Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Nov Sun 17, 2019 1:53 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 23 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Packard Bell 48 just has static
PostPosted: Jun Wed 12, 2019 8:27 pm 
Member

Joined: Nov Thu 20, 2014 4:52 pm
Posts: 128
I just get static and checking voltages I have no voltage on pin 4 of the 6A8 and same on pin 4 of the first 6K7. The second 6K7 has 16 volts dc on pin 4.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Thu 13, 2019 1:10 am 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 5833
Location: Near Brandon, Iowa
You have an open resistor between the tube screen pins and the B+ rail.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Thu 13, 2019 1:34 am 
Member

Joined: Nov Thu 20, 2014 4:52 pm
Posts: 128
Yes, it sounds simple but there is no B+ resistor. It seems that the 15K resistor is missing and doesn't look like it was ever there. So I jumped one in where the diagram shows it and then I get screen voltage but the radio just howls. Maybe another problem now.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Thu 13, 2019 5:38 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 33139
Location: SoCal, 91387
You need to get the schematic, and trace the wiring, starting with the 6A8. If there are components missing, then of course you need to add them, per the schematic values.
I have a Packard Bell model 48, which I had to almost completely rewire, but it is now one of my most sensitive radios.


Attachments:
Packard Bell wood.JPG
Packard Bell wood.JPG [ 242.35 KiB | Viewed 465 times ]

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////
Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Thu 13, 2019 10:44 am 
Member
User avatar

Joined: Jul Mon 26, 2010 8:30 pm
Posts: 26797
Location: Annapolis, MD
Have the capacitors been replaced?
All coils and transformers checked?

If so, then check DC voltages beginning at the rectifier. Check the B+ current** by measuring the drop across the field coil.


**This won't be the total--the local oscillator gets B+ from the high side of the field coil. To get that current, check the drop on the 10K resistor thats connected to the rectifier cathode (high B+)

_________________
-Mark
"Measure voltage, but THINK current." --anon.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Thu 13, 2019 12:08 pm 
Member

Joined: Nov Thu 20, 2014 4:52 pm
Posts: 128
Thanks for tips. About how much voltage should I have on pin 4 of the 6K7 tubes? One had zero and the second one has only 19 volts dc on pin 4.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Thu 13, 2019 2:27 pm 
Member
User avatar

Joined: Jul Mon 26, 2010 8:30 pm
Posts: 26797
Location: Annapolis, MD
Pin 4 is the screen. It will be similar to the plate voltage but typically lower.
Note an unusual way of specing the resistors---"M" is thousands, and "w" (actually omega) is millions. The numbers with no units are ohms.

You have to follow the DC wiring to see exactly what various voltages should be.

And...
Quote:
Have the capacitors been replaced?
All coils and transformers checked?

_________________
-Mark
"Measure voltage, but THINK current." --anon.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Thu 13, 2019 10:40 pm 
Member

Joined: Nov Thu 20, 2014 4:52 pm
Posts: 128
Replaced all capacitors except for the micas and checked all coils. Checked all tubes. Found where 15k resistor had been cut out and replaced. Still just static.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Thu 13, 2019 10:52 pm 
Member

Joined: Jan Mon 16, 2012 4:15 pm
Posts: 5833
Location: Near Brandon, Iowa
andrefranc wrote:
Replaced all capacitors except for the micas and checked all coils. Checked all tubes. Found where 15k resistor had been cut out and replaced. Still just static.

It's not a confidence-builder when you try to revive a radio that has a missing part. Did the previous owner attempt a repair, remove the part, and sideline the radio, never to get back to it... or did the owner REALLY NEED a 15K resistor for another project, and the set now in your hands became a convenient junk chassis from which to harvest it?


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Fri 14, 2019 3:15 pm 
Member

Joined: Nov Thu 20, 2014 4:52 pm
Posts: 128
Seems like the oscillator is not running. I have no negative dc voltage on pin 5 of the 6A8. The band switch knob has 10 positions you can turn it to ... is that the way it should be?


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Fri 14, 2019 3:40 pm 
Member
User avatar

Joined: Jul Mon 26, 2010 8:30 pm
Posts: 26797
Location: Annapolis, MD
andrefranc wrote:
Seems like the oscillator is not running. I have no negative dc voltage on pin 5 of the 6A8. The band switch knob has 10 positions you can turn it to ... is that the way it should be?

No!!--that set has only 2 or 3 bands. The switch should have stops to limit the rotation.

Close inspection while turning the switch should reveal the issue.

_________________
-Mark
"Measure voltage, but THINK current." --anon.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Fri 14, 2019 7:10 pm 
Member

Joined: Nov Thu 20, 2014 4:52 pm
Posts: 128
Starting with the band switch all the way counterclockwise what position is the BC band? It appears to me it is 3 positions clockwise. Is that right?


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Fri 14, 2019 7:17 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 33139
Location: SoCal, 91387
Looking at it from the front, the BCB position on the bandswitch is the right most, or fully clockwise.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Fri 14, 2019 9:36 pm 
Member
User avatar

Joined: Jul Mon 26, 2010 8:30 pm
Posts: 26797
Location: Annapolis, MD
Normally, BC would be fully counter-clockwise------but then this is a Packard-Bell......;) ;) :)

A "feature" of this design might help sort things out. The same oscillator coil is used for both BC and the 1st SW band. For BC the oscillator is on the high side of the incoming signal, and for SW-1, the LO is on the low side.

On the schematic, note that the same oscillator coil is connected to positions 1 and 2 on the bandswitch

_________________
-Mark
"Measure voltage, but THINK current." --anon.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Sat 15, 2019 1:44 am 
Member

Joined: Nov Thu 20, 2014 4:52 pm
Posts: 128
When I ohm from pin 8 of the 6A8 down through a 50K resistor and back up threw a coil to pin 5 I get continuity so seems like that coil is good. What else could be bad and how do I check it? Seems like if the oscillator quits then you have to junk the set. No solution and no way to get osc coils.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Sat 15, 2019 2:18 am 
Member
User avatar

Joined: Jul Mon 26, 2010 8:30 pm
Posts: 26797
Location: Annapolis, MD
No--you do not have to junk the set. If a coil is bad, it can be rewound. If it is for BC, you can get a universal type.
And if the coils are OK, we WILL get the oscillator working.

But you just verified that the BC coil has continuity--at least from end-to-end.

Next steps:
Verify the coils directly--not going through and resistors. And verify all 3 connections to each coil
Verify the bandswitch function---for both sections of the oscillator bandswitch.

_________________
-Mark
"Measure voltage, but THINK current." --anon.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Sat 15, 2019 3:09 pm 
Member

Joined: Nov Thu 20, 2014 4:52 pm
Posts: 128
There are 3 different coils that seem to be associated with the front end and the 6A8. I have no idea which one could be in the osc circuit. Looking at the bottom of chassis there is one towards the right corner which might be a candidate. It has two windings. One winding went to ground and had no continuity. Removed the whole coil and that winding was not making connection at either end so repaired it and now has continuity both ends. No difference to the radio. One of the other coils connects to one end of the 50K resistor. Removed that coil and checked continuity. It seems to have at least 3 windings and appears to have continuity. Hard to tell but seems OK. No obvious opens. This might be some sort of input X-former. One other coil on top of the chassis might be an osc coil. Not sure. Haven't checked it yet. Looks very hard to remove. This is beginning to look like the osc in the Philco 89 where no matter what you do it won't osc.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Sat 15, 2019 3:39 pm 
Member
User avatar

Joined: Jul Mon 26, 2010 8:30 pm
Posts: 26797
Location: Annapolis, MD
The 3 coils that you see to the left of the 6A8 are the front-end RF coils--each one has 2 windings. (They are in fact transformers) Note the two sections of the bandswitch that select which winding gets connected.
None of the 3 transformers above have anything to do with the oscillator.

Shown below the 6K7 are the TWO oscillator coils. As stated earlier, the one on the right is shared between BC and the "low SW" band. These are both tapped coils that operate as autotransformers.
For each coil, the larger section goes to the oscillator grid (grid #1), and the smaller section goes to the oscillator anode (grid #2).

How to tell which coil is which:
1. how they connect to the bandswitch
2. size: All things equal, the TUNED section of the RF and OSC coils will have inductance inversely proportional to the square of the frequency. IOW, the larger coils are for the BC band, and the smallest are for the upper SW band.

_________________
-Mark
"Measure voltage, but THINK current." --anon.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Sat 15, 2019 8:10 pm 
Member

Joined: Nov Thu 20, 2014 4:52 pm
Posts: 128
Thanks for info on coils. See the 25k resistor connected to pin 8 of the 6A8 and the other end of that resistor goes directly to a 4200 mica on my radio but the schematic shows it going through a coil first. Is that just a mistake on the drawing or is my radio wired wrong? Maybe doesn't matter but just noticed that.


Top
 Profile  
 
 Post subject: Re: Packard Bell 48 just has static
PostPosted: Jun Sun 16, 2019 2:30 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 33139
Location: SoCal, 91387
I would suggest that you re-read the first sentence of my first post, and follow it. Since you aren't getting signal the way it's currently wired, try doing it according to the schematic.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
Post New Topic Post Reply  [ 23 posts ]  Moderators: Marcc, Norm Leal Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: 37oldsguy, Chris108, Marcc and 15 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB