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Old 21st October 2004, 10:23 PM   #1
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Question Ss Diodes??

A lot of diodes out there and Iím a little bit . There are fast recovery, ultra fast, schotky, e.t.c.
I have seen the MUR ones, HFA, BYV and some other I donít remember.
I know that many of you out there had tried some of them and have an opinion upon this topic.
Which to choose?
Over here you will ask me, for how many Volts and how much current.
Iíd like to put them in the PSU of my P-P amp. One PSU for two 6L6 P-P channels (L+R). Iíll use HT at 420V and about 50-60mA idle current.
Mention that secondary will be with CT so, not bridge over here.
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Old 22nd October 2004, 12:30 AM   #2
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Hi,

Quote:
Iíll use HT at 420V and about 50-60mA idle current.
Basically you want the diodes to be as "quiet" as possible.
As you may know solid state diodes_at least most of them do_exhibit commutation peaks that can cause reverse voltage peaks and create nasty RFI noise.

The better types_for audio use_ are the ones commonly known as "soft recovery" types or better still Schottky diodes.
Unfortunately for high voltages the new silicium carbide Schottky diodes are just hitting the shops and are relatively expensive.
The only manufacturer of such diodes I know of is U.S. based Cree.

By using snubber networks across each individual diode, ordinary diode types can be made pretty quiet but the values of the RC network components are best determined by experimenting while looking at an o-scope's output.

All in all, a tube rectifier is still the better way IMO. A damper diode is reported to give excellent results as do the hybrid rectifiers using a pair of SS diodes and a FW tube rectifier configured as a Graetz bridge.

Be ware that SS diode cause considerably less voltage drop than any tube diode would.

Cheers,
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Old 22nd October 2004, 01:29 AM   #3
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Default Re: Ss Diodes??

Quote:
Originally posted by resident
A lot of diodes out there and Iím a little bit . There are fast recovery, ultra fast, schotky, e.t.c.
I have seen the MUR ones, HFA, BYV and some other I donít remember.
Well, application specific of course. High speed diodes (including schottky) are only needed in high speed applications such as switching power supplies. Normal recovery and/or glass passivated (more durable, AFAIK) types are suitable for 50/60Hz operation.

All diodes posess a recovery time, which means it keeps conducting after the terminal voltage reverses. (Normal recovery is on the order of 1uS, compared to the 8.33mS half cycle of 60Hz AC. Schottkys are down around 5nS!) This pulls current back out of the filter capacitor, causing a momentary current spike. This most commonly manifests itself as noise coupled through the power transformer to the heater winding - any amplifier of mine which had diode noise was quieted right down with proper heater practices.

Quote:
Iíd like to put them in the PSU of my P-P amp. One PSU for two 6L6 P-P channels (L+R). Iíll use HT at 420V and about 50-60mA idle current.
Mention that secondary will be with CT so, not bridge over here.
Er, stereo PP 6L6's? That's going to draw four times what you claim (around 250mA).

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Old 22nd October 2004, 03:46 AM   #4
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I have tried a hybrid Graetz bridge, with MUR4100E SS diodes in the negative half and 6D22S TV thermionic damper diodes in the positive half. This arrangement is supposed to be just as quiet as an all-thermionic bridge.

I then tried an all-SS bridge, to get a bit more voltage. I didn't notice any increase in noise as a result. However, I'm using smoothing chokes and 0.1uF capacitors in parallel with the normal electrolytic smoothing capacitors, which I suppose must help in getting rid of any noise from the diodes.
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Old 22nd October 2004, 07:07 AM   #5
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Quote:
I didn't notice any increase in noise as a result.
Diode noise is not something you are likely to hear in isolation. It does, however, change the sonic character of the amp in a very profound way no matter how many chokes you have in the PS and how much you've tweaked the heaters.

I haven't tried schottkys but all other SS rectifiers i've tried sounded as crap.
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Old 22nd October 2004, 07:50 AM   #6
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Quote:
I haven't tried schottkys but all other SS rectifiers i've tried sounded as crap.
I must admit, I expected to hear some averse effect from changing to all-SS rectification but I didn't. However, I can't claim to have carried out any real comparison testing. Anyway, quite a few modern designs use SS rectification, so I suppose they can't be all that bad.
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Old 22nd October 2004, 01:08 PM   #7
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I see that many of you prefer diode rectifiers.
I have done the holes so, I don't know if I can put a diode rectifier.

If I can, which do you suggest?Remember that I'm using only one PSU for two channels.
Quote:
Er, stereo PP 6L6's? That's going to draw four times what you claim (around 250mA).
Yes I know.I'm thinking to use a diode up to 0.5A.
@analog sa
Quote:
I haven't tried schottkys but all other SS rectifiers i've tried sounded as crap.
Don't be so sure about this.Many people prefer SS diodes.What are they?Stupid?
Many people prefer SS amps!Many people prefer SE amps and many P-P.Other prefer horns and other normal ones.
Who is wrong????????????????????????????????????????
@sch3mat1c
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any amplifier of mine which had diode noise was quieted right down with proper heater practices.
With proper heater practices?What do you mean?
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Old 22nd October 2004, 02:53 PM   #8
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Quote:
Many people prefer SS diodes.What are they?Stupid?
You'd be amazed as how many are actually stupid . Or deaf.

Commercial equipment understandably prefers SS; if i were a manufacturer i wouldn't hesitate using SS too - cheap, easy, less PS troubles, reliabilty, good bass; and how many of the potential customers can hear anyway?

The issue with the bass is btw a real one. None of the vacuum rectifiers i've tried produce particularly good bass. If you want really high quality bass you need MERCURY. I don't think any manufacturer would ever dream of using such devices in a commercial venture. And most DIYers with children, pets or wives may think twice.
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Old 22nd October 2004, 06:00 PM   #9
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Quote:
You'd be amazed as how many are actually stupid . Or deaf.
I agree with you!

Quote:
If you want really high quality bass you need MERCURY.
Mercury?Mmmm...This is brand of tube rectifier?Which type of tube?

Quote:
Commercial equipment understandably prefers SS; if i were a manufacturer i wouldn't hesitate using SS too - cheap, easy, less PS troubles, reliabilty, good bass; and how many of the potential customers can hear anyway?
ha ha LOL!
Yes, how many can hear anyway?I have visit many that listen from crap systems and I can't believe that they like them.I'm not an expert but I have listen good systems(most of them are diy) and I'm trying to upgrade mine ,too.
Anyway thanks that you are helping me and sorry if I reply to you a little bit awfull.
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Old 22nd October 2004, 07:51 PM   #10
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Quote:
Originally posted by analog_sa
Diode noise is not something you are likely to hear in isolation. It does, however, change the sonic character of the amp in a very profound way no matter how many chokes you have in the PS and how much you've tweaked the heaters.
If there has EVER, ANYWHERE been a better argument for the truth of psychoacoustics, I haven't read it.

Tim
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