Is the voltage drop across a vacume tube rectifier significantly higher
than a solid state plug in replacement? Previous owner of my HX-50
changed over to SS. I am changing out capacitors and just curious.

73
Bob
N9NEO

wrote:
Is the voltage drop across a vacume tube rectifier significantly higher
than a solid state plug in replacement?

Yes, for the most part. But how much depends on the load.

Previous owner of my HX-50
changed over to SS. I am changing out capacitors and just curious.

Measure the supply voltages and compare with the schematic. If they
are all too high, add in a dropping resistor.

Derate all the capacitors anyway, though. They'll last longer before
the next replacement.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Question for Scott: i work in the tv shop of a major hotel/casino in
vegas...what am i missing, derate ? ex. if a 10 ufd @ 16 volt needs to
be replaced, usually it is replaced with a 25 volt...that helps with
spare part inventory, and records show, so far no second replacement,
of cap. Please no flaming, i really want know...TIA Gene

"Gene" wrote in message
oups.com...
Question for Scott: i work in the tv shop of a major hotel/casino in
vegas...what am i missing, derate ? ex. if a 10 ufd @ 16 volt needs to
be replaced, usually it is replaced with a 25 volt...that helps with
spare part inventory, and records show, so far no second replacement,
of cap. Please no flaming, i really want know...TIA Gene


I think you figured it out: by derating he meant using a higher voltage
rated part to replace the original. If a small additional cost isn't
objectionable, you'll also find there's a higher temperature rated series
of electrolytic caps available too.

Pete

Measure the supply voltages and compare with the schematic. If they
are all too high, add in a dropping resistor.

Putting a series resistor would degrade the power supply regulation performance. This may or may not be important, depending on application.

The safest way to proceed would to put a (properly polarized) zener diode (or a series of several zener diodes, up to getting the required voltage and dissipation power) in series with the circuit, so that voltage drop gets (nearly) constant, independently of load variations.

73

Tony I0JX

"Antonio Vernucci" wrote in message
...
Measure the supply voltages and compare with the schematic. If they
are all too high, add in a dropping resistor.

Putting a series resistor would degrade the power supply regulation
performance. This may or may not be important, depending on application.

The safest way to proceed would to put a (properly polarized) zener diode
(or a series of several zener diodes, up to getting the required voltage and
dissipation power) in series with the circuit, so that voltage drop gets
(nearly) constant, independently of load variations.

73

Tony I0JX

What about the internal IR losses of the original vacuum tube? The
regulation should be
nearly the same if done right.

Pete

What about the internal IR losses of the original vacuum tube? The
regulation should be
nearly the same if done right.

Pete

yes, but why having it the same if one can get it better

Tony

What about the internal IR losses of the original vacuum tube? The
regulation should be
nearly the same if done right.

Pete

yes, but why having it the same if one can get it better

Tony

However, it should be noted that supply voltage regulation will actually
decrease if you use diodes, rather than be improved.

Here is an example. Let us assume we have 100 volt primary and 100 volt
secondary, and that the normal rectifier has a 10 volt voltage drop. We
replace the tube with 2 series diodes, which have a 1 volt total drop and
then add 9 volts of zeners. That gives us a 10 volt drop, equal to the
tube. Now, assume there is a 10 volt drop in primary line voltage.
Secondary voltage is 90, less 10 volts, which is 80 volts. The output
voltage has dropped by 11%, while the input voltage has dropped 10%. If we
still had the original tube (or a diode and resistor), then the 10 volt
primary drop will result in 90 volts on the secondary - but the voltage drop
will be fairly linear across the tube (and resistor), so will only be
probably 9 volts. Resulting voltage out of the power supply is 81 volts
rather than the 80 volts using the zener diode. In that case, primary
voltage drops 10% and seconddary voltage drops 10%.

In this special case, we have created a deregulator.

73, Colin K7FM

Gene wrote:
Question for Scott: i work in the tv shop of a major hotel/casino in
vegas...what am i missing, derate ? ex. if a 10 ufd @ 16 volt needs to
be replaced, usually it is replaced with a 25 volt...that helps with
spare part inventory, and records show, so far no second replacement,
of cap. Please no flaming, i really want know...TIA Gene

You're not missing anything. Although I recommend buying only caps
rated for 105'C because they seem also to last longer than the 85'C
spec ones. But that's exactly what I mean.
-scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Uncle Peter wrote:
"Antonio Vernucci" wrote in message
t...
Measure the supply voltages and compare with the schematic. If they
are all too high, add in a dropping resistor.

Putting a series resistor would degrade the power supply regulation
performance. This may or may not be important, depending on application.

Yes, but it will degrade it to the same level which using the original
rectifier tube would.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."