[ARC5] Dust-Off those TU-10s; BC-375 on 30 Meters!

[Geoff]

If anyone has a BC-375 and a few useful tuning units to donate to the cause 
please send it this way.  I have several tubes Id like to evaluate as 
possible subs.

Carl


----- Original Message ----- 
From: "David Stinson" <arc5 at ix.netcom.com>
To: "ARC-5 List" <arc5 at mailman.qth.net>
Sent: Sunday, October 27, 2013 12:43 AM
Subject: [ARC5] Dust-Off those TU-10s; BC-375 on 30 Meters!


>I always meant to try this and it works: fixing BC-375 thermal drift with 
>reduced B+.
>
> The major reason guys don't try to operate the BC-375 on 40 and 30 meters 
> is thermal drift.  Install a TU-10, let everything warm-up for 15-20 
> minutes, set it to 10108 KC, key-down and listen to the MO slide smooothly 
> up the band as the tubes and tuning components heat up.  On 40 meters, it 
> can move as much
> as 3 KCs over a single CW exchange.
>
> Now, with only 550 volts on the plates, using either the 211s or the 1625s 
> at 20-25W out, the thermal drift is cured as long as
> you use a gas-free tube.  It does chirp, but no worse than many of
> the rigs during the Classic Exchange.    Proper adjustment of the keying 
> relay will help a great deal.  But it no longer wanders, even on 10.1 MC.
>
> How do you tell if your NOS tube is really gas-free?
> Stick it in the MO stage *at reduced B+*.
> Let everything warm-up, then key-down for a few seconds.  If the MO 
> wanders around,the tube is gassy.  Even a small amount of gas that won't 
> hurt in the PA stage will booger-up your MO.    These tubes are 70 years 
> old and many of them have at least some gas, so swap them around until you 
> find a "good-un."
>
> Once finished with the tube-substitute experiments,
> gonna get that keying relay "right" and make some BC-375 contacts on 30 
> meters, just to fluster the noobs ;-).
>
> 73 DE Dave AB5S
>
> P.S. got the rig to modulate the 1625s properly for AM.
>       The 10Y stopped emitting for some reason.
>       Changed it and will resolder the pins tomorrow.
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