On Nov 16, 2006, at 1:30 PM, Robert B. Bonner wrote:
Below,
-----Original Message-----
From: ham_amplifiers@... [mailto:ham_amplifiers@...]
On Behalf Of R L Measures
Sent: Thursday, November 16, 2006 2:48 PM
To: ham_amplifiers@...
Subject: Re: [ham_amplifiers] NOS cermic-metal tube burn in
On Nov 16, 2006, at 11:06 AM, Robert B. Bonner wrote:
RL,
Because he adjusted the BIAS to make the 400-500 ma of resting plate
current.
You have to very closely read his message. There's a very slight
language
barrier.
I wondered about that problem after I clicked Send. However, if the
tubes will draw 500mA, there can not be a lack of emission provided
they do that briefly at 0 grid volts.
**** Yes exactly, the emission seems good by rocking the bias. Have to be
careful here as 400ma is 800 watts dissipation. But if it was just a quick
check...
I'm hoping he's not going all the way to zero control grid volts,
To check emission capability for Class AB1 operation, one must (very briefly) measure the anode-I at 0 grid volts.
I'm sure
he's just moving it a bit.
That's why I figured the issue is alignment and driver power. Or possibly
some other issue not finals related. We'll have to wait for his response to
the questions.
That's why I'm wondering a couple things. Curious what tubes were
in the
transmitter previously... and if the unit makes full power with a
different
set of tubes.
I'm thinking these 4CX250's are quite possibly just being
difficult. It
doesn't take much to detune the driver tuning and lose drive. I'm
not
familiar with the durability of Chinese 4CX250's in storage, but
the Eimac
ones are like concrete. Seems you can pull an Eimac one out of the
soup and
crank it up any day of the week.
I've seen a number of Eimac pulls that were kaput.
****I was referring to new old stock 4CX250's the 20 year old ones or more,
they just seem to keep right on ticking no matter where you get them from if
new. Pulls are always a crap shoot.
I just had a beautiful 1 YO 3CPX1500A7 test bad last night. Obviously a
hammered cathode as it drew no plate current, made no grid current or RF.
But the filament warmed up nicely. This one was a new tube placed in an MRI
and it faulted... Obviously the fault was a violent one. Really too bad, I
was getting emotionally attached to that tube, now I need to send it back to
the guy. I had thought I had a great purchase there.
Do you have access to a high-potential tester?
I had a new low hours 8877 back in 1980 do the same thing without a fault.
There was a time that Eimac had issues with quality on the 8877, a weld came
loose INSIDE the tube separating the cathode from the pins.
Did you autopsy the tube, or did you base this diagnosis on ohmmeter measurements?
Just after turning it on when keyed my 77SX went to half resting current.
This was my amplifier and I just about lost it. I worked for a medium sized
Eimac dealer at the time. I talked directly first to Eimac, then ETO and
since that tube was within warranty I went through all the standard return
paperwork. They tore the tube apart and in fact it was the warrantable
quality failure problem and they sent me a new tube.
What failed?
The KWS-1 is a persnickety device in the first place, but once
lined up they
work well.
... and the audio quality is superb.
**** Yes for an early SSB rig they were great.
They were better than later Collins transmitters because they used a 2.7KHz mechanical filter -- i. e., one that was wide enough to pass a humanoid male voice with minimal loss of lows. Later Collins transmitters used a 2.4KHz filter, which is wide enough for female voices but not male voices other than those like that of Verne Troyer, a.k.a. "Mini Me" of Austin Powers movie fame.
I'm more of a KW-1 fan only
because they were total brutes. I'm sure you agree.
I am not a fan of AM because it's a watt-waster and most of the Hams who run AM are lock-to-talk time-wasters.
I think the Collins
engineers sort of let us down a little by not putting bigger tubes in them
from the start.
Agreed, Bob, but in those days the choices were few between the 7580/4cx250R and the 8170.
They of course wanted a transmitter to match the 75A-4 but
still. The 4X150 was a sexy little tube.
Six of them in parallel would have been about right for the then legal 1000w DC indicated input on SSB.
...
R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org
