[Amps] Updated amp pictures

[Vic K2VCO]

Interesting points.

1) I measured the air gap of the capacitor with a feeler gauge and it is about 0.012". If 
air breaks down at 30 kV/inch, then it is good for only 360V. 1500W at a 1:1 SWR is about 
273V into 50 ohms. So I think you may have a point here! I am going to try to actually 
measure the breakdown voltage to get more information.

2) Are you sure your choke wasn't damaged by heat rather than RF? I intend to put a piece 
of supercharger hose over the anode to conduct the hot air out of the enclosure. It will 
also serve as insulation against radiated heat. The nearest point of the choke to the 
anode is 1-5/8". I can move the choke, but I wonder if anyone else cares to comment about 
this.

3) The bandswitch is much better than the usual ones from the standpoint of 
current-carrying capability. There is also plenty of clearance between the contacts and 
any metal parts. The only issue is the distance between the contacts, which is certainly 
as great as those in the switches in Alpha, etc. amplifiers -- never mind the ones in 
AL-1500's, etc.! So I am not worried about it.

On 5/29/2013 4:03 PM, Bill Turner wrote:
> ORIGINAL MESSAGE:          (may be snipped)
>
> On Tue, 28 May 2013 17:15:33 -0700, you wrote:
>
>> Thanks. I'm not the best metalworker, and I'm no kind of an engineer, so my work doesn't
>> compare with that of some of the guys who regularly post here. But hopefully it will be of
>> interest.
> REPLY:
>
> Hi Vic:  I have three comments on the 4CX1000A amplifier which might be of
> use to you.
>
> 1. The load cap appears to be a standard broadcast band variable. If that is
> so, it's voltage rating is right on the edge. As long as your SWR is 1:1 it
> will probably work, but much above that and you can expect some arcing at
> that power lever. Once an air variable arcs, small blisters form at the
> point of the arc and it becomes even more prone to arc. If you ever
> accidentally transmit into the wrong antenna, bye-bye load cap.
>
> 2. The plate choke is much too close to the tube's anode, IMO. I made this
> mistake once and eventually the choke burned. Even though there is only a
> few pF between the anode and the windings, at the extreme voltages present,
> a lot of current can flow especially on the higher frequencies. You might
> get lucky and not have a problem, but watch for burned insulation on the
> turns nearest the anode. Not only that, but you are inadvertently setting up
> a second parallel resonant circuit with that same capacitance and a portion
> of the plate choke. Again, you might get lucky, but beware.
>
> 2. The band switch looks awfully small for a legal limit amp. A REAL legal
> limit bandswitch should be about four inches across and cost several hundred
> dollars. One should not skimp here. Ask Carl how many undersized band
> switches he has replaced over the years.  :-)
>
> Otherwise, looks good. Having fun?
>
> 73, Bill W6WRT
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-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/