[AMRadio] Tank numbers
Dan Hall
kj7fx at tdn.com
Mon Mar 4 19:53:16 EST 2002
Thanks Bill:
I'm looking to set it on 3870 and environs. Those numbers actually are quite
close given what I have arrived at experimentally. I'll set it for what
you've given, (need to work out C1 a little bit. I may have the caps I need)
and give it some smoke when I get the drive issues worked out.
Thanks
Dan
----- Original Message -----
From: "Bill Coleman" <n2bc at stny.rr.com>
To: <amradio at mailman.qth.net>
Sent: Monday, March 04, 2002 4:24 PM
Subject: Re: [AMRadio] Need some help here
> Dan, not sure what freq you are aiming at, but have included the results
of
> a PI and PI-L calc spreadsheet I built from W5FD's Q based formulas. If
> you have Lotus 123 I'b be glad to send it to ya. Or hollar & I can plug
in
> other values. The Efficiency% stuff is only used to show plate
dissipation
> & power out, does not alter the tank values. I used the 2KV & 400mA
values
> you noted.
>
> 73, Bill N2BC
>
> INPUT DATA PI Calculations PI - L Calculations
> PA Ep 2000 Plate Load 2500 Q1 10.83 Ql 2.24
> PA Ip (Amps) 0.400 Input Watts 800 Q2 1.17 Qoutx 9.76
> Efficiency % 60 Output Watts 480 XC1 230.8 Q1L 7.38
> K 2.00 Plate Dis 320 XC2 42.78 Q2L 2.38
> Rout 50 XL 253.6 XL2 112
> ImageR 300 XP2 134
> Qout 12 K Values Class A 1.3 XC1L 338.6
> Class AB 1.5 to 1.7 XP1 126.1
> Class B 1.57 to 1.8 XL1 439.6
> Class C 2 XC2L 65.0
>
> Freq C1 (pf) L1 (uH) C2 (pf) Freq C1 (pf) L1 (uH) C2 (pf) L2 (uH)
>
> 1.800 383 22.42 2067 1.800 261 38.87 1360 9.89
> 1.900 363 21.24 1958 1.900 247 36.82 1289 9.37
> 2.000 345 20.18 1860 2.000 235 34.98 1224 8.90
>
> 3.500 197 11.53 1063 3.500 134 19.99 700 5.08
> 3.750 184 10.76 992 3.750 125 18.66 653 4.75
> 4.000 172 10.09 930 4.000 118 17.49 612 4.45
>
> 7.000 99 5.77 532 7.000 67 10.00 350 2.54
> 7.300 94 5.53 510 7.300 64 9.58 335 2.44
>
>
> ~~~~~~~~~~~~~~~~
> Bill Coleman N2BC
> http://home.stny.rr.com/n2bc
> ----- Original Message -----
> From: "Dan Hall" <kj7fx at tdn.com>
> To: <amradio at mailman.qth.net>
> Sent: Monday, March 04, 2002 7:08 PM
> Subject: Re: [AMRadio] Need some help here
>
>
> > Thanks Bill:
> > I will comment on your comments with some snippage.
> >
> > > Well, Dan, I am of the firm belief that these transmitters are
> > > single-frequency beasts only.
> >
> > I have gathered that, and yes I will go back to a single frequency
scheme.
> >
> >
> > I have
> > > tried to stay with the existing circuitry as much as possible, even to
> the
> > > extent where in most cases to the transmitter can be retuned back to
the
> > > broadcast band.
> >
> > Me too.
> >
> > (exciter coil)
> > > I have found that some coils can't be tapped down without excessive
> loss.
> > > The unused turns should be shorted out with a strap.
> >
> > I'll take another look at shorting things before I take out the original
> > coil and wind a new one. The bias comes to the PA tubes from a resistor
> > network to ground via the center of this coil.
> >
> >
> > Can you look at this
> > > signal with a 'scope? If it isn't a clean sine-wave, then you may
have
> to
> > > use other sets of taps on the coil or replace the coil. If you see a
> > > sine-wave with a big dip where the peak belongs, you indeed have
> problems
> > > with the unused coil turns.
> >
> > Bingo! Very ugly sine at the grids of the 833As and it changes
drastically
> > when tuning the exciter through resonance. The purer the waveform the
> lower
> > the output it seems.
> >
> > >> 2000 Volts? That sounds low, but perhaps that is correct for 833's
> At
> > any rate, they should put out well over
> > > 1000 watts at full output.
> >
> > The main power transformer has two HV taps one at 2230VAC and the other
at
> > 3300VAC. I'm using the lower voltage tap to reduce the power output.
> >
> >
> > I favor a PI-L arrangement if you have a choice,
> > > and can help you configure one if you need.
> >
> > It's a PI-L, I'm using 145pf fixed C1, around 9mmh L1, 750pf C2 and
> around
> > 4.5mmh L2. The coils are variable with shorting of the unused portion
and
> C2
> > is a 80-1300pf variable in parallel with a 300PF fixed. I can make this
> > fixed with a 3000pf and a 1000pf in series.
> >
> >
> > . You may
> > > have to also short intermediate turns so the coil can't adsorb energy
in
> > the
> > > unused portion. Use a scope to verify the output waveshape is a good
> > > sine-wave.
> >
> > After I get the drive in shape I'll look at this
> >
> >
> >
> > > Another problem may be the RF choke in the B+ line. Make sure it
isn't
> > > resonant. I have had to replace the RF choke in several transmitters.
> >
> > I'll check
> > >
> >
> > > Not sure why the PA would ever act as a doubler, but sounds like tank
> >
> > This when waaaay out of tune, experimenting
> >
> >
> > >Regarding the
> > > tank circuit, how are you tuning it? I calculate the tube impedance
> from
> > > specified voltage and current, multiplied by a factor, think it is
0.8.
> I
> > > then take a film resistor of somewhere around that value (surprisingly
> it
> > > has turned out to be 3300 ohms in many cases) and, with power
> disconnected
> > > to the transmitter, attach it between one of the PA plates and ground.
> I
> > > then connect an Autek RF-Analyst to the antenna terminals, and adjust
> the
> > > plate tank circuitry for an SWR of 1:1. It must be 1:1, anything
higher
> > is
> > > not acceptable. MFJ units don't seem to work in this application. I
> > then
> > > remove the resistor (important!), turn on the power, and the
trasmitter
> is
> > > tuned and ready to go!
> >
> > Sounds like a plan, do you use a guessed at current based on .7
efficiency
> > and desired output?
> > I am using an AADE L/C meter to set values based on the charts in the
1990
> > handbook. At that, C1 is way out of wack but I attributed it to stray
> > capacitances.
> >
> > Lets say for sake of arguement that I want to shoot for 2000VDC at
400mils
> >
> > Thanks Bill, and I think this stuff is of great use for most on the
list.
> >
> > Dan
> >
> > .qth.net/mailman/listinfo/amradio
> >
> >
> > _______________________________________________
> > AMRadio mailing list
> > AMRadio at mailman.qth.net
> > http://mailman.qth.net/mailman/listinfo/amradio
> >
>
>
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