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 Post subject: Hammarlund 140-XA first run observations
PostPosted: Jan Sat 07, 2017 9:32 pm 
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Joined: Jan Thu 15, 2015 4:56 pm
Posts: 94
Location: Winona, Mn.
Recapped the power supply. The old 4 section cap was actually leaking some goo when I pulled it from the chassis. Fired it up and no smoke. Had a short lead for antenna purposes. Local AM stations 1230 & 1380 dialed in at 1245 & close to 1400 respectively. Is that normal? Got a couple of religious and Spanish speaking stations on the higher bands. (late morning Cental time). I was surprised with my minuscule antenna. Headphone use came with a decent hum. 8 ohm speaker did not. After about an hour I felt the power transformer. Pretty + warm. Is that normal? Chassis was not in the cabinet. S meter works for signal strength. However it will not go any lower than 2 on the dial when surfing in AVC mode. If I turn the Sensitivity from 10 down to 8.5 or lower it pegs the needle at less than 0. That can't be right. Seems like it would be hard on the movement.

Tonight I plan to take voltage readings and see what is what on that subject. Longer antenna, too.

Any comments would be appreciated. This is my first Ham radio so I am in the dark as what to expect on performance and what is right or wrong with it, at this stage. RDubb


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 Post subject: Re: Hammarlund 140-XA first run observations
PostPosted: Jan Sun 08, 2017 12:22 pm 
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Joined: Jan Fri 06, 2012 8:47 pm
Posts: 6059
R_Dubb wrote:
Local AM stations 1230 & 1380 dialed in at 1245 & close to 1400 respectively. Is that normal?
The right hand bandspread needs to be set to 100 on the bottom scale for accurate readings on the left hand dial. If it is still off, a slight alignment probably needs to be performed. How this is done is usually explained in the documentation. An accurate signal generator and voltmeter would be required.
R_Dubb wrote:
Headphone use came with a decent hum. 8 ohm speaker did not.
Communication headphones generally did not provide much audio below 300 Hz while HiFi headphones will provide a lot of audio down to as low as 20 Hz. So hearing hum with current HiFi headphones would not be unusual.
R_Dubb wrote:
After about an hour I felt the power transformer. Pretty + warm. Is that normal?
Yes, since you are describing it as pretty warm rather than blistering hot, this is pretty normal.
R_Dubb wrote:
However it will not go any lower than 2 on the dial when surfing in AVC mode. If I turn the Sensitivity from 10 down to 8.5 or lower it pegs the needle at less than 0. That can't be right. Seems like it would be hard on the movement.
With the Sensitivity turned down the small screw adjustment at the bottom of the S-meter should be adjusted so that the meter sits at zero. Then once the sensitivity is turned back up you get-what-you-get.

Readings above zero just tell you that the background noise when you are off of a station is just that noisy. It's not unusual to see this especially when using a wire inside the house as an antenna. With an antenna outside away for noise sources this may be better.

Curtis Eickerman

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 Post subject: Re: Hammarlund 140-XA first run observations
PostPosted: Jan Mon 09, 2017 4:18 pm 
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Joined: Jan Thu 15, 2015 4:56 pm
Posts: 94
Location: Winona, Mn.
Thanks Curtis, for your detailed comments on my observations.

I read the 4 step procedure for adjusting the S meter. Set controls to specified settings / receiver off / mechanically set zero on meter / power and AVC on with V4 removed adj meter to zero with R19. The 4th procedure says with AVC on and V4 replaced, adj meter sensitivity with SENS pot R23. (?) What am I using for a reference to adjust the sensitivity?

Another observation below. I took voltage readings on all of the tubes. In coming voltage was set at 117 AC. Everything seems relative except for V2 RF 6BA6 pin 5. Aim point is 505 but my reading shows 164. (Typo?) The schematic for the 140-X shows 200 for aim point on the same pin.

Any comments on tube voltages would be appreciated. I also found another modification to the circuit but that is another thread. RDubb...

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 Post subject: Re: Hammarlund 140-XA first run observations
PostPosted: Jan Mon 09, 2017 4:50 pm 
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R_Dubb wrote:
The 4th procedure says with AVC on and V4 replaced, adj meter sensitivity with SENS pot R23. (?) What am I using for a reference to adjust the sensitivity?
Good question and the answer will not be nearly as good.

What you use to adjust the sensitivity pot is largely subjective although there has been something of a standard for years. Part of the problem with receivers like this is that the S-meter response will tend to vary from band to band and there is not much you can do about it.

However, if you would like a standard signal to work with the answer would be a 50 µV carrier to produce an S-9 signal. Now the question becomes how do you get a 50 µV signal. Well that kind of depends on the generator. 50 µV from a 50 Ohm generator would be -73 dBm output into a 50 ohm load. Some generators are calibrated to do such things (typically modern and expensive), some are not (most vintage generators).

The alternative is to produce or find a signal that you consider to be "good" but not overwhelmingly strong and set the sensitivity pot so that this signal represents S-9. Typically this would be a signal that is strong enough that you hear very little background static or hiss (i.e., a nice clear signal).

You can tweak that sensitivity pot until you are satisfied that a good signal shows up as around S-9 and a really really really strong signal pushes the upper end of the meter. Then a weak signal sould be down in the noise wherever that might be (typically 0 to S-5, but sometimes even higher depending upon you local noise sources).

R_Dubb wrote:
Everything seems relative except for V2 RF 6BA6 pin 5. Aim point is 505 but my reading shows 164. (Typo?)
I guarantee that 505 is not correct. The maximum tube rating for a 6BA6 is 330 and they are typically used between 100 and 250. I would venture that what you have is just fine.

By the way, if you ever want AVC action while you are listening to SSB stations here are some audio derived AVC circuits that could be added as a modification without any real change to the receiver itself (removing a ground connection at the Man-AVC-BFO switch, then attaching a circuit to the top of the volume control, 105 V line, ground and the AVC line at the Man-AVC-BFO switch. http://curtiseickerman.weebly.com/technical.html )

The circuit was used with an HQ-129X, but the HQ-140X is the same receiver design just with the miniature tubes. With this AGC I found a more extensive product detector modification to be unnecessary.

I used the tube version of the Audio Hang AGC for years. I never got to try the solid state versions that could easily be contained under the chassis.

Curtis Eickerman

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