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Fast Recovery Diodes

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Anonymous
February 22, 2005 8:41:24 PM

Archived from groups: rec.audio.tech (More info?)

I've built several pieces of electronic gear from kits and I can read
schematics. I have a factory guitar amplifier and I've been told that
if I add FRED's that I will get better note separation on chords and
better low end. I have a schematic of the amp. Where do I put the
FRED's? Are they inline between certain components or are they added as
bypass to components. Should I look for any diodes anywhere in the
circuit and just replace those?

And here is the big question. DANGEROUS VOLTAGES! The two tube amps I
have built I did so from parts and when I plugged them in they worked so
there was no trouble shooting and any trimming was safe. With this tube
guitar amp unplugged and installing these FRED's am I playing with fire?
Do I have to drain all the caps prior to doing work? How do I do that
safely and is there anything else?

Thanks.

Also - if I get the go ahead to proceed with this mod who makes the best
FRED's?

More about : fast recovery diodes

Anonymous
February 22, 2005 9:09:31 PM

Archived from groups: rec.audio.tech (More info?)

You are trying to follow some type of myth. There are many of these around.

Fast Recovery Diodes are used in specific types of switching power supply
designs, and in specific applications where high speed polarized damping of
high speed pulses are required, as such in the flyback and or scan circuits.
The damper diode in a TV high voltage section is a fast recovery type diode
These are mainly used in TV equipment.

FRD's have specific specification ranges to fit the applications that they
are to be fitted to. I would guess that they can be used as expensive
rectifiers in your tube amp, but this would be a waste, and may not perform
as well as the standard type of diodes.

When the AC from the main power transformer is being rectified, it is best
to use a soft type of rectifier, such as a tube rectifier that is normal for
a tube amplifier. Standard silicon diodes may be used, but damping
resistors, with some added small bypass caps should be used. The choice of
the diodes, and related parts are very dependent on the required specs for
the design. This has to do with noise factors, and the current pull of the
supply section that is being handled.

In a tube amplifier, running the tube heaters on DC may help to keep some of
the AC background hum or line noise down to a bit of a lower level. This is
not as simple as putting rectifiers, and large filter caps to drive the tube
heaters. A full blown adequate DC supply would be required.

I remember seeing in many tube amplifiers a hum bucking type of
configuration being used in the heater design, using a type of balance pot
to keep the ground reference balanced between the heaters. A simple form of
this is to have the heater source floating from ground, and feeding the tube
heaters. A wirewound variable resistor of a few Watts rated is wired to each
side of the heater supply, and the centre is put to ground. This control is
mounted on the chassis preferably at the rear of the amp, and set up as a
service adjustment. This control is to obtain the best hum balance. Going by
memory this control was generally a 100 ohm linear, wire wound, 2 Watt
control. The procedure was to set this control for the minimum amount of
background hum. In many amplifiers, it was not critical. But at some
locations, where there were electrical grounding problems, this adjustment
helped out.

One thing you can also do in the wiring of a tube amplifier, is that the
heaters should all be wired back to a central distribution for the heater
supply. Even though they are wired in parallel in these amplifiers, it is
best to have them all in a star or spoke like configuration for the heater
supply distribution. I have seen tube heaters wired in a sort of daisy chain
parallel affair. This is not a good way to do it.

In the lower cost amplifiers, I have seen one side of the tube heaters
connected directly to ground. Then the supply side is wired in a sort of
daisy chain from the source all the way to the last tube. This is not a
balanced heater supply, and can be susceptible to have more hum and noise
radiated back from the heaters.

I hope this all helped to set you a bit straighter with this.

--

Another big rip-off I see these days, are the very expensive AC cords for
amplifiers and electronic equipment. All of this equipment uses DC after the
power supply for the operation where the sound is processed. As long as an
AC cord that is rated for the current pull of the device is used, there is
no difference if it is made of gold, silver, or whatever!

If you were to see the wiring from the AC outlet, to the breaker panel, and
then to the wires to power utility company's distribution, your nice cheap
AC cord looks a lot better! As long as the AC has a distortion of less than
about 5% with no serious spiking, it is good enough to run any electronic
equipment. What is important is that the proper supply volts are present,
and that the current source is adequate to be stable.


--

Jerry G.
======


"Terrified" <crantz7z@windsurf.net> wrote in message
news:BCOSd.9250$qd6.32@fe12.lga...
I've built several pieces of electronic gear from kits and I can read
schematics. I have a factory guitar amplifier and I've been told that
if I add FRED's that I will get better note separation on chords and
better low end. I have a schematic of the amp. Where do I put the
FRED's? Are they inline between certain components or are they added as
bypass to components. Should I look for any diodes anywhere in the
circuit and just replace those?

And here is the big question. DANGEROUS VOLTAGES! The two tube amps I
have built I did so from parts and when I plugged them in they worked so
there was no trouble shooting and any trimming was safe. With this tube
guitar amp unplugged and installing these FRED's am I playing with fire?
Do I have to drain all the caps prior to doing work? How do I do that
safely and is there anything else?

