I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have. Which one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off of the
semi rectifier ?
Steve

Stevey wrote:
I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have. Which one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off of the
semi rectifier ?
Steve



The circuit will only pass current when both devices are "on". So if
the semi rectifiers turn off first, then no current is outputted no
matter how slow the tube is to turn off. But in a practical sense,
this is not a real issue. The only time rectifiers actually pass
current is at the top of the AC waveform input. And that is to
"top off" the filter caps (assuming no filter choke). The rest of
the amplifier draws off charge from the filter caps, which results
in a slow voltage drop. Then the next AC voltage peak comes along
and "refills" the missing charge. This is the ripple voltage on
the B+.

"Stevey" said:

I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have. Which one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off of the
semi rectifier ?

I assume you mean "turn on" of the rectifier.
So you have transformers without a center tap (CT).
OK. Now, any solid state diode will turn "on" IMMEDIATELY.
Rectifier tubes for domestic use come in two flavors: directly heated
and indirectly heated.
The difference is that DH rects have a filament that at the same time
is cathode, and the IDH rects have a separate cathode, sometimes
connected to one of the heater pins, sometimes separate.
A DH rect will turn on faster than a IDH rect, think of it as 5
seconds vs. 30-40 sec. (sometimes even more).

If your purpose is to let the HT come up slowly to spare your supply
capacitors, this arrangement won't work.
The 2 solid state diodes will conduct immediately and charge the caps.
What's worse, they'll have to do it by themselves until the tube is
warm enough.

Another thing to consider is that the voltage drop over an average
silicon diode is 0.6...1 Volt, while a DHR may cost you 50 or more,
and a IDHR about 30 or so. This is current-dependable.
So, the SS diodes will have to do most of the work, resulting in more
50 (or 60) Hz supply ripple.
A true bridge, whether tube or solid state will have 100 or 120 Hz
ripple.

In short, I don't see any advantage in such an arrangement.

If you want slow start-up, use a bridge and an indirectly heated
rectifier afterwards.
Or, a huge resistor that gets shorted by a relay after several
seconds.

BTW the "sharp" turn-on of the SS rectifier may be limited by careful
selection of the type of diode , and/or a snubber cap over every diode
in the bridge.

For power supply designing, a good place to look is at
www.duncanamps.com
Look for a program called PSUD.
You can design your supply to your personal wishes and demands and
even see how components will be stressed (or not).

Good luck!

--
Sander deWaal
"SOA of a KT88? Sufficient."

Thanks for the reply. I do mean turn off. I am trying to see if I can
eliminate
the turn off noise of the semiconductor diode.

Steve
"Sander deWaal" wrote in message
...
"Stevey" said:

I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have. Which
one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off of
the
semi rectifier ?

I assume you mean "turn on" of the rectifier.
So you have transformers without a center tap (CT).
OK. Now, any solid state diode will turn "on" IMMEDIATELY.
Rectifier tubes for domestic use come in two flavors: directly heated
and indirectly heated.
The difference is that DH rects have a filament that at the same time
is cathode, and the IDH rects have a separate cathode, sometimes
connected to one of the heater pins, sometimes separate.
A DH rect will turn on faster than a IDH rect, think of it as 5
seconds vs. 30-40 sec. (sometimes even more).

If your purpose is to let the HT come up slowly to spare your supply
capacitors, this arrangement won't work.
The 2 solid state diodes will conduct immediately and charge the caps.
What's worse, they'll have to do it by themselves until the tube is
warm enough.

Another thing to consider is that the voltage drop over an average
silicon diode is 0.6...1 Volt, while a DHR may cost you 50 or more,
and a IDHR about 30 or so. This is current-dependable.
So, the SS diodes will have to do most of the work, resulting in more
50 (or 60) Hz supply ripple.
A true bridge, whether tube or solid state will have 100 or 120 Hz
ripple.

In short, I don't see any advantage in such an arrangement.

If you want slow start-up, use a bridge and an indirectly heated
rectifier afterwards.
Or, a huge resistor that gets shorted by a relay after several
seconds.

BTW the "sharp" turn-on of the SS rectifier may be limited by careful
selection of the type of diode , and/or a snubber cap over every diode
in the bridge.

For power supply designing, a good place to look is at
www.duncanamps.com
Look for a program called PSUD.
You can design your supply to your personal wishes and demands and
even see how components will be stressed (or not).

