Well, perhaps he merely tickled the input of the YC156 through
the MFJ with a tiny amount of drive. All the same, there is
nothing to be gained in doing this without the filaments preheated
and plate voltage applied, as he learned. And the YC156 isn't
unique in this reality. It sounded to me like a pretty clueless
thing to try -- especially since he didn't tell us that the drive
power was held very low. The YC156 specifications indicate
that the tube is particularly susceptible to damage from applying
voltages without preheating the filament due to the choice of
filament coatings.
----- Original Message -----
From: "W0UN -- John Brosnahan" <shr@swtexas.net>
To: "Leigh S. Jones" <kr6x@kr6x.com>
Sent: Thursday, September 16, 2004 9:55 PM
Subject: Re: [Amps] input matching question on the YC156?
> Think he was only applying RF from his MFJ--not serious drive
> power from a TX.
>
> > Now I have a MFJ I'm able to "play a little" and do a cold test
setup
> >first.
>
> --John W0UN
>
>
>
> At 11:54 PM 9/16/2004, you wrote:
> >Neil
> >
> >I can't imagine that this has gone on all day and no one has told
you.
> >I may get a little heavy handed here. Sorry in advance. Applying
> >drive power without pre-heating the filaments is not allowed for
this
> >tube. I'm not an Eimac employee, but I have read the 3CPX5000A7
> >data sheet.
> >
> >Two simple rules:
> >
> >rule 1: never apply plate voltage to the tube nor apply drive power
> >until after the prescribed filament warm-up period has elapsed
> >
> >rule 2: never apply drive power until plate voltage has been
applied
> >
> >details:
> >
> >1) apply forced air cooling
> >2) apply filament voltage
> >3) delay according to tube manufacturers instructions
> >4) apply plate voltage
> >5) connect antenna switch
> >6) allow cathode current (bias to operating level)
> >7) apply drive power to transmit
> >8) stop applying drive power
> >9) bias to cut-off cathode current
> >10) disconnect antenna switch
> >11) repeat steps 5-10 in order as many times as needed
> >12) remove plate voltage
> >13) remove filament voltage
> >14) delay according to tube manufacturers instructions
> >15) remove forced air cooling
> >
> >Sorry if this sounds like me preaching to you, but someone has
> >to tell you.
> >
> >KR6X
> >
> >----- Original Message -----
> >From: "Neil Carr G0JHC" <g0jhc@blueyonder.co.uk>
> >To: <amps@contesting.com>
> >Sent: Thursday, September 16, 2004 8:16 AM
> >Subject: [Amps] input matching question on the YC156?
> >
> >
> >I'm currently playing around with a YC156 and have and have
discovered
> >an
> >interesting phenomena which I'm having difficultly explaining.
> >
> >On previous amps I have never really bothered tuning the i/p
> >matching
> >until I've hit it with RF (I build single band amps, so its quite
easy
> >to
> >guess).
> >
> >
> > Now I have a MFJ I'm able to "play a little" and do a cold test
setup
> >first.
> >
> >
> >I set my input matching up for 1:0 SWR with the MFJ, at this time
the
> >heaters are not on. Soon as I switch them on SWR shoots up to 2:1,
> >then over
> >a 6 minute period gradually to 4:1.
> >
> >So I retuned for 1:0 SWR once things had settled down, after 6
> >minutes, and
> >it stays rock solid all day long.
> >
> >Of course in the real world I'm not going to ever engage the i/p
> >circuit
> >until minute 6 of warm up with this tube, at which time the i/p SWR
is
> >always now 1:0, but I'm puzzled in what may be happening?
> >
> >Has anyone else ever experienced this with either the YC156 or any
> >other
> >tube?
> >
> >This is how its set up now.
> >
> >
> >Heaters off swr = 4:1 on i/p match
> >
> >Switch heaters on, swr immediately goes to 3:1
> >
> >After min 1 swr = 3:0
> >
> >After min 2 swr = 2.9
> >
> >After min 3 swr = 2.7
> >
> >After min 4 swr = 1.8
> >
> >After min 5 swr 1.3
> >
> >After min 6 swr 1.0 ..and stays there until the heaters go off.
> >
> >
> >
> >This to me looks like a thermal "thing" due to the large size of
the
> >heaters on a YC156 and heat expansion.
> >
> >
> >What do others think?
> >
> >
> >Neil G0JHC
> >
> >
> >
> >
> >
> >
> >
> >_______________________________________________
> >Amps mailing list
> >Amps@contesting.com
> >http://lists.contesting.com/mailman/listinfo/amps
> >
> >_______________________________________________
> >Amps mailing list
> >Amps@contesting.com
> >http://lists.contesting.com/mailman/listinfo/amps
>
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