[qguy]

Can anyone tell me how to bias the RM-9, cant seem to find a manual out there.. thanks

[audiodoc]

You need a small flat. The LED toward the rear of the top plate has a potentiometer next to it to adjust bias.Turn the pot until the LED glows red.Should put you around -1.8v for bias.I soldered a wire off of the 15 ohm 15watt resistor and with an alligator clip on it to dangle outside for easy access(insulated of course).Put a dc volt meter to it to get the best accuracy although it's not really necessary.I set mine to -2.0 but it runs the 6550's a little more warmer.Make sure the 6550's or whatever you are using are a matched quad set.I've done quite a few tweaks to my RM-9 and improved it's fabulous sound even more.Let me know if this is helpful for you.

Mike

[jman66]

Also let the amp run for at least 1/2 hour before making the adjustments.
Don't forget to balance out the input driver tubes too...press the button next to the driver tube and turn the potentiometer until the LED is extinguished. Do this for each channel.

[audiodoc]

That's it.

Mike aa

[audiodoc]

For those interested-I changed the wooden cabinet to a dovetail 3/4" maple wood with a solid oak bottom for a MAJOR increase in sound quality.Any one want photos?

Mike aa

[Ericus Rex]

   yesssss......photos........ummmmm...... ...

[audiodoc]

  Here are photos of my maple cabinet using box joints I built about 3 years ago.I was learning how to use my router and made different joints .I also have an oak cabinet for another RM-9 but one of the output transformers is cooked.I will be replacing it soon.The amp is floating on marbles which is sandwiched between 2 Home Depot cabinet door knobs(home made roller blocks),sitting on a sandbox that weighs about 50 lbs.The amp is really clear and clean with excellent isolation from vibration.I then isolated each foot print on the plinth by cutting it into a diamond shape to dissipate any amp vibration. What do you think guys?The tube damping rings are teflon and really cut down on microphonics(came from ebay).The yellow wire is my bias adjustment for the Tungsol 6550's.

[Roger A. Modjeski]

I carefully worded a single sentence to instruct someone finding the amp long after I am gone. One needs do no more than read that sentence and do what it says.

BTW, bias is not critical. It can vary as much as 25% with little effect on the sound of the amp or life of the tubes.

As to transformers, out of 1800 outputs I have only had 2 go bad in 22 years. We made them very carefully. All parts are available. We do an complete go-over of any RM-9 for $400 and bring it up to specs. Mods are extra.

[audiodoc]

Roger-how do you like the cabinet ?Any comments?

Mike

[Roger A. Modjeski]

When it comes to wood, to each his own. My desire was to have a very low rise on the frame which took some doing.

BTW. the side getters on those 6550s seem to be going at an uneven rate. How many hours do you have on those tubes? Have you checked the current in them individually?

[audiodoc]

I checked them all for transconductance on my Hickok 752 tube tester.They all are within 10% or each other.No noise.The older tubes are not of the same batch and are-for sure older.I've swapped out various Tungsol 6550's and can distiguish no differences.I'm not getting any ill effects from any of them.Tube life is strong and they keep going.Bias up fine.I'm only running from 340 hz up using an electronic crossover with Innersound Eros II electrostatic speakers.Amp stays cool.Sweet stuff.