B.26. Sommerkamp FL-dx-500

FL-dx-500 transmitter:
Bought my rig as secondhand from Lowe Electronics, and the price, £120.- wasn't much in 1974,
so I took it as an invitation to experiment. Also got the circuit diagram for FL-200B, it is surprisingly very much
the same circuit. Some parts may be better to copy from FL-200B, but my FL-dx-500 was an early version.
Later versions have transistorized VFO. It wasn't too much to do in the British Post Office, then,
so it was also pleasant to have a private project to work with when you were waiting for something else
to solve in the laboratory.
The worst problem was that the mechanical filter didn't last too long. The rig was then totally
rebuilt with 9MHz SSB generator (KVG XF9A xtal filter), this was very effective in an other way, too. The
old transmitter had extremely many spurious responses due to the improper mixer from 455kHz to 9MHz,
found that it was impossible to have sufficient gain with the 12AT7 mixer if you tried to balance it properly.
Another bad problem was the VFO. It was changed to 6U8, where the triode was used in VFO, and
pentode as buffer. It was soon discovered that the old buffer was a very bad construction, and it pulled
the oscillator frequency by over 300kHz. Also made some improvement for the 6BM8 voltage regulator.
Never liked the FR-dx-500, G3NUE Geoff had it, but I found the Drake 2-B to be far better.




Lived in Leamington Spa in 74, when I purchased this transceiver. Modified the ALC and got very good reports from the
local friends, they mentioned that "they could understand my poor English language much better". The modification is only
addition of a 3300 ohm resistor in series with the ALC time constant capacitor.It was some discussions going about
the level of improvement using ALC instead of a compressor, but it was stated that you could only achieve 1dB, it
was an article in QST around 1971 on this matter. And my issue were borrowed from some persons on some
occasions when the theme was discussed, hi.

See the following Scandinavian articles:
FL-DX-500 Ombyging av sender                  LA8AK  QTC 87-12-530
FL-DX-400/500 Forbedringer  +150V REG         LA8AK  AR  75-01-008
FL-dx-500 på 30m bandet                       SM7VY  QTC 85-05-185
FR-dx-500 på 30m bandet                       SM7VY  QTC 85-05-185
FT-200/250 Forbedring av AGC                  LA8AK  OZ  78-03-120
FT-DX-100/150 MOSFET i HF trinnet                    AR  73-12-293

Here is what I got in return from LA3JA, when he bought my FL-dx-500 in 1982 for NOK1,- (10 pence),
and I paid him 10p for the 84'model receiver (made by D.N.R.T.), so it was really a swap.

Sommerkamp FT-100/FT-dx-150:
Du kan hente en manual og diagram på http://oz8yr.qrz.dk under diagrammer.