[Hallicrafters] TO schematic

Roy Morgan k1lky68 at gmail.com
Mon Feb 29 21:58:10 EST 2016

On Feb 29, 2016, at 6:54 PM, Paul Kraemer <elespe at lisco.com> wrote:

> Anyone have a link to a schematic of the TO keyer?  Or copy they would share?
> I have keyer but doesn’t do anything except the tubes light
> Would like to try to fix it


Here are a few of notes on the thing, and I”ll send my full notes file separately to you off list with some further information and gathered posts.  I also will send a nice picture of W9TO himself as a rather young ham with really really period equipment.

- The mercury relay may only work correctly when upright. The mercury slides to where it should not be.  (this is type HG 1002. This has a coil resistance of about 4000 ohms and operates on about 10 ma in the plate of a 12AU7 in this keyer.)

- Be prepared with this statement in case any one official asks:
“I can neither confirm nor deny that I am in possession of any device that contains mercury.”

- The high value resistors have most likely drifted high.  Replace them all.  5.6 meg, 2.2 meg, 680K, 470K ...

- Though type 12AU7 tubes may be called for or installed, the best ones are the 5963 “computer rated” tubes especially made for long “off” periods with no plate current:  this avoids trouble with “cathode interface”, a kind of degradation of the cathode performance over time with no current.  (V1, V2, and V3)

- Some capacitors can cause trouble, even if they are ceramic ones, so don’t leave them out of suspicion if things don’t work. (the .001s and .02s in the multivibrator sections.)

- You can add a single contact key jack so you can run your straight key in addition to the paddles

- The sound of the internal speaker is “unpleasant”.  This can be fixed with a series L and C to the speaker and jack.

- It’s wise to replace any original two-wire cord with a three wire grounded one.  Add a fuse while you are at it!  (The transformer is hard to find a replacement for.)

- There  was an article:  "Improving the HA-1 Keyer" in the March 1968 CQ magazine (page 60, 61, 126).   I don’t have it and would appreciate a copy.

- check the integrity of ground connections: riveted terminal strip terminals and tube socket grounds.

- the 0A2 and 0B2 can cause trouble even if they light up nicely.


Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958

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