W6WRT comments interspersed below:
On Tue, 21 Jul 2009 06:15:46 -0700, "k7fm" <k7fm@teleport.com> wrote:
>
>I thought that somewhere on my amateur license, or in the rules, there was a
>clause that you had to be able to build amplifiers using cheap tubes. I
>cannot find that language right at the moment.
I don't see an emoticon but I assume that was an attempt at humor. There never
was such a requirement.
> But, if an 8877 costs $700
Brand new Chinese 8877s are $550, but your point is taken. I'm using one in my
homebrew amp and it has been 100% satisfactory so far. eBay item number
260425826378. Equivalent power level tetrodes, brand new, are in the same price
range.
>and you see a box of 4CX250 tubes sitting at a swap meet with 50 cents per
>tube, that seems to be a good reason to think about using the 4CX250.
No argument there, especially if they are brand new. I have had nothing but bad
luck with "pulls". They are "pulled" for a reason - they are approaching the end
of their useful life. I am far from a wealthy individual, but I will only use
new tubes in any amp I intend to keep. If I am just fooling around, that might
be different.
>The reason to use them in some sort of grounded grid configuration, rather
>than
>grounded cathode are numerous:
>
>1. You can eliminate the necessary stabilized screen supply and bias
>supply.
>2. Grounded grid is more stable
>3. Grounded grid is cleaner than grounded cathode (lower imd). This is
>relevant since the 4CX250 is not especially clean when operated grounded
>cathode.
>4. The extra drive power of grounded grid is easily handled by hams with
>100 watt rigs.
>5/ Some hams like to experiment with unconventional ways of doing things,
>especially if it saves lots of money.
Reasons 1-4 are reasons to use GG, not necessarily reasons to use tetrodes. I
would like to see some data on reason #3.
Reason 5 is a good one, no argument there either.
So your arguments boil down to cost and availability. That is basically what I
said in my original post - "If you have one lying around".
73, Bill W6WRT
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