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Author Topic: ALC control gone?  (Read 720 times)
G0IFL
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Posts: 4




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« on: October 19, 2009, 06:26:42 PM »

Hi..my Heatherlite Hunter amp seems to have lost the ALC control form the radio (FT767). When I key up the power is at max. The ALC appears to be working from the deflections I see on the radios meter...but is there a way I can be certain the amp is at fault and not the radio?

rgds
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VR2AX
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Posts: 585




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« Reply #1 on: October 20, 2009, 05:42:24 AM »

There may be a distinction,  between the radio's internal ALC (what protects the finals in the radio), and the ALC output voltage from the radio back to the amp, which controls the amp's output.

There are two possible areas to check, the ALC output voltage from the amp, and the ALC circuitry within the Heatherlite amp. It is probably easier to check the former initially, if you have a voltmeter. Disconnect the radio from the amp, run it to a adummy load, and measure the voltage on the ALC output cable using a voltmeter (or DVM) when keyed. You will see fairly quickly whether the radio is providing a ALC voltage output or not.

If the radio is producing a 'normal' ALC output, the amp ALC control circuitry is at fault.
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K0XU
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Posts: 294




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« Reply #2 on: October 20, 2009, 06:15:53 AM »

VR2AX is a little confusing. Disconnect the ALC line only and, while transmitting, check the voltage FROM the amp. The higher the voltage on the ALC input of the radio, the less the output of the radio.

Jim
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VR2AX
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Posts: 585




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« Reply #3 on: October 20, 2009, 06:53:11 PM »

K0XU is correct. I am a little confusing myself.

You should indeed measure the voltage coming from the amp. It should be a negative-going voltage, that is the negative value of the voltage increases as the amp output increases (I hope I am not confusing again).
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KM3F
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Posts: 501




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« Reply #4 on: October 20, 2009, 08:05:00 PM »

This may or may not be helpfull.
On my AL80B with ALC feedback to the exciter, the ALC control on the amplifier determines the amount of feedback to the radio.
In a tune position such as CW, varying the ALC on the amplifier will change the drive level the radio give the amplifier as denoted by the power meter. A loop sitution.
This is how I know it's working.
The external ALC does the same thing as the power control and SWR shut down function but through a different path to control the output of the radio's final stage.
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G0IFL
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Posts: 4




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« Reply #5 on: October 20, 2009, 10:17:39 PM »

Tnxs for the advice....
My eqpt is boxed at the moment due to a recent relocation to Switzerland.
If I remember correctly, when I wound the output up to full 100W from the radio, it had the tendancy to blow the main fuse in the amp. I had to run the output at a lower level to prevent this and any flash over of the valve. I think the damage is probably amp orientated as, on chatting to an employee of Amp UK (they took over the Heatherlite business I believe) I was informed the circuitry was prone to become 'defective' if the amp was stored for sometime...especially if in the loft space and exposed to climate changes. I did cover the thing up but it was stored for some length...although, it did work OK, apart from the fuse problem, for some time before I noticed it went full power with no ALC control...oh, 1 more thing...when I noted this I was told that I had quite bad feedback on my signal (which I could easily determine thru the audio monitor cct). Disconnecting the ALC lead cured this problem of feedback....but obviously gave full output from the amp. I was told it could be simple as a dry joint in the amp but, not wishing to play around in there, my only option is finding someone to look at it for me.

Tnxs once again.
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VR2AX
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Posts: 585




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« Reply #6 on: October 21, 2009, 05:02:15 AM »

I would sell the HH and buy an Ameritron AL-80B - hopefully tax free when you get to Switzerland. Modern, well designed amp. Save a lot of headaches later.
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K7KBN
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Posts: 2782




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« Reply #7 on: October 21, 2009, 04:49:27 PM »

Hmmm - 20M tower with a six-element SteppIR.

On top of the Matterhorn!
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73
Pat K7KBN
CWO4 USNR Ret.
N9AOP
Member

Posts: 135




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« Reply #8 on: October 23, 2009, 02:10:36 AM »

If you are running TenTec equipment, there is no ALC to worry about.  Everything seems to work out just fine without it.
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