[drakelist] AC-4 power supply diodes

[Eric Webner]

I am working on my T-4XC (again!). I thought I would check out the power supply first, to make sure all voltages are good. They all measured (with DVM) good DC voltage, with very little AC (except for the filament supply, of course). Will such a measurement be accurate, or do I need a scope to check for AC?
 
There have been some discussions about replacing the electrolytic filter caps and possibly the rectifier diodes. I see no leakage around any of the caps, and would hope to not have to hassle with it. The diodes would be much easier to replace, and I would like to know if it is practical to replace them while the unit is open, or should I "not fix what ain't broke?" If replacement is warranted, is there a suitable replacement or cross-reference for the B5G5 diodes? I'd like to use my 1N400x rectifiers that I have in my junk box, if that is appropriate.
 
Thanks for all your help!
 
73,
 
Eric
KA8FAN
 
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Re: [drakelist] AC-4 power supply diodes

[Garey Barrell]

Garey Barrell <[EMAIL PROTECTED]> made an utterence to the drakelist gang
--
The 1N4007 is fine.  The B5G5 is a 600V @ 1A diode.
It's hard to determine the quality of the filter caps without an ESR 
meter or scope.  If they are original, they will fail sooner rather 
than later.   Don't forget the bias supply filter.  This supply can 
actually cause more damage to the transmitter or power supply when 
it fails than the HV supply.

Axial lead and Twist-Lok filter caps are getting very hard to find, 
so the board at


looks to be a very good alternative that should last another 30 years!
73, Garey - K4OAH
Eric Webner wrote:
I am working on my T-4XC (again!). I thought I would check out the power supply first, to make sure all voltages are good. They all measured (with DVM) good DC voltage, with very little AC (except for the filament supply, of course). Will such a measurement be accurate, or do I need a scope to check for AC?
 
There have been some discussions about replacing the electrolytic filter caps and possibly the rectifier diodes. I see no leakage around any of the caps, and would hope to not have to hassle with it. The diodes would be much easier to replace, and I would like to know if it is practical to replace them while the unit is open, or should I "not fix what ain't broke?" If replacement is warranted, is there a suitable replacement or cross-reference for the B5G5 diodes? I'd like to use my 1N400x rectifiers that I have in my junk box, if that is appropriate.
 
Thanks for all your help!
 
73,
 
Eric
KA8FAN
 
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Re: [drakelist] AC-4 power supply diodes

[Gerry]

The life of an electrolytic capacitor is directly 
related to applied voltage, ripple voltage, and temperature. It used to be that 
electrolytics were rated for at least 1,000 hours of operation at maximum 
specified voltage and temperature. The only way to find this out is to look up 
the data sheet or catalog information both of which are probably unavailable due 
to the passing of time. Since the Drake power supply has fuse protection, I say 
don't fix what isn't broke. Assuming of course that the proper fuse is in place. 
As long as the measured voltages concur with the specifications in the manual, 
don't lose sleep over it.

  - Original Message - 
  From: 
  Eric Webner 

  To: Drakelist 
  Sent: Sunday, December 26, 2004 1:58 
  PM
  Subject: [drakelist] AC-4 power supply 
  diodes
  
  I am working on my T-4XC (again!). I thought I would check out the power 
  supply first, to make sure all voltages are good. They all measured (with DVM) 
  good DC voltage, with very little AC (except for the filament supply, of 
  course). Will such a measurement be accurate, or do I need a scope to check 
  for AC?
   
  There have been some discussions about replacing the electrolytic filter 
  caps and possibly the rectifier diodes. I see no leakage around any of the 
  caps, and would hope to not have to hassle with it. The diodes would be much 
  easier to replace, and I would like to know if it is practical to replace them 
  while the unit is open, or should I "not fix what ain't broke?" If replacement 
  is warranted, is there a suitable replacement or cross-reference for the B5G5 
  diodes? I'd like to use my 1N400x rectifiers that I have in my junk box, if 
  that is appropriate.
   
  Thanks for all your help!
   
