Why doesn't Audio Research let you bias tubes individually in their amps? ...

[joeinid]

Why the reliance on matched pairs that drift over time? Why not adjust each tube as they drift on their own?

My CJ gear lets me bias each tube with a simple turn of the bias pot and it's superb easy to do, no meter necessary.

[Mike]

Or better yet: http://www.vac-amps.com/press/factsheets/iQsystem.pdf

[joeinid]

Thanks Mike, but I'd like to keep my gear affordable. :rolleyes:

VAC is obscenely priced for me. :(



Or better yet: http://www.vac-amps.com/press/factsheets/iQsystem.pdf

[Mike]

Joe, when I had my REF250's, I could bias the tubes individually.

14354

See the front, V1, V2, etc. worked like a charm.

Is there a specific ARC amp you're thinking about that doesn't?

[joeinid]

For example on the GS150:

The GS150 operates with paired vacuum tubes; one tube provides adjustment for a second ‘slave’ tube. For example, V1 provides adjustment for both V1 and V2, V3 provides adjustment for both V3 and V4, and so on. When making adjustments,understand that one adjustment pot affects the bias of two power output tubes.

Remember that one tube is slaved to the adjustment of another tube; readjusting the bias for the first tube will change the bias of the paired slave tube.If the bias difference between the two output tubes cannot be maintained within the acceptable range on the panel meter, one or more of the output tubes may need replacement.

[Mike]

You bias them together and together they must stay within the acceptable range. If they don't then one or both need to be replaced.

ARC is basically saying some bias drift between the two tubes is acceptable, but when both combined drift out of the acceptable range, then one or both need to be replaced.

My question would be: how do you know which one needs to be replaced?

[mep]

The ARC Ref 75 lets you bias each tube individually. ARC amps have varied over the years on how easy or hard they are to bias. I think the D-79 and the Ref 75 are among the easiest to bias because of the built in meters. I would give the nod to the D-79 over the Ref 75 in terms of how easy it is to bias because on the D-79, it was much easier to reach the bias pot from the front panel. The Ref 75 requires a little 'fishing' with the yellow bias tool that comes with the amp in order to land on the bias adjustment screw.

The absolute worst tube amp I ever owned in terms of craziness to set the bias was the Jadis Defy 7 MKII. One bias pot for each bank of 3 tubes and you have to take a reading from each tube and then average those readings and adjust the bias accordinginly with the single pot in order to be in the proper bias range. Each tweak of the bias pot requires you to retake the bias measurement for each tube. You can quickly tell how well matched (or not) your tubes are. Oh, and did I mention that you have to flip the 100 lb amp on its side, remove the bottom cover, be handy with a DVM and have your dickers around HV in order to take the readings and make the adjustments?

And now go back and take a look at companies like Marantz who were making tube amps back in the 1950s with built in meters and easy bias adjustments from the top panel. Look at pictures of the old Model 2, Model 5, Model 8, and 8B. The Model 9 was arguably their most sexy looking power amp and was the first time a Marantz power amp sported a face plate with their cool looking bias meters mounted in the front.

[Garth]

My Bias is for Ayre gear

[joeinid]

Ha!

Me too :D

[joeinid]

Thank you Mark. I appreciate the info.



The ARC Ref 75 lets you bias each tube individually. ARC amps have varied over the years on how easy or hard they are to bias. I think the D-79 and the Ref 75 are among the easiest to bias because of the built in meters. I would give the nod to the D-79 over the Ref 75 in terms of how easy it is to bias because on the D-79, it was much easier to reach the bias pot from the front panel. The Ref 75 requires a little 'fishing' with the yellow bias tool that comes with the amp in order to land on the bias adjustment screw.

The absolute worst tube amp I ever owned in terms of craziness to set the bias was the Jadis Defy 7 MKII. One bias pot for each bank of 3 tubes and you have to take a reading from each tube and then average those readings and adjust the bias accordinginly with the single pot in order to be in the proper bias range. Each tweak of the bias pot requires you to retake the bias measurement for each tube. You can quickly tell how well matched (or not) your tubes are. Oh, and did I mention that you have to flip the 100 lb amp on its side, remove the bottom cover, be handy with a DVM and have your dickers around HV in order to take the readings and make the adjustments?

And now go back and take a look at companies like Marantz who were making tube amps back in the 1950s with built in meters and easy bias adjustments from the top panel. Look at pictures of the old Model 2, Model 5, Model 8, and 8B. The Model 9 was arguably their most sexy looking power amp and was the first time a Marantz power amp sported a face plate with their cool looking bias meters mounted in the front.

[JDLaudio]

Thanks Mike, but I'd like to keep my gear affordable. :rolleyes:

VAC is obscenely priced for me. :(

VAC has some exciting new products coming soon (possibly being demo'ed at the upcoming CES). They will be introducing a new switchable stereo/mono amplifer using their latest version of auto-biasing..........FOR UNDER 10K !!!!!! The amp will offer 170 watts in mono configuration, and 85 watts per channel in stereo. So you could start out with one amp, using it in stereo.......then add another at a later date, for the ultimate in mono operation.
They also have their VAC 200 switchable stereo/mono amplifer available for 14K. This is an awesome amp, from personal experience. So VAC does offer some awesome new gear at wonderful price points. Many new products are in the works, so STAY TUNED !!

