• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Is it safe to start (power up) tube amp with tubes removed?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
R

Radni

Member
Joined 2014
In my tube power amp, I had to remove old cooling fan and installed a new one. But when I powered up the amp (with tubes on) I find the fan is simply not running. Now I wish to open the amp (with tubes removed) and inspect from inside to,see if the fan is getting the power (12 volt DC) or not. I will have a techie friend to help, in fact he will do the job. I want to know is it ok or safe to give power supply to the amp while it is open (upside down and no tubes installed)?
 
Mooly

Mooly

Administrator
Joined 2007
Paid Member
It is safe in principle however you need to be aware that dangerous voltage may remain on any high voltage reservoir caps. Also, some amps use caps that are under rated for voltage in the knowledge that when the amp is working and the valves are drawing current that the rail voltage will fall a little. Off load and the voltage rating of the cap may be exceeded.

So it all depends on the design of the amp. A good design will also have bleed resistors incorporated to safely discharge the caps over a few 10's of seconds.
 
anatech

anatech

Administrator
Joined 2004
Paid Member
Hi Nigel,
I can only assume he is using a DC fan. It might have a controller inside the motor assembly, so there is that wrinkle. An AC fan would work by switching resistors in series with the fan. Not a pretty solution, but it works and everyone building an amplifier in the old days that way. The search for the right values would be empirical. Oh, what fun!

-Chris
 
R

Radni

Member
Joined 2014
My fan is a DC fan . It is made by a company called SOFASCO , the label says DC Brushless Fan Motor , model SD5010V12 HB , DC 12 Volt, 0.16A. Made in Taiwan .
Size is 50x50 mm , 10 mm thickness( depth) . It simply ha two wires ( black and RED) running out for supply .
It seems like it is not getting any 12 V supply on starting up of the amp. I cannot understand why.
I am thinking to get a 12 V DC battery to hook this fan to it and test it out. Just to rule out any problem with the new fan itself.
 
C

cnpope

Member
Joined 2009
Radni said:
I want to know is it ok or safe to give power supply to the amp while it is open ( upside down and no tubes installed )?
Click to expand...

You didn't, I think, say whether the amplifier uses a tube rectifier or a solid-state one. If the former, then as long as that rectifier is removed along with all the other tubes, then there will be no problem with possible over-voltages on the HT capacitors. If, on the other hand, it uses solid-state rectifiers, then the over-voltage risk that others have mentioned will arise.
 
R

Radni

Member
Joined 2014
Or , I was thinking : Can I power up the amp only in "stand by" mode to check if fan getting power of 12v or not, in "stand by " mode there there will not be much power supply to other circuits in the amp and thereby possible damage , voltage over build up , etc will be avoided. Is my understanding correct ?
 
Last edited:
R

Radni

Member
Joined 2014
Thanks Chris,
My amp is Audio Electronic Supply AE-25 SuperAmp , Signature , Push Pull Type ( from Cary Audio ) , where tube elements are KT88 ( 4 nos as output tubes, Gold Lion) , 6922 ( 2 no. As Input and driver , Mullard GB) and EL84 ( 2 nos . As Current Source) . I suppose this would qualify for me to power it up without any tubes ( all 8 tubes removed ) . Your final word would give me lot of confidence .
BTW , all these 8 tubes on it are bought from PCX , sounding unbelievably great!
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom