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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Sep Wed 16, 2020 5:36 am 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 16
To answer KA8GEF

To my can cap with the filter caps i have four posts. The one post with 4 wires going to it i get band 1 .370-.390AC fluctuates. 18v to the left of that pin on band 1.
198v to 200v fluctuates on the post opposite the 4 wire post on band 1. 290 to 360v ac fluctuating on the pin to the right of the post with 4 wires on band 1.

on band 3 i get 4wire post 389, 390v it goes down to 320s when i tune a station. 4wire post is 10uf, left post is 10uf, opposite post is 30uf, right post is 20uf 25v
left pin i get 18.2v
opposite i get 197-200v fluctuates
right pin i get 11 to 14v fluctuates

on band 2 i get 4wire post .36 - .37 v when i tune in to nasty noise when nothing is tuned in i get 319-322v fluctuates
left pin i get 17, 18 v when tuned to nasty noise .5xxv fluctuates
opposite i get 194-198v
right pin i get 20 v give or take when nothing is tuned in when i tune in nasty noise i get 320v fluctuating

on band 4 i get 4 wire post 335 volts fluctuating slightly
left pin i get 18.6v fluctuating a tiny bit
opposite i get 204v small fluctuation
right pin i get 12, 13v when nothings tuned and 30 to 40v fluctuating when a station is tuned.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Sep Wed 16, 2020 1:42 pm 
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Joined: Oct Fri 09, 2009 9:25 pm
Posts: 369
Location: Cleveland, Ohio
First of all- applying a direct 'voltage' as you stated, to that s-meter could potentially damage the winding! Those meters typically are only 1ma full scale.

Also, the 'muffled' audio that you noted is hard to nail down without actually hearing it. I suspect IF alignment but- that should be looked at last.

There are a few control positions that affect/impact signal and resulting audio to varying degrees. One needs to fully understand these controls (!) and their functionality in massaging the specific stage or circuit response- and that the resulting audio will be affected by their settings:

- Selectivity- turn off or to '0'- otherwise you are limiting bandwidth
- Phasing- if selectivity is off, no impact
- Noise limiter- off- tends to muffle/limit audio response
- BFO- off- and pitch- not used for AM signals
- RF gain/sensitivity- controls stage/signal gain
- Tone- set on high setting- otherwise higher audio frequencies are heavily attenuated

Now listen to a properly tuned BCB AM signal and evaluate. Also, what kind of speaker is being used?

I am trying to worm through your voltage measurements off the filter caps. Most of that is irrelevant (i.e. ac component) but at first glance, the PS voltages appear within reason. Did you check the plate and screen voltages on the tubes for each stage? See my previously posted voltage/resistance chart if you do not have one.

Those buzzing 'noises' that you are mentioning on the BC band may be due to what is being used for an antenna. Florescent lights, computer PS hash etc. will wreak havoc, especially on the broadcast band, especially if introduced within the work area. Which antenna terminals are you using? Experiment with the two terminals/ground. Is the jumper installed?

I would not suspect any 'mica disease' until all other issues are investigated/resolved, including full alignment at the end of the process.

The key is a systematic approach to troubleshooting and problem solving. It is easy to introduce/target issues that may not really exist. We all struggle with that!

I hope this helps.

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 SX25 restoration
PostPosted: Sep Wed 16, 2020 2:51 pm 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 16
Thanks for that info. I am awaiting 5 new tubes in the mail including the 6f6s, 80 rectifier and 6j5gt and 6h6.
I am also getting a vintage fluke rf generator which is on the way and should be here in a few weeks.

If i still have problems after installing the new tubes I think I will start investigating voltage leakage from mica.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Sep Wed 16, 2020 4:29 pm 
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Joined: Oct Fri 09, 2009 9:25 pm
Posts: 369
Location: Cleveland, Ohio
Why replace the rectifier? It is obviously working.

Tube pin voltage/resistance measurements are a critical step. FWIW, replacing micas without identifying a clearly failing or suspect cap can be an exercise in futility.

Of course a sig gen and a 'scope will provide a much better perspective on stage gain/performance than live signals, but they are not absolutely critical. Fairly acceptable troubleshooting and alignment can be achieved without either. A sweep generator certainly helps with crystal filter alignment but people have succeeded without it as well.

Todd
ka8gef

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


Last edited by KA8GEF on Sep Tue 22, 2020 12:48 pm, edited 2 times in total.

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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Sep Wed 16, 2020 10:41 pm 
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Joined: May Wed 20, 2020 1:33 am
Posts: 122
Location: Rockford, IL
In my experience muffled sounding reception was cured by properly alignment the IFs.


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Sep Mon 21, 2020 11:43 pm 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 16
Here is a video update.

https://www.youtube.com/watch?v=d0QmI3kb5q4&ab


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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Sep Wed 23, 2020 12:45 am 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 16
I think I found an issue and I hope it will fix band 2. In the first pic it is the coil on the right side second down from the top.

The second pic is a more close up.

I can't find continuity between the posts on the upper side where the raised windings are.

You can see where the was is worn away and it was rubbing on the red wire.

I might pull it and see if I can fix it.


Mike.
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 Post subject: Re: Hallicrafters SX25 restoration
PostPosted: Sep Wed 23, 2020 5:28 am 
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Joined: Aug Tue 25, 2020 10:22 pm
Posts: 16
S meter is working on band one well on the other bands there doesn't seem to be enough of a gap in signal strength.


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