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

[Ronnie Hull]

Good luck Carl! I have been offering good money for a 375 for a year and haven't heard a peep out of a soul!

Sent from Ronnie's IPhone

> On Oct 27, 2013, at 10:00 AM, "Geoff" <geoffrey at jeremy.mv.com> wrote:
> 
> 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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