6al5's Anyone?

[John Campbell]

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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