Good luck!

--
Sander deWaal
"SOA of a KT88? Sufficient."

Robert,

Will the tube rectify mask the turn off noise of the semiconductor diode?

Steve

"Robert Casey" wrote in message
...
Stevey wrote:
I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have. Which
one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off of
the
semi rectifier ?
Steve



The circuit will only pass current when both devices are "on". So if
the semi rectifiers turn off first, then no current is outputted no
matter how slow the tube is to turn off. But in a practical sense,
this is not a real issue. The only time rectifiers actually pass
current is at the top of the AC waveform input. And that is to
"top off" the filter caps (assuming no filter choke). The rest of
the amplifier draws off charge from the filter caps, which results
in a slow voltage drop. Then the next AC voltage peak comes along
and "refills" the missing charge. This is the ripple voltage on
the B+.

"Stevey"

I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have. Which
one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off of
the
semi rectifier ?


** Normal rectifier diodes like the 1N4007 have slow turn offs.




............ Phil

Stevey wrote:

Robert,

Will the tube rectify mask the turn off noise of the semiconductor diode?

Steve

I routinely use IN5408 diodes in bridge formation for B+ supplies,
and the diode noise from the PS which finds its way to the output
is less than the HD at all levels.

I cannot see any need to use a combination of SS and tube diodes.

If you want a bridge rectifier *and* slow turn on then use a GZ34/32 rectifier
for a series diode after the C1
of a CLC fiter, with both diodes paralleled.
You may also need to have some series R between the bridge and C1, to keep the
charge
current pulses to the same value as you would have with an all tube rectifier.
This will reduce transformer noise and heat dissipation in the windings, and
trim
the DC working voltage to be equal to what you would get with an all tube
rectifier,
if that is what you wanted in the first place.

I try to situate the rectifier diodes very close to the transformer winding,
with
the tranny in a steel case, so any noise is screened off well.

Patrick Turner.









"Robert Casey" wrote in message
...
Stevey wrote:
I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have. Which
one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off of
the
semi rectifier ?
Steve



The circuit will only pass current when both devices are "on". So if
the semi rectifiers turn off first, then no current is outputted no
matter how slow the tube is to turn off. But in a practical sense,
this is not a real issue. The only time rectifiers actually pass
current is at the top of the AC waveform input. And that is to
"top off" the filter caps (assuming no filter choke). The rest of
the amplifier draws off charge from the filter caps, which results
in a slow voltage drop. Then the next AC voltage peak comes along
and "refills" the missing charge. This is the ripple voltage on
the B+.

"Patrick Turner"

Stevey wrote:


Will the tube rectify mask the turn off noise of the semiconductor
diode?


I cannot see any need to use a combination of SS and tube diodes.


** Cos the tranny has no CT you insufferable old fool.



If you want a bridge rectifier *and* slow turn on ...


* The OP wants slow diode turn off - you illiterate.




............ Phil

I was thinking by using the tube rectifier with semiconductor diodes to
implement
the bridge will lower the noise generated by the diodes. You are saying the
noise
generated by using four diodes is insignificant as long as the right kind of
diode are used ?

Thanks Patrick,

Steve

"Patrick Turner" wrote in message
...


Stevey wrote:

Robert,

Will the tube rectify mask the turn off noise of the semiconductor
diode?

Steve

I routinely use IN5408 diodes in bridge formation for B+ supplies,
and the diode noise from the PS which finds its way to the output
is less than the HD at all levels.

I cannot see any need to use a combination of SS and tube diodes.

If you want a bridge rectifier *and* slow turn on then use a GZ34/32
rectifier
for a series diode after the C1
of a CLC fiter, with both diodes paralleled.
You may also need to have some series R between the bridge and C1, to keep
the
charge
current pulses to the same value as you would have with an all tube
rectifier.
This will reduce transformer noise and heat dissipation in the windings,
and
trim
the DC working voltage to be equal to what you would get with an all tube
rectifier,
if that is what you wanted in the first place.

I try to situate the rectifier diodes very close to the transformer
winding,
with
the tranny in a steel case, so any noise is screened off well.

Patrick Turner.









