[Boatanchors] Audio drive needed for 813 (x 4) AM modulator

[Sandy]

|

Chris,
    Sounds like the modulator is in Class AB1 probably.  NO POWER required to
drive the 813's just voltage only.  In AB1 there isn't any grid current drawn by
the modulators.  The 5 watt audio amp should do the job adequately.  I am assuming
the modulator input driver transformer has a 600 ohm line input?
Also your audio amp. has a 600 ohm line output.  (Whichever, the driver output should
naturally match the impedance of the modulator input.)  Unavoidably
some "power" is required, but it isn't requred by the 813's themselves, it gets
"lost" in the coupling circuitry/components.

73,
Sandy W5TVW
| I'm still working on the restoration of the 1-KW AM transmitter
| I inherited from the former W6MSC  (see http://www.yipyap.com).
|
| The modulator uses four 813 tubes, two pairs each side of a push-pull.
| There is an audio transformer, but no other active devices in the
| audio chain before the 813s.  So I will need to provide whatever
| audio drive is necessary by other means.
|
| >From my RCA TT book, it says the grid circuit resistance is 30k ohms max.
| And the peak AF grid#1-to-grid#1 voltage is around 180.  (is that the
| total swing of voltage or the positive peak?)  Assuming thats the
| total swing, I'm calculating about 1.1 watts drive per tube.   I need to
| have an audio amp will will put out somewhere around 5 watts.  Since
| volume controls come cheap a little extra would be better, maybe 10 watts.
|
| One line in the RCA TT book has me puzzled, it says
|
| "Maximum-Signal Driving Power(Approx.)   0 watts."
|
| What does that mean?
|
| Chris
| kc0atc
| chris at yipyap.com
||