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Just came back home, turned on my amp, and one of my RCA 5U4G rectifier tubes flashed for half a second. I have only had these rectifiers in for about a week now but it hasn't happened prior to this. I know this is common in some tubes. It's also weird how only one of them did this. Any clue?
Follow Ups:
so, guys, if I replace the 1200 ufd caps with say, 40 ufd caps, am I good to go and stop flashing the rectifiers, or is there more to this that would need to be done? thanks
Yikes! 1200 mike after a tube rect. With 40 mike caps it'd hum like billyo. I'd convert the psu to a CLC system if the amp was mine and there was space, say 40 mike then 5 henry low DCR choke (to replace that 20 ohm resistor) followed by 200 mike etc. The power tranny would have a much easier time of it too.
Just my thoughts
Todd
Dennis Hadd is insane with that circuit and he basically uses it in every amp from the cheapest AES to the top of the line Cary. He bought loads of the 1200uf@450v nichicon caps and hooks them in series for 600uf@900v but,coming straight out of 5ar4 or 5u4 is just not feasible.
I can understand him using that in his amps with Solid state rectification but not coming directly coming off a rectifier tube.
If the power supply waveform isn't pretty,neither is the sound in most cases.
He leaves behind a legacy of some of the poorest examples of audio engineering from a "major hi-end" manufacturer.
Dennis Had is a business man. He knows thru the school of hard knocks how to extract maximum dollars for a product. He started years ago with little and is a millionaire today. His previous background was building RF amplifiers for the ham radio community with some great RF amps that are collector items today.
And your point is what? He went thru the school of hard knocks and therefore wore a chip on his shoulder and was entitled to screw his customers?
Every direct customer service contact/dealing I ever had (no pun intended)with Cary Audio was handled poorly.
I own a Cary pre-amp. The power supply as supplied from the factory was an absolute piece of garbage. I lost many valuable 6922 tubes until I figured out how to fix the problem. Basically, I had to re-engineer the PS and wound up rebuilding much of the rest of the unit.
Point is, he is not an audio designer. Never was.
correct.
I think he meant well but the main point was the bottom line. I used to make isolation bases for Cary Audio, back in the 90's and I believe he wanted everyone to do well but there was the bottom line first, which is most always the way it is.
My amp had a 1200uf right after the tube (2) rectifier not in series but presented a 1200uf "short".
So Denny retired. When did that happen?
The Elaborate DAC=Johnny's Balloon Meshplate 27 Balanced Preamp=Balanced Six Pacs=Newform Research 645
iRiver H140/MB-1 dual dac/Monica II Dac, modified Woo 6/Protector Balanced amp/Ultrasone Ed. 9/JH13 Pro IEM's
see images at: www.pbase.
in terms of max voltage and power dissipation, or am I thinking of some other geezer?
You mean David Manley? smile......................sky high voltage.............everything run at the ragged edge ................ He ran 7189's from the TT {tiny triodes} in pentode @ 525 volts Sansui 500 A I own runs them in pentode @ 460 volts on the plate and I thought THAT was outrageous. I suppose if you back off the current one could go even higher but sheesh. I have had the same GE 7189 A's running about 2-4 hours a day for a year now for the living room XM/TV set up. Maybe they are tougher than I think and Manley knew it..................maybe I'm too conservative.
The Mind has No Firewall~ U.S. Army War College.
put in some horrible PCB on the tube amps that were dangerous.
The Elaborate DAC=Johnny's Balloon Meshplate 27 Balanced Preamp=Balanced Six Pacs=Newform Research 645
iRiver H140/MB-1 dual dac/Monica II Dac, modified Woo 6/Protector Balanced amp/Ultrasone Ed. 9/JH13 Pro IEM's
see images at: www.pbase.
That a company of this stature would design such an obviously flawed power supply, and offer zero support to fix the problem.
Jeff
when I realized that the string of NOS pre-war and mil-spec 5U4G I have gone through were sacrificed, expensively, for this design flaw. I had thought it was the tubes, or me, and here it is the fracking design.
Lots of good tubes lie dead in the tube burial ground. I really am sorta pissed at my dealer and Dennis, as they surely knew about this--and my amp even got a Cary recommended modification to ease the start-up problem. I guess it wasn't enough.
Sidebar: I recently talked to Cary about this and they insist on me using directly heated rectifiers like the 5U4G that I have been using, and not the indirectly heated ones like the 5V4--which was the original spec'ed rectifier. Whatever. Dennis, want to buy an interesting rectifier sculpture??
Jeff,
The 5V4 is even less tolerant of a large 1st filter cap. value than the 5U4 is. It's a miracle that any vacuum rectifier survives even 1 turn on cycle in that PSU design.
