Hallicrafters
S-40A the BFO drifts a lot, but I cured it by using a half watt grid leak resistor.
For his HRO, G3RZP fitted a simple product detector/BFO. He used a 6SJ7, but virtually any pentode
would be suitable. This arrangement prove suitable for fitting into almost any of the vintage 'boatanchor'
receivers designed before introduction of amateur SSB. It has the advantage for all modes over diode
detector which require volts of input to minimize distortion. But still IF level must be reduced for proper
ssb operation! See Technical topics G3VA, Radcom, January 2004, pg 45.
The concept is certainly not suitable for any receiver, only the receivers where the original BFO uses
ECO circuit, so if it is grid/anode-connected you still need to use the next suggested circuit as forAR-88.
Plug-in Product detector for AR-88 (RCA) and similar receivers
Before you start thinking about how to construct an SSB adapter or modification for your receiver,
it is most important to see which type BFO is used. If is is an ECO type, then 6SA7 or 6BE6 type
converter may be the most suitable for conversion, but it is a Hartley or grid-to-anode type Colpitts
oscillator then you must use 6K8, ECH35, ECH81/6AJ8 or similar triode/heptode, the latter applies
for AR-88. Too many modifications changes uneccessarily much and it is no good way, the more you
change the less is the chance for success, and it is even harder to finish, so it is often most likely the
receiver is wrecked and dumped next the year.
It is a suggested circuit diagram if you don't wish to modify the receiver more than it is always easy
to convert it back to the original state. I've studied the circuit diagram to see if it is possible to build
a PLUG-IN adapter which goes on to the original BFO valve socket and only minor wiring changes
are made, they are probably not much important if you wish to use the receiver as it was before
Siemens 745 E310 receiver has 12AT7/ECC81 as detector/BFO, but it is useless
for SSB reception. It is relatively easy to modify it for proper SSB reception by some simple changes,
it is some mechanical work, but no real challenge.The first step is to reduce the input level to the
product detector so it is not overloaded by a normal IF level. You must open the IF can and remove
11C4 capacitor, mount 560 and 5600pF capcitors underneath and connect the center to the screened
cable going to the valve grid. A grid leak must also be added since the grid is no longer grounded
through the coil. Then 11W3 is changed and a .02µF capacitor is added between the cathodes.
11W9 is changed to 22k. The screen grid voltage for IF output stage is stabilized for better AGC operation
IF-stage chassis details for Siemens Funk 745 E310 receiver, the drawing shows parts mentioned
in the modifications mentioned above
Eddystone EC10A Receiver: IF-output, detectors and 1st audio stage.
For some strange reason this receiver is not suitable for SSB. So I was asked to convert one 16 years ago.
If I could have chosen, the product detector should have used MC1496P, S042P or NE604. But in this
case it is difficult because
of the negative supply voltage, it would probably caused some problems with suitable decoupling.
A DG-mosfet seems easier to use. BFO injection is adjusted for 3-4V drain voltage (ca. 2mA drain current).
To avoid selfoscillation in the IF, audio cables should be screened such that they don't radiate signal back
to a critical point in the IF..
Product detector for Eddystone EC10A solidstate receiver using 3N140 or 40673 dual gate mosfet.
Remember to remove C67 such that BFO-signal does not go into the IF when the product
detector is installed. If you should need to replace the audio stage transistor, BC557 is a
suggested device, emitter resistor must be reduced to 680W .
förzer notes to come later
I enjoy collecting these items and I will show them on my website for others to enjoy. I am not interested in selling them, however - please do not ask.
Instead, I hope to help others who collect this type of gear and would like to hear from them.
Last update: 2005.01.09