>Hi all - let's start a new discussion topic. I am generally considered a
>reliable source of info but I have to admit that my experience on hf is
>limited. Well to the question and I would like all to consider this one.
>
>I will only have the time and money to build one hf amplifier and would
>like constructive inputs for the initial thoughts I have.
>
>Power supply I can happily tackle but the rf deck is the trickiest.
>
>I have the following parts already.
>
> Tube - Mullard / Philips QY5-3000A (tetrode - don't get confused by the 5
>in the part number) plate dissipation 3000W. Fmax = 220 MHz and rated for
>SSB operation. (Was used for tv ultra-linear duty on band 3 170 - 220
>MHz in the UK). Vmax = 5kV and g2max = 1kV. Mullard data gives an output
>of 1,5kW at 30 MHz ssb duty with IMD typically 33 to 42 dB. Plus, I have
>the base and g2 decoupling gear from an old tv broadcast transmitter.
>Other tube specs I can post if needed.
>
>Tank inductor - big (about 4" dia and 12" long) probably suitable for the
>low bands.
Is this a variable inductor?
>Others I can wind from 1/4" copper tube which I have on hand.
>
>Various variable capacitors - none really suitable for the anode tuning but
>probably OK for load capacitor duty. Best one about 250pF with approx. 6kV
>rating - tested at 8kV dc.
>
>Several high power vacuum relays - about 10kV is the highest rating.
>
>Lots of high voltage / current rf fixed capacitors.
>
>Suitable blower - blows the QSL cards off the wall at 10 feet and frightens
>the dog!
>
>Now - why can't I build the tank circuit using the vacuum relays to
>switch in fixed capacitors for each band.
What is the max. anode current of the QY5-3000A? The grid C? Feedback C?
What is the RF current rating of the vac. relays @16 or so MHz,. What
type of vac. relays?
>I have enough relays for this if
>one uses 160m, 80m, 40m, 20m, 15m and 10m. (My transceiver doesn't have
>the new WARC bands so I don't need to include them initially). Using a
>relatively small vacuum variable for the anode tuning and eliminating the
>normal tank circuit band-switch seems to me to be the way to go, in view of
>the problems some amplifiers suffer from.
>
>Overall physical size doesn't really matter. (The power supply will be a
>separate item for versatility). I can have the required metal-work
>fabricated locally by a craftsman I know. (Rather have enough room to make
>the thing work efficiently than try and jam it all into a box which happens
>to be available). I plan to pressurise the anode compartment and use a
>scheme similar to the K2RIW design for 432 MHz with a chimney for the
>exhaust.
>
>Basic spec. At least 1kW out on ssb or cw - with no strain.
>
>Yes - We should shortly get a 1kW licence class here. (I have just
>finished writing the new regulations for the R.A. and part of the regs
>covers IMD and not running an amplifier at it's limit and removing the
>silly existing regulation which makes it an offence to own an amplifier
>capable of more than 400W! -
The 8170-8171 (20db max) amplifier I built could operate in Class A and
not put out more than 90% of allowable power. However, if a certain
unlabeled switch was correctly set, 10db more was available. // note:
under no circumstances should a schematic diagram of such a machine be
made available to official inquisitors. // However, I am unalterably
opposed to running more power than is needed to communicate, or in
causing interference to electronic appliances. .
> so big amplifiers will become the order of the day).
>
>Finally - If possible, the amplifier should also operate on 6m with similar
>output.
>
With minimal distance between the tune-C and the anode, this should be
possible if you use a vertically mounted vacuum variable tune-C.
>Anyway, is there a flaw I haven't spotted.
> Come on guys what have I
>missed.
You have not told us enough. .
>All ideas considered.
>
- later, John
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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