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Author Topic: Is idle 2.4 KV key down 1.9 KV too much KV drop?  (Read 2552 times)
VE7ALQ
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« on: January 29, 2005, 08:34:57 AM »

I just got my Yaesu fl2100z linear working!  Because I only have access to a 117 VAC circuit, I had the linear rejumpered for 117 VAC.  Key up the linear voltmeter shows 2400 volts, key down the linear voltmeter shows 1900 volts when drawing rated 500 milliamperes.  Is this voltage drop excessive?  The room lights flicker when I send Morse Code, however the 15 amp breaker in the fuse box does not blow.
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K0BG
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« Reply #1 on: January 29, 2005, 10:50:10 AM »

This is about right. The amp uses a voltage doubler circuit in its HF supply and this amount of voltage drop when using 120V is normal. It will be a little less on 240V, but not by much.

Alan, KØBG
www.k0bg.com
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K3HVG
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« Reply #2 on: February 02, 2005, 05:22:12 AM »

You may find that if you provide a dedicated 220v connection, it will yield a much more stable high voltage with far less drop.  After all, the current, and hence I/R losses, in the delivery of the ac service, are halved.  I've tried my L-4Bs on 110v and it simply did not work out well, at all.  
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WB2WIK
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« Reply #3 on: February 02, 2005, 09:53:34 AM »

A voltage doubler is certainly capable of far better regulation than that, but it depends on the design.

My AL-80B uses a doubler HV supply and is very "stiff," like a conventional full wave bridge circuit with substantial filtering would be.  It provides 3000V key-up and 2700V key-down at >500mA.  That's far better regulation (10%) than you're talking about (21%), with a higher-powered supply.

What I worry about when I see such a big "dip" (2.4kV to 1.9kV is a pretty big drop) is "what happened?"  I mean, this could be simple IR losses in stuff, but it can also be lack of filtering which will cause 500v of ripple to appear on your signal.  That ripple can manifest itself in distortion, or even audible hum when tuning up or using CW.

I'd go for the 240V line and try it again, to see what improvement that creates.  At the very least, you might want to carefully listen using wide-response headphones (so you can hear 120 Hz!) and a second receiver while you're sending a full-power carrier to see if you hear any hum on the signal.  If you hear it, so will others, and that's not good.

WB2WIK/6
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VE7ALQ
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« Reply #4 on: February 02, 2005, 10:00:54 AM »

Please let me clarify. The B+ voltage on my Yaesu fl2100z drops from 2.3 KV down to 1.9 KV under load (500 milliamperes).  A similar amplifier I have(Yaesu fl2100b) drops from 2.4 KV down to 2.0 KV under load, also 500 milliamperes.  I live in an apartment and do not have access to 234 VAC, and would prefer not to bother the landlord about putting 234 KV in.  I do have a 117 volt 30 amp circuit in the kitchen for my Microwave and/or electric kettle.  Again I do not like the idea of a long run of wire between that outlet and my linear.  Right now my Yaesu fl2100z amplifier is on a 15 amp circuit with a 15 amp breaker, and has yet to blow the breaker.  I am looking into fusing the Linear with a 15 amp slow blow agc-style fuse, currently it has a 25(!) amp agc-style fuse, and the manual calls for a 20(!) amp agc-style fuse when running on 117 VAC.
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N3ZKP
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« Reply #5 on: February 03, 2005, 05:33:26 AM »

My AL-80A is on a 120V 20A circuit with nothing else on the circuit. My full-power HV drops from 3000v to 2700v key down. My lights do not dim, my lights do not flicker.

Flickering lights generally indicate an overload situation. I'm betting that circuit is marginal, even if the breaker doesn't trip. You should have nothing else on the circuit - no radios, no lights, no nothing. Take everything else off the circuit and see if the situation improves.

Lon

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N3ZKP
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« Reply #6 on: February 03, 2005, 05:35:39 AM »

BTW, If I lived in an apartment with no possibility of a dedicated circuit for an amp, I wouldn't run one.

Lon
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WB2WIK
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« Reply #7 on: February 03, 2005, 09:14:54 AM »

VE7ALQ, you've answered your own question, actually.

The fact is, you have the amplifier, and you're going to use it regardless of how it's working.  If you want advice on the fuse rating, I'd use whatever Yaesu recommends -- if that's AGC20, then use that value.

One thing for certain: If you have a fire or something (unlikely, of course), and a fire inspector finds that you're using the equipment exactly as recommended by its manufacturer (including the 20A fuse), you're not likely to be found in violation of anything.  If you change component ratings, you could be found liable for making an unauthorized modification to CSA/UL recognized equipment.  I'd always just stick with the manufacturer's ratings.

WB2WIK/6
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VE7ALQ
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« Reply #8 on: February 03, 2005, 10:51:23 AM »

Would it be acceptable to put in the linear a 15 amp slow blow fuse to match the 15 amp breaker on the circuit? Although Yaesu recommends a 20 amp fuse, I am reluctant to use a higher rated fuse than the breaker on the entire 117 VAC circuit. Currently there is a 25 amp fuse in the linear which came fused that way from the person I bought it.  That 25 amp fuse is definitely a no-no and I am trying to replace it with either a 20 amp fuse or better yet a 15 amp slow blow fuse A.S.A.P. I think that most of the 20 amp capacity on the fuse is required by the inrush current, to charge the capacitors in the Yaesu fl2100z, so a slow-blow fuse at 15 amps would offer more protection and yet would not blow when the Yaesu linear is powered on.
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