"Robert Casey" wrote in message
...
Stevey wrote:
I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have.
Which
one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off
of
the
semi rectifier ?
Steve



The circuit will only pass current when both devices are "on". So if
the semi rectifiers turn off first, then no current is outputted no
matter how slow the tube is to turn off. But in a practical sense,
this is not a real issue. The only time rectifiers actually pass
current is at the top of the AC waveform input. And that is to
"top off" the filter caps (assuming no filter choke). The rest of
the amplifier draws off charge from the filter caps, which results
in a slow voltage drop. Then the next AC voltage peak comes along
and "refills" the missing charge. This is the ripple voltage on
the B+.

Phil Allison wrote:

"Patrick Turner"

Stevey wrote:


Will the tube rectify mask the turn off noise of the semiconductor
diode?


I cannot see any need to use a combination of SS and tube diodes.

** Cos the tranny has no CT you insufferable old fool.

Well, young master Obnoxous Twerp, I knew that.

Itd'd be silly using both SS and tube rectifiers when there is a more
sensible option as
I have suggested.
I have tried fast and slow diodes, and heard precisely zero sound change.

If we are to argue about turn off times in rectifiers working in linear PS
running off mains F,
it'd seem an irrelevant argument; I would have though "fast" diodes are only
needed in
HF applications such as SMPS.




If you want a bridge rectifier *and* slow turn on ...

* The OP wants slow diode turn off - you illiterate.

Let them have whatever they want. It won't change the sound.

Patrick Turner.



........... Phil

Stevey wrote:

I was thinking by using the tube rectifier with semiconductor diodes to
implement
the bridge will lower the noise generated by the diodes. You are saying the
noise
generated by using four diodes is insignificant as long as the right kind of
diode are used ?

Thanks Patrick,

Steve

Indeed that's what I meant.
In fact I have tried "fast" SS diodes which ppl claim improves the music,
and heard zero sound improvements.
cheaper standard IN5408 are all you'll ever need.

I have built lots of amps for lots of people.

I have found that power trannies can be slightly mechanically noisy
if you have an SS diode feeding the input cap, especially
if the cap = 470 uF, which is possible with SS diodes, but unthinkable with a
tube rectifier,
where one would use only 47 uF, because tube peak current cannot be allowed to
go above a small value, compared with the 3 amps rating of an SS diode.
The resulting current peaks are higher than a tube rectifier whose electronic
character
is like an SS diode with between 30 and 60 ohms of resistance in series.

So to reduce the high charge currents I use about 50 ohms in series with the SS
diodes.
This reduces the regulation of the B+, but in a tube amp, its not important,
because most are used within their class A ability for 90% of the music.

The ripple voltage with 470 uF will be 1/10 that when 47 uF is used, regardless
of
diode type or series R. If you have a choke of only 1H and a second 470 uF,
the ripple will be reduced by factor = 0.0054, or the same as
10H and 47 uF.
But the 470 uF will give a far lower impedance anchor to the CT of the OPT,
and less didtortion on AB amps.

So with CLC, using 470 uF caps and 1H or 2H choke, the ripple
voltage in the B+ is reduced to quite negligible levels.

Patrick Turner




"Patrick Turner" wrote in message
...


Stevey wrote:

Robert,

Will the tube rectify mask the turn off noise of the semiconductor
diode?

Steve

I routinely use IN5408 diodes in bridge formation for B+ supplies,
and the diode noise from the PS which finds its way to the output
is less than the HD at all levels.

I cannot see any need to use a combination of SS and tube diodes.

If you want a bridge rectifier *and* slow turn on then use a GZ34/32
rectifier
for a series diode after the C1
of a CLC fiter, with both diodes paralleled.
You may also need to have some series R between the bridge and C1, to keep
the
charge
current pulses to the same value as you would have with an all tube
rectifier.
This will reduce transformer noise and heat dissipation in the windings,
and
trim
the DC working voltage to be equal to what you would get with an all tube
rectifier,
if that is what you wanted in the first place.

I try to situate the rectifier diodes very close to the transformer
winding,
with
the tranny in a steel case, so any noise is screened off well.

Patrick Turner.









"Robert Casey" wrote in message
...
Stevey wrote:
I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have.
Which
one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off
of
the
semi rectifier ?
Steve



The circuit will only pass current when both devices are "on". So if
the semi rectifiers turn off first, then no current is outputted no
matter how slow the tube is to turn off. But in a practical sense,
this is not a real issue. The only time rectifiers actually pass
current is at the top of the AC waveform input. And that is to
"top off" the filter caps (assuming no filter choke). The rest of
the amplifier draws off charge from the filter caps, which results
in a slow voltage drop. Then the next AC voltage peak comes along
and "refills" the missing charge. This is the ripple voltage on
the B+.

