[AMRadio] Ranger... good news, bad news


Peter Markavage manualman at juno.com
Sun Nov 5 21:44:38 EST 2006


I've been using the SB-200 on AM since about the mid 90's. Still have the
same original tubes that were put in the unit in 1969. I can drive it
with the CE100V, 756PRO II, 706MKIIG, Johnson Ranger,  and even a
Lafayette HA-410(on 10 meters). I've never seen the tubes show any color.
I do use, in addition to the internal fan, an external fan as an exhaust
on the top of the unit. Output of the SB-200 is generally around 125
watts. I also made the "tuned input" component changes several years ago
in my SB-200 as per http://www.ne7x.com/sb200/heathkit-sb200.htm
It made a big difference when I run the Ranger and the 100V into the
SB-200 on 75 meters.

Pete, wa2cwa

On Sun, 5 Nov 2006 19:00:26 -0600 "John Coleman ARS WA5BXO"
<wa5bxo2006 at pctechref.com> writes:
>         I was going to comment earlier about the statement that this 
> Ranger
> would not hold it's on against the rice box with the SB200.  As Jim 
> pointed
> out there should not be but a DB or so difference if the ranger is 
> working
> properly and properly tuned.  I am curious as to what power his 
> ranger will
> put into dummy load and what the modulation looks like.  I think I 
> read in
> this thread about someone reducing the drive on the Ranger's grid.  
> That is
> a sure fire way to ruin the output tube (6146).  The single 6146 in 
> class C
> service as it is in the Ranger should have 2.5 to 3 milliamps of 
> drive on it
> at all times. Do not reduce the grid current drive to reduce power 
> on the
> Ranger.  If memory serves me right the 6146 is to be used at about 
> 65 watts
> plate input on AM plate modulation. It should be putting out between 
> 40 - 45
> watts carrier and develop about 180 watts PEP. (Could be a little 
> more with
> a good modulation XFMR)  That's only about 2-3 DBs below what the 
> SB200 will
> do as an AM linier when operated properly.  Now 3 DBs is not to be 
> taken
> lightly when the going is rough but if your going to do a lot of 
> work for a
> DB or 2 then put the work in the antenna or a bigger rig that will 
> get you
> 10 DB gain.
> 
>         I have used the SB200 on AM and it does OK but I would not 
> want to
> do it for a long time.  Those tubes get real hot.  I use the SB200 
> as a
> driver for my big rig.  The input to the SB200 is about 5 - 10 watts 
> and the
> output of the SB200 is about 50 - 70 watts carrier this drives the 
> grid of
> my big class C plate modulated final.  But even using the SB200 to 
> put out
> 50 - 70 watts it get real hot and the tube show some color.  I think 
> the
> best thing I can do to increase the efficiency of the SB200 at low 
> power, is
> to reduce the plate voltage to about 1500 instead of 2500.  I added a 
> switch
> to the front panel of mine to increase the bias voltage making it 
> harder to
> drive.  I thought that this would decrease the conduction angle 
> enough to
> reduce the heat but the trouble is that the plate is still not 
> reaching
> saturation at the low power level so I figure that if I reduce the 
> plate
> supply voltage and increase the drive then I can come closer to the 
> non
> linear class C service for continuous CW and the efficiency will 
> surly
> increase.  The idea is to use the rice box rig at low power so it 
> will last
> a long time and have the SB200 to make up the slack. But I want it 
> to last a
> long time as well.  BJ and I like the flexibility of this type of 
> operation.
> That is to be able to flip some switches and use the SB200 as linier 
> on SSB
> as it was intended and then flip the switches back so as to lower 
> the output
> but raise the efficiency for continuous carrier operation as 
> required by the
> big class C final.  We have been operating it linearly with the 2500 
> volts
> supply and reducing the drive from the rice box carrier source but 
> it has
> always bothered me that it is so inefficient and those tubes show 
> color.  As
> I recall the PS in the SB200 is a voltage double type circuit 
> perhaps a
> little circuit change up with some HV switches might be in order 
> here?
> Any Ideas on this?
> 
> 
> John, WA5BXO
> 
>     BTW the stock plate RF choke in the SB200 is NOT large enough on 
> 75 mtr
> and a lot of RF gets back into the PS causing weird AC modulation at 
> low
> carrier levels.  BJ and I thought it was the Filter Caps so we got 
> new ones.
> No help.  We found that the weird modulation on the output carrier 
> would
> come and go at different levels of drive at low power and only on 75 
> mtrs.
> We measured the DC at the POWER supply B+ point as it went through 
> the
> chassis to the plate choke and found some RF there and guess what 
> the RF was
> getting back to the diodes in the PS and modulating with the AC.  It 
> was
> real weird.  Placed a RF choke under the chassis and an extra RF 
> bypass
> cured the whole thing.
> 
> 73, John, WA5BXO
> 
> 
> 
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