Thanks.

Also - if I get the go ahead to proceed with this mod who makes the best
FRED's?
Anonymous
February 23, 2005 1:50:08 PM

Archived from groups: rec.audio.tech (More info?)

"Jerry G." <jerryg50@hotmail.com> wrote in message
news:381uj7F5ctdj5U1@uni-berlin.de...

>
> Another big rip-off I see these days, are the very expensive AC cords for
> amplifiers and electronic equipment. All of this equipment uses DC after
> the
> power supply for the operation where the sound is processed. As long as an
> AC cord that is rated for the current pull of the device is used, there is
> no difference if it is made of gold, silver, or whatever!
>
> If you were to see the wiring from the AC outlet, to the breaker panel,
> and
> then to the wires to power utility company's distribution, your nice cheap
> AC cord looks a lot better! As long as the AC has a distortion of less
> than
> about 5% with no serious spiking, it is good enough to run any electronic
> equipment. What is important is that the proper supply volts are present,
> and that the current source is adequate to be stable.
>
>
Have you seen the expensive duplex outlets? I would love to be a mouse in
the telephone room of the power company billing office when someone calls
and wants the service wiring upgraded to OFC pole to home. Some company's
already sell "updated" ring wiring for homes!

I feel fortunate to live in a rural comunity, I have my very own pole pig,
pretty clean power.
Anonymous
February 23, 2005 3:21:35 PM

Archived from groups: rec.audio.tech (More info?)

Jerry G. wrote:
> You are trying to follow some type of myth. There are many of these around.
>
> Fast Recovery Diodes are used in specific types of switching power supply
> designs, and in specific applications where high speed polarized damping of
> SNIP

Here is the link for reference as to what I now know is HYPE

http://vacuumtube.com/Products.htm##Fast%20Recovery%20D...

Scroll to the bottom last mod offered

Fast Recovery Diodes (FREDs) and Schottky Diodes
Anonymous
February 23, 2005 11:09:30 PM

Archived from groups: rec.audio.tech (More info?)

"Terrified" <crantz7z@windsurf.net> wrote in message
news:o 53Td.19789$jX5.14508@fe08.lga...
> Jerry G. wrote:
>> You are trying to follow some type of myth. There are many of these
>> around.
>>
>> Fast Recovery Diodes are used in specific types of switching power
>> supply designs, and in specific applications where high speed
>> polarized damping of SNIP
>
> Here is the link for reference as to what I now know is HYPE
>
> http://vacuumtube.com/Products.htm##Fast%20Recovery%20D...
>
> Scroll to the bottom last mod offered
>
> Fast Recovery Diodes (FREDs) and Schottky Diodes

It is just breathtaking to think that people are that mercenary to take
such advantage of ignorant tube-heads. Maybe it is their own fault
for not studying how the real electronics work.
February 23, 2005 11:15:40 PM

Archived from groups: rec.audio.tech (More info?)

On Wed, 23 Feb 2005 12:21:35 -0500, Terrified wrote:

> Jerry G. wrote:
>> You are trying to follow some type of myth. There are many of these
>> around.
>>
>> Fast Recovery Diodes are used in specific types of switching power
>> supply designs, and in specific applications where high speed polarized
>> damping of SNIP
>
> Here is the link for reference as to what I now know is HYPE
>
> http://vacuumtube.com/Products.htm##Fast%20Recovery%20D...
>
> Scroll to the bottom last mod offered
>
> Fast Recovery Diodes (FREDs) and Schottky Diodes


By all means experiment. That is what all this is about! Be very careful
though, playing with valve (tube for those of you on the other side of the
big pond...) amps can be fatal - literally. You must *always* follow
safety precautions when working on high voltages or in situations where
high voltages could possibly occur. You only get one life...

If your amp has a valve rectifier and you change it to any solid state
type then you must be fully aware of what will happen. Unless you make
other changes the high voltage rail will go much higher due to the lower
voltage drop in the rec. This will, in many cases, damage things like
capacitors and may even damage some output valves in some cases!

The diode "myth" isn't complete twaddle. It has some basis in truth as
the effect on rectification can be seen on a scope trace. Whether anyone
can genuinely *hear* the difference in types of diodes is something else!

--
Mick
(no M$ software on here... :-) )
Web: http://www.nascom.info
Web: http://projectedsound.tk
February 25, 2005 1:31:11 AM

Archived from groups: rec.audio.tech (More info?)

Terrified <crantz7z@windsurf.net> wrote in news:BCOSd.9250$qd6.32@fe12.lga:

> I've built several pieces of electronic gear from kits and I can read
> schematics. I have a factory guitar amplifier and I've been told

By another musician, a friend, an audiophile?

that
> if I add FRED's that I will get better note separation on chords


No you won't.

and
> better low end.

No you won't.

I have a schematic of the amp. Where do I put the
> FRED's? Are they inline between certain components or are they added as
> bypass to components. Should I look for any diodes anywhere in the
> circuit and just replace those?

This says you are not qusalified to do this. Stop before you permanently
damage your equipment or yourself.
!