I'm a user not an engineer, so I can't give you any theory but I do know that
there is a slow turn on with hybrid bridges - I use them in my equipment with
damper diodes. I also have a note here from Morgan Lundberg as follows:

"You can make a bridge rectifier out of a full-wave (dual anode) tube rectifier
and a couple of high-voltage silicon diodes (e.g. UF4007). The latter take care
of the negative half-cycles (anodes connected together to ground, cathodes to
each end of secondary) and eliminate the need for a CT. As the resistance of
the tube dominates heavily, this will probably sound just like a tube
rectifier. The output voltage of this hybrid bridge will be about:
Vout = [Vsec(rms @ intended load current) * 1.4] - 0.7V - volt. drop of tube
rect. at load current The load current and first filter cap. size should be no
bigger than the values given in the tube data. You might also want to check
that the output impedance of the secondary is high enough that you don't exceed
peak current rating of the tube"

I've found that in ballpark figures the voltage out should be about half way
between an all SS bridge and what you'd expect from an all tube bridge (e.g. as
measured in PSUD). Andy

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

"Patrick Turner"
Phil Allison:


I cannot see any need to use a combination of SS and tube diodes.

** Cos the tranny has no CT you insufferable old fool.


Well, young master Obnoxious Twerp, I knew that.


** Blatant stinking lie.



Itd'd be silly using both SS and tube rectifiers when there is a more
sensible option as I have suggested.


** A fool thinks all his worst notions are sensible.

But only a criminal tries to force them on others.





............... Phil

"Stevey" said:

Thanks for the reply. I do mean turn off. I am trying to see if I can
eliminate
the turn off noise of the semiconductor diode.

I'm sorry, but I don't know what you mean by that.
Do you mean plopping noises and/or DC shifts or something when
switching off? Is this an OTL amplifier?
In any case, a simple speaker relay, supplied by a bridge from the AC
filament will shut off the output immediately when you switch off the
amp.

--
Sander deWaal
"SOA of a KT88? Sufficient."

In message , Phil Allison
writes

"Stevey"

I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have. Which
one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off of
the
semi rectifier ?


** Normal rectifier diodes like the 1N4007 have slow turn offs.




........... Phil




Phil is quite right, and I'm surprised everyone else isn't aware of the
phenomena, although as an SMPSU designer then I know that SS diode
turn-off is crucial!

The effect is seen on capacitor input filters, where the diode is only
conducting for short periods. As the voltage on the anode of the diode
drops below the capacitor voltage at the cathode, there is a short but
noticeable reverse conduction through the diode until the stored charge
at the P-N junction has been removed. The reverse conduction can then
very suddenly stop (within picoseconds), causing significant EMC
problems.

The best combination is a fast diode with 'soft recovery'
characteristics, which means that there is not much reverse conduction,
and the small amount of reverse conduction turns off gently.

At 100Hz it's not too much of a problem, but in continuous-conduction
SMPSU power factor correction stages at 100kHz the diode characteristics
can mean the difference between a nice cool power stage, or melted
solder on the legs of the diode.
--
Chris Morriss

Stevey wrote:
Robert,

Will the tube rectify mask the turn off noise of the semiconductor diode?


I would think so, as IIRC a tube rectifier does not conduct backwards
for a short period of time like a SS diode does. Anyway, one can
wire in parallel to each SS diode a high voltage 0.01uF or so cap
(ceramics are fine for this here) with at least 2KV rating. You see
this in AM and SW radios to reduce locally induced noise getting into
the radio's receiver circuits.

Cute idea. My impression is that it will work the same as the tube going on
and like the either going off since that is determined by the caps, not the
diodes.

"Stevey" wrote in message
news:THbPc.210283$JR4.90449@attbi_s54...
I am planning to use a tube rectifier and 2 semiconductor diodes to
implement a bridge
rectifier so I can use the power transformers that I already have. Which
one
will turn off first ?
Will the soft turn off of the tube rectifier mask the sharp turn off of
the
semi rectifier ?
Steve