Noise reduction --- for Solid State rectification (in TUBE AMPLIFIERS)

S

S Swanson

Well-Known Member
I Usually don't care For Mr Carlson's Lab - ( you tube ) But thought I certainly need to grow in this hobby - so took a chance on a video about reducing noise in the power supply - In all fairness the video IS informative - compelling even - His focus was on the use of a low value Cap across the Diodes in the power supply as a way to reduce NOISE - Seems to work -- and then a demonstration of the reduction of NOISE via his test equipment -- IN THAT he was demonstrating the Difference on a TUBE AMPLIFIER - I kept thinking IS THIS COMMONLY done ? or known ?- it seems like a good way to get a Jump on the Noise issue -THOUGHTS--
 
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Yep. I did on our BEWITCH.

The design features a pair of heavy duty 5U4C tubes combined for rectification but still has a pair of diodes in the chain.

I don't have the gear to measure any improvements, but figured it can't hurt.

Certainly sounds no worse. :biggrin:
 
.01 mFd @1 kv ceramic disc caps mounted/soldered across all SS diodes/rectifiers on every tube to SS rectification conversion "music reproducing tube amplifier" that my customers, friends and myself own no matter the brand since my first conversion in1977 to snub the SS rectifier`s high frequency on/off switching noise from getting into the audio circuits.
Felt the desire to do so before there was ever a internet to try to inform me the desirability to do so, based on buying and reading various reputable books on servicing radio/audio electronics.
 
I wonder if you would want to use Y class safety caps in this application, so that a failure (they usually fail open) would increase the noise but reduce the possibility of shorting across the diode?

Just a thought on fail safe design.

Shelly_D
 
shelly_d said:
I wonder if you would want to use Y class safety caps in this application, so that a failure (they usually fail open) would increase the noise but reduce the possibility of shorting across the diode?

Just a thought on fail safe design.

Shelly_D
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I don`t know Shelly, but the earliest SS rectification multi decades old conversion done to my own personal purchased used in 74 or 5 Mc. MC 30ties using standard 1 Kv. rated ceramic disc caps haven`t failed yet.

My SS conversion always uses (2) 1N4007s in series of each rectifier HV leg for best PIV reliability, so there is a paralleled cap across each 1N4007 for a total of 4 with one more from the string of rectifiers output to ground at the rectifier`s socket to snub any residual HF switching noise that might be left over, and can help curtail any outside strong RFI that might find its way into the PS` main HV node (as Barney Fife would exclaim: "Nip it in the Bud" !)
 
Bill Ferris said:
I don`t know Shelly, but the earliest SS rectification multi decades old conversion done to my own personal purchased used in 74 or 5 Mc. MC 30ties using standard 1 Kv. rated ceramic disc caps haven`t failed yet.

My SS conversion always uses (2) 1N4007s in series of each rectifier HV leg for best PIV reliability, so there is a paralleled cap across each 1N4007 for a total of 4 with one more from the string of rectifiers output to ground at the rectifier`s socket to snub any residual HF switching noise that might be left over, and can help curtail any outside strong RFI that might find its way into the PS` main HV node (as Barney Fife would exclaim: "Nip it in the Bud" !)
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I use the same value as you @Bill, 0.01µF @ 1kV, ceramic.

As far back as I can remember I have always bypassed SS rectifiers. I believe the recommendation and explanation was in a Texas Instruments or Motorola "proper use of semiconductors" type of handbook. It really does make a measurable reduction in noise, and I believe they also made reference to reducing possible junction damage due to spikes and transients.

I grabbed a couple of huge fistfuls of caps for this from our local electronics surplus store (anybody remember Addison Electronics in Montreal?) when I was a kid, and I actually still have a bunch left. I use them for general use, ie. across 1N400x and bridge rectifiers. I don't bother with them for my usual favourite, the UF5408, which is an ultrafast rectifier with "soft recovery". It's a very quiet critter, that one :)
 
Yes Sir.
I was also concerned with the "radiated HF switching noise RFI" within the chassis from the rectifiers finding its way into sensitive high gain/impedance circuits raising the overall noise floor.
While I have still bulk amount of previous purchase of 1N4007s from the early nineties, I also have a 100 or so of the UF5408 improved SS rectifiers in a bag for use in high gain audio tube amp tube rect. to SS conversions, and my silly OCD when I occasionally use them, is to also still snub with the ceramic caps as with the 1N4007s, for just incase.
And like you Art, I bulk purchased the .01 @1Kv ceramic decades ago, and find they also function quite well across relay contacts for snubbing 120/240 VAC motor contact arcing applications, thus extending the life of the contacts by reducing carbonizing & pitting.
 
gadget73 said:
Some early solid state rectified things did this from the factory in the early 60s.
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I remember working on an Ampeg VT-22 that had 100nF disc caps across each main rectifier diode. They looked OEM, but you'll never find those bypass caps in any schematic.

Guitar amp manufacturers (especially Ampeg) did post-production mods all the time. Schematics always needed to be looked at with a grain of salt.

:thumbsup:
 
Mr Boochie said:
I remember working on an Ampeg VT-22 that had 100nF disc caps across each main rectifier diode. They looked OEM, but you'll never find those bypass caps in any schematic.

Guitar amp manufacturers (especially Ampeg) did post-production mods all the time. Schematics always needed to be looked at with a grain of salt.

:thumbsup:
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That is what I always worry about - Errors or Mistakes - My untrained eye would not catch --Of course some would ---the more experienced among us == That's not me ---- thank you for the SAGE advice
 
Bill Ferris said:
Yes Sir.
I was also concerned with the "radiated HF switching noise RFI" within the chassis from the rectifiers finding its way into sensitive high gain/impedance circuits raising the overall noise floor.
While I have still bulk amount of previous purchase of 1N4007s from the early nineties, I also have a 100 or so of the UF5408 improved SS rectifiers in a bag for use in high gain audio tube amp tube rect. to SS conversions, and my silly OCD when I occasionally use them, is to also still snub with the ceramic caps as with the 1N4007s, for just incase.
And like you Art, I bulk purchased the .01 @1Kv ceramic decades ago, and find they also function quite well across relay contacts for snubbing 120/240 VAC motor contact arcing applications, thus extending the life of the contacts by reducing carbonizing & pitting.
Click to expand...
Bill Ferris said:
I don`t know Shelly, but the earliest SS rectification multi decades old conversion done to my own personal purchased used in 74 or 5 Mc. MC 30ties using standard 1 Kv. rated ceramic disc caps haven`t failed yet.

My SS conversion always uses (2) 1N4007s in series of each rectifier HV leg for best PIV reliability, so there is a paralleled cap across each 1N4007 for a total of 4 with one more from the string of rectifiers output to ground at the rectifier`s socket to snub any residual HF switching noise that might be left over, and can help curtail any outside strong RFI that might find its way into the PS` main HV node (as Barney Fife would exclaim: "Nip it in the Bud" !)
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Funny quote - I have heard variations of that - one being nip it in the BUTT - not sure what that means - but the thought is probably the same -- Hear with the Question should I do it ? that is Shunt (correct word? ) the Diode? So far I am getting a yes -- seems nothing to loose and a amp with a little less noise seems a no- brainer
 
by some manufacturers its been done for 30 years in both tube and SS gear. Others do very little to lower the noise.

You may also want to consider trying to run that diode noise to ground by adding a small film bypass cap on your main PS filter cap.
 
Be easy enough to check with a scope or signal tracer, and do either a direct or comparative difference check with or without.

For whatever its worth I haven't ever noticed hash or blips on the HV output from stuff I have put silicon in but I've also never made it a point to really look.
 
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