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Re: [Amps] Gonset 903 2 meter amplifier question

To: <>, <>, <>
Subject: Re: [Amps] Gonset 903 2 meter amplifier question
From: "jeremy-ca" <>
Date: Mon, 31 Mar 2008 00:07:31 -0400
List-post: <">>
35V is NOT correct for the 4X150 screen, go back to the way it was after you 
get the parasitics settled down. The screen should be fed from a series of 2 
or 3 VR tubes and be around 300V.  A 4X150 shouldnt require neutralization 
on 2M and I see no mention of it in the rather poor BAMA manual.

Be sure you have proper bias on the control grid otherwise the tube will 
take off.


----- Original Message ----- 
From: <>
To: <>; <>
Sent: Sunday, March 30, 2008 10:47 PM
Subject: Re: [Amps] Gonset 903 2 meter amplifier question

> Larry, your descriptions sounds like a classic example of self 
> oscillation.
> The usual fix for that is adjustment of the grid/plate neutralization 
> circuit.
> There is plenty of info about this in any ARRL handbook printed in the 
> last
> 50 or 60 years.
> 73,
> Gerald K5GW
> In a message dated 3/30/2008 9:15:31 P.M. Central Daylight Time,
> writes:
> Hello guys, trying to get one of these amps back on the air, and  I am
> having a little bit of difficulty. I hope this is an easy question for 
> some
> of you, and would appreciate the knowledge feedback! Here's the  history 
> of
> my amp... purchased on ebay with the hopes of learning about  tube amps 
> from
> restoring it, but the electrical problems were more  elaborate than I was
> told (said it needed the HV transformer, and would be  including the spare
> with the amp). I found the diode stack blown, the  capacitors were moldy, 
> so
> I knew they needed to be replaced. The HV xformer  is fine, so I have a 
> spare
> now. Also needed to replace the tune resistor  since it was broken (4k 100
> watt ceramic). The screen supply xformer is  reading 140V instead of ~35V, 
> so
> I installed a small xformer for that  circuit. Now, she powers up fine 
> with
> no sparks or blown fuses, so I think  I'm getting somewhere with it. My
> problem is this... when I turn the HV on,  I see an output on the 
> wattmeter -
> about 80 watts or so, with my plate  current at ~70ma (70ma is spec for 
> the
> 4x150a). I am NOT transmitting into  the amp when this happens! If I 
> provide
> a 5-10 watt input at this point,  nothing happens on the bird. The dummy 
> load
> IS heating up also. Now, if I  try to tune the amp with an RF input 
> present,
> I get the bird to INCREASE in  what I'll call "stray RF", and the meter 
> will
> also DECREASE more and more  as I tune the amp. As an example, if the bird
> reads 50 watts - with 10  watts input, no change. Tuning the amp more, if 
> the
> bird reads 150 watts  and I apply an input of 10 watts, the needle drops 
> to
> 130 watts. With 200  watts with no input, after I apply the 10 watt input,
> the meter drops to  ~75 watts, but at this point, my plate current is WAY
> over 350ma, and the  fuse blows. It almost seems like something is 
> backwards,
> but I don't know  what. Where is this RF coming from if I'm not giving the
> amp an input? Is  there a voltage somewhere that's too high, which is 
> causing
> the "stray RF"?  I've also heard a carrier on my receiver which "comes &
> goes" while I'm  tuning this thing. Again, you experienced guys might have
> fixed something  like this before, but I'm too new to understand what's
> happening. Any help  will be appreciated. Oh, I did try 3 different 
> tubes -
> all with the same  result. They are known to be working from my FAA
> amplifier. Thanks...  Larry
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