[Hammarlund] HQ-110 stability, or, making a silk purse out of a pig's ear,

[Robert Jefferis]

Yes, the HQ-145 is a bit of a sleeper. I have one that I purchased new in 1961. Could not afford a 170 or 180 then. I still use it regularly for SWL, AM, and even occasional CW. Not quite stable enough, or selective enough for regular SSB work though. 

Bob KF6BC
On Feb 9, 2010, at 3:35 PM, Carl wrote:

> Or get a HQ-170 and not have to rebuild it so it works well.
> 
> The HQ-145 is also a nice GC and Ham set, sort of a scaled down HQ-180 and 
> mostly off the radar..
> 
> Carl
> KM1H
> 
> 
> ----- Original Message ----- 
> From: "Kenneth G. Gordon" <kgordon2006 at verizon.net>
> To: <Hammarlund at mailman.qth.net>
> Sent: Tuesday, February 09, 2010 5:54 PM
> Subject: [Hammarlund] HQ-110 stability, or,making a silk purse out of a 
> pig's ear,
> 
> 
>> I spent some time last night studying the schematic and the manual
>> for the subject receiver and discovered a few interesting things,
>> most of which were NOT covered in the manual.
>> 
>> First of all, the 0B2 regulator is connected not simply to the HF
>> oscillator, but also to the screen of the 1st IF amplifier and to both
>> "screens" of the 1st mixer, the 6BE6 V-2, AND is fed to the RF
>> amp's AGC rectifier, providing "delayed" AGC voltage for the RF
>> stage.
>> 
>> Thus, any problem with the regulator would also effect the mixer, RF
>> amp, and 1st IF amp. Conversely, any problem with the mixer, RF
>> amp, the RF amp's AGC rectifier, and/or 1st IF amp tubes, could
>> also cause a problem at the HF oscillator.
>> 
>> Secondly, the BFO is NOT regulated at all, but receives its plate
>> voltage directly from the output of the second HV filter cap. I
>> suppose that due to the NEXT issue, the BFO output must have to
>> be at a fairly high level, and couldn't run effectively from 108VDC
>> regulated. It also probably draws too much current for the 0B2 to
>> handle.
>> 
>> Thirdly, and to me most interesting, is that the 2nd IF amp, the
>> pentode section of a 6AZ8, is also used as a "linear detector" (since
>> when is a detector or, in this case, a mixer "linear"?) for CW/SSB,
>> the BFO output being fed to this tube's grid.
>> 
>> Audio from the plate of this stage, when in the CW or SSB condition,
>> bypasses the last IF transformer's two tuned circuits, and is fed
>> directly to the grid of the first audio amp.  This reduces CW/SSB
>> selectivity, and makes it impossible to use the AGC and "S" meter
>> on CW or SSB.
>> 
>> This also reduces the available audio level, a fact mentioned in the
>> manual. The manual says to "turn up the audio gain a bit..." on
>> CW/SSB.
>> 
>> The 2nd IF stage obviously functions as a sort of product detector
>> for CW or SSB.
>> 
>> Lastly, the AGC is tuned for AM, being a fast-attack, fast-decay
>> type, which is NOT suitable for CW or SSB.
>> 
>> It is very interesting to me what Hammarlund engineers did with this
>> receiver, accomplishng a lot with a little.
>> 
>> However, I feel that there can be considerable improvement made
>> to the operation of this receiver with a little effort.
>> 
>> I am considering doing the following:
>> 
>> Install a REAL dual-triode product detector which will take its IF
>> signal from the output of the last IF transformer, thus preserving as
>> much selectivity as possible, and enabling the use of AGC and "S"
>> meter in CW/SSB.
>> 
>> I would use a 7963 subminiature very hi-mu dual-triode since it can
>> be mounted on a terminal strip below deck.
>> 
>> I would remove the BFO signal being fed to the 2nd IF stage and
>> connect the BFO to the new product detector, adjusting the BFO
>> output for the proper level.
>> 
>> Then I would disconnect the audio signal to the 1st audio amp from
>> the 2nd IF, connecting the audio signal from the separate product
>> detector in its place at the mode switch.
>> 
>> I would leave the AM detector and the two AGC rectifiers in place.
>> 
>> I would change the MAN-AGC switch to one with at least one more
>> position so that I could enable fast and slow AGC, adding a
>> capacitor to the AGC circuit where appropriate.
>> 
>> The regulator circuit must be looked at carefully.
>> 
>> I may use some strategically placed zeners of the proper values. For
>> one thing, I think the BFO voltages should be regulated, and I hope
>> to be able to separate the regulated voltage sources from one
>> another to preclude interaction.
>> 
>> Well, so much for that.
>> 
>> Ken Gordon W7EKB
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