6al5's Anyone?

[Jordan Arndt]

John Campbell wrote:
>
> hello....
>
>     On the Collins question...I'm not a Collins man, but I presume that
> the 300 Ohm input is probably balanced. Why don't you try running down
> to Radio Shack and getting a 300/75 Ohm TV balun and trying it on the
> Collins. They are only about 3 to 5 bux. I don't know what the low
> frequency cutoff of these baluns is, but for the price it would be worth
> a try. Certainly easier than redesigning the receiver front end.
> Just a thought..........73...John (W8JNC)
>
> >Date:         Thu, 7 Jan 1999 06:23:42 -0800
> >Reply-To:     Edward B Richards <k6uuz at JUNO.COM>
> >From:         Edward B Richards <k6uuz at JUNO.COM>
> >Subject:      Re: 6al5's Anyone?
> >To:           HEATH at LISTSERV.TEMPE.GOV
> >
> >Dave;
> >Some thoughts:
> >1. In my 50 years of repairing radios I don't think I have found 3 bad
> >6AL5 tubes. They are a dual diode and very long life. I suggest you
> pass
> >this one by and should you ever need one you can get it for less than
> the
> >$10 you mention,
> >2, On the Collins antenna impedance, if you use a 4:1 balun you will
> have
> >a 75 ohm input which, using 75 ohm coax, is a perfect match for a
> dipole
> >antenna (theoretically, in free space).
> >Regards and Happy Y2K-1.  Ed Richards
> >
> >
> >On Thu, 7 Jan 1999 07:26:26 -0600 "James D. Mayfield"
> ><kb9bnr at REVEALED.NET> writes:
> >>I am not trying to get in to the tube business. I had a call yesterday
> >>from
> >>a guy I know and he offered me some 6al5's NOS mil spec tubes. I have
> >>to
> >>buy them in lots of 100. I would not mind having ten for myself but I
> >>don't
> >>need 100. If I could find 7 or 8 of you guys that would commit to
> >>buying 10
> >>each for $10.00 shipped to you, I will get these for us. Do I have any
> >>takers? I will buy more if the demand is there.
> >>
> >>By the way I got my first Collins, this week. It's a 75A1, and it's in
> >>very
> >>nice shape. The alignment was a bit out of wack, but a few minutes on
> >>the
> >>bench and it was working just fine.
> >>
> >>Also here is a good question for you Collins guys. The gent I bought
> >>it
> >>from told me that since it was designed for use with a 300 ohm
> >>antenna, it
> >>would be a little deaf it feed with 50 ohm coax. That is certainly the
> >>case. I found that if I feed the input signal directly to pin one of
> >>v1
> >>(6ak5) then the radio really comes to life! but this seems wrong to
> >>me. I
> >>was told and I agree that it should be feed thru a cap to pin one, but
> >>I
> >>have no idea what value. Looking at the handbook last night, I saw
> >>several
> >>circuits that used a 100 or up to 250 pf cap to the input. What do you
> >>think.....
> >>
> >>73 Dave
> >>
> >>*********************************************
> >>Dave Mayfield KB9BNR
> >>Personal Web Page
> >>http://home.revealed.net/qste/bnr/kb9bnr.html
> >>
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P.S. any of the TV type baluns I tried were so-so especially on the
lower frequencies.... agn 73 de Jordan...

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