  73,
   
  Eric
  KA8FAN
   
  
  
  Do you Yahoo!?Meet the all-new My Yahoo! 
  – Try it today! 

[drakelist] KA1FAN diode question

[KC8YY]

To all
 
Finally, a voice of REASON rising out of the "cap" and "recap"
CRAP! I have replaced a lot of condensers and capacitors,
in over 50 years of repairing, designing and building electronic
equipment, but i've never replaced a "cap" in or "recapped" a
radio. I have, however, worn many caps, and even capped a
gas line. I had several tires recapped for my old Pontiac!
There are many ways to determine if a CAPACITOR is
defective. If it is, replace it. IF IT AIN'T BROKE, DON'T FIX IT!
We used to call wholesale replacement of components the
"shotgun" servicing method, not looked upon as a favorable
procedure by a technically competent person.
 
73   Bob, KC8YY

Fw: [drakelist] KA1FAN diode question

[Lee Bahr]

In my estimation, replacing 45 year old electrolytics and poor quality 
paper caps that are 45 years old is not doing shotgun or unreasonable 
restoration. On the contrary, it is the prudent way.  You are not 
being stupid, lazy, or ignorant.  You are being wise and smart.  In 
fact you have engaged in a lot of extra work up front.  I have found very 
few paper caps that old that don't leak.  Plus electrolytic manufacturers 
back then never designed their caps to last this long.  A leaky cap can 
introduce hum and if and when it shorts, it can take out a lot of components 
hard to come by today. (Look at a government issue R-390A 
receiver.  It's power supply electrolytics were plug in)!  I 
would rather take preventative measures and use modern fresh and better made 
components to protect my radio and the parts in it which are becoming ever so 
more scarce.  Maybe sometimes you can repair a radio without doing the 
above, but you sure have not restored it and you probably have set in motion a 
ticking time bomb.  Just have your bias supply fail by taking the 
cheap route and see what you think needed to be replaced as a precautionary 
measure once you have the failure.  We are taking about 45 year old 
equipment here.  You don't order parts from the factory anymore for these 
radios.  They are not 5 years old. We are not working, "on the 
clock",  and trying to figure out how to keep the repair charges down 
to $100 by putting in only $2.00 worth of parts into a repair that takes 5 
minutes to accomplish.   Protect your radio by replacing 
problematic parts before you have a catastrophic failure.  These radios are 
already taking a pounding by having 123 volts pumped into their primaries rather 
then the designed 110 volts of yester year.  Todays caps are made much 
better, have MUCH better tolerence, are smaller and cost very little.  
Diodes are made better with closer tolerances and of greater current capacity 
and give me much peace of mind knowing at least these parts won't let me 
down.  Even installing a relay circuit to switch on power from the small 
on-off switch thus taking the load off the switch makes sence today.  
Try and find a new switch when this puppy fails!  While we are at it, 
don't forget to replace all the out of tolerance resistors too!  (Sometimes 
with a modern higher wattage unit of equal size).
 
I just had my auto's timing belt replaced at 60,000 miles per the mfg 
maintenance schedule.  The price was $400 but that was much cheaper then it 
would cost me to rebuild my engine if the old belt failed and  I neglected 
to replace it as specified in my manual.  Just think what the manufacturer 
would have in the manual if they knew I would be driving this car 45 years later 
to keep it running reliably!  To each his own, but the chief engineer at 
radio station w0vt plans to keep on taking preventative measures with this 
station's vintage equipment.  If you don't head this advice and your radio 
blows up, let me know, I'd be happy to buy your radio as a parts radio for a few 
pennies on the dollar.
 
Lee Bahr, w0vt
Houston
 
 
 
Finally, a voice of REASON rising out of the "cap" and "recap"
CRAP! I have replaced a lot of condensers and capacitors,
in over 50 years of repairing, designing and building electronic
equipment, but i've never replaced a "cap" in or "recapped" a
radio
If it is, replace it. IF IT AIN'T BROKE, DON'T FIX IT!
We used to call wholesale replacement of components the
"shotgun" servicing method, not looked upon as a favorable
procedure by a technically competent person.
 
73   Bob, KC8YY