[Boatanchors] 6BA6 Tubes

[Richard Knoppow]

----- Original Message ----- 
From: "Al Klase" <al at ar88.net>
To: <boatanchors at mailman.qth.net>
Sent: Thursday, December 15, 2011 7:05 PM
Subject: Re: [Boatanchors] 6BA6 Tubes


Yes, all the tube substitution books say a 6AU6 is an 
acceptable sub for
a 6BA6.

This is just WRONG!   It's OK in a pinch, but the 'AU6 is a 
sharp-cutoff
pentode, while the 6BA6 is a remote-cutoff device.

Remote-cutoff is the magic that allows a communication 
receiver to
control the enormous gain that's available is such a radio. 
Loading up
a radio like 75A3 with sharp cutoff pentodes is going to 
completely mess
up the AVC resulting in distortion on strong signals.

Here's my list:  6BA6/W/WA - 5749 - 6660 (caution 1/2" 
taller)  6BA6's
are cheap and available.  Why mess around?

6BJ6 - 6662 - 7694 might be OK, but gain is a bit lower and 
the heaters
are 150 mA vs. 300 mA so be careful in series string 
applications.

Al

    We must have been typing at the same time:-)
    FWIW, the the difference between remote cut-off and 
sharp cut-off tubes is mostly in the physical construction 
of the grids. Sharp cut-off grids have wires which are 
spaced uniformly from end to end. In a remote cut-off tube 
they are widely spaced near the center and become more 
narrowly spaced at both ends. As the bias is increased the 
beam of electrons from the cathode is increasingly blocked 
by the closely spaced wires but can pass through those near 
the center. The result is a gradual cut-off of the beam 
current as bias is increased. In a sharp cut off tube the 
electron beam is decreased uniformly across the grid so it 
is cut off comparitively quickly with increased bias. If you 
have defective tubes you can dissect them and see the 
difference.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com



On 12/15/2011 9:29 PM, Mike McCarthy, W1NR wrote:
> 6BA6's can be substituted with the following:
>
> EF93, 7543, 7496, 6BZ6§, 6AU6A, 6AU6, 6BA6WA, 6BA6W, 6CG6, 
> 6HR6, 6660,
> 5749, 6BD6
>
> The 5749 is the same as the 6BA6W. I think I used that one 
> in a Drake
> restoration a while back. So, it looks like the 6AU6 is an 
> acceptable
> sub according to the substitution guide. Of course, all of 
> these have
> subtle differences that may or may not appear depending on 
> the circuit.
> The 6BZ6 is flagged as not being compatible in some 
> circuits.
>
> Mike, W1NR
>
>
> On 12/15/2011 01:51 AM, Joe Walden wrote:
>> Hello again,from Joe W. w5jdy in Norman,Ok 73069..  I am 
>> in the need of four
>> 6BA6 vacuum tubes for a Collins 75A3..  Not to sure why 
>> but the previous
>> owner put 6AU6's in the place of the 6BA6's??  I looked 
>> on Ebay but didn't
>> see anything like I wanted..  Would rather give the money 
>> to a ham anyway..
>> I would like new ones but even used tested-good would 
>> just be fine..  Please
>> contact me direct at:   w5jdy at cox.net     Thanks Joe
>>
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/


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