Randy's "New" VT-50

So far pretty nice. I like the sound and the feel quite a bit. I would love to get a clear top like what I see shown on the Ref 6 :)....

How do I know when tubes are in need of replacement? Just planning for down the road.... Does the amplifier require being sent to ARC for tube replacement? I see people talking about putting 88's, or something like that in it. Are they the larger output tubes? And, since ARC literally labeled them to which socket each tube goes in, if you replace tubes with something else is this not also important?

Just some thoughts. So far I have been pretty much playing it almost exclusively, but I think at some point I might want to switch in the Ampzilla for a change of pace.
 
Randy

Even if you play it a couple of hours a day you have several years before you have to worry about replacing the tubes. Just enjoy.
 
Thanks Jack... I was thinking it would be quite some time, but I also love to understand my equipment. I do have to say though, this ARC is very impressive! Really enjoying it so far... I am also going to be adding a STP-SE back into the system!
 
Randy Myers said:
Thanks Jack... I was thinking it would be quite some time, but I also love to understand my equipment. I do have to say though, this ARC is very impressive! Really enjoying it so far... I am also going to be adding a STP-SE back into the system!
Click to expand...

Randy, Jack is right. I'm not an hour-counter...but I think if you assume these tubes, to have ~100 hours on them; you won't be far off, in one direction or another.

But...to answer your questions (and again...any of the hard-core experts, feel free to correct me): when a tube starts to go bad, the unit will start to sound "wrong"; maybe some distortion, maybe what they call "tube rush"...which is like an "windy" sound, along with the audio signal. Of course, if you have a complete failure; the unit probably won't play at all.

When/if, the time comes...to replace either a single bad tube or the quad; you don't need to worry about the numbering. Obviously...with a single, bad tube; that's where the replacement will go...and you'll likely need to re-bias. With a whole quad...doesn't matter, where the new tubes go; but...that will DEFINITELY require a re-bias, and that's when you'll want to take note...which tube is where.

That's what the numbering is about; it's in that position, that the unit has been biased. So if you ever have to remove the tubes...like I did, to ship it to you; it's important they go back in the same place :)

The unit does not have to be sent to ARC, just to roll or replace the tubes; but depending on what, and how often you're having it done...it might not be a bad idea. For example...let's say 6 months from now, you decide you want to try a quad of KT-88s (yes, the larger power tubes; your current ones, being 6550-Cs. Which, BTW; if you're not replacing because they're shot...you'll absolutely, want to keep around. You can switch in and out, to tinker with sound...which is what we are referring to, when we say rolling; although, unlike pre-amps...which don't require it...it's not as easy, because of the need to re-bias); no...I would not send that away, to ARC to have done. One...they most likely, won't even do it...lol. ARC doesn't believe in "rolling"; they believe they've picked the perfect tube, designed the circuit around that tube...and that you, the owner, are only serving your silly, audiophile, futzing nature...by messing with it. Not saying they're wrong...lol; but...it is your prerogative, which is why you'll need to do it.

Two...even if they would do it; it would be crazy expensive, if you were doing so...on any kind of "regular" basis (as I said...like 6 months from now). OTOH...if say, 3 years from now; you feel the tubes have a certain amount of hours on them...are going "bad"...and you would like to completely re-tube. While you still don't have to...that might be worthwhile, sending to Plymouth. I have heard, the input tubes (the smaller ones. 6922s in this case http://www.arcdb.ws/VT50/VT50.html...are a b*tch to re-bias. That you have to bias them first...then bias the power tubes; then go back, and re-check the input tubes again!).

But to reiterate: Jack is right; just enjoy for now. You actually do, have the "best" tube; and ones, you really can't even get anymore. Now...adding an STP-SE; that's a GREAT idea! It was an excellent pairing!!

 
Hey Chris, as well as Jack, I very much appreciate your wonderful input! Like each phase in re-learning this crazy hobby, I want to understand not only what I am doing, but as important to me, I simply want to understand how this all works.

Back a long long time ago I had some tube McIntosh equipment and I do not recall ever hearing about biasing. Not to say it was not done, I am sure it was, but I just don't ever remember hearing about it.

At this point in time I have no interest in rolling tubes. I currently believe that ARC knows a whole lot more than I on what works best in their amplifier. I was just curious on how it is determined that tubes are getting close to needing replacement. I also believe that even with gear that counts hours on tubes there has to be a variance, meaning that just because they say tubes last about 2000 hours does not mean that all tubes are worn out at that point. I am sure that most probably last much longer than that.

If they last for years then I would probably be inclined to have ARC do the job for me... Assuming of course I stay with this amplifier for that long... but at this point I would certainly say that is a distinct possibility!
 
The ARC VT-50 is one of the easiest amps to check and set bias in the VT product line. If memory serves me correctly based on a friend of mine who used to own one, the bias test points are at the top of each board with clearly marked test points. If you are handy with a DVM, it shouldn't be a big deal to check your bias settings periodically and make adjustments as necessary. If you are like the last owner of your amp, you may blow it up and have to send it back to ARC for repairs. :( Buying new output tubes or switching from 6550s to KT-88s will require knowing how to set the bias properly. If you can't do it or know someone who can do it for you, it's best to send it back to ARC.
 
It seems easy enough. Using alligator clips on each side of the bias resistor. I will have to get a meter... pretty cheap... but setting the meter correct is something I have to learn.
 
Randy Myers said:
It seems easy enough. Using alligator clips on each side of the bias resistor. I will have to get a meter... pretty cheap... but setting the meter correct is something I have to learn.
Click to expand...

