[AMPS] Building my first amp

[Ron Hooper]

Thomas Bowes wrote:
> 
> I am contemplating building my first amplifier and am looking for a bit
> of advice as to things to watch out for. The amp will mostly likely be
> based upon 4-1000's since they are the power tube that I have the most
> of. I already have a mil-spec filament transformer, a socket, chimney,
> and six 4-1000's (got 'em cheap). I would like to be able to run the amp
> in sideband, AM, and CW, with the possibility of messing around with
> some cathode modulation of the thing in class C mode. By all means I
> want the thing to be capable of continuous duty, even though I am not
> currently a contester.
> 
> Any suggestions as to what kind of voltages I should be looking for in a
> transformer? I have heard tell of guys running 6000v on the plates, but
> not being well versed in such things I hesitate to do so without a bit
> of advice.
> I have an enormous HV transformer rated at 2500 volts and about 5 amps
> (or more). The voltage seems to be a bit light for 4-1000's but I
> suppose that I could run a doubler. So how 'bout it folks, whadaya
> think?
> --
> "Tom"
> 
> Thomas Bowes
> KK8M
> 35332 Churchill
> Richmond, Michigan 48062-1179
> 
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Hi Tom,
  The 4-1000 makes a great tube to run in an amp. Most folks run them in
grounded grid configuration and it will require a higher drive power. It
will prove to be the most stable and easier to construct. One hundred
watts of drive will be more than enough to get a kw output, depending on
the plate voltage. The higher the plate voltage the more sensitive the
tube will be to the drive level. Since you said its your first amp I got
to mention the high voltage hazards. Lots of the components available
have a rating of 5000 volts. If your going to 6kv DC be sure to use 
over rated components in the power supply. Dont try to push the ratings
here. Have a good bleeder on the HV supply and a meter that stays in the
circuit. Dont never assume the supply is de-energized, ALWAYS short the
DC buss to ground before touching anything, even if the meter says 0
volts. Get into a habit of that quickly, it could save your life.
Several folks killed from a much lesser supply. 
  I dont like voltage doubler's but it sounds like the transformer you
have would be to low with just a bridge on it about 3500 dc, no load.
However depending on how much power your looking to get out, 3500 would
still be a good amout especially if you have a Ft1000, with 200 watts to
drive it. With a doubler your going to get close to 7000 volts DC no
load. The tube will probably handle that much DC from what I have heard.
I got to believe the tank circuit components will also have to be well
rated if your going to run that much voltage, which might also drive up
the cost of building the amp. No dought it will put out more power but
hazards of arcing over on the band switch, varable capacitor's, SO239's
will increase. Even the antenna ratings will have to be looked at. Most
traps will burn out, especially if the swr is not good. The low pass
filters that are rated 2500 watts usually burn out before you get to
2500 watts. So with higher output things are going to happen. Just be
ready for them...Good Luck
Ron W4WA

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