4 Blown Soft Recovery Diodes...Are TV Damper Tubes more Reliable? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 26th January 2015, 09:22 PM   #1
diyAudio Member
 
Join Date: Dec 2010
Default 4 Blown Soft Recovery Diodes...Are TV Damper Tubes more Reliable?

Just wondering how reliable soft recovery diodes are. Namely the NTE569.

600V, 3A, 250ns switching time.

I used 4 of them for a bridge...my 3A breaker tripped and found all were testing 600ohms both ways. I love breakers rather than fuses.

The power supply was a 120Vpri. -230Vsec. Isolation Transformer going to the bridge. 100u capacitor as the 1st cap. Both EL34 Tubes are pulling 40mA each -80mA total.
No humming was observed before the breaker tripped and a whisp of white smoke from the transformer. The Transformer core was still cool I'm guessing the wires rapidly heated.

I believe that 1 diode went out first as I have been getting more vibration from the transformer from influx current when turned on... Plus the amp was clipping...I'm thinking power starvation.
I'm still trouble shooting how this happened...

I had a ST35 diode go out as well last year. I didn't build it...

I've been considering using tube rectifiers...I have 2 6AX4GTB's.
Are tube rectifiers more reliable...or do they go as suddenly?

I haven't blown any tubes...burned up transistors and mosfets when making SS amps though a few years ago. (cutting my teeth on electronics) Tubes just seem more rugged in general.
  Reply With Quote
Old 26th January 2015, 09:51 PM   #2
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 7
Quote:
Originally Posted by rcollege View Post
Just wondering how reliable soft recovery diodes are. Namely the NTE569.

600V, 3A, 250ns switching time.

I used 4 of them for a bridge...my 3A breaker tripped and found all were testing 600ohms both ways. I love breakers rather than fuses.

The power supply was a 120Vpri. -230Vsec. Isolation Transformer going to the bridge. 100u capacitor as the 1st cap. Both EL34 Tubes are pulling 40mA each -80mA total.
No humming was observed before the breaker tripped and a whisp of white smoke from the transformer. The Transformer core was still cool I'm guessing the wires rapidly heated.
They're plenty reliable, but you were pushing that 600V spec. I would prefer more leeway than that. Also, did you connect a MOV across the primary? A bypass capacitor across the secondary? (I like 0.015uF/3.0KV capacitors for this) SS diodes need protection from high voltage spikes. For these voltages, I'd prefer 1.0KV diodes. So far, I haven't lost one yet.

Quote:
I've been considering using tube rectifiers...I have 2 6AX4GTB's.
Are tube rectifiers more reliable...or do they go as suddenly?

I haven't blown any tubes...burned up transistors and mosfets when making SS amps though a few years ago. (cutting my teeth on electronics) Tubes just seem more rugged in general.
Hollow state diodes are tougher when it comes to occasional spikes. However, they can poof just as suddenly, especially when they go gassy. Then you'll get arcing on power-up. Low heater voltages can cause that too since cool cathodes compromise the PRV and Isurge ratings.

If you convert from SS, keep in mind you will lose voltage since the forward voltages of hollow state diodes is a good deal higher than that of Si diodes.

Hope you didn't poof the PTX.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 26th January 2015, 10:01 PM   #3
diyAudio Member
 
oldschooltube's Avatar
 
Join Date: May 2011
Location: Quad Cities USA
I like using tv damper diode tubes as well for rectifiers. They do have their drawbacks however. First cap generally cannot be over 40uF and they have significantly more voltage drop as compared to ss diodes. The heaters usually are quite power hungry too. If you account for these things before a build all is usually well but retrofitting in place of solid state diodes in my experiences usually means changing power transformer too.

As far as reliability they will last for years if operated within their acceptable limits. They will however die a spectacular death if the limits are grossly exceeded.
__________________
Marty: "Why don't you just make 10 louder?"
Nigel: "...These go to 11."
  Reply With Quote
Old 27th January 2015, 12:34 AM   #4
diyAudio Member
 
Join Date: Dec 2010
Thanks for your replies. I haven't used the bypass caps.

Am I reading the data sheet right? It seems the 6ax4 can put out 125mA
So my power supply would be limited to 125mA...for input capacitor filtering?
Is this correct?
I have a 470vct 200mA transformer...i want to use to run some 6l6gc's, 6550's, el34's in triode mode. 2-3watts would suffice.

Just trying to learn about the tube rectifiers to avoid accidental firework displays.

