[AMRadio] Power Levels

[James M. Walker]

This is an obvious error there Don, as I have Stock, as in un modified
BC-610 transmitters. The (I) version has no such taps, the HV transformer
has (6) input terminals for
110 and 115 VAC input, IE; if the AC input is 110 VAC
the terminals are selected to handle that, if the AC input is
115 VAC another set of terminals are selected. The output of the high
voltage transformer remains the same
such that the DC output from the power supply provides
2400 VDC in CW mode and 2270 (measured) in AM
mode. The MANUAL states that the unit should be tuned
in CW to "FULL OUTPUT POWER" at 400 MA, and
then switched to AM mode, which will give a plate current indication of 390
MA. this = 885.3 watts input
dc to the final, assuming the bias is at 110VDC minus.

What manual are you reading this from, and I have heard of people modifying
BC-610s to try and get more power
but they always end up burning up the plate coils, and the
other components in the unit.

The manual clearly states that if you need to maintain
control over the AC to the HV transformer A variable
transformer is used and terminals are provided for THAT purpose, it is also
recommended that the AC input NOT
exceed the rated values of the transformer. IE; "you can't
get BLOOD from a turnip", if you exceed the ratings it
will work for a while, but "MAY"cause unrepairable
damage to the HV transformer. A picture of the transformer can be provided
if necessary, showing the
wiring diagram and the terminal layout and also the rated
specifications.

The RF plate current is measured only for the 250TH, the modulator cathode
current is measured with a separate
meter for that function, 0 - 300 MA full scale, the standard procedure for
the BC-610 is as described above,if the plate current fluctuates downward it
is an
indication in this system that the modulation level is too
high for the rated plate volt grid bias and output loading.

The BC-610 manual calls for 400 MA in CW and 390
MA in AM, as the RF plate current. At 2400 VDC in
CW that is 960 watts, NO MODS necessary OR applied. The MANUAL also states
the grid drive to the
250TH should be between 50 MA and 70 MA with the
maximum at 100 MA. My grid current runs at 70 MA
bias is 110VDC minus also per the manual and measured.
The bias circuit for the 250TH also provides the bias to the 807 (pair)
driver tubes and the 6V6 and 6L6. If not
set according to the MANUAL, the drive level is in fact
decreased. No speculation, the driver stage gets "funky"
if the level is changed and there is an annoying tendency
to burning up the RF chokes in the circuits.

I will not speculate what other may have done, my experiences with the units
I own are as stated above, my
units work as described in the MANUAL, and I have NO problems with tube
life/death, my (E) model has the
original 250TH which I installed after unpacking it unused
while in Germany, it traveled from there to Buffalo, NY
in the unit and ran here for 10 Years of use, the unit moved to a friend in
Schenectady, NY where it ran for 20
plus years, and returned to me, still using the original 250TH and providing
full power output, and NOT MODIFIED.

The manual calls out BC-610 E,F,G,H,I and T-213.

I purchased several 100TH tubes and also 250TH tubes
at a whopping cost of approximately 20.00 each roughly
10.00 more than the military paid Eimac for them All in
unopened boxes, they will probably be around after I
die and still unopened.

That is the reality of the units I am currently using, sorry
if that doesn't meet with others expectations of what a
BC-610 "OUGHT" to do.
Jim
WB2FCN
http://eshop1.chem.buffalo.edu



> It sounds like someone made  the "high power" modification.  You will note
> the plate transformer has two taps on the primary... one is marked "2000"
> and the other "2500", which should be the DC output voltage of the power
> supply if the correct a.c. line voltage (115 volts, I believe) is applied
> between each of said terminals and the common terminal.  The tube is
> supposed to run 2000 volts an AM and 2500 volts on CW.  I suspect the 390
> mills is the total drain from the power supply, final plate current plus
> modulator plate current, since both  run off the same power supply.
> According to the tube manual, in plate modulated service, the 250TH is
rated
> 2000 wolts at 250 mills, to give 335 watts carrier out with 60 mills grid
> drive.
>
> The stock BC-610 switches the 115 volts ac from the 2000 volt tap to the
> 2500 volt tap when you switch from AM mode to CW mode.  The earliest
version
> of  the 610 (610-B, I believe), as well as the pre-WWII HT-4, used a
> transformer that only had one ratio that gave 2000 volts DC out of the
power
> supply.
>
> No doubt the 250TH will function at the higher voltage and current, but at
> the expense of tube life.  After WWII, it was not uncommon for hams to put
> both wires to the transformer on the 2500 volt tap, to leave the plate
> voltage at 2500 wolts on AM.  I doubt if that made much if any difference
on
> the receive end, but it did represent an increase in power.  But those
were
> the days when 250TH's and 100TH's were still plentiful and inexpensive.
>
> Don K4KYV
>
>
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