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tube rectifiers [message #8308] Wed, 07 July 2004 17:31 Go to next message
rohit is currently offline  rohit
Messages: 5
Registered: May 2009
Esquire
Greetings all,
I am building a tube amp and considering rectification. I can use tube diodes, standard silicon diodes or FR diodes. I would like some input on this subject.
Rohit

Re: tube rectifiers [message #8311 is a reply to message #8308] Wed, 07 July 2004 23:17 Go to previous messageGo to next message
metasonix is currently offline  metasonix
Messages: 103
Registered: May 2009
Viscount
A tube rectifier has a major advantage, built-in slow warmup. But it has a lot of disadvantages--wasting power, needing a separate filament winding, causing massive destruction if it develops gas, etc.

Cheap diodes have slew-rate problems which can increase the noise floor in the amp. I'd use FREDs, and a time delay switch or standby switch. And recommend you precede each diode with a 100-ohm 5w resistor to reduce the turn-on surge. That simple trick can increase reliability of the power supply considerably.

Re: tube rectifiers [message #8312 is a reply to message #8311] Thu, 08 July 2004 06:41 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Mr M; Do you mean that the tube rectifier wastes amplifier power or electricity? Can you wire the standby switch to become completely removed from the circuit after warm-up? Thanks Again,J.R.

Re: tube rectifiers [message #8313 is a reply to message #8311] Thu, 08 July 2004 16:59 Go to previous messageGo to next message
rohit is currently offline  rohit
Messages: 5
Registered: May 2009
Esquire
Thanks for your reply,
I think I prefer FREDs, but I do not understand why one would not want the DC level to raise to full value right away. If there were a surge as like happens from low resistance filaments in circuit, I could understand. There is not. Why is having full rail voltage on output tube plate during warmup of its filament a problem?
Rohit

Re: tube rectifiers [message #8314 is a reply to message #8312] Thu, 08 July 2004 22:43 Go to previous messageGo to next message
metasonix is currently offline  metasonix
Messages: 103
Registered: May 2009
Viscount
>Why is having full rail voltage on output tube plate during warmup of its filament a problem?

It can cause damage to the tube's cathode coating. It is called cathode stripping. A problem mostly to power tubes running from plate supplies of 400v or greater. IMO, new current production power tubes are more prone to this than NOS.

>Do you mean that the tube rectifier wastes amplifier power or electricity?

It wastes electricity, adds heat to the system (never a good thing), and represents an additional stress on a power transformer.

>Can you wire the standby switch to become completely removed from the circuit after warm-up?

No. Why would you want that?


Re: tube rectifiers [message #8317 is a reply to message #8314] Fri, 09 July 2004 17:34 Go to previous messageGo to next message
rohit is currently offline  rohit
Messages: 5
Registered: May 2009
Esquire
Thanks for your advices,
I think there is no harm adding a delay relay for B+. Please tell me more about "cathode stripping" and what exactly is causing it. What is exactly happening?
Rohit

Re: tube rectifiers [message #8318 is a reply to message #8314] Fri, 09 July 2004 20:44 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Cathode stripping, how would you know it's happening? Then only if the B+ is high, say if you are using 211 triodes or somesuch why is it an issue? Also the power trans. needs to be a little beefier with tube rec. that shouldn't be too difficult. I'm just playing devils advocate here but in the case of the surge circuit wouldn't you want all switches and/or relays out of the circuit if at all possible? Thanks again, J.R.( The KT88 amp looks nice but too powerful, whatever happened to that nice PP 2a3 amp J. Eckland built? When are we going to hear from Natalie Stone again, does she know she has a fan club? Motorcycles and Altec 287 amps; There _is_ a God!)

Re: tube rectifiers [message #8319 is a reply to message #8318] Sat, 10 July 2004 02:44 Go to previous messageGo to next message
metasonix is currently offline  metasonix
Messages: 103
Registered: May 2009
Viscount
>Cathode stripping, how would you know it's happening?

You wouldn't---it damages the coating and shortens the tube's life.
It leaves no other traces.

>Then only if the B+ is high, say if you are using 211 triodes or somesuch why is it an issue?

Only applies to oxide cathodes or oxide-coated filaments. Power tubes with thoriated filaments (like most 211s) are not harmed by it.

>the case of the surge circuit wouldn't you want all switches and/or relays out of the circuit

I don't agree in the case of COMMERCIAL amps. They have to be reliable and usable. You can wire your own amp however you wish. And accept any reliability issues that result.

>whatever happened to that nice PP 2a3 amp J. Eckland built?

He's still got the thing and it does sounds great--but not as good as the KT88 amp!

>When are we going to hear from Natalie Stone

Beats me--ask the publisher.


Re: tube rectifiers [message #8320 is a reply to message #8319] Sat, 10 July 2004 12:39 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
Hope you know I appreciate your input. The KT 88 looks good; what makes it better than the 2a3? You have access to many different combinations that we don't so we must rely on your opinion here. The other thing is can you tell us what speakers you are using? Thanks again Mr. Metasonix.

Re: tube rectifiers [message #8330 is a reply to message #8317] Sat, 17 July 2004 21:59 Go to previous message
metasonix is currently offline  metasonix
Messages: 103
Registered: May 2009
Viscount
it is a problem for power tubes. If you apply plate voltage when the cathode is still cold, it can damage the cathode coating. It becomes a problem only above 400v plate voltage. Some of my references claim it's a phantom, because (supposedly) modern tubes have good cathode coatings. But current production tubes aren't as well made as 20-30 years ago, so it's better to be conservative in this area.


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