Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Heathkit HP-23 has low voltage.  (Read 5124 times)
AF6EC
Member

Posts: 23




Ignore
« on: June 23, 2012, 12:19:11 AM »

Hi,     I acquired an old HP-23 and fired it up. The HV was about 740 volts open circuit and the specs call for 820. The AC supply to the circuit was 270 volts, which I thought was close enough to the spec of 282. The low voltage measured 342 and spec is 350.

I decided a rebuild was in order and proceeded to replace all the components except the diodes, power transformer, and choke.

However, upon completion, the voltages remained the same. My question is:  does the 12 volt difference in AC specs relate to the reduced HV or is there some other reason for the HV to be 76 volts lower than spec.

Thanks for your thoughts.     Jim    AF6EC
Logged
AC5UP
Member

Posts: 3834




Ignore
« Reply #1 on: June 23, 2012, 02:44:47 AM »

The math says your supply is within less than 10% of spec.......... Considering the vintage that's "normal".

When you look at the schizmatic for voltages, also look for the disclaimer of test conditions. Could be something like 117 VAC input and measured with a VTVM or 20,000 Ohms-per-volt VOM. Unless you're set up the same as the factory test condition there will be a differential, and even if your test setup was an exact match there will be parts tolerance to consider.

Parts weren't as tight back then.

BTW: Seems odd you didn't replace the diodes. New diodes are more tolerant of abuse and very inexpensive. (?)
Logged

Never change a password on a Friday                
KA5N
Member

Posts: 4380




Ignore
« Reply #2 on: June 23, 2012, 02:52:54 AM »

Have you checked your line voltage?  Does anything overheat when the supply is on but not
loaded  (excessive heating or burnt odor would indicate a problem).   Have you tried it with your
transceiver to see what happens under load?

Allen KA5N
Logged
K8AXW
Member

Posts: 3723




Ignore
« Reply #3 on: June 23, 2012, 08:23:54 AM »

6EC:  Check this link for some interesting HP23 refurbishing reading:

http://willydog5.com/index.php?option=com_content&view=article&id=116:rebuilding-heathkit-hp23-power-supplies&catid=47:restorations&Itemid=147

I don't understand this:  "The AC supply to the circuit was 270 volts,"
Logged
KA5N
Member

Posts: 4380




Ignore
« Reply #4 on: June 23, 2012, 01:16:01 PM »

What he is calling the  "AC" supply is the transformer secondary windings.  There is nothing that can be done to increase these voltages except increase the line voltage or use a variac.
Why you didn't change out the silicon rectifiers is beyond my ken.  Heath used 600V piv units
(what was available at the time).  Today you can buy 1000v piv units for a dime each.
Consider that the rectifier circuits are voltage doublers, so the output voltage is pretty much
locked in, unless you have one of the supplies which has a switch for low voltage for either
250 vdc or 300 vdc.
Try the supply and see how it works, cause you can't change much voltage wise.

Allen KA5N
Logged
N2EY
Member

Posts: 3877




Ignore
« Reply #5 on: June 23, 2012, 03:04:30 PM »

Consider that the rectifier circuits are voltage doublers, so the output voltage is pretty much
locked in, unless you have one of the supplies which has a switch for low voltage for either
250 vdc or 300 vdc.

The HP-23 uses some tricky circuits and one needs to understand how it works.

All models of HP-23 I know of are capable of providing either a nominal 250 or 300 volt LV output. The LV transformer winding is tapped, and tap selection decides which voltage you get. In some models the selection is done by a switch, while on other you have to move a wire inside the unit to select the correct tap.

Since the LV and HV rectifier circuits are indeed voltage doublers, the transformer windings are lower voltage than the output. The LV winding is about 120 volts or so. It also powers the bias rectifier, which is half-wave.

I agree 100% that all diodes should be replaced by 1N4007s or better. (1N5408 is a good choice).

In fact, the reason so many 1960s era SS HV power supplies used voltage doublers was to save money on the rectifiers! That's no longer a consideration.

73 de Jim, N2EY
Logged
WB2EOD
Member

Posts: 218




Ignore
« Reply #6 on: June 26, 2012, 04:05:53 PM »

Given a plus/minus 10% on such circuits, your supply is probably OK.  Rebuilding was probably a prudent decision.  If one of those 125 uf electrolytics shorted out, it could take the choke or transformer along with it.  I've had a few of these supplies cross my bench.  Given that the choke and transformer are OK I generally gut and rebuild them.  Kits are available from oldheathkitparts.com and others

Just curious, do you have an SB series transceiver along with the power supply?


73
Roy
WB2EOD
Logged
N4NYY
Member

Posts: 4745




Ignore
« Reply #7 on: June 27, 2012, 06:18:04 AM »

I was going to rebuild one of these for a club member, but I found a retrofit kit that replaces all the components and fits in there nicely.

http://www.ultrawebb.com/OHP/HP-23D.htm
Logged
AF6EC
Member

Posts: 23




Ignore
« Reply #8 on: June 28, 2012, 09:47:36 PM »

Gentlemen:

Thanks for all your replies. I did replace all the diodes per your suggestions, however there was no basic change in the voltages. I did measure the line voltage from time to time and did note some small changes in the output voltages. At 117 VAC the output went to 754 volts which is 92% of spec, and might do an OK job in the real world. One thing of note is that the resistors do get too hot to touch, but none have failed. I do have an SB-102 that was bought "as is" and after I rebuild the supply cable, I will to fire up the transceiver. If there is an interest, I will post the results.

I did know there were some rebuild kits available, but I got a great price on the caps at ALL Electronics. In regard to that, I was able to remove the mounts from the original caps and use super glue to attach the new caps and remount in the existing holes.

Again, your replies are greatfully appreciated.     Jim   AF6EC
Logged
ZL1BBW
Member

Posts: 370




Ignore
« Reply #9 on: July 05, 2012, 01:37:17 PM »

Just a thought, when I was using a HP23 PSU.  The best meter I could get was an AVO, and there is no way in the world that you could really tell if it was 272 or 280 volts, main concern is was there volts and which end of the scale.  So it may be that it always ran low volts, just that with a DMM you can now tell.
Logged

ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!