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Post subject: Tube amp safety
Posted: Wed May 11, 2011 11:09 am
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Forgive the elementary question. If you are changing out tubes (power and preamp), are there any safety dangers? I have been reading about the risks associated with capacitors discharging. But isn't that only if you open up the guts of the chassis? While changing tubes, the capacitors etc. are all encased. I want to do my own tube upgrade and re-bias, but need to be an educated consumer here. Thanks to all who might want to lend a little expertise. This forum is a great place!!


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Post subject: Re: Tube amp safety
Posted: Wed May 11, 2011 11:47 am
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No real worries about power cap discharge (as long as amp is off-- I usually unplug it, just to be sure)... when changing out tubes. As long as amp's chassis remains in the cabinet.

One thing, if you are tube rolling, be sure the correct type is replaced into each socket. I try to do it one gain stage tube, at-a-time (smaller 9-pin miniature tube). And buy and use "matched" pair of comparable power tubes. Matached quads, if you have four power tubes.

Replace the RECTIFIER (if it's tube type) separately from the power tubes, to avoid a very bad misplacement guaranteed to lead to early 4th of July fireworks and potentially big $$$ repairs. (Yes, the rectifier will fit into most power tube sockets and vice-versa).

BTW--- if you are swapping tube around, to check for tonal changes, they may be HOT. I use a Mechanix glove to pull and replace tubes. Good gripping power and protects you from heat and accidentally dropping the tubes (this happens more times, than I like to mention).

Make sure that the tube go back into the sockets ALIGNED like the originals. Larger octals (power tubes & rectifiers have a key in the center pin). Smaller 9-pin mini's have an opened position, where no pins are placed. Try very hard NOT to bend the pins. Esp those smaller 9-pins. As this sometimes mucks-up the contact with the sockets. I use a flashlight to guarantee alingment.

I usually remove any panel which may get in the way of pulling and replacing tubes.

Good luck and take your time.


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Post subject: Re: Tube amp safety
Posted: Wed May 11, 2011 11:49 am
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On some amps, you must remove a back cover panel (Tweed type amps) which will expose the inner chassis and components. Just keep your fingers out of there and you will have no problems. Oh, and make sure the amp is unplugged when you swap tubes. :D

Where you will run into possible danger is when you rebias the power tubes (on amps that require it) after changing them. There you are working on a powered up amp with plate voltages above 400 VDC. Then you might want to consider the purchase of a bias probe which will eliminate the need to poke around inside a live amp with a voltmeter.

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Post subject: Re: Tube amp safety
Posted: Wed May 11, 2011 12:58 pm
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Rooting around inside an amp without knowledge can be very hazardous to one's health -- doubly so if the chassis is plugged in and powered up.

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Extreme caution is urged.

:shock:

Arjay

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Post subject: Re: Tube amp safety
Posted: Wed May 11, 2011 2:34 pm
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On combo amp (excepted Vox) the valves can be easilly removed.
For preamp section it ususally always the same references (ECC83/ECC82/ECC81) and no need of bias adjusment by circuit design. Then using advices given by other fellow members, changing a valve is not an issue.
For power stages, a lot of circuits require bias adjustment in order to get the best of the amp. To do that it is necessary to adjust under supply and that exactly the case where there is high voltage (>400V) and your fingers ! Then if you you don't feel confortable with electronics and electrical safety, contact a tech to make maintenance on your amp. 8) 8) 8) 8) 8) 8) 8) 8) 8)

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Post subject: Re: Tube amp safety
Posted: Thu May 12, 2011 3:19 am
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+100 with what these folks all say!

Just changing tubes, with the power off, is not dangerous as long as the glass doesn't break in your hands!

If you do more than that, heed Arjay's signage ( love it btw ). Getting zapped with B+ can do some damage!

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Post subject: Re: Tube amp safety
Posted: Thu May 12, 2011 9:11 am
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Retroverbial wrote:
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:lol: :lol: :lol: LMAO!!!

How would you know what it felt like if you're dead?? :mrgreen:


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Post subject: Re: Tube amp safety
Posted: Thu May 12, 2011 9:44 am
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For the record, the amp in question is a Fender DRRI. In accessing the bias adjustment (a screw I think), would you be coming in contact with high voltage? I understand the statement about not "rooting" around inside the guts. No interest in doing that.


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Post subject: Re: Tube amp safety
Posted: Thu May 12, 2011 9:52 am
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The DRRI is one of the easiest to bias IMO, you don't have to remove anything to reach the bias pot.


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Post subject: Re: Tube amp safety
Posted: Thu May 12, 2011 10:36 am
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StratCat5762 wrote:
For the record, the amp in question is a Fender DRRI. In accessing the bias adjustment (a screw I think), would you be coming in contact with high voltage? I understand the statement about not "rooting" around inside the guts. No interest in doing that.


Title says "Deluxe Reissue" but it looks like a DRRI on the table:

http://www.eurotubes.com/euro-Fender-DeluxeV.htm

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Post subject: Re: Tube amp safety
Posted: Sat May 14, 2011 7:00 am
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The results are in. Thanks to all that responded! I have ordered a full retube set from Eurotubes along with a bias meter. With proper care taken in the process, this should be an easy job.


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Post subject: Re: Tube amp safety
Posted: Sat May 14, 2011 7:07 am
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Congrats and have fun. :D

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Post subject: Re: Tube amp safety
Posted: Fri May 20, 2011 6:50 pm
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Epilogue - Experience is a good teacher. To all those who would like to rebias their amp and have one with the bias adjustment or trim pot accessible and not in the chassis, this is not a hard operation to perform. Not dangerous. You can do it yourself and not pay a tech. Just follow a few simple precautions like making sure the sockets and pins are clean and not burning yourself with a hot tube. Also, if you are installing new power tubes, be prepared to go back and do a final bias after you have played your amp a bit. I put a set of JJs in my DRRI and, along with the Weber 12F150 speaker upgrade, I could not be happier.


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