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 Post subject: Hallicrafters HT 32 sidebands
PostPosted: Mar Tue 12, 2019 11:30 pm 
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Joined: Jan Fri 25, 2013 12:28 am
Posts: 42
Location: Albany. NY 12208
Thank you for everyone that advised me with respect to getting my HT 32 up and running. The alignment solved the issues related tuning up on all bands.

In testing the transmitter I noted that if I tune up for cw or am and then switch to upper sideband with a 1000 cycle tone the tone is right there with no frequency adjustment. When I switch to lower sideband the 1000 cycle tone is approximately 8 khz below the tone on upper sideband.

As an example: if I tune up on cw or am at 14270 I hear the tone on upper sideband right there. When I switch to lower sideband I hear the tone at 14262.

Is this normal? If not, what should it be?

Thank you for your advice.

Jonathan


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 Post subject: Re: Hallicrafters HT 32 sidebands
PostPosted: Mar Wed 13, 2019 3:29 am 
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Jonathan,

That discrepancy means one or both of the oscillators used to choose upper or lower sideband is off frequency. The basic SSB signal is always generated at 4.95 Mhz. in the HT-32 and the filter circuits following the balanced modulator pass only the upper sideband. When USB is chosen a 4.05 Mhz. oscillator is mixed with the 4.95 Mhz. USB signal coming from the sideband generator to produce 9 Mhz. USB output into the IF section. For LSB, a 13.95 Mhz. oscillator is used and this produces a 9 Mhz. difference output and inverts the sideband since the mixer is providing the difference instead of the sum output (with 13.95 Mhz. injection it also produces an 18.9 Mhz. USB signal via summing but this is of course rejected by the 9 Mhz. IF strip and ONLY the 9 Mhz. LSB signal passes through with this high side injection).

It is probably just the 13.95 oscillator used for LSB that is off but I would confirm that the carrier oscillator is exactly on 4.05 and then also confirm the 4.95 and 13.95 are on frequency or determine which are off. There are trimmer caps for these crystals which may have enough range to pull the crystal to its proper frequency but again measure all oscillators to make sure that you aren't adjusting a correctly operating oscillator in order to compensate for the true fault.

Rodger WQ9E


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 Post subject: Re: Hallicrafters HT 32 sidebands
PostPosted: Mar Wed 13, 2019 11:53 pm 
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Joined: Jan Fri 25, 2013 12:28 am
Posts: 42
Location: Albany. NY 12208
Thank you Roger,
I checked the frequencies for the oscillators and I found the carrier oscillator was right on at 4.95 mhz, the upper sideband oscillator was right on at 4.05 mhz, the lower sideband oscillator was off a bit 13.942. I tried adjusting the lower frequency trimmer capacitor but could not get it higher than 13.942. There is no other adjustment.

Is it necessary to have the lower sideband signal aligned exactly with the dsb carrier and cw signal? I realize the the coupling transformers are tuned precisely to 9 mhz but assuming that a strong signal at 8.992 is coming through those transformers to be mixed with the vfo signal is that a problem?

Thank you,

Jonathan


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 Post subject: Re: Hallicrafters HT 32 sidebands
PostPosted: Mar Thu 14, 2019 3:26 am 
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Jonathan,

It should be fine except your calibration will be off. The bandpass of the 9 Mhz. IF is in the tens of kilohertz so that won't be an issue.

However, for $1.30 plus shipping (maybe add to your next Mouser order), Mouser lists a crystal for 13.94916 Mhz (how is that for accuracy?!) that would probably work fine in your HT-32. It is surface mount so you would have to add leads but it would be a low cost experiment to probably put your HT-32 back on frequency.

https://www.mouser.com/ProductDetail/AB ... xTmA%3D%3D

Rodger WQ9E


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 Post subject: Re: Hallicrafters HT 32 sidebands
PostPosted: Mar Thu 14, 2019 1:28 pm 
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Joined: Jan Fri 25, 2013 12:28 am
Posts: 42
Location: Albany. NY 12208
Thank you Roger,
!
That is about as close as it gets!

Jonathan


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 Post subject: Re: Hallicrafters HT 32 sidebands
PostPosted: Apr Wed 24, 2019 1:10 pm 
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Joined: Oct Fri 09, 2009 9:25 pm
Posts: 408
Location: Cleveland, Ohio
Hello Jonathon, Rodger.....we are also running into a similar circumstance (erratic/non-oscillating 13.95Mhz LSB crystal) in an HT-32A.

