Audio Research Ref 600mkIII bias levels

tubeman victor

New Member
Aug 17, 2010
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Sydney Australia
Hi,
I,m interested in bias levels for ref 600(mk2,3 )and ref 300(mkII) used by others in their amps.The factory level is 65ma and I do use this(6550,but will go kt88 as rec) but even the factory approved tech (only 1 in oz ) when he visits always rebias down to 55ma / each tube.He states that for reliabity/longer tube life etc this is recommended.(note I rebias back to 65ma sounds better)

Ref 600 had/have a bad reputation which I suspect is low quality tubes,heat, overbiasing (accidently ,I saw 100ma when adjusting 1 day) and the DUST which caused most of my troubles and bad tubes.

Why I posted for other,s opinion and experiences is I spoke to another amp designer/builder and he said very unreliable amps and must rebias down also.

My amps now that I clean dust out every 3mths and run lower fan speed have been very reliable and with tubes tested can provide many yrs of trouble free operation.Vacuuming amps today.

http://www.audioresearch.com/ref600.html
Look forward to your reply,s (1st post)
Regards Victor.
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 22, 2010
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Monument, CO
I do not know "the" answer to your question. I can say that:

1. While heat is needed for tubes to operate, too much is bad, and can hurt other components as well. Lower bias reduces heat, and will indeed lengthen tube life. However...

2. Higher bias increases gain and tends to lower the noise floor slightly (gain is linear, noise floor square root, and of course the feedback reduces the impact of higher gain in the tube itself). It also tends to reduce distortion since higher bias provides (generally) more headroom. There is a long history of audiophiles cranking up the bias for better sound but to the detriment of lifetime and reliability (see 1).

3. Why not hit a middle ground at 60 mA and see what happens?

4. If you switch to KT88's you can bias them higher. There will still be more heat, but they are designed for a bit higher bias.

5. Keeping the amp clean is good for keeping the heat down, and a little air cooling can't hurt.

All imo - Don
 

Steve Williams

Site Founder, Site Owner, Administrator
Victor

Welcome to the forum

I owned ARC Ref 600mk lll. I was lucky as I always set the bias to 65 as it sounded better and fortunately I had no explosions. The opinions you have heard are certainly anecdotal but do exist. My good friend Marty who is a member here had ARC Ref 300 Mk ll and had no problems with both 6550s and KT 88s. The Sovtek KT 88s had a wonderful midrange but at the expense of some bass which the 6550s had. When Marty bought 610Ts he had 2 explosions which prompted him to sell. He is now the proud owner of Sigfried's and loves them. I will get Marty to chime in
 

tubeman victor

New Member
Aug 17, 2010
8
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0
Sydney Australia
Thankyou Steve and DonH,

The ref600mkI ,did have problems with tube quality control and with dust inside amps it did end with flashes of light and sound.

In my case 2 were tube failures,and the all others were dust on circuit traces and thus jumping trace,s with moisture in air(note room airconditioned,amps covered when not in use)
Some may need to clean amps monthly etc but this will reduce amp problems by 85%.I would be interested in why the 610t has trouble(tube quality ? dust ? or other parts failing then tube,s let go?
I do get a lot of dust in my room,even with 2 filters etc.Moisture will if present in amp to fail instantly but this is the same for any amp tube or SS?

With kt88 do you still bias at 65ma ?

Very happy this forum is open,as in Oz less than 10 ref 600 in various MK,s and ref300 around the same qty,but I seem to be the only one on forum,s with them.So I prefer actual experience with the amps than heresay.

Ps they do sound very good,I have a 300b system too thats nice too.

Cheers Victor.
 

Steve Williams

Site Founder, Site Owner, Administrator
Victor I loved my 600 Mk but I must say that here in California where summer temps can get quite hot I can attest that with the amps on (62tubes IIRC) plus an ARC Ref 2 Mk ll at the time with 8 tubes it was like a steam bath in my room. I finally had to install a separate 3rd dedicated central air system for that room only.
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 22, 2010
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306
1,670
Monument, CO
Warm, humid ocean air carries a lot of moisture and salt that is a double-whammy for high-voltage traces (makes the dust more conductive). Air conditioning tends to condense moisture out, potentially further compounding the problem, then put some moistened salted dust across a 600 V supply rail and BOOM!

I don't recall where the KT88's run; I recall running them a little hotter, like 75 - 80 mA, for best sound. there are also variations in 88's and 6550's so it's best to ask or look up the required bias in a tube manual (unfortunately, mine is in the black hole downstairs masquerading as a storage closest).
 

tubeman victor

New Member
Aug 17, 2010
8
0
0
Sydney Australia
Just an update,

In my cleaning amps,I found 1 trace melted and it,s resistor damaged(3 times normal size),check with A.R. tech he said to see if tube will bias or not.Checked today (Waiting for some sparks) and tube will bias fine all tube have been stable for 1.5 yrs.So amp is working but,tech is coming sunday to check amp,new resistor,tube and replace trace.

I do live near water and room is airconditioned with 4 power amps,and 3 pre amps(2 tube) for 2 ch/5.4 HT so room is nice and toasty.

Cheers Victor.
 

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