[HBR] HBR transmitter

Sat Jul 10 10:23:05 EDT 2010

Thanks for the Info Walt,

I am currently testing a configuration of:  6C4 buffer/doubler and a 12AT7
mixer/ oscillator and using a 6CL6 as an amplifier.  I am switching crystals
when going from 80 to 40 metesr on the transmitter oscillator stage  in 
order to provide
a proper injection frequency to the mixer. A variable capacitor on the
mixer stage  is utilized for peaking when switching from 80 to 40 meters.
An additional 6CL6 amplifier will be added to drive a power tube or I may
just  quit there and run low power CW.

 I am current obtaining the drive off of the plate of the HBR-14 receiver
Oscillator via a 5 pf capacitor and I  have not checked for frequency shift
when going front transmit to receive so will put that on the "test" list.  I
have noted that you suggested obtaining drive off of the receive mixer grid
and will investigate that suggestion which I assume was made because of the
addition isolation provided by the capacitor feeding the grid of the
receiver mixer.

I have not come up with a keying scheme yet but will probably have to add a
keying stage or  leave the oscillator on and key the other stages.

The HBR that I built does drift quite a bit during initial warm up.   :-)
 Takes about an hour to completely warm up but is more than useable for CW
contacts.  I have not reworked the oscillator as my original goal was to
build the receiver as published to experience the 1950's.

I have not progressed far enough  with the project yet to check receiver
muting and problems associated with that, so that will be an additional item
to the  "test" list ----but I have been using the receiver on CW by just
turning down the RF gain during transmit , crude but allows monitoring of
the CW keying and just turn  the gain back up during receive- this was a
very common procedure years ago.

73

breck

--------------------------------------------------
From: "Walt Hutchens" <waltah at earthlink.net>
Sent: Saturday, July 10, 2010 4:42 AM
To: <HBR at mailman.qth.net>
Subject: Re: [HBR] HBR transmitter

>> I am working on a small CW mixer/ transmitter using the HBR-14
>> oscillator to control the frequency. Is anyone else doing this?
>
> I'm not doing it, but there's no reason this shouldn't work. You can
> either key the conventional way -- all signal frequency stages -- or
> bias everything appropriately and just key the IF frequency injection
> oscillator.
>
> There are some issues:
>
> The HBRs are a well-engineered approach to a high quality receiver (by
> 1950's-60's standards) that any careful and determined ham could
> build. They are NOT the most stable receivers possible, even using the
> technology of that time -- some loss of warm up stability was one of
> the trade-offs for other good things in the design. Thus your
> transmitter will drift some during warm-up.
>
> The use of the second harmonic of the oscillator frequency on some
> bands will need to be considered.  The injection signal for the
> transmitter should be taken from the receiver mixer grid, via a
> suitable buffer.
>
> (That buffer will need to be left on when receiving in order to avoid
> changing the load on the oscillator.)
>
> The second harmonic trick works well for the HBRs because the mixer
> (signal) grid coil (where the oscillator is also injected) serves to
> select that harmonic. If you try to take take the oscillator signal
> from somewhere else, you'll get so much fundamental that you'll have a
> very tough time.
>
> Without having the circuit in front of me I can't remember how the HBR
> does muting but you'll need to be sure that the technique doesn't
> change the load on the oscillator. If it does, then the oscillator
> will be on a slightly different freq. when you are transmitting and
> the amount of this change will vary from one band to another so it
> can't be permanently compensated in the IF freq. oscillator.
>
> Even the change in the load on the receiver power supply causing
> oscillator voltages to change slightly may be an issue. It may be
> necessary to mute by shorting the receiver antenna terminals and audio
> output and even more may be needed on the higher bands, since AGC
> voltage will change, changing the IF/RF stage currents.
>
> VR tubes aren't perfect ...
>
> I think I would start by studying the problem of keeping the receiver
> oscillator frequency from shifting when the receiver is muted.  Once
> that's taken care of, the rest should be do-able.
>
> The usual timing issues will apply -- the receiver should be silenced
> before the transmitter signal comes up.  Of course if muting is
> done manually that's not a problem.
>
> This is a very appealing approach to a low to moderate power vintage
> ham station and should be a lot of fun to build up and use!
>
> Walt
> KJ4KV
>
>
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