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Re: [Amps] FAA AM-4164 trouble

Subject: Re: [Amps] FAA AM-4164 trouble
Date: Sun, 2 Mar 2008 16:41:02 EST
List-post: <">>
Hi Larry, you wrote:>>
> >Hi John. I hope N1RWY's page comes back - I still would like some  of the 
information he had there. 
*** I don't know what happened to Jay's page. Perhaps he has an alias with  
the ARRL and you can email him. A quick Google came up with _n1rwy_ 
, you may try that.  Also Google AM6155 as there are other sites of interest. 

>>I got the amp back in October & performed the mods myself to  get it on 2 
Meters. Do I need those cathode resistors since your amp doesn't  have them? 
What would be the effect of taking them out, since your amp doesn't  have them? 
***The resistors add negative feedback to the amplifier. Whether you remove  
them or not depends upon how you modified the input, and what tube you plan to 
 use. The downside of the resistors is the need for a bit more drive (and  
imperceptible IMD due to varying cathode bias). 
***My input compartment is virtually gutted and matched using link  coupling.
>>As far as I know, the 6155's difference was the plunger setting  inside the 
*** The 6155 grid section is different. The grid coaxial cavity is shorter  
(as it was meant for UHF), the VHF version uses a swamping resistor on the 
grid,  plenty of additional capacitance, and the screen is heavily by-passed - 
 not found on the UHF version.
*** It is my belief, the output cavities are the same (less the bolt-on  
input compartments).
>> I think that's why the problem  started in the first place - the 4X150's 
just aren't right for this amplifier. 
*** I don't know. The 8930 and the 150  (other than plate dissipation) have 
same interelectrode capacitances.  Eimac did rate the 150 for 150 MHz and the 
8930 for 500 MHz, so  perhaps the tube decided to take off. 
*** Did you run the heaters for a while?  Like hours to a day to outgas the 
tube? Did you check the various electrodes for  dc shorts? And, as I said 
off-reflector; it is always best to bring up the  screen and HV slowly.
>>Guess it's back to the drawing board  for a replacement tube. Well, not 
back too far. I'll have to find the 8930, or  set the amp up for the GS-36B 
Either way, I need a backup tube - I don't  know what type of abuse my 
original tube has been through. I get around 400  watts output with 10 - 15 
*** If you have an original 8930, and it is  putting out 400 watts reliably, 
that is good. The best I got was 500 watts with  a fresh tube. What do you run 
the screen voltage at? A small boost in the screen  will have a dramatic 
effect on output. Just don't raise it so far that you draw  excessive screen 
**** There was a fellow in Hawaii selling  NOS 8930's still in the unsealed 
can for about $90. If you can't find him, maybe  I can. You can get the 
GS-36B/4CX400 on eBay from the QRO-Stuff store.  Personally, I wouldn't do 
with him (I'll gladly detail this tidbit off  the reflector). This tube will 
give you another 100 watts of plate dissipation.  As the plate diameter is a 
smaller that the 8930, you will have to bend the  fingerstock for good 
contact. And, while it may be up for SSB, I am not sure the  power supply is up 
FM service with this tube. Personally, I would stick with  the 8930.
>>Do you operate any meteor scatter? I  didn't look up your location, but if 
we're in range of each other, maybe we can  give it a try sometime?
***I am in North Central Illinois and a 2  meter and ATV freak. It will have 
to be Scatter or one hell of an  opening!
>>> 73's for now, & thanks for  your information. You really sound like  you 
know allot about these amplifiers (insert firm handshake  here).    ...Larry 
*** No, I know just enough to be dangerous  (firm handshake back at 'ya).
-John,  N9RF

**************Ideas to please picky eaters. Watch video on AOL Living.      
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