开云体育

-----Original Message-----
From: ham_amplifiers@... [mailto:ham_amplifiers@...]
On Behalf Of R L Measures
Sent: Friday, November 17, 2006 5:55 AM
To: ham_amplifiers@...
Subject: Re: [ham_amplifiers] NOS cermic-metal tube burn in


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.

*** OK

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?

*** Currently no, I put the tube into one of my ham amplifiers and fired it
up.

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?

*** In the case of the 8877 back in 1980 it was pretty obvious the amp was
working one day and then when fired up the next one of the tubes wasn't
home. I did the pull one out at a time to figure out which one didn’t come
online and then placed the calls.

I checked filaments and both tubes were OK. All the cathode pins were still
connected together. But apparently something else had stopped working.

The tube was returned to Eimac and they did the autopsy. They informed me
of the result and that it was a warranty issue and that the tube would be
replaced. On the next production run I received a new tube. At that time
the whole process took about a month. During that time the amp was
reconverted back to a 77DX and I sold it. :-(

The new owner wanted it converted back and provided the money to start
building 77 conversions. This led me down the road to many 77 console
conversions and eventually the 77DD amplifier.

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?

*** A weld in the actual cathode, I never saw the tube again. But the pins
stay connected and the cathode separates from the pins.

I figure this 3CPX1500 has the same type of failure, though not a warrantee
able situation in this failed in an MRI machine tube.

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.

*** OK. While I've never personally owned a KWS-1. I did a really large
trade at one time in Collins gear. I have owned many late S-Lines however
not any recently.

My personal keeper at the time was a 32S-3A with a DX engineering processor
and a D104. Coupled to a reasonable amplifier (30S-1, Homebrewed 3-1000,
and finally a Harris RF-103A) and a big antenna I had a beautiful sounding
signal.

I had just graduated with my bachelors, took my first après-school job.
Bought a small house that just happened to have a Telrex Bertha in the back
yard. Not too bad at 24... SO I took down my 160 foot 55G on the lake at
my parents home and moved to town.

Back during that cycle I was quite the DX hog. I'd spend the evenings going
up and down 20 meters working everybody. AT least once an evening or more
the DX would say.. BOB, you were not the loudest signal in the pileup, but
I just had to come back to YOU as you have the best sounding audio I have
ever heard.

It did have good punch. And it did sound good. I have spent the next 26
years attempting to get the audio sound back. IT HASN’T EVER HAPPENED.
Which is a huge disappointment.

I've tried every different rig, played with audio...

There is no way to duplicate the Collins mechanical filter without a Collins
mechanical filter...

I think to finally get what I'm looking for will require implementing these
components.

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.

*** Yes no AM is just a toy. Most of my time is spent fast break SSB (not
vox) talking to my buddies from 35 years ago still or working DX.

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.

*** Yeah, there you go. But still no self respecting Collins engineer would
ever stick 6 in a box and call it a day. Then Collins would not be a
collector's item but stacked in piles next to Galaxy sweep tube KW's.

BOB DD
...
R L Measures, AG6K, 805.386.3734
r@..., rlm@..., www.somis.org






Yahoo! Groups Links