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john dozier 7th June 2011 06:50 PM

Silicon carbide rectifiers
 
Has anyone used these in tube amps? Are they a substantial improvement in SQ over hexfreds? Thanks for any input as I am considering using them.

hesener 7th June 2011 08:26 PM

yes, I tried them and they perform wonderful, very low noise. make sure to limit the surge current on turn-on as (at least the first generations of) SiC diodes did not appreciate, and left for the big electron hunting grounds somewhere over the rainbow after a few turn-ons......

CZ101 6th August 2011 12:58 AM

Quote:

Originally Posted by hesener (Post 2597977)
yes, I tried them and they perform wonderful, very low noise. make sure to limit the surge current on turn-on as (at least the first generations of) SiC diodes did not appreciate, and left for the big electron hunting grounds somewhere over the rainbow after a few turn-ons......

Would you (or anybody) care to elaborate on this?

I just purchased some Cree SiC rectifier diodes that I intend to install in a Peavey Classic 30 guitar amp.

Is there anything I should look out for regarding these diodes in an amp such as this?

CZ101 6th August 2011 01:25 AM

Quote:

Originally Posted by hesener (Post 2597977)
yes, I tried them and they perform wonderful, very low noise. make sure to limit the surge current on turn-on as (at least the first generations of) SiC diodes did not appreciate, and left for the big electron hunting grounds somewhere over the rainbow after a few turn-ons......

Would you (or anybody) care to elaborate on this?

I just purchased some Cree SiC diodes as replacements for the N10003's and N10007's in my Peavey Classic 30 guitar amp.

Should I be concerned about in-rush current?

hesener 8th August 2011 08:54 AM

Hi, as with rectifier tubes the surge current coming from turning on at peak input voltage and empty 'lytics can kill SiC rectifier diodes - the first generatiosn just were not up to the task. Newer generations should be fine, but remember they are not built for this purpose, rather for high-frequency rectification in PFC circuits - usually they don'T see high current peaks in that application.

What type of diodes have you bought (part numbers), what does the data sheet say (peak current rating, usually in the "absolute maximum ratings" section)? Are you using chokes in this amplifier, and how large are the capacitors?

CZ101 9th August 2011 09:38 PM

Quote:

Originally Posted by hesener (Post 2664456)
Hi, as with rectifier tubes the surge current coming from turning on at peak input voltage and empty 'lytics can kill SiC rectifier diodes - the first generatiosn just were not up to the task. Newer generations should be fine, but remember they are not built for this purpose, rather for high-frequency rectification in PFC circuits - usually they don'T see high current peaks in that application.

What type of diodes have you bought (part numbers), what does the data sheet say (peak current rating, usually in the "absolute maximum ratings" section)? Are you using chokes in this amplifier, and how large are the capacitors?

Thanks Hesener for your reply...


For the 1N4003 (still getting used to these part #'s) replacements, I got these: C3D02060F

Forward Repetitive Surge Current @25 ̊C - 12A, @110 ̊C - 7.8A
Non-Repetitive Forward Surge Current @25 ̊C - 20A, @110 ̊C - 16A
Non-Repetitive Peak Forward Surge Current 10 μs Pulse @25 ̊C - 65A

post-rectifier filter capacitance ≈ 6,600 μF (w/ Roederstien EGM's - up from 4,400 μF stock caps)

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

and for the 1N4007 replacements, these: C4D02120A

Forward Repetitive Surge Current @25 ̊C - 13A, @110 ̊C - 8A
Non-Repetitive Forward Surge Current @25 ̊C - 19A, @110 ̊C - 16.5A

post-rectifier filter capacitance ≈ 160 μF (stock value w/ F&T and Evox Rifa replacements)

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

I've read about people using MOV's to limit in-rush current for solid-state rectified tube amps. The rationale has something to do with the heaters being given enough time to warm up so as to avoid cold-cathode tube damage. Would the MOV's be advisable?

It seems that the MOV's could have a damping effect on the amplifier's peak current demands...

metalsculptor 13th August 2011 09:56 AM

Quote:

Originally Posted by CZ101 (Post 2666480)

I've read about people using MOV's to limit in-rush current for solid-state rectified tube amps. The rationale has something to do with the heaters being given enough time to warm up so as to avoid cold-cathode tube damage. Would the MOV's be advisable?

It seems that the MOV's could have a damping effect on the amplifier's peak current demands...

I assume you mean NTC thermistors not MOV's a MOV will not work as an inrush current surge limiter.

Use the usual resistor relay arrangment on the primary of the HV transformer with a separate heater supply this will not suffer from the NTC thermistor limitations.
With 4000 uF of filter you might also want to delay the turn off of the heater supply as well if having HV with a cold cathode is a concern.

CZ101 14th August 2011 05:36 PM

Quote:

Originally Posted by metalsculptor (Post 2670390)
With 4000 uF of filter you might also want to delay the turn off of the heater supply as well if having HV with a cold cathode is a concern.

AKAIK the 6,600uF is for the heater supply - which will obviously drain more slowly than the 160uF

hukkfinn 16th March 2013 05:09 PM

Quote:

Originally Posted by john dozier (Post 2597878)
Has anyone used these in tube amps? Are they a substantial improvement in SQ over hexfreds? Thanks for any input as I am considering using them.

We used $1.06 Cree SiC rectifiers in a power supply for a tubed preamp recently and they sounded much worse than hexfreds. The SiC's had a funky, weird quality in the high end that made the system almost unlistenable.

NOTE that this power supply is very unusual, so using them with something normal might yield different results.

Back to hexfreds for us.

metalsculptor 17th March 2013 09:13 AM

Quote:

Originally Posted by hukkfinn (Post 3413741)
We used $1.06 Cree SiC rectifiers in a power supply for a tubed preamp recently and they sounded much worse than hexfreds. The SiC's had a funky, weird quality in the high end that made the system almost unlistenable.

Any chance of connecting an AC coupled oscilloscope to the B+ and posting a picture of the trace when the undesirable effect manifests itself?


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