Jonathon, did you pick up that crystal from Mouser and did it work for you?

Rodger, I was wondering if the -30vdc grid voltage (12AU7) across this crystal or drive from the previous stage would not be too much for the xtal to function properly in this HT-32 oscillator circuit? If so, would a voltage dropping resistor in series help in this case? The spec sheet also notes a 6pf max shunt capacitance.

Your thoughts would be appreciated....

Thanks.

Todd
ka8gef

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'Itoshiki oshieo idaki'
-Let us never lose the lessons we have learned.


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 Post subject: Re: Hallicrafters HT 32 sidebands
PostPosted: Apr Thu 25, 2019 12:30 am 
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Todd,

That is a very low power oscillator in the HT-32 so I expect even this tiny crystal will be fine. At some point we may be forced to start using a low power solid state oscillator plus additional buffer/amplifier stages to use increasingly small and scarce crystal elements but I would try one of these crystals in the existing circuit because it is a very inexpensive experiment.

The shunt capacitance specified in the data sheet is the capacitance presented by the crystal unit itself, not the external circuit. It is largely a function of the size and spacing of the electrodes plated to the crystal. The shunt capacitance inherent in the crystal impacts the amount the crystal can be pulled in frequency by external capacitance.

If you try one in your HT-32 please let us know how it turns out. These little crystals won't work in a typical osc/buffer/multiplier CW or AM/CW transmitter because the oscillator stage is designed to produce a fair amount of power but it should work OK in converter type stages which require very little crystal output. I used a similar SMD crystal (with leads added) to replace a missing crystal in my Star SR-700A receiver which uses the triode section of a 6EA8 as the crystal controlled HFO and it is working fine in that application.

Rodger WQ9E


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 Post subject: Re: Hallicrafters HT 32 sidebands
PostPosted: Apr Thu 25, 2019 3:05 am 
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Location: Cleveland, Ohio
Rodger, thanks very much....will give it a try and advise. I can see why these HT-32 series rigs were relatively expensive (new ~$675-$725) back in the day. They are pretty complex and heavy duty in design and it appears that Hallicrafters utilized quality components.

Thanks again.

Todd
ka8gef

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'Itoshiki oshieo idaki'
-Let us never lose the lessons we have learned.


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 Post subject: Re: Hallicrafters HT 32 sidebands
PostPosted: Apr Thu 25, 2019 10:40 pm 
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Joined: Jan Fri 25, 2013 12:28 am
Posts: 42
Location: Albany. NY 12208
Todd,
I have not tried the crystal recommended by Roger. It is quite a job to get at the crystal to replace it so I will use the transmitter as is for a bit and see how it holds up. I have not had the transmitter on the air yet but when I do I will post my observations.

Jonathan


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 Post subject: Re: Hallicrafters HT 32 sidebands
PostPosted: Nov Sat 14, 2020 1:00 am 
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Joined: May Wed 07, 2014 1:39 am
Posts: 25
Did anyone every try the new crystal in this application? I happened to see this thread, and I am having EXACTLY the same issue with my HT-32A! Even the difference in frequency on the LSB oscillator is exactly the same.

I have a couple of parts units and I tried replacing the LSB crystal from another sub chassis -- no change whatsoever. The LSB oscillator will only tune between about 13.943 and 13.940 with the trimmer capacitor. Two different crystals exhibit the exact same symptom.

The USB oscillator is about 500 Hz off -- closest I can get it. The carrier frequency is dead on.

I tried a different tube as well -- no change.

Anyone solved this?



Jeff

WB3JIH


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HT32aCarrier.JPG [ 198.48 KiB | Viewed 512 times ]
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 Post subject: Re: Hallicrafters HT 32 sidebands
PostPosted: Nov Mon 16, 2020 9:04 am 
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Joined: Mar Tue 10, 2020 5:11 am
Posts: 445
Location: Mission Viejo, CA
So, the crystal seems to have drifted DOWN in frequency... try putting some C in series with it. I would expect it may take 100 pF or so. You'll likely have to experiment with the value. But I also read that crystal is apparently difficult to get to, which probably means doing experiments with the circuitry like adding caps or even replacing the crystal will be a bear?

SteveH


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