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Thursday, 24 May 2018

Splashing Out Somewhat


I decided to get myself a new toy. The idea is that this replaces the linear amp, the antenna switching, the radio switching on HF plus the ATU - all in one box. Also it doesn't need to "warm up" or tuning on each band.

So I brought it home, somewhat excited:

Now, I first tried it with my TS-990 as the exciter. The manual doesn't actually tell me anything about required drive levels, but anything from the TS-990 generates "INPUT OVERLOAD" error - even only with 5W output. So more consultation of the manual and it seems they are keen on you using ALC connections to control the exciter drive levels, so I hook up the ALC line and then this is what happens:

Now that's really quite strange.

Next I try the IC-7610, connect up the ALC and PTT lines and it seems to work OK, however, I have very little control over the RF out - in fact I cant get the amplifier to deliver less than just over 500W output even on the lowest power output setting. That's not very clever - I want to be able to control the RF and gain of the amplifier.

So, some email back and forth to the manufacturer and it seems there are two versions of this amp. One for the US market which includes an attenuator in the drive line so that 25-30W of RF is required for full output, and an EU version without the attenuator.

SPE sent me this table which shows the input RF needed for full output by band and power setting (you can have the amp on Low, Med, High):

So at this point I fell off my chair! This amp eneds only 2W of drive on the low bands for maximum output. The only way that low level of drive is possible with most modern transcievers is by using the ALC all the time to restrict the output of the rig - which is exactly how this amp is "designed" to operate. I think the issue with the TS-990 is that despite ramping the ALC voltage to the most -ve it can, the output is still too high to drive the linear.

Either way, there is no way you can set the controls to deliver, say, 200W output. You can have maximum bananas (which seems to be 500W, 1Kw and 1.3Kw) depending on the Low, Med or High selection of the amp power switch.

The manufacturer recommends you run your rig at FULL RF output and rely 100% on the ALC circuitry to protect the MOSFET in the linear from being fried. I personally don't like this theory at all.

Needless to say the amplifier has been returned today for modification to the USA version so I have some hope of controlling the RF output.

Here you see the drive level of 3W:

which produces 508W out in the "low" power setting:

Bonkers, don't you think?

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