I have a new amplifier (again)

In my last post, I said that I’d be replacing the broken Expert with a valve amplifier and I’ve done just that. I now have an Acom 1500 sitting on the shelf in my shack.

Acom 1500

There simply wasn’t enough room on my desk to fit the amplifier and the Kenwood TS-890 so I had to do a fair bit of work to strengthen the shelf. I reinforced the shelf itself, fitted three extra brackets holding it to the wall and added a couple of legs to stop it from sagging under the not insubstantial weight.

I’ve had this for a couple of weeks and have just finished a three hour stint operating an RTTY/PSK contest with the amplifier ticking over nicely at 400W. Although I enjoyed the ‘instant on’ and ‘no tune’ of the solid state amplifier, I’m much happier with a tube amp. If I’d done that stint with an LDMOS amp it would have got to a point where the fans were on continually and they’d have been ramping up with each separate transmission.

Not so with the Acom. It just sat there on the shelf with the fan running at the default level, gently warming the shack. It’s a constant level, it didn’t get any faster at all.

I’m already very familiar with the operation of Acom amplifiers because of my previous Acom 1000. Apart from the fact that this has three aerial outputs and that it’s had a facelift, the operation of this is identical. I’ve already worked out the base settings for each band and they’re printed out on a sheet next to the amp along with a helpful note to remind me which ANT position selects which of my aerials.

The only slight downside to a valve amplifier is the three minute warm up period when it’s first switched on but that does mean that I won’t just turn it on when I don’t really need it. This will only get used during contests or when DX chasing and certainly not for regular daily use when it’s not needed.

Because I have it on a shelf, the back few inches are below another shelf – There’s a good six inch gap between the top of the amplifier and the shelf above but the exhaust fan at the rear is beneath the shelf. To stop a build up of hot air above the amp, I’ve got a nice quiet Noctua fan on top of the amplifier, blowing the warm exhaust air away from the shelf. It works really well. There’s a similar sized space between the back of the amplifier and the wall so there’s plenty of room for the intake fan.

Fan blowing the exhaust air away from the shelf

It seems cleaner than the solid state amplifier as well. I’m driving it in exactly the same way, when I’m running data, I’m displaying no ALC on the radio but with the Expert some strange things were happening at the same output level. For example, if I transmitted on 40m with the Expert on, my smart speakers in the front room downstairs would start playing random music. If I transmitted on 30m, my internet would sometimes disconnect and on 17m there was a slight hum on my headphones. With the Acom, I get none of these issues whatsoever when I’m transmitting at the same power. I have GM3SEK chokes on all my feeders just outside the shack and at the feed points to the aerials.

I’m looking forward to this amplifier giving me years of good service.

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