[joeinid]

Wow Jerry. Thank so much. Exciting times ahead.

[JDLaudio]

Wow Jerry. Thank so much. Exciting times ahead.

I think so. Their auto-biasing is an incredible technology.

[Mike]

VAC has some exciting new products coming soon (possibly being demo'ed at the upcoming CES). They will be introducing a new switchable stereo/mono amplifer using their latest version of auto-biasing..........FOR UNDER 10K !!!!!! The amp will offer 170 watts in mono configuration, and 85 watts per channel in stereo. So you could start out with one amp, using it in stereo.......then add another at a later date, for the ultimate in mono operation.
They also have their VAC 200 switchable stereo/mono amplifer available for 14K. This is an awesome amp, from personal experience. So VAC does offer some awesome new gear at wonderful price points. Many new products are in the works, so STAY TUNED !!

Awesome! Very much needed! Glad to see VAC pricing return to planet earth.


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[RedSectorA]

VTL also has auto bias as well as tube fault sensing system and shut off in the case of impending tube failure. That's the only way I would go back to tubed power amps

[bzr]

Joe, just buy a PrimaLuna HP, theys are goood!!

[joeinid]

VTL also has auto bias as well as tube fault sensing system and shut off in the case of impending tube failure. That's the only way I would go back to tubed power amps

I love my tube gear but I play music a lot. Like 10-14 hours a day a lot. Some of that time I may be asleep like grandpa in the chair :D but boy do I love it. One of the simple pleasures. Tube failure protection is getting more important to me.


Joe, just buy a PrimaLuna HP, theys are goood!!

Kev,

I am sooooooo close to getting the trio, you don't know. I think I will in the coming year. I am just waiting to see what CES 2016 brings the audio world.

McIntosh 2301's, MC275VI's and MC75-II's have tube sentry and will shut down the amp. Gotta love it.

[Myles B. Astor]

IIRC ARC feels that the individual biasing degrades the sound of an amp.

Remember cj may not always be absolute cutting edge. For Lew and Bill, reliability, among all factors, is one of the most important considerations in the design of their tube products. Lew and Bill feel that tubes got a rap in the past -- and in some cases justifiably -- for blowing up. That Q/C factor tremendously impacted the sales of tube equipment.

[Garth]

IIRC ARC feels that the individual biasing degrades the sound of an amp.

Remember cj may not always be absolute cutting edge. For Lew and Bill, reliability, among all factors, is one of the most important considerations in the design of their tube products. Lew and Bill feel that tubes got a rap in the past -- and in some cases justifiably -- for blowing up. That Q/C factor tremendously impacted the sales of tube equipment.

I blew up a CJ P1 fire smoke and repair bill

[Myles B. Astor]

Sorry to hear that Garth.

I've had three problems in 30 years with cj. (other than that pesky muting circuit issue that almost everyone had in the premier 3 and put the preamp into a permament mute.) Worst was a resistor that blew in an eight year old cj MV75A1. That said, eight year old Krell KSA100s blew transistors too. And certainly we're talking about the most modern designs as the Prem 1 was a very early---and very high power for the day--tube amplifier. I had a number of friends in prem 1s that had no issues either.

[Joe P]

Unlike the McIntosh MC275, at least ARC gives you some bias control on the GS150.

Had a MC275 MK5 here last year, and one of the KT88 was obviously running hot, and it sounded like crap, but there was nothing I could do about it.

People rave about this amp, but I wouldn't own any McIntosh tube amp after this experience.

[Bifwynne]

You bias them together and together they must stay within the acceptable range. If they don't then one or both need to be replaced.

ARC is basically saying some bias drift between the two tubes is acceptable, but when both combined drift out of the acceptable range, then one or both need to be replaced.

My question would be: how do you know which one needs to be replaced?

Mike, it's not that complicated. What Joe says is true. The tube pairs in the more recent ARC Ref amps are designed with one tube being the set tube and the other being the slave tube. And yes, as you said, tube bias may drift.

That said, unless a tube arcs, in my experience, the power tubes run out of juice at pretty much the same time. As a general matter, the KT-120s and 6550s had useful lives of 2000 hours or thereabouts. The KT-150s are supposed to run out considerably longer.

Now ... in the case of power tubes sourced from ARC, they usually bias pretty close to each other. And btw, the ARC manual says that the power tube pairs are considered in spec if the bias is between 57 and 73 mVs. IOW, the tubes are in spec if the set tube bias is set at 65 mVs (recommended value) and the slave tube bias ranges between 57 and 73 mVs. As a practical matter, my tubes spec within a 60 to 70 mV range, and most of the time it's between 63 to 68 mVs ... and they don't drift very much.

As to the question of why ARC uses this set up .... I'm not sure. I seem to recall one of the ARC tech reps telling me that ARC has a strong design bias (pun) to keep the circuit as simple and uncluttered as possible. If I had my druthers, as a consumer, I would rather have individual tube bias adjustment capability.

Bruce

[slowgeezr]

Balanced Audio Technology (BAT) also has intelligent automatic biasing.