[AMRadio] 3-500Z @ 4 kV (Was: Johnson trannies...)


Kim Elmore cw_de_n5op at sbcglobal.net
Sat Jun 4 16:21:02 EDT 2011


I changed the subject line so as not to continue committing a thread hijack.

I never looked into the IMD characteristics before I did this, to be 
honest. Almost all my operating is CW, so that doesn't so much matter 
to me. But I looed at the the spec sheet I have (c 1980) and it says 
that 3rd order IMD is -40 dB at 3.5 kV and 5th order is -45 dB. 
Nothing is listed for 5th order below 2.5 kV, so it must simply be 
below -46 dB. The best 3rd order appears to be at 1.5 kV, where it's 
-46 dB. Third order IMD increases to -33 dB at 2.5 KV, then stays 
steady at -40 dB for 3.0 and 3.5 kV, where the table ends. Under load 
(400 mA CW) I see about 3.6 kV B+, but with SSB or a two-tone test, 
it's closer to 3.8 kV. Originally, the B+ dropped to about 2.7 kV 
with 400 mA CW and was up around 2.9-3.0 kV with a two-tone test. It 
may well be that the IMD isn't as good as it was, but probably isn't 
too much worse.

I can do AM with the amp and my Orion II, but I'd rather do AM with 
my Dad's Globe Champion 350, but have a problem somewhere between the 
VFO and the AX-9909 finals. Jim Wilhite and I have looked at it and 
we're still scratching our heads as to just what's going on. I 
strongly suspect that my problem is self induced, but for the life of 
me can't find what I've done to cause it.

The VFO is fine and doing exactly what it's supposed to do with the 
output amplitudes it's supposed to have. It's somewhere in the 6CL6 
buffer or 2E26 driver. The symptoms are strange: there's no drive for 
40-10 m and it doesn't act right on 160 and 80 m, either. Resonating 
the grid no longer gives me the big peaks I remember. There's always 
a background grid current of between 5-10 mA, and the peaks are not 
the pin-bending amounts the rig had before I got into it. This Champ 
has never "liked" crystals (slow to take off, if at all), but I have 
a couple that work on 80 m. These act exactly as I'd expect, but when 
I use the VFO, things change for the worse. But, Jim and I have gone 
over the VFO and it seems fine in and out of the rig.

If there are any other Globe Champ 350 aficionados out there that 
have experience with the rig, I'm all ears!

Kim N5OP

At 01:37 PM 6/4/2011, you wrote:
>IMD deteriorates with the 3-500 when the Ep starts getting up over 3
>KV (according to what I have read).
>
>I've seen a table with 3rd order spec's for different Ep from 1.5 KV
>up to the limit, of course I can't remember the source for the data
>which is why I try to avoid technical disputes--I can remember general
>facts but can never say where I got them--but I remember at around 2
>KV the tube looked pretty darn good with the 3rd order down around 40
>dB or more, at 3 KV it was okay but at 3.3 or higher it began to get
>less than 30 dB down from fundamental and be marginally legal.   I
>have no idea how the measurements were made so don't take it as
>gospel.
>
>I still think it is a great tube, 20 w. grid dissipation for one
>thing--a ham has to almost have to be deliberately trying to damage
>one to damage it (or not know what he is doing).  I went through a
>period where I contemplated the ceramic tube route, but decided to
>stick with glass.
>
>73
>
>Rob
>K5UJ
>
>
>On Sat, Jun 4, 2011 at 10:19 AM, Kim Elmore <cw_de_n5op at sbcglobal.net> wrote:
> > I noticed the same thing with a transformer that Dahl designed for me
> > many years ago. It's a replacement for the original AL-80A
> > transformer designed to generate about 3.6 kV B+ under load using a
> > FWB instead of a doubler. This was the result of a question that went
> > like "I wonder how much I'd get if I ran the 3-500Z right up against
> > its voltage rating limit?" I had to alter the output network values
> > because this changed the output impedance (something I had not
> > considered until I tried tuning up the amp) but with the appropriate
> > changes it's well-behaved. All the effort bought me a bit over 1 dB,
> > and so wasn't worth it from the standpoint of increased output, but
> > the knowledge gained was far beyond price.
> >
> > Kim N5OP
> >
> > At 08:04 AM 6/4/2011, you wrote:
> >>yeah but the big question is do they still sell it and for how much.
> >>
> >>The Dahl drop in replacement for the B+ transformer in the Ten Tec
> >>Centurion amp mysteriously disappeared from their list a few years
> >>ago; I have no idea why but I'm sure glad I got mine before that
> >>happened.  It is far and away better than the stock transformer.
> >>
> >>73
> >>
> >>Rob
> >>K5UJ
> >>
> >>On Fri, Jun 3, 2011 at 10:41 AM, Kim Elmore 
> <cw_de_n5op at sbcglobal.net> wrote:
> >> > Hi Jim,
> >> >
> >> > I do believe that you pulled that right off of the Peter Dahl/Harback
> >> > web site :) It's pretty handy for stuff like that. It's amazing how
> >> > many different transformers they've re-engineered for the old rigs!
> >> >
> >> > 73,
> >> >
> >> > Kim N5OP
> >> >
> >> > At 09:11 PM 6/2/2011, you wrote:
> >> >>I think this is what you are seeking:
> >> >>
> >> >>JOHNSON VALIANT DRIVER XFMR
> >> >>P/N 22.1286, T4
> >> >>CORE) EI-062 X .75           STYLE #) 01  E-I LAMINATED CORE
> >> >>PR) 230 OHMS DC (12AU7 AUDIO DRIVER PLATE)
> >> >>
> >> >>S1) 800 OHMS CT (PP 6146 MODULATOR GRIDS)
> >> >>
> >> >>DM) HT =  1.643 WT =  1.955 DT =  1.438 MD =  0.000 MW =  2.375
> >> >>
> >> >>
> >> >>
> >> >>----- Original Message -----
> >> >>
> >> >>
> >> >>
> >> >> > Thanks, Darrell. Do you, or anyone else on the list, happen to know
> >> >> > the
> >> >> > specifications of the driver transformer in the Valiant?
> >> >> >
> >> >> > -----Original Message-----
> >> >>
> >> >> >
> >> >> > Not the same transformer. The Ranger uses an interstage transformer
> >> >> > (step-up). The Valiant uses a driver transformer (step-down).
> >> >> >
> >> >> > Darrell, WA5VGO
> >> >>
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