Loctal tubes used the "button base" to hold the tube elements so they were inside the glass envelope vacuum.  I believe that they were released at about the same time as RCA released the seven pin miniature tube design which are physically much smaller but also use the "button base" concept.  I guess that it was market forces that chose the subminiature tubes over loctals for new designs.
Jim

Logic is a systematic method of coming to the wrong conclusion with confidence.  Murphy


On Monday, July 6, 2026 at 12:50:02 PM CDT, Ray Fantini via Milsurplus <[email protected]> wrote:


Wow man, it's amazing what you people know. Never knew any of this about the loctal and now got to try that. Maybe because of the difficulty in dealing with the sockets they never caught on? 
Between dealing with these weird tubes and now knowing what all those countless boxes of crystal sets were for with the cryptic three-digit numbers were used in I think I learned a lot from dealing with this old 659. Waiting for parts to compleat repairs of the power supply and hope to get this set up and running soon, had the receiver running with substitute components for testing and it's not that bad going full quieting at around 10 to 13 uV and useable down at around 3 uV with a big fat IF passband but figuring if it had to work with things like the BC-1000 (SCR-300) it has to be capable of about 30 kHz so think netting with more modern sets like the PRC-25 or VRC-12 won't be that big an issue. Finding a legal frequency may be more of a problem. Think the VRC-12 stuff may go down to 29.6 as a Red Flag channel?  Will have to go out to the mutt and crank on the RT-524, maybe once I get this all resolved can do a video of a BC-659 in a GPW having a QSO with the VRC-12 in the mutt? 

Ray F/KA3EKH



From: [email protected] <[email protected]> on behalf of sbjohnston--- via Milsurplus <[email protected]>
Sent: Monday, July 6, 2026 12:06 PM
To: [email protected] <[email protected]>
Subject: Re: [Milsurplus] BC-659 Fun and Games


Thanks John.  I have never before heard that there was a trick to pulling loctal tubes out of their sockets.  I am eager to try it on my next project involving loctal tubes.

I got a 7C5 out of my loctal bin to look at the “bump”.  Interesting - I always thought those bumps were to aid in orientation when inserting the tube (it marks the center post's key).

When I am repairing/restoring equipment using loctals, I generally do not pull any tubes unless they are suspect in some way.  If the stage is performing as I expect, I leave them be out of concern I would cause intermittents just by disturbing the pin-to-socket connections.  Now I have to worry about pulling with the right tilt, too.  Of course, in the many past decades the owners might have repeatedly pulled the tubes and loosened the sockets, so all bets are off really.

My biggest gripe with loctals has been that some sockets have excessively strong circular springs gripping the center post.  Maybe with the proper tilt that won't be the case.

For those unfamiliar with the bump...  It is on the side of the metal base (above the chassis line), as opposed to the bump on the end of the center post that goes down into the socket.  

See the attached close up picture of the bump in question…

image0.jpeg





Steve WD8DAS  


 

______________________________________________________________
Milsurplus mailing list
Home: http://mailman.qth.net/mailman/listinfo/milsurplus
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html