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

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Modernizing Heathkit HP-20  (Read 8691 times)
NOTREADYYET
Member

Posts: 11




Ignore
« on: June 07, 2008, 07:59:37 AM »

 I bought an HP-20 on EBay by accident. It was sold for parts, as-is. No big deal. It looks like the transformer can be salvaged if it still puts out all the required voltages.

 I like to play with power supplies, and have built a number for solid state electronics projects, so I decided to build a pseudo HP-20 around the transformer.

 The first problem is that I don't have a parts list, and the schematic doesn't show the WVDC ratings for the Caps. Does anyone out there have a list of the ratings?

 Second, I would like to convert the filament voltages from AC to DC because DC is easier (cheaper) to regulate. Any downsides?

 Third, I see 'line chokes' on the schematic at the mains input. How about using MOVs instead?

 Last, for now, does a 15 second soft-start seem reasonable?

 Thanks
Logged
KA5N
Member

Posts: 4380




Ignore
« Reply #1 on: June 07, 2008, 10:44:00 AM »

An HP20 is a power supply for a tube type transmitter or transceiver and supplies about 600 volts (HV)for the final plates and about 250-300 volts (LV) for other supply voltage and 6.3 VAC for the tube filaments.  450 VDC rating will work for all the electrolytic capacitors.  There is no reason to regulate the filament voltage and certainly no reason to "change" it to DC. Just ignore the line chokes and the associated capacitors.  You don't need a soft start circuit for the intended usage, if you plan to use it for some other purpose ... who knows?
Allen  
Logged
NOTREADYYET
Member

Posts: 11




Ignore
« Reply #2 on: June 07, 2008, 06:06:33 PM »

 Here are some pictures of the subject: http://good-times.webshots.com/album/563722002xAyTOK

 I bought the HP-20 to power an HW-12. Also bought an HP-23 and a D kit for it, but the HP-23 is too cherry for my purposes.

 I don't like stressing electrolytics. I've blown a few up. Nasty smell and they make my wife nervous.

 Why not regulate the filament voltages? It's cheap and easy to regulate both current and voltage. I would think it would enhance both tube life and performance.

 I think that soft start for filament voltages is mandatory. With all of the capacitors involved I don't like the idea of surges. Naturally, the HV circuit soft starts would not be enabled until the LV was up to speed.

 I read somewhere here that it can be harmful to apply grid and plate voltage with low filament voltage. I don't understand. If the filament is producing less than the normal number of free electrons, what would that hurt?

 Good to know that I can forget the line chokes. They must have some sort of passive as well as dynamic resistance. I'd like to avoid that.

Thanks

 
Logged
KA5N
Member

Posts: 4380




Ignore
« Reply #3 on: June 07, 2008, 06:43:05 PM »

450 vdc electrolytics won't be stressed.  The input chokes and capacitors are to keep RF from feeding back into the AC line and aren't really worth worrying about.  
I think some of your other ideas are off base.  But you do as you like.  Turning on the LV before the HV could cause you to blow the screen grids in the final and driver tubes.  Of the ten of thousands of Heathkit transmitters and receivers that have worked for years none had DC operated filaments (except mobile units)or had regulated current and voltage on the filaments. Input surges won't cause a problem in the filament voltage as they will cause the voltage to be a bit low for a second or so. Soft starters for an HW-12 are a waste of time and money.
Good luck
Allen
Logged
NOTREADYYET
Member

Posts: 11




Ignore
« Reply #4 on: June 08, 2008, 07:03:09 AM »

Is there any chance that DC filament voltages would reduce hum? I thought I read somewhere that it would. Also, from what I've read, the tubes don't care.

 I guess that one of the reasons I am considering this is that I have a bunch of extra LM317s, bridge rectifiers and 2N3055s lying around.
Logged
W9GB
Member

Posts: 3379




Ignore
« Reply #5 on: June 18, 2019, 03:49:20 PM »

Heathkit of the Month #26 (February 2011)
by Bob Eckweiler, AF6C

Heathkit HP-20 and HP-23A/B/C/E
AC Power Supply Family.
http://www.w6ze.org/Heathkit/Heathkit_026_HP23C.pdf
Logged
N2DTS
Member

Posts: 965




Ignore
« Reply #6 on: June 18, 2019, 04:22:30 PM »

If you 'hifi' the audio to where it passes 60 Hz well, running the mic preamp tube filaments off DC prevents hum.
Best to do that only for the mic preamp though.
For the rest, it only takes the transformer winding, to do DC it takes a lot of power parts and filtering.
Filament voltage is not critical, I have yet to have one fail in 40 years.
Logged
WA2CWA
Member

Posts: 568


WWW

Ignore
« Reply #7 on: June 18, 2019, 11:23:57 PM »

You two guys must be bored. Both of you responded to a thread that was lasted posted 11 years ago.

Logged
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!