What you can do is to install 1200 PIV Silicon carbide (SiC) Schottky diodes, along with resistors, in an Octal plug everywhere a 5U4 goes in those questionable designs. SS diodes are not much faster turning on than directly heated vacuum rectifiers are. Schottky diodes are just as quiet as vacuum diodes. The part you need is made by Cree. It's DigiKey stock # C2D05120A-ND and the cost is $9.32 per diode. Yes, that's expensive "grit", but it's a heck of lot less costly than blown 5U4GBs, NOS or current production, are.
Is a schematic available for perusal?
Eli D.
It seems to me that the circuit not only demands too much of the rectifiers at switch-on, but also at switch-off.
Unless PIV is an issue all the time in operation, I actually forget.
;-)!
valve rectifiers sound better though, eh!? Sag and stuff?! ;-)!
Tim B
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/tim_bailey.htm
Best to find a location to put in a 10uf Solen and a 50 ohm resistor before the existing B+ string.
___
Long Live Dr.Gizmo
I said 1200 PIV Schotkys, with resistors wired in series. The idea is to roughly emulate 5U4 forward drop, while having large 1st filter capacitance tolerance.
One way or another, the rail voltage has to come in right. On that point, we are in agreement.
Eli D.
But no luck.
Jeff
Greetings- In this particular power supply, there is a .22 uf cap before the 1200 uf cap. Do you think that is enough capacitance to soften the "blow" of the big 1200 uf??? regards, wpod
Wow! Talk about asking for trouble...
The .22 uf is in parallel with the 1200 uf, so it will actually add a tiny bit more to the rectifier's woes.
And a standby switch - boy, when you throw that switch with a discharged 1200 uf cap and a hot CV378 - it's amazing they don't pop every time!!
Plus - do I see the 450 volt caps are exposed to 465-470 volts??
Essentially all that is limiting the inrush current is the power trafo secondary winding resistance. And it's not just on startup that large current pulses will occur.
This PS needs some re-engineering if you intend to use a tube rectifier. Don't waste those expensive RCAs!! Keep in mind too that a recto failure can cause other damage.
If this schematic and the voltages on it are accurate it is a totally irresponsible and wreckless design IMHO. I find it hard to believe any commercial amp maker would employ this circuit. There is much more wrong with it than right with it!
Hundreds of these lovely tubes have burned up prematurely in these poorly designed amps. Grrrrrrrrrrrrr!
Jeff
Trolling around the web revealed a few posts from people having the same problem. One even said that their questions to Cary Audio went unanswered. Now that's costumer service for ya.
You should send them the bill for all those roasted rectifier tubes. I bet you won't get a reply.
Jeff
I have posted some recent messages about this topic concerning my Cary amp. The gist is, Cary employs a circuit that can really tax rectifiers, may cause them to arc now and then, and probably kills them before their time. There have been some suggestions made. Do a search.
Edits: 04/17/10
but they tax their rectifiers so bad that the are often good for a week or two, sometimes less, sometimes, if a good 5AR4, longer. A thermistor or inductor but most of the time there isn't going to be room for the right sized inductor so thermistor, L90, right after the rectifier.
The Elaborate DAC=Johnny's Balloon Meshplate 27 Balanced Preamp=Balanced Six Pacs=Newform Research 645
iRiver H140/MB-1 dual dac/Monica II Dac, modified Woo 6/Protector Balanced amp/Ultrasone Ed. 9/JH13 Pro IEM's
see images at: www.pbase.
Edits: 04/17/10
So, I'm assuming that my Cary amp is taxing the rectifiers and this one particular rectifier is on its way out?
My amp is the Cary SLI-80 F1, All Triode/Zero NFB, with v-caps
bullshit.......i've had the same nos rca 5u4G cokebottle rectifiers in my sli-80, f-1 for 5 years now...running an average of 4 hours a day, everyday. nary a problem....the amp continues to satisfy me immensely
I also have a Cary SLI-80 (but not triode-wired) upgraded by 0.22uf V-caps. I am going to replace them with Jensen CIO caps as I attribute a somewhat dry and mechanical sound to V-caps.
Never had a problem with rectifiers (always used 5U4G type - Sylvania, RCA and Kenrad). The stock Sovtek 5U4G rectifiers produce much cleaner sound (not mellow and dark as with vintage rectifiers).
Also, this started happening once I changed the output tubes. I'm going to switch back to the EH 5U4GB and see if it still happens.
Do you change the bias every time you change recfifier tubes?
Not sure if that is directed towards me, or in general, but yes I do. It's easy enough to do. Better safe than sorry.
So, I switched to the EH rectifiers that I had previously and there was no flashing or sparks.
Not all new production are safe: I blew up a JJ 5U4GB a while ago.
Some tubes will not do it, at least for a while. My gripe is the more desirable NOS tubes will do it, and get blowed up before long.
On the bright side, rectifiers of this type are cheap and plentiful still.
RCA 5U4GB actually. Not sure if it makes a difference.
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