-The
EIMAC -8930 based 144 MHz Power Amplifier.
This amplifier was build about 3 years ago,
because we figured we could use a bit more "punch" on the 144 MHz band in the
national fieldday contest. I started on the project 5 week`s prior to the event;
I was busy in my basement workshop right up to 30 min. before the start, but due
to lack of experience, and some downright stupid mistakes, I did not complete
the box in time... After the fieldday was over, I left the amplifier sitting on
the shelf for more than 5 months, until it was finally completed at christmas...
What needed to be done was a minor change in the tankcircuit, and a new g2
supply... It took 4 hours to complete this, and another hour to "tweak"
the resonantcircuits, and then it would quietly deliver some 450-500 watts
PEP.... We used this amplifier for the next few years, and then I got rid of it....
- But please spend a few minutes with the fotos, and se how I managed to squezee
a 3/4 kilowatt amplifier into a shoebox... Including the HV-supply !
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Amplifier in busines ! Here it is sitting next to the YAESU FT-847 on the national -V -U -SHF FD... The size is 15 x 30 x 36 cm, and it weights in at 21 kg. |
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A viev of the hindside... All in and output`s are proberly marked, and so are the fuses ! Highvoltage fuse in the upper center... |
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Left to right: 2 115 -450 V transformers, LV transformer, and highvoltage capacitors with voltage doubler. Anode box in bagground. |
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Another perspective of the amplifier topside... 600 Watt coax relay in the lower right corner... |
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Close-up on the output coax relay... 600 watts capability... |
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Center front is the grid box; to the left of that is the circuitboards containing 12V, PTT, g1 and g2 supplies. |
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AC input filter; the LV filter is located below the HV soft-start resistors and soft-start relays are placed on the circuitboard; centered to the left. |
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Iplate measuring resistors top left, blower inlet, and soft-start timer circuit above (RC combination) To the right the 3 min. HV on-delay timer. |
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Circuit board top is g1 regulation, center board 12 V dc and PTT, and lower boards contains the g2 regulator. This is a zenerdiode stack beefed up with a rugged high voltage transistor. |
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To the left is HV interlock circuit, filament inrush protection resistor, and to the right the 3 min. HV on timer. The attenuator is inplace to improve indput VSWR. Input coax relay on the lower right. |
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The LV transformer is placed in between the plate box and the front ! Here is also the relative output meter circuit located. |
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Another perspective of the bottomside of the amplifier.... |
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I hope you enjoyed the tour ! Unfortunaley i do
not have any pic`s of the inside of the grid and plate box. Also, the drawings
for this amplifier; mostly a pile of small notes, where handed over with the
amplifier, when it was sold.
