[TowerTalk] FW: Tuner SWR won't stay down

[Jim Thomson]

Date: Sat, 03 Jan 2015 16:46:03 -0800
From: Tom Osborne <w7why at frontier.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] FW:  Tuner SWR won't stay down

Hi Kelly

Figured it out and got it fixed.  It was the cap.  Not sure which one 
yet as I took them both out and replaced them with a couple caps from a 
homebrew tuner I had.  Loaded 500 watts into it and was steady for about 
30 seconds or so.  Before after about 5 seconds the SWR would start to 
climb.

One thing I did notice when I took the caps out was that one of them 
turned a whole lot easier than the other one did.  I'm thinking maybe 
that set screw at the end of the cap may need tightening. There's a lock 
nut that holds the screw so may loosen that and tighten up the drag a 
bit and see it that don't help.  73
Tom W7WHY



On 1/3/2015 2:20 PM, ve4xt at mymts.net wrote:
> Hi Tom
>
> Did you disconnect the part leading from c103 and the link coil to the switch? If not, then c103, the link coil and the trio of capacitors on the input would still be in the circuit.
>
>
> K

##  If any of you folks ever build one of these tuners, do yourself a favour, and use vac caps.   Surplus 12-500 pf @ 15 kv ceramic types,
+hb  tubing coils + heavy duty model 85/86/88 switch..or  a heavy duty roller is the real ticket.  A  T type tuner built like that is virtually bomb proof.
Plan B is to just fix the real issue..right at the ant feedpoint.   Pretty simple matter to add a few uh at the feedpoint, via vac relay.  Then your low
band ants are dead flat across the band.  You only require .5 uh to shift resonace from 7300...down to 7000.  Another option is the seco systmens Tornado drive.
A pair of compressible coils.  They also make a single compressible coil version for verticals.  Same deal, flat swr across the entire band.  Used with the mating
mfj / ameritron SDC-103 screwdriver controller,  with its  10 x pre-sets..it’s a winner.  Bring up the nearest pre-set, then tune up /down from there.   Digital
turns counter too.   

##  If open wire line used,  I would opt for a real, true balanced tuner... like the type that uses a dual ganged roller coils + one single 12-500 pf cap.
##  Air variable caps work just fine in any tuner... provided they are constructed correctly. 

Jim  VE7RF