ACOM 1000 Tube Replacement

My Acom 100 amplifier bit the dust. The tube went bad. Originally I thought it may need to go to the shop to have it replaced, but to my surprise it is very easy for an old Ham like me to accomplish. As always, working on amplifiers is extremely dangerous. Please take extreme care if you attempt to replace the GU74B tube in the Acom 1000 amplifier. See the full instructions below.

Acom 1000 Protection Error PR06…

To start this off I’ll tell you why the tube needed replacing.

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One day I got an error after the countdown. See photo below. It would not come online and show “Ready” after the warmup.

The tube was weak and it just gave out one morning.

acom 1000 error

Acom support was very helpful and we determined it was most likely the tube that was bad.

Acom 1000 Tube Replacement


After deciding it was bad I bought a replacement off of Ebay that came from the Ukraine.

It showed up a few weeks after I ordered it. See link below.

I wish I had taken some photos, but it is pretty easy to get out. I’ll show you what to do in the video below.

See the full instructions I followed: Acom 1000 Tube Replacement and Conditioning NOS GU74b Tubes in your ACOM-1000 Amplifier.

UPDATE: 12/20/2021 – EXCELLENT Instructions Here – I found this later.

Acom 1000 Idling Current Adjustment

This may be the most important part of replacing the Acom 1000 tube. The idling current is very easy to adjust using R1 and R2. See video below.

Use a small-size, flat-tip, insulated screwdriver for next adjustments. On the MAINS PCB, find the two trimmer potentiometers RP1 and RP2 (marked “BIAS1” and “BIAS2”). They control the idling (zero-signal) plate current of the tubes for low- and high- RF-drive levels respectively.
Please note that RP2 will affect both idling levels, while RP1 – only the low level. That is why, the high level is adjusted the first, and only then is set the low level (according to the procedure described below). – Acom 1000 Tube Replacement PDF

See the full instructions I followed: Acom 1000 Tube Replacement

Thank you

More on the Icom 7610 and 7300 radios to come.

If you have any questions, please ask them here. I prefer the comment section here or in YouTube over e-mail because your comments and questions will help others as well.

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Please stay in touch and best 73,

Rich, K0PIR


GU74B Tube from Ukraine. If he’s out, there are similar deals on eBay.

Acom 1000 Operating Manual – Mine is the older version of the 1000 amplifier.

Acom 1000 Tube Replacement FULL Instructions, from GMDX Scotlands DX Association

Conditioning NOS GU74b Tubes in your ACOM-1000 Amplifier. – VE1DX

EXCELLENT Instructions Here – I found this later.

As always, working on amplifiers is extremely dangerous. Take extreme care and follow at your own risk.

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I'm an Amateur Radio enthusiast. I love the hobby and experimenting with radios, antennas and software. On my YouTube channel I upload videos on the Icom 7300 and Icom 7610 along with Ham radio software programs. I hope to inspire people to try new things in Amateur Radio.

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jim oberg
8 months ago

Nice web site.

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