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Author Topic: Getting started with new amp  (Read 4173 times)
AD6KA
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Posts: 2236




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« Reply #15 on: August 30, 2012, 07:42:32 AM »

Sounds like what I should do is start lookinn for a antenna tuner, any suggestions on a good tuner, I have heard good and bad about MFJ but I really don't know. Figure I should get something at the legal limit would be smart
Thanks George

I would get the dummy load first.
After all, even if you plan to run less
than full power, you have to first tune
the amp to full power......then back off the
input drive and leave the settings alone.

Good legal limit tuner?
I LOVE my Dentron MT-3000A,

But it does take up a lot of real estate
on the desk...and they are becoming
harder to find.
73, Ken  AD6KA
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KC4MOP
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Posts: 731




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« Reply #16 on: August 30, 2012, 02:14:39 PM »



Good legal limit tuner?
I LOVE my Dentron MT-3000A,

But it does take up a lot of real estate
on the desk...and they are becoming
harder to find.
73, Ken  AD6KA
I missed several times on ebay to get on of those MT-3000A's. Still command a high resale. I did get a nice deal from eHam ads on a Dentron 3KA tuner.
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WB4M
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Posts: 119




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« Reply #17 on: August 30, 2012, 09:31:03 PM »

K8AXW
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W8JI
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Posts: 9304


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« Reply #18 on: August 31, 2012, 03:37:29 AM »

Quote
You really only need a external relay with older amps than have higher keying voltages like a SB200, SB220, L4B etc that have not been modified.

That isn't always true.

Older amplifiers generally do not have back-pulse cancelling diodes. When the relay line opens, voltage can spike to 50-100 volts or more.  While this Dentron is a 12 V relay, Dentron never looked at voltages closely. The 12V  supply comes from a 12V winding that is a capacitor input, and actual voltage is around 18 volts. Current is around 175-250 mA, depending on the TX light used. About 125-150 mA is the relay coil, which is rated at 100 mA but is operated over the rated voltage. The rest is amp current.

While the steady relay voltage and steady current is safe for his particular rig, the back-pulse from the Dentron when the relay opens exceeds 50 volts. Oddly, the backpulse voltage from Dentron's also varies with the particular lamp used in the transmit indicator! With no bulb, the peak voltage can be 80-100 volts. With a high current bulb, it is much less.

This probably will not hurt the Yaesu transistor, but it is only rated at 60 volts. The Dentron has no diode across the relay coil, and one should be added. $.10 spent in the Dentron can save wear and tear on the keying transistor.

We should all remember many radios use small reed relays or small transistors to key amplifiers, and just because an amplifier says it has 12 volts doesn't mean it is always + 12 volts with no nasty spikes. :-)
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K8AXW
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Posts: 3722




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« Reply #19 on: August 31, 2012, 09:25:38 AM »

WB4M:  Yes??

K8AXW
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