[AMRadio] Solid State 575 mercury vapor RectifierReplacementsneeded

sbjohnston at aol.com sbjohnston at aol.com
Mon Oct 5 09:26:59 EDT 2009

```Thanks to everyone for pointing out my brain lapse  -grin-  apparently
I got confused in my calculations.

I wrote:

>To calculate the value of resistor, use Ohms law R=E/I and P=IxE where
R is in ohms,
>E is the desired drop in volts, and I is the current in amps, and P in
watts
>For example, lets say your B+ is 50 volts too high. The load draws
0.250 amps.
>R= 50/.25 = 200 ohms.
>P= 0.25x200=50 watts.

The last line should be

P= 0.25x50=12.5 watts.

When I came up with 50 watts, I thought to myself at the time, "that
seems like a big resistor, oh well... la-dee-dah..." and I went about
my business instead of checking my work.  I should trust the Force when
feel an error coming on like that.

Steve WD8DAS

sbjohnston at aol.com
http://www.wd8das.net/
---------------------------------------------------------
Radio is your best entertainment value.
---------------------------------------------------------

-----Original Message-----
From: sbjohnston at aol.com
To: amradio at mailman.qth.net
Sent: Sun, Oct 4, 2009 3:17 pm
Subject: Re: [AMRadio] Solid State 575 mercury vapor
RectifierReplacementsneeded

Jim W5JO wrote:

>What kind of resistor do you use in this type of rectifier build to

>simulate the voltage drop?

I prefer cylindrical wirewound power resistors for this job (they seem
to be able to take more surge20current than the sandy rectangular ones
in case of a fault downstream).

To calculate the value of resistor, use Ohms law R=E/I  and P=IxEwhere
R is in ohms, E is the desired drop in volts, and I is the current in
amps, and P in watts

For example, lets say your B+ is 50 volts too high.  The load draws
0.250 amps.

R= 50/.25 = 200 ohms.

P= 0.25x200=50 watts.

If the resistor ends up to be hard to find or expensive, it might be
easier to eliminate the reasons why the higher B+ is a problem.  And
more efficient too.   Upgrading some capacitors could be a reasonable
approach.

Steve WD8DAS

sbjohnston at aol.com

http://www.wd8das.net/

---------------------------------------------------------

Radio is your best entertainment value.

---------------------------------------------------------

-----Original Message-----

From: Jim Wilhite <w5jo at brightok.net>

To: Discussion of AM Radio in the Amateur Service
<amradio at mailman.qth.net>

Sent: Sun, Oct 4, 2009 10:40 am

Subject: Re: [AMRadio] Solid State 575 mercury vapor
RectifierReplacementsneeded

Steve,

What kind of resistor do you use in this type of rectifier build to

simulate the voltage drop?

Jim/W
5JO

----- Original Message -----

> I've made my own solid-state plug-in replacement rectifiers for a

> variety of tube types.  I look up the tube specs and select

> solid-state

> diodes that stack up appropriately for current and forward and
reverse

> voltages. I usually end up using either 1N4007s or 1N5408s.  From

> on-lline sources like Digikey or Mouser or All Electronics the diodes

> are very inexpensive, ten cents to maybe 30 cents each.

>

> I put the diodes on a rectangular piece of perfboard sized to fit

> upright with its bottom end tucked within the sides of the base of
the

> defunct tube it is replacing.  A small L bracket holds it in place.

>

> If you use diodes from the same "run" (which is easy if they are sold

> on the paper tapes used by manufacturers today) then I find no

> equalizing components are needed.  I add a few more diodes than the

> calculated voltage required for an extra measure of safety and have

> never had a failure, even in broadcast rigs on the air 24/7 with lots

> of lightning and power bumps to deal with.

>

> You can expect somewhat higher voltage from the new stack than the

> original tube rectifier - if that is a problem for the rig, then add
aC2

> series power resistor to simulate the internal voltage drop of the

> earlier tube.  So far I've only needed to do that once when the new

> higher B+ exceeded the rating of the by-pass caps in the other

> sections

> of the rig.  Otherwise the rigs seemed to thrive on the higher

> voltage.

>

> Steve WD8DAS

______________________________________________________________

Our Main Website: http://www.amfone.net

AMRadio mailing list

Searchable Archives:
http://www.mail-archive.com/amradio@mailman.qth.net/

List Rules (must read!): http://w5ami.net/amradiofaq.html

List Home: http://mailman.qth.net/mailman/listinfo/amradio

Post: AMRadio at mailman.qth.net

To unsubscribe, send an email to amradio-request at mailman.qth.net with

the word unsubscribe in the message body.

This list hosted by: http://www.qsl.net

Please help support this email list: http://www.qsl.net/donate.html

```

More information about the AMRadio mailing list

This page last updated 16 Dec 2017.