[ARC5] Radios and the Canal - Hammarlunds

[Richard Knoppow]

    I have an HQ-129-X which is quite stable given its type 
and age.  I used a BC-779 as my station receiver for several 
years.  I had modified its RF section and used an ECO copied 
from a General Radio frequency meter. I also added a VR tube 
for the LO. That eliminated all drift from changes in 
voltages, however, there was considerable warm up drift and 
I just left the receiver running continuously.  The original 
LO is reasonably stable if a VR tube or solid state 
regulator is added, otherwise it will pull with changes in 
AVC bias. Fundamentally its a reasonably stable receiver.  I 
did not know about the TC cap. I have to resurrect this 
receiver, which has been in storage for a long time and will 
try the cap.
    I think most of the older vacuum tube receivers were not 
very stable, when the Collins 75A-1 came out it was an 
epiphany for the industry and set new standards for 
stability and calibration accuracy.
    I have an AR-88F which I recently restored. It is very 
stable and needs little warm-up. It appears that every RF 
and oscillator circuit in the receiver is temperature 
compensated including the crystal filter.
    The audio amplifier has a feedback circuit which 
probably accounts for its good audio. Otherwise single-ended 
amplifiers, especially those with pentodes, are pretty 
awful. A few other communications receivers use feedback 
with single-ended amps, the GPR-90 has it and I think the 
75A-4 but I will have to look again.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com
----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: <Arc5 at mailman.qth.net>
Sent: Friday, May 17, 2013 8:42 AM
Subject: Re: [ARC5] Radios and the Canal - Hammarlunds


>> I had a HQ145X and when I got it it drifted so much it 
>> was really
>> useless for CW or SSB and almost useless for AM! I found 
>> that the HFO
>> was the drifting part but the tube tested good. I subbed 
>> in several
>> others I had and the VFO settled right down!
>
> Yes. Hammarlund used the 6C4 HFO in almost all of their 
> models after the
> HQ-129X.
>
> My HQ-110C drifted like mad until I subbed a few 6C4WAs 
> and finally some
> of the military ruggedized versions that had a number like 
> "6139" or
> something. Then it settled right down. I also subbed the 
> 6BE6 first mixer tube
> for a mil version, and THAT helped too.
>
> Concerning the earlier versions: I had a brand new BC-779 
> back in the day.
> It drifted quite a bit until it was well warmed up.
>
> Like Todd mentioned, the manual flatly states that it 
> needs to be well
> warmed up. I never turned mine off in fact, and had it 
> mounted in a rack.
>
> As I have mentioned before, I added a triode product 
> detector to it and used
> it extensively for several years for RTTY on 20 meters and 
> below.
>
> On 20 meters, when listening to a weak steady carrier, it 
> drifted
> back-and-forth a few cycles all the time. It was actually 
> very pleasant to hear
> and never interefered with reception.
>
> Hammarlund brought out a service bulletin after WWII 
> sometime, I don't
> know the date: that was a factory recommendation that one 
> add a 3 pfd
> N-750 temperature compensating capacitor to the HFO 
> capacitor which
> would drop the warm-up drift to very low. I never did that 
> though.
>
> Maybe when I restore one of the three BC-779s I have here, 
> I'll try it.
>
> Adding a BC-453 "Q-5er" makes those receivers really handy 
> for CW and
> RTTY, BTW.
>
> Ken W7EKB
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: 
> http://www.qsl.net/donate.html