Tube bias and related ramblings very exciting

My adventure with KT88's or an occurance that will soon take place which might be an adventure...

Some people might say that Solid State gear is HiFi for the lazy man. They would not say (the women anyway) that is was HiFi for lazy women because the women I know work their butts off, but that’s another issue altogether. I don’t know how enthusiastically I would argue their accusation. My system at home is all Solid State, and I am very happy with it. Doesn’t that expression Solid State just give you a feeling of power and safety? Solid State is like the Fort Knox of stereo gear. Just like Fort Knox there is nothing left to guard there either. So much for the Gold Standard! Anyway after receiving copious amounts of abuse (and that from friends) over the distinct lack of tubes in my system I decided to try a tube integrated amp for my office.

I bought an Audio Institute VR 120 from a gentleman in California. I should have known better! When was the last time you met a gentleman from California. Actually I have nothing against this gentleman other than his unresponsiveness. He turned out to be very pleasant in our subsequent conversations, but the Audio Institute VR 120 ended up being made in China, which I did not know prior to the purchase. The gentleman assured me that the integrated amplifier had been modded and upgraded by a highly respected designer and owner of another company and was in perfect working order. I will not name that other company as I have no way to verify these claims.

Upon arrival the unit sounded very good in my little office. The synergy with the rest of my poor quality gear and my decent speakers was audible. There was synergy everywhere, within days there was synergy oozing from my pores! When it’s hot out the office is quite warm, like a sauna, which might explain the oozing. Until the day I turned the VR 120 on and nothing happened. I dragged the unit down to the local repair shop, behind my truck. I was quite nervous when I saw his hands tremble, kinda like Mohammed Ali. I was not sure if I was more concerned for him or the integrated amp. After a couple of days the repairman called and said everything was done and it worked fine. When I went to pick it up the guy told me that the bias was off and caused the fuse which I could not find, to blow. There were no instructions as to which of the 6550 tubes to use in which socket so I just placed them in randomly. One of the tubes, he explained was on the way out and the bias mismatch blew the fuse. When I dragged it back to work I carried it inside the truck, to avoid harming the tubes. I have had the VR 120 back for several weeks and everything is working fine.

Now we integrate another story. Several weeks ago I was invited to Dallas Texas to visit a good friend. So as not to embarrass this friend he will remain nameless, but for the sake of this story I will call him Albert Porter. Not Albert, not Mr. Porter, but Albert Porter, said as if it were just one word. There is no resemblance between Albert Porter and any other human being living or dead. I doubt that this world could support two people like Albert Porter! He is a genuinely pleasant fellow but altogether singular in his uniqueness. He was a sense of humor that I hope will never be matched, for obvious reasons to anyone who has ever met him.

During the time of this visit I mentioned my tube situation to the fictional character of Albert Porter. He suggested several options for solving the issue. Only one which involved the tubes and/or the VR 120. The rest cannot be mentioned in polite company, but after all it’s only you reading this so... never mind!

After leaving Albert’s home, with everything that was not nailed down, I had the odd sensation of having forgotten something. I check through my luggage and all of Mr. Porter’s electronics were in there, then I remembered the tubes. I called Albert Porter immediately and ask what he was doing (just to be polite). He said he was trying to listen to some music but something wasn’t working right. I told him that we should not get bogged down in minute details, and that we should address the real issue of importance at the moment; the tubes for my integrated amp. He suggested a quad of KT88's. I asked him to order the tubes from the right company and ship them to when they arrived. I even indicated I would pay him for the tubes when he knew how much the tubes and shipping would cost.

The days has come. The tubes arrived and I have no idea what to do with them. The owners manual has absolutely no information whatsoever regarding bias settings. I emailed the seller twice but he never responded. Since I do not speak Chinese, I have not contacted the factory either.

So what do I do now? I know I need a meter from Radio Shack or someone like them, and a screwdriver to make the adjustment, but where should the level be set? I have never done this before so I appreciate your help!
Whew! Best case for SS I ever heard.
Too, too, much! ROTFLMAO. Talk about getting educated the hard way.

Try calling the techie that fixed your amp. He apparently knew what the bias should be. Next time get an amp with auto bias circuits - that should work for you SS guys.

BTW I showered, I'm all dressed up, and still no one wants to go to dinner with me. :-)

P.S. One was just listed in an auction on Audiogon. It closed with out bidders on 6/25/05. The lister put his name and phone number in his ad. Perhaps you can just give him a call. If you can't find this in Audiogon closed auctions, its on "Google".
Nrchy, your biggest mistake was not having Albert Porter buy the new 6550/KT88 solid state tube replacement plug-in modules. No bias adjustments needed. Great tube sound with SS no hassle maintenance. Only bad thing though, they are made in China.
I think now you have to invite Albert over for a listening session. Is that anything like"pump your own gas"? Better have some Cognac on hand.
I don't have the same tube amp likes yours But the idea may help. My tube amp are a pair of Heathkit W4-AM (link here I recently did the bias by myself. It was required few things as follow:

- a flat screw driver.
- two mono audio male connectors with two lead wires on the other ends to measure.(connector looks like the one frequently see on the micro phone end, 12mm diameter?). I bought this cable interconnect from radio shack 1 foot lenght for around 3 bucks then cut them in half.
- Two DVM meters ( I have one and borrowed one from friend)
*If you have only one DVM, it works too but you have to ON/OFF and moving back and forward to adjust.

The way I bias my tubes as follow:

- I stripped the cut cable interconnect ends to have two lead wires to connect to DVM. this DVM is set to measure current in 100 mA or higher. Do the same with the other cable interconnect and DVM.

- Since it is measuring DC current I turned off the amp, plug the other end of interconnects (audio connectors) on both female connectors on the amp.

- Watching on both DVM screens while turning on the amp. If any DVM shows negative current I turn the amp off then switch the wires. This step may not need but I like to see positive flowing current.

- In one of my amps initially one showed 39 mA and other showed 43 mA. I used flat screw driver slowly turn the pot to where both DVM indicated the same reading. It ended up around 41 mA on DVM screens. The other amp ended up around 44 mA. I refer letting the amp stable (warm up) for few minutes before adjusting.

- It's done.

IMO to bias tubes means to set the quiet current (pause the music during biasing)of both tubes as close as the same to reduce distortion and longer life for tubes. If you are noted the sound is better after adjustment or at least you know your tubes working in the right setting.

Excellent story, Nrchy. Not only informative, but both fun and funny. Bravo!

While perhaps a coincidence, this Albert Porter character you've conjured up for the story seems eerily familiar. Could it be.............. Nah, couldn't be...

As an aside, may I offer that if you would like to contact the factory, my wife is from China and can take care of the language barrier.
Unless I hear anything different I will follow 123henry97's advice. This is my first try at something like this so any advice is appreciated.
Nrchy, on a serious note, you really should find out exactly how to set the Power Tube bias voltage recommended by the Amp's manufacture. I have an Audio Research VT50 Power Amp and the bias voltage setting is 65mv for the 6550. If the bias voltage is set too high you could damage the KT88 tubes. You may want to post a question on AA in Amps. Have you tried a search on Google for a USA printed owners manual.
Okay, so here it is. I replaced the 6550's with the KT 88s yesterday. The bias for each of the four tubes is currently set to 70.0-70.1mv. That seems high to me, but I don't have any way of knowing where to set them. Any ideas???
Just a WAG. Without specifics on the amp thats all you get. Something around 50ma should be a safe setting.
I posted a question on AA. So far, there has only been one response.