23
In such a case, it is possible that the high voltage is still shown on the meter, but it does not reach the tube. In
any case, this is a major fault. Put the amplifier on STBY and the flashing will stop. Then switch the power off
and contact your supplier.
12.7
Sparks / Discharges in RF area
Very high RF voltages are present in the amplifier during the operation at high power. Incursion of dust or even
suicidal insects can cause such temporary problems.
12.8
SWR cut-off
The factory adjustment for SWR protection is about 2.6: 1. This adjustment can be changed, but the best is to
operate with a properly matched antenna. Should your DX-3SP 'see' bad SWR, it will shut down for 3 seconds
(in bypass mode).
12.9
Frequent over-drive protection cut-off
As previously described in the tuning and operation sections, there is a protection system acting on DX-3SP
input overdrive. When the drive reaches the limit where signal distortion begins to occur, the overdrive indicator
on the front panel will warn you to reduce the drive. If you increase the drive even further, a cut-off protection is
activated.
After about 2 seconds of amplifier bypass, the operation is resumed, but if you have not reduced the drive, the
protection will be activated again. To stop it, you must reduce the input power drive. This protection is not
adjustable - you must not exceed the limit.
12.10 Tube replacement
It is very unlikely that you will ever need to replace an FU-728F. If there is a need for that, the tube is easy to
replace. However, contact your supplier, because a bias adjustment is required for the new tube.
See also
Appendix 3.
13 WARRANTY / SERVICE
The full FOUR YEARS warranty for DX-3SP amplifiers covers all parts and labour, except for the tubes. The
tubes are under a limited warranty for one year only.
