{Collins} Re: 75A2



The 75A-2 has 2 models.....the early models with the metal escutcheon
has a different tube lineup than the later models with the bakelite
escutcheon similar to the A-4.
The older model has V1 6AK5, V2 6BE6. there may be other differences as
well.


Regards

Dave Harmon
NSRCA 586
K6XYZ[at]comcast[dot]net
Torrance, Ca.

-----Original Message-----
From: collins-bounce@xxxxxxxxxxxxxxxxxxxxx
[mailto:collins-bounce@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of rrkrr
Sent: Thursday, July 22, 2004 12:33 PM
To: K7OX@xxxxxxx
Cc: collins@xxxxxxxxxxxxx
Subject: {Collins} Re: 75A2

Gary,
The 6BE6 and 6BA7 are both pentagrid converter tubes (heptodes).  The 
6BE6 has a 7-pin base and the 6BA7 has a 9-pin base.  I believe the 6BA7

is a newer design.  I don't have any first hand information about the 
75A-2, but my guess is that the 6BA7 was a later model change in the 
75A-2.  The 75A-4 receiver used 6BA7 mixer tubes from the outset.

If you think you want to modify your receiver to a newer design, I would

have a look at some of the mods published for the 75A-4, rather than 
changing to the 6BA7.  Pentagrid converters are rather noisy mixer tubes

and there are better alternatives out there that provide lower noise 
figure and better dynamic range.  I would recommend the mixer designs 
described by N0DMS in the Electric Radio Modification Compendium for the

75A-4.

Bob
WB4TGG

GARY ELLIOT wrote:

>As I continue with my restoration of a 75A2 I have run into some
discrepancies, namely the reproduction manual that came with the
receiver has the 1St & 2ND mixers listed as 6BA7's.  Yet the chassis is
stamped V2 & V4 as 6BE6's.  The schematic shows the output of the 70E12
PTO to pin 2 of the 6BA7.  Yet my radio has the output of the PTO
connected to Pin 1.  Also there are some different resistor values
associated with this scoket then is shown on the schematic.
>Was there a service bulletin or any mods that may have appeared in Ham
Magazines changing the mixers in the 75A2 ?  The schematic I am working
off is dated April 1954.
>
>Couple other questions regarding the 75A2, does any one make the
Kilocycles (round dial) reproductions ?
>
>I also need the PTO coupling which is apparently .25 inch on one end
and 3/16 or some other close dia on the PTO shaft, not having a
micrometer I can't measure the actual shaft size on the 70E-12 PTO.
>
>The difference in the mixers has me rather confused and appreciate any
comments from anyone familiar with this receiver, Thanks
>
>73 Gary
>
>
>Sponsored by the Collins Collectors Association
http://www.collinsradio.org
>Nets: Tues: 3.805 Mc-2000 Central / Thur: 3.875 Mc-2000 Central
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>
>
>  
>

Sponsored by the Collins Collectors Association
http://www.collinsradio.org
Nets: Tues: 3.805 Mc-2000 Central / Thur: 3.875 Mc-2000 Central
Fri: 3.895 Mc-2000 Pacific / Sun: 14.263 Mc-2000 UTC
1st Wed (of the month) AM Net 3.880 Mc-2000 local (ET, CT, MT, PT)
Sun AM Net: 29.050 Mc-1200 Central


Sponsored by the Collins Collectors Association http://www.collinsradio.org
Nets: Tues: 3.805 Mc-2000 Central / Thur: 3.875 Mc-2000 Central
Fri: 3.895 Mc-2000 Pacific / Sun: 14.263 Mc-2000 UTC
1st Wed (of the month) AM Net 3.880 Mc-2000 local (ET, CT, MT, PT)
Sun AM Net: 29.050 Mc-1200 Central






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