[TenTec] Hercules II Power Source

[John - G3JAG]

The power gain is not necessarily exactly the same for different Herc
IIs. The final transistors are matched by TT, but two sets may well not
have the same gain. TT can and do adjust the gain, but only into the
same ballpark, not to complete identity.

It is also affected by the actual voltage reaching the finals, as
opposed to what the PSU puts out. When you say 14 volts from the 9420,
that is the voltage each rail should be set to internally, at the
respective capacitor terminals. TT say not to set it any higher (to
compensate for voltage drop in the cables) as that will upset the
control circuitry. It follows that the voltage at the finals will
always be less than 14. How much less depends on the resistance in
circuit. In my case, I discovered that there was at least one
intermittent dry joint in the Herc II distribution/relay board. The
effect was to create a spectacular imbalance in the amplifier, one pair
of finals getting practically no power under load. 

Incidentally the dry joint was apparently not a recent development; it
may have been responsible for the self-destruction of two finals some
time back.

If you see low gain, then it may be worth opening the Herc up and
checking carefully for any problem in this area. I re-soldered all the
rivetted connections, relay terminals etc. on the control board after
measuring some strange variations in standing current (I think it
should be exactly 1/2 amp per set of two finals - the individual DC bias
voltages are NOT a reliable guide to actual idling current). I also had
this intermittent and humongous voltage drop for one pair under load.

Its a tedious job and needs a large soldering iron, but in my case it
was well worth the effort. 

John G3JAG

On 31-Dec-99 Jim Reid wrote:
> 
> Gregg, K7KJ wrote:
> 
>> Jim:
>> Just checked my 10 year old Hercules II/9420 PS on 7.025 into a
>> dummy
>> load using a VFD wattmeter: 26w in/ 540w out, 35w in/ 600w out, and
>> will
>> put out well over 600w (with the red LED on!). Keep in mind the 9420
>> puts out 14.0 vdc, no load.
> 
> Now that is interesting,  Gregg.  That is exactly 13 dB gain on the
> first pair,  and 12.3 dB on the second.  My numbers show my
> solid state amp is producing only about 8 dB gain,  hmmmmm?
> Yes,  84 in, 570 out is only a numerical gain of 6.8x's, or some
> 8.3 dB.  I can crank the Astrons up to 14 vdc,  but probably won't.
> 
> Herc. II typicals from the TT web page:
> 
> "RF Power: 1000 watts input. 500/600 watts output, depending 
> on frequency and load impedance. 
> 
> Drive Power: 65 to 80 watts typical for 500 watts output. 
> 
> (Or a typical Herc.  gain of around 9 dB down to only 7.9dB,
> with 80 in and 500 out)
> 
> Primary Power: RF deck, 12 to 14 volts at 100 amps, maximum"
> 
> Your Herc. II at 13 dB gain is a real "hot one",  Gregg,  hi.
> 
> Does the 9420 PS have a current meter,  if so,  how much
> current is being drawn?
> 
> Happy New Year and 73,  Jim,  KH7M
> On the Garden Island of Kauai,  temp outside:  75 F.
> 
> 
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E-Mail: John - G3JAG <patents@dx0man.prestel.co.uk>
Date: 01-Jan-00
Time: 01:44:06

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