>
>> I'm new to the list but have read the archives and want to build
>> an amp. The guys at the club said that I should try a 4-1000 tube
>> because they are "very forgiving".
I have a 4-1000A amp here that was a homebrew I bought. I have been
fighting it for the last 6 or 8 months plus....It's almost done now.
>
>The tube might forgive you, but you might not forgive it! 4-1000A's
>are notoriously unstable at high anode voltages, and getting a
>bit scarce.
I haven't found the tube to be any more unstable at 6 KV. The best thing
about the tube is that you can really run it hard and it won't die. As
for scarcity, Surplus Sales of Nebraska sells them if you want to pay
bucks for a used on. RF Parts still sells new ones (the tube is still
manufactured by Triton Technologies). And lots of guys have these for
sale that you can get for about $100.
>
>You will need about 5-6 kV and a good bit of drive to get 1500 watts
>out in grounded grid. The driving impedance is high, and that makes
>the gain low.
Tom is correct here. The tube has plenty of gain on 80 and 40, but
begins to drop on 15 and 10. I get around 1600 to 1800 on 80 and 40
while only about 1000 on 10. This is with about 95 watts drive.
If I were to build a 4-1000A from scratch I might like to try it in grid
driven configuration. I am not sure how much more difficult that would
be than GG, but it would have a lot more gain.
>
>If you do run high anode voltages in an attempt to get
>enough gain, you will probably run into troubles.
*Knock on wood* but I haven't seen that. Just gotta make sure your stuff
can handle it.
>
>I'd suggest you consider something with a MRI pullout tube Rich, like
>an 8877 or a pair of 3CX800's. They operate at lower voltages, have
>better IMD performance, are much more stable, and are more commonly
>available.
>
>From what I have heard the 4-1000A has great IMD and audio performance.
However, other tubes are far easier to work with. Still there is a LOT
of romance in the old firebottle. It has been a dream of mine for about
10 years to have one of these.
>Everything will be a lot easier, and you'll get a lot more power
>gain.
True possibly. The input matching networks were a real pain in the butt.
I managed to get them though. And working around 5 to 6 KV is really
scarry. Gotta be VERY careful. Also, stuff likes to get REAL hot. The
tube generates lots of heat. Gotta have good cooling. But if you wish
to have an amp you can beat the snot out of, the 4-1000 is good. Lots of
contesters us them. There are several of us on the reflector here that
have either modified or built these.
>
>If you do want to build a 4-1000, maybe someone can suggest a good
>article. I've tossed all my old magazines out.
I have a couple of articles and app notes. The most important part is to
have a good layout. I don't know, but it didn't seem all that overly
difficult working with mine. Just had to be careful. Of course since
it's the only tube amp I've really built or modified (mainly modified and
improved), I admittedly, don't have much experience.
If you'd like I can send you what I have.
BTW: Seems like in all my old RCA tube manuals, they mention the
4-1000A's main purpose is for "renewal purposes." What's that? They
also mention it functions good as a modulator, oscillator and amplifier.
Have fun. I'll try to help any way I can.
73,
Jon
KE9NA
-------------------------------------
Jon Ogden
KE9NA
http://www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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