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Jay 31st March 2003 08:58 AM

Tube Regulator
 
Iím building a pre-amp using 12AT7. In the regulator section (after rectifier) there will be 2 tubes, one of them is a 12AT7. Can I replace the 12AT7 with 12AX7?

12AT7 max. plate current = 15mA
12AT7 max. plate dissipation = 2.5W

12AX7 max. plate current = 6mA
12AX7 max. plate dissipation = 1.1W

fdegrove 31st March 2003 09:37 AM

RE: Tube Regulator
 
Hi,

Replacing one for the other isn't likely to work, you'll need to adjust some values.

What is the function of the 12AT7 and how much current do you need to regulate?

Cheers,;)

siu sin man tho 31st March 2003 09:57 AM

my pre use 6bx7 to regulate the voltage ude to its high cirrent & low internal rersistance.
I use 12ax7 to control the voltage.

thanks

thomas

www.diyaudiocraft.com

Jay 31st March 2003 11:56 AM

HmmmmÖ.

<B>Fdegrove</B>, I think I will need to think hard to calculate the required current for the pre-amp :bawling: The transformer is 300V-CT-300V. I think it works similarly with <B>siu sin man tho</B> pre-amp.

I just thought that 6mA maximum plate current wonít be a problem for a common pre-amp circuit. What if I just try the 12AX7 and see if no red light emitted from the 12AX7 and no degradation in the sound quality? I have plenty of 12AX7.

I plan to buy (for 1 channel) three Mullard CV4024 and 1 Chinese (or RCA) 12AT7 to experiment with types (before buying for 2 channels)

Cheers,:)

siu sin man tho 31st March 2003 12:24 PM

hi jay,

pls be care for the 12ax7, try amperex. amperex had A LOWER INTERNAL RESISTANCE. More swing U will get.

thanks

thomas

www.diyaudiocraft.com

:eek:

fdegrove 1st April 2003 11:26 PM

IF ONLY...
 
Hi,

Quote:

Fdegrove, I think I will need to think hard to calculate the required current for the pre-amp The transformer is 300V-CT-300V. I think it works similarly with siu sin man tho pre-amp.
Well, if we had an idea about this regulators' composition it would be great help to you.
Short of that it's rather pointless.

Cheers,;)

valveluver 2nd April 2003 01:42 AM

Vacuum regulators
 
I have seen gaseous regulators such as 0C3

I have seen triodes used as regulators such as the 6080.

I think it is posible to design a good stable power supply for vacuum tube amplifiers. The use of choke input filters is a must.

Some folks are hung up on vacuum rectifiers. Vacuum rectifiers present poor regulation. My advice is to say goodbye to 5U4s etc. I have heard all sorts of arguments for vacuum regulation. With a properly designed filter, switching noise is not an issue.

valveluver 2nd April 2003 01:47 AM

another thought on preamps
 
Pre-amplifiers typically use class-a amplification. The load does not change. Why do you need regulation?

Brett 2nd April 2003 03:15 AM

Re: Vacuum regulators
 
Quote:

Originally posted by valveluver
Some folks are hung up on vacuum rectifiers. Vacuum rectifiers present poor regulation.
Not in class A PP or differential circuits.

Quote:

My advice is to say goodbye to 5U4s etc. I have heard all sorts of arguments for vacuum regulation. With a properly designed filter, switching noise is not an issue.
I don't agree. It's not hard to see it on a spec-an, and snubbers are only effective for a given load. As the duty cylcle changes with load (say class AB), so does the hash spectrum. PSU chokes don't do much at all to filter switching noise, not do most PSU caps.

There are better diodes than the 5U4 etc.

Brett 2nd April 2003 03:16 AM

Re: another thought on preamps
 
Quote:

Originally posted by valveluver
Pre-amplifiers typically use class-a amplification. The load does not change. Why do you need regulation?
Single ended, the load changes with signal.


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