I'm not particularly interested in 50MHz, no allocation here, but even
at HF I think conversions could be further explored.
I have an Alpha 78 and whilst it does work, sort of, 1500 watts at 100mA
of grid current and exhaust air hot enough to toast bread! I'm not
particularly impressed with the idea of circa $1200 for a replacement
set of tubes. It had crossed my mind to swap the 8874's for 3CX800's but
the prices I see for a pair suggest the work would not really be worth it.
If you have a 'source' do tell. I promise it'll be our secret :-)
I don't think an 8877 will fit. Maybe with an external blower and a new
plenum it could be done and at about $800 for the tube might be the most
cost effective, in relative terms only of course. Single tube amps are
good. I don't think any of the russian tubes will fit, they all look way
to big physically and I seem to think they all need, or like, lots more
air, and there is essentially no space to build a screen supply and
convert it to a tetrode amp. One way might be to make it a two box amp
with an external supply using the same components. That would release a
lot more room in the box I guess. But when all said and done it might
just be better with some of these amps to just sell them on and put the
funds toward something more current. I know that rather goes against
'the amateur way' but I could more rewardingly use the time and effort
on some other aspect of the hobby perhaps.
73
Martin, HS0ZED
Roger Halstead wrote:
> With all this talk of conversions, I'd think the old Alpha 76 series would
> be ideal. The tubes are rated for well above 50 MHz, they are easy to
> drive, and 76As are going for less than the price for a pair of tubes.
>
> Although the 8874s are getting scarse and expensive, they are relatively
> easy to convert to one or two 3CX-800s as even the two-holer has plenty of
> room for three 8874s, two 3 CX-800s, or even a single 8877. However the 8877
> requires building a plenum and using a squirrel cage blower for cooling.
>
> I picked up a 2002A with a good 3CX800 for a very good price at a local swap
> to run on 2-meters and have the Tokyo Hy-Power HL1.5Kfx which runs about 750
> to 800 out (Measured on the Bird) on 6-meters. Admittedly the 1.5Kfx did
> cost a *little* more that the conversions that have been discussed, but now
> I'm looking at building something up for 6 and 2 for the station in here and
> I want to stay conservative at the legal limit if possible.
>
> At one time the $CX-1600B looked promising, but they are no longer
> available. The 8877 and 3CX800s are available and easy to drive. Smaller
> tubes as well as the 3-500Zs are not under consideration. I already have a
> Henry 2K4 with a heavy duty transformer that could be converted to either
> band with the appropriate tubes, but the thing is a monster and I'd like to
> stick with something I can put on the desk top.
>
> TIA for any socially acceptable suggestions,
>
> Roger (K8RI)
>
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>
>
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