Discussion in 'Radio Circuits, Repair & Performance' started by KC3EGP, Jan 29, 2017.
Were you running a digital mode ?
No digital but some auto-generated CW.
That is a digital mode.
You should run reduced power.
I have been told that since...I had asked the question before and was told not like 100% digital.
My manual only mentions to run at 50 to 30% power on RTTY and Packet/Data if more than a few mins of use is req...but I will reduce power on CW in the future as well if that's the case.
Something I have learned on FET finals I have repaired. Check the power supply voltage and make sure it is not dropping under full load. This will not only reduce power it will also damage the finals.
I will look out for that when I get it back...not noticed any drops on the PSU...but easy to miss.
The duty cycle of properly timed Morse is about 40% regardless of keying rate, which means
that 100 W Morse correponds to about 40 W of key-down carrier in the long term.
Taking listening pauses into account, it becomes even less.
Duty cycle comes into play when considering the heating of the final transistors.
There may be some systematic problem connected to heat-cycling of the transistors around,
which could be quite difficult to pin down.
Not all RF power transistors stand-up to the cyclic heat-expansion and contraction that keying involves.
Suggest that you contact the local Yaesu representative for their view of the problem.
Its with them at the moment Karl.
"Suggest that you contact the local Yaesu representative for their view of the problem"
I did ask Yaesu when it first went back for repair Karl...they suggested only use 10w CW which seems bizarre.
And also suggested I don't us AM at more than 10w.
The manual states 25 or 30wAM I just dont remember without looking...I had used AM very briefly in an 80m net....they say the 450 is very weak in the AM department
If a piece of radio hardware has such characteristics that it breaks down randomly during normal use at rated power, there is either a serious design flaw or a systematic component problem.
Both alternatives are quite bad from the manufacturer's point of view.
The AM power restriction is derived from the distorsion properties of the
linear amplifier chain, so if more than 25 W of carrier is used, the output waveform may clip and distort.
ALC action could make this worse. Amateur transceiver are not designed for low-distorsion AM generation.
I work with Quality Assurance and Integrated Logistics Support for commercial and military radio gear, and have actually seen a problem that resembled yours.
It turned out to be power transistors that had internal bonding flaws that lead to the destruction of the device after a few thousand off-on cycles at elevated temperatures. Changing the transistor to a type with better properties cured the problem.
There could also be build-related RF or DC instabilities which are triggered by some event external to the radio. If this turns out to be the cause, it is in my opinion a design flaw.
Properly made protection circuits should handle such situations without damaging the transistors.