Last edited by rcollege; 27th January 2015 at 12:38 AM.
  Reply With Quote
Old 27th January 2015, 09:16 AM   #5
diyAudio Member
 
Join Date: Aug 2008
The bridge blew because you were running it at the limit. Solild state devices need to be derated for real world usege, you cant use them for max current AND max voltage AND higher temperature at the same time.You can find all this info in the datasheet.
Also, tube rectifiers waste a lot of heat.
Anyway, I use like fast-soft recovery diodes for my projects, Philips BYM- series, 600V or 1000V
  Reply With Quote
Old 27th January 2015, 10:53 AM   #6
piano3 is offline piano3  United Kingdom
diyAudio Member
 
Join Date: Aug 2010
Location: London,UK
I'm confused; why is a single 230V RMS winding pushing the specs of 600V diodes in a bridge?
  Reply With Quote
Old 27th January 2015, 01:38 PM   #7
GoatGuy is offline GoatGuy  United States
diyAudio Member
 
Join Date: Dec 2012
Location: SF Bay Area
230 V × 1.414 = 352 V
Technically, that's not pushing the diodes.
But, if you have spikes coming down the mains…

Alternately,
Might be the pulsed amperage that the 100 μF first-caps induces.
A quick-fix is just to put a simple resistor in series.
Drops the total HV some, but rarely matters much.
Especially if you're giving consideration to vacuum-state rectification.

That whiff of white smoke from the transformer … might seem innocuous enough, but to me it sounds not-so-good. You might want to just test the open output 230 V winding, isolated from the rest of the now-dead bridge rectification section. Easy to do. "turn it on". There should be no more smoke. If there is, its developed an internal short, and things will get progressively more expensive to repair.

Whatever Miles Prower sez… is also to be taken as golden.

GoatGuy
__________________
Five things matter in audio · LED underlit tubes, gold connectors bearing bright plastic ID bands, speaker cable thicker than your thumb, a hundred pounds of granite under the turntable, and those little spikey-things under the speakers.
  Reply With Quote
Old 27th January 2015, 02:05 PM   #8
diyAudio Member
 
Tom Bavis's Avatar
 
Join Date: Jun 2002
Location: Macedon NY
+352V peak on the filter cap, -352 on the negative peak of AC when it reverses, so 704V. This is split across two diodes in a full-wave bridge, so SHOULD be OK. But unequal leakage and / or capacitance in the diodes will result in unequal voltage drop in the reverse direction. And of course, transients DO occur.
  Reply With Quote
Old 27th January 2015, 02:29 PM   #9
GoatGuy is offline GoatGuy  United States
diyAudio Member
 
Join Date: Dec 2012
Location: SF Bay Area
Default reverse balancing resistors

Quote:
Originally Posted by Tom Bavis View Post
+325V peak on the filter cap, –325 on the negative peak of AC when it reverses, so 650V. This is split across two diodes in a full-wave bridge, so SHOULD be OK. But unequal leakage and / or capacitance in the diodes will result in unequal voltage drop in the reverse direction. And of course, transients DO occur.
And there you are: FACTS… much better ones.

Tom Bavis cites why it is a REALLY good idea to bypass diodes with high-value resistors. 1 MΩ is good. Use ˝ watt. 10%, carbon comp is fine. And … get either 800 PIV diodes or 1000 PIV diodes.

So... put one in parallel with each diode.

GoatGuy
__________________
Five things matter in audio · LED underlit tubes, gold connectors bearing bright plastic ID bands, speaker cable thicker than your thumb, a hundred pounds of granite under the turntable, and those little spikey-things under the speakers.
  Reply With Quote
Old 27th January 2015, 02:52 PM   #10
Merlinb is offline Merlinb  United Kingdom
diyAudio Member
 
Merlinb's Avatar
 
Join Date: May 2006
Location: Lancashire
Quote:
Originally Posted by piano3 View Post
I'm confused; why is a single 230V RMS winding pushing the specs of 600V diodes in a bridge?
I suspect the OP is actually using a two-phase rectifier, not a bridge rectifier. These diodes should have no trouble in a 230V bridge rectifier.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
TV Damper Diodes Jack Thomas Tubes / Valves 8 10th September 2007 05:23 PM
tv damper diodes jarthel Tubes / Valves 1 19th April 2007 04:41 AM
TV Damper Diodes CarlyBoy Tubes / Valves 5 19th November 2006 10:20 PM
Schottky or ultrafast soft recovery diodes? novec Power Supplies 10 21st September 2006 01:57 PM


New To Site? Need Help?

All times are GMT. The time now is 05:27 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright ©1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2