Hi Mike,

Sorry if this is teaching you to suck eggs...  As Steve has suggested, your
tune up method is a potential hazard.  All it needs is a moments inattention
or distraction, and you could put 180 watts of input into the amp <smile>.

I don't use a valve amp, but I do use a 200 watt radio, and this is why it
is imperative to have the ALC line adjusted between radio and amp,  This ALC
is a safety device, and makes sure I can never over drive the amp.

As Steve says, switching between high and low power might lead to a mistake
one day.  For this reason, I always have the radio transmit on about 10
watts, and always run the amp.  Just too much to think about if I were to
regularly go bare foot.

If I were you, I would leave the 102 on the drive level needed for 600
watts, is it 50 watts, and never exceed it.  If the 102 can handle an ALC
line to the rig, I would fit one.

Personally, I wouldn't transmit QRO into an antenna with a 30 to 1 SWR
either, but realise that amateurs regularly tune impedances of several
thousand ohms <smile>.

There was an article in one of the radio magazines about tuners having
misleading ratings.  Some of the ATUs rated at 1 kilowatt were only good at
this power when the impedence is 50 ohms.  Kind of defeats the object
<smile>...

Best wishes, Kelvin Marsh - M0AID

Working to improve accessibility for radio amateurs with disabilities

www.active-elements.org

For accessibility evaluations of amateur equipment and MP3 manuals

-----Original Message-----
From: For blind ham radio operators [mailto:[log in to unmask]]
On Behalf Of Michael Ryan
Sent: 07 April 2014 18:33
To: [log in to unmask]
Subject: Re failed tubes

Hi Lloyd, Steve and all: 
I actually did all those coax jumper and feed line tests, dummy load put out
at the base of the antenna, a couple of months back when I had my 75M SWR
spike. 
All the coax jumpers and feed line was good. Its not until my tuner was
swapped out for a friends that the problem went away. That same friend took
my tuner apart and discovered some damage to the roller inductor and
capacitor. He cleaned it up as best he could and once again we tried it out.

Worked flawlessly handling 200W but caused a Hiss in the amp when I
attempted 500W. Now earlier today, I had a chat with the friend who has my
amp and apparently he did the SWR test between rig and amp this morning and
discovered an 8/1 SWR on all bands and a group of blown resisters. 
The thing is, the amp gave no sign of this on friday night on 75/40M, no
hissing, cracking or smells what so ever, I ran my usual 600W.  
John, this amp has a separate band coil for 40, 75, 160 and one for 30/20,
one for 17/15 and I believe one for 12/10 but not sure as this position on
the band switch is marked aux. 
You place the amp on this setting for 10/12M providing the mod is done. I
didn't tune up there to see if the mod was done because I don't operate on
those bands. 
I think its starting to look like this amp just had bad tubes but we'll see
what happens. 
I also can't help but wonder if I shouldn't put a buffer between the 102 and
amp due to the high max power capability of the 102. 
When tuning up, I'd have the amp in standby and would  tune up for the 102's
max power of 180W CW. 
I would then reduce the output to my 20W amp tune up level and go from
there, finishing with the 75W max drive, then reduced to the 45/50W of
operating drive. Running the amp at 600W CW with that drive level, 800W on
SSB. 
Another thing is, my grid and plate would hover between 175/200 and 450/600
and wouldn't pin on the numbers, just bounce up and down. 
All these numbers are perfectly fine as long as the needles don't pin on 200
and 750. 

73: 
Mike VO1AX