You should be reading the bias on the milliamp scale (ma).
 
mep said:
You should be reading the bias on the milliamp scale (ma).
Click to expand...
I'm afraid that trying to directly read current with a mulimeter by tapping across a resistor as Randy mentioned will not work. To directly read current with a multimeter requires the circuit path to be open and flow through the meter. If the test points are across a resistor as Randy stated then voltage is actually being measured, and using Ohm's law it's simple to determine the bias current if necessary. The resulting current (I, in amps) will equal the measured voltage (V, in volts) divided by resistance (R, in ohms). Setting the meter correctly isn't something to worry about since digital multimeters will clearly alert you if you're out of the set range which you can then easily reset accordingly. Hope this helps!
 
mep said:
Straight out of the horse's mouth:

www.audioresearch.com/ContentsFiles/VT50_BiasAdjust.pdf
Click to expand...
And ARC's instructions confirm exactly what I posted, that you're actually making voltage measurements and not current. Your initial direction to Randy was: "You should be reading the bias on the milliamp scale (ma)" which was the reason for my post, the meter should correctly be set to read voltage.
 
Those instructions are for doing a full tube biasing when replacing all tubes. ARC suggest having them do this :).... in their manual they suggest doing the output tubes once in a while... here are some good instructions for this....

"I would strongly suggest that you contact ARC for an info sheet on
biasing and a lecture about being careful. Do you have your
instruction manual? Everything should be explained there. I have a
VT50, and I'm assuming the procedure is the same, only doubled for
the VT100 since there are 8 tubes vs 4. The test leads should be
placed one on each leg of the black resistors at the top of the
circuit boards on either side of the amp. Since there is one
resistor per side on the VT50 (one per pair of tubes), I'm assuming
there are two per side on the VT100. The key to this whole procedure
is that you spend $5 at Radio Shack to get multimeter test leads that
clip on to the resistor legs, rather than the pin type that you just
hold on the legs. ARC told me they have already received two or
three VT50s back for repair after people fried their circuit boards
(and potentially themselves) by slipping with the test leads and
touching either the chassis or some other part of the amp. BE
CAREFUL. Once the leads are clipped on to the resistor and you let
the amp settle for 20-30min under zero-signal conditions, read the
bias and make appropriate adjustments using the trimpot also located
up at the top of the circuit board on either side. Use a
plastic-handle adjusting device. ARC says that once a new tube set
is settled in, you should only have to check bias every 6 mos or so,
depending on usage.

1:yes the meter leads should be clamped on either side of the resistor
2:set your meter for dc mV 200mV range
3:turn the amp on and watch the bias if it goes higher than 65mv bring it back with the blue pot adjustment, both sides should be watched, it's good to have two meters.
4:Then after about 1/2hr of warm up check again and re-ajust and again after about 1hr. Then check again a few hours later."
 
Randy Myers said:
Those instructions are for doing a full tube biasing when replacing all tubes. ARC suggest having them do this :).... in their manual they suggest doing the output tubes once in a while... here are some good instructions for this....

"I would strongly suggest that you contact ARC for an info sheet on
biasing and a lecture about being careful. Do you have your
instruction manual? Everything should be explained there. I have a
VT50, and I'm assuming the procedure is the same, only doubled for
the VT100 since there are 8 tubes vs 4. The test leads should be
placed one on each leg of the black resistors at the top of the
circuit boards on either side of the amp. Since there is one
resistor per side on the VT50 (one per pair of tubes), I'm assuming
there are two per side on the VT100. The key to this whole procedure
is that you spend $5 at Radio Shack to get multimeter test leads that
clip on to the resistor legs, rather than the pin type that you just
hold on the legs. ARC told me they have already received two or
three VT50s back for repair after people fried their circuit boards
(and potentially themselves) by slipping with the test leads and
touching either the chassis or some other part of the amp. BE
CAREFUL. Once the leads are clipped on to the resistor and you let
the amp settle for 20-30min under zero-signal conditions, read the
bias and make appropriate adjustments using the trimpot also located
up at the top of the circuit board on either side. Use a
plastic-handle adjusting device. ARC says that once a new tube set
is settled in, you should only have to check bias every 6 mos or so,
depending on usage.

1:yes the meter leads should be clamped on either side of the resistor
2:set your meter for dc mV 200mV range
3:turn the amp on and watch the bias if it goes higher than 65mv bring it back with the blue pot adjustment, both sides should be watched, it's good to have two meters.
4:Then after about 1/2hr of warm up check again and re-ajust and again after about 1hr. Then check again a few hours later."
Click to expand...
Again this confirms exactly what I originally posted, that you are measuring voltage across the resistor and not current.
 
Good good... I am very comfortable inside electronics, building Hager amps and many computers, etc. However I have never used a volt meter... therefore my wanting to understand exactly what I am doing... again thanks for all the input!
 
Randy Myers said:
The key to this whole procedure is that you spend $5 at Radio Shack to get multimeter test leads that
clip on to the resistor legs, rather than the pin type that you just hold on the legs. ARC told me they have already received two or
three VT50s back for repair after people fried their circuit boards (and potentially themselves) by slipping with the test leads and touching either the chassis or some other part of the amp.
Click to expand...

ALL good stuff; but I would just reiterate this part.

I know; everyone pokes fun, and likes to kid that I'm an idiot...for blowing up my unit. I can look back on it now, and while not exactly laugh; consider it a lesson learned.

However...I am not an idiot; and my point being, is that I could have sworn the leads never strayed. Yet...Sizzle, POP!!

So...laugh all you want; but it can happen, pretty easily. Get the f*cking clips! LOL
 
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