can you please help me around how to use my first tube amp?


Hi, I picked up on a whim an older tube amp, first I have ever had that is non automatic biasing and outside of that really no nothing about tube amps

Its a used 10 year old or so Rogue Audio Atlas Magnum power amp with KT 120 power tubes

the pre amp/dac will be RME adi-2 and speakers are Sonus Faber Lumina V's (4ohm)

I was thinking I would also also try it without preamp from a bluesound node

I believe the stock setting is 8ohm on the amp and you need to crack the lid to adjust down to 4

nervous about installing and biasing the tubes

can anybody advise what happens if I run the amp without the tubes being biased correctly?

also, can I run this from the 8ohm default so I dont have to open it up?

finally, how do I know when i need new power tubes and pre tubes?

any other advice will be appreciated

 

 

 

 

 

 

 

 

 

audiocanada

you will probably also need a cheap digital voltmeter - you can get them online - not sure of cost in Canada. Easy to bias the tubes, as the other posters have given great instructions. You can probably get the manual online and download and print it. And call them if you have questions.

Guys - Rogue amps have the bias meter built in lol. He doesn’t need to run out for a multimeter.

Probably too late now.  The first thing I would do is to Open It Up.  Check for over heated resistors, leaking capacitors, burnt wires, dead roaches...  And while you are in there change the output ohms tap.  10 years.  Might start thinking of recapping the unit.

Test the Tubes.  Find someone who has a Tube Tester.  Or buy one.  Mutual Conductance Tube Tester. You're getting into tubes.  Mind as well start getting the tools to support your hobby. Write down the values of each tube.  Check them every 6 months to a year.  See if the values are deteriorating.

If it has been sitting or stored for a while, I would do a slow power up without the tubes.  But you probably don't have a variac.  Remove the tubes.  I usually put in a smaller rated fuse in but eh, lets chance some excitement. Plug it in, get ready to jump away and flip the switch on.  No pop, sparks or flames you doing good.  Put the tubes back in.

Checking the Capacitors.  I would have done this when doing the internal inspection with a cap tester.  Hook up the speakers, turn it on and listen for a 60/120hz hum or buzz as the tubes warm up.  Should be dead silent.  If you hear anything, probably the filter capacitor.  It can get destructively loud.  If you see the plates inside the power tubes start glowing cherry red, shut it down.  Probably a shorted coupling capacitor or internal short and can damage the tube.

Bias the tubes per the manual.

Good Listening

The rogue amp comes with a meter already built into the amp. No need at all for a multimeter.  Some of you guys make it more difficult than need be.  Why would the person need a multi meter when the amp comes with one built into the chassis and has markings for optimal bias?

While a visual inspection  of the inside of the amp is helpful, one sort of needs experience to spot a burnt resistor or a bulging capacitor or other visual signs of distress.  Having access to a tube tester is also nice, but decent ones are not cheap. 

I don't think testing capacitors makes much sense.  Capacitors generally can be tested only if they are removed from the circuit.  The only in-circuit test that might indicate a problem is ESR (equivalent series resistance), and this is at best a rough measure.  Also, most capacitor testing that can be found on multimeters is essentially useless because they only make measurements at very low voltages.  The proper meters are dedicated capacitor/inductor meters and these can be very expensive (common price for a used high voltage capacitor tester is in the $800 plus range).

 

It is best if you can find a dealer or someone in your area with experience with tube gear to check your amp out.  At 10 years of age, your amp is pretty young.  My tube amp is about 15 years old, but, it is built mostly with parts that are in the 70-year age range (only the power transformer is "new").  I have not had to so much as replace a tube during this time.