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


It is currently Jun Mon 17, 2019 12:39 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 8 posts ] 
Author Message
 Post subject: Collins R-390A Power supply chokes
PostPosted: May Tue 14, 2019 2:18 pm 
Member

Joined: Jan Fri 20, 2012 10:25 pm
Posts: 129
Location: Warminster, PA
Working on an R-390A and have found that both of the chokes in the power supply circuit seem to be bad. L601, the swinging choke, has a DCR of 8 ohms and the case says approx 137 ohms. The other choke (ref des escapes me at the moment) measures about 60 ohms.

Is this a typical failure of these parts? I have two other audio chassis where the chokes measure within reason so I have a pretty good feeling these are shot.

Thoughts?

Tom
W3TA

PS: what lead me down this path is a higher then expected B+ (SS rectifiers and 220 ohm resistor mod) and a raspy audio tone when tuning CW signals.


Top
 Profile  
 
 Post subject: Re: Collins R-390A Power supply chokes
PostPosted: May Tue 14, 2019 4:47 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3246
Location: Seattle WA US
What type of meter are you using to make your resistance measurements? I have found that some top quality digital meters give erratic results when measuring resistance in series with significant inductance. Suggest you confirm your measurements with an old fashioned VOM, (Tripplett, Simpson, or Heathkit, etc) before doing anything drastic.

-Chuck K7MCG


Top
 Profile  
 
 Post subject: Re: Collins R-390A Power supply chokes
PostPosted: May Tue 14, 2019 6:18 pm 
Member

Joined: Jan Fri 20, 2012 10:25 pm
Posts: 129
Location: Warminster, PA
K7MCG wrote:
What type of meter are you using to make your resistance measurements? I have found that some top quality digital meters give erratic results when measuring resistance in series with significant inductance. Suggest you confirm your measurements with an old fashioned VOM, (Tripplett, Simpson, or Heathkit, etc) before doing anything drastic.

-Chuck K7MCG


My initial measurements were all made with a Fluke DVM. I have three audio modules, two measure within reason and the one in question doesn't. I'll double check tonight with my Hickok VOM just to be sure before I condemn these.

Tom
W3TA


Top
 Profile  
 
 Post subject: Re: Collins R-390A Power supply chokes
PostPosted: May Wed 15, 2019 1:23 am 
Member

Joined: Jan Fri 20, 2012 10:25 pm
Posts: 129
Location: Warminster, PA
Swapped out both L601 and L602. Now B+ is where it should be and the audio tones are no longer raspy.


L601 measures 8 ohms and L602 measures 60 ohms. Both are well short of where they should be and obviously contributing to the issues I was seeing.

Tom
W3TA


Top
 Profile  
 
 Post subject: Re: Collins R-390A Power supply chokes
PostPosted: May Wed 15, 2019 1:39 am 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 265
Location: San Jose, Ca.
Tom, No, these usually do not go bad. Do you know if they were over heating? They should be warm, not hot. Is this rx a 3-fuse unit? Does it have the right fuse in F102? Are C606 A & B leaky? Bummmmmer!

Regards, Larry


Top
 Profile  
 
 Post subject: Re: Collins R-390A Power supply chokes
PostPosted: May Wed 15, 2019 12:50 pm 
Member

Joined: Jan Fri 20, 2012 10:25 pm
Posts: 129
Location: Warminster, PA
I too was surprised. It is a three fuse unit and I rebuilt both of the electrolytics before ever powering it up.

The radio was having some fuse blowing issues. Measured the current and the 1/8 amp fuse line had approx 130mA of draw and the 1/4 amp line had approx 270mA draw. At first I suspected that this was due to a leaky caps somewhere but now I believe it was due to the high B+ due to the suspect chokes.

After replacing the chokes the B+ that used to be close to 300V is now at approx 210V where is needs to be. I need to go back and measure the fuse current again.

Another tid bit, both audio transformers seem to be reading half of what the transformers in the other two audio chassis measure. primaryies are around 60 ohms vs 120 ohms.

No evidence of overheating on either the chokes or the audio xfmrs. Audio out sounds good and at reasonable volume levels (not measured - yet....).

Tom
W3TA


Top
 Profile  
 
 Post subject: Re: Collins R-390A Power supply chokes
PostPosted: May Wed 15, 2019 9:49 pm 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 265
Location: San Jose, Ca.
Tom, Sounds like they were bad when you got it. Too bad. Repairing the electrolytics is the main B+ thing to do before powering it up. Getting it down to 210 vdc should bring the current draw down a lot.

Regards, Larry


Top
 Profile  
 
 Post subject: Re: Collins R-390A Power supply chokes
PostPosted: May Thu 16, 2019 1:51 pm 
Member

Joined: Jan Fri 20, 2012 10:25 pm
Posts: 129
Location: Warminster, PA
Radios is working well now. Sensitivity below 1uV on all bands except two where it is 1.5uV. I'll call that good.

A couple more little things to do then this one is done!

Tom
W3TA


Top
 Profile  
 
Post New Topic Post Reply  [ 8 posts ]  Moderator: Sandy

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB