2. amps-preamps
  3. 130971-73700

KT150s in Audio Research Reference 75 (non SE)

Hey all.  Need some advice. 
I've just dropped in KT150s into my Ref 75 (non SE). 

I purchased "perfect pairs" from TheTubeStore.  

I cannot bias them.  They are all too hot.  There are a couple (of the 4) that if I turn the bias pot all they way down will get very close to the bias range (per the needles).  There are another two that even with the pot turned all the way down are reading past the bias range and the needles are about 7mm beyond the bias range. 

Two questions:
1) Am I doing something wrong?
2) Will it hurt anything to run this a little over the ideal bias range, or just shorten the tube life?  Will it impact sound? 

I thought KT150s were drop in for KT120s.  Am I wrong? 

Thanks!

jo1mtb
jo1mtb OP
121 posts
 
Im just going to hold off and upgrade to SE first.
Thanks all!
gpgr4blu
1,093 posts
 
I spoke in person to a very highly placed ARC representative (whose name I promised not to reveal but all who follow ARC would know) in late 2014 just around the time that the Galileo series was in production and prior to the release of the SE amp versions (which the rep hinted would come soon). I asked if I could drop KT150s into my Ref 150. He said that ARC had tested the KT 150s for months in the standard models and that there would be no harm in dropping the KT150s into my amp although he also said that ARC had not obtained sufficient quantities of the tubes to sell them direct. He suggested that I wait for ARC to sell them in the future or, if I was in a hurry, to purchase from Upscale Audio. 
I did so, biased the tubes at the standard 65mVs and am currently beyond 1,800 hours with nothing but satisfaction. Months later the SE series came out and, of course, contained modifications specifically designed to accommodate the KT150 tubes. Nevertheless, I understand from those who have compared the SE to non-SE amps with KT150s that the tubes alone get you most of the gains in sound that the SE provides in a combination of the KT150 tubes and hardware upgrades.
I am sure ARC would never officially say this now--after all they want to sell the SE versions--but look at the posts here on Audiogon and Audio Aficianado in late 2014 and early 2015 regarding the issue and you will see a number of non SE owners dropping KT150s into their Ref series amps. All came back with favorable results and no problems were reported.    
jo1mtb OP
121 posts
 
@gpgr4blu 
I really appreciate all the information.  I believe everyone, so it's a bit perplexing. 
In the end, they simply won't bias in my Ref 75.  I did get them matched for the Ref 75SE from TheTubeStore.  
They all have stickers that say perfect pair and "81" is written on the labels.  
Nonetheless, they won't bias properly.  
So, I'm not going to run them.  I've put some new KT120s I had in, and they biased quick and easy.  
I'll just look to upgrade to SE soon, and keep the KT150s as spares for down the road. 
Thanks all. 
minorl
1,016 posts
 

To me, this is a simple matter of trust.

I have no reason whatsoever to not trust the Audio Research technical expert's statement. Also, since my REF 250s are probably out of warranty, I really don't want to take this chance.

But, people being how they are want to upgrade and experiment.  In cases like this, a simple phone call to the manufacturer is always the first thing I would do.  no reason not to trust them.

George Meyer audio is an authorized repair service for several brands, including Mark Levinson and Audio Research.  They also told me that dropping KT150s into the non-REF series is not a good idea.

Let me just say this.  no company would replace/upgrade the power supply transformers just to sell an SE version if it wasn't necessary.  I haven't seen one example yet of Audio Research telling people not to tube roll for other amps.  Only in the case of the KT150s have I seen this recommendation.

So, as the saying goes, you takes your chances.  When the transformer or other components fail, don't stand their wild eyed and say, wow! I didn't expect that.

This is like taking a stock turbo charger out of a car and replacing it with a monster turbo without making the necessary adjustments to timing and intake, etc. to ensure the motor doesn't blow up with too much boost and internal pressure.

It'll work for a while, but when it goes, it will be spectacular and dramatic.

I know the OP decided against this, but for me, when I can afford to upgrade to SE and I deem it necessary (too totally different things), I will do so. 

What I would like to do, is (asking for trouble now) borrow a pair of REF 250 SE amps and do a side by side comparison with my REF 250 amps and actually hear the difference.  That would be fun.

Long post, sorry.

I heard a dramatic side by side difference between my REF 3 pre amp (still an outstanding pre-amp) and a REF 5SE pre amp.  Wow!  even my non audiophile guest heard and appreciated the sonic differences.  I did not hear that much of a difference between the REF 5SE and the REF 6.  However, truth be told, the REF 6 came to me with only 24 hours on it.  So, since I traded the REF 5SE in for the REF 6, I couldn't hear the side by side after the REF 6 was broken in.

As with high performance cars, same with electronics, if one knows what they are getting into and can afford the consequences, then as long as one's eyes are open, do what you like.  But, if you can't afford to replace thousands of dollars of blown transformers and other components, I definitely wouldn't go down this path.

enjoy

jo1mtb OP
121 posts
 
I just purchased a Ref 75 SE.  Should have it Friday.  I will be selling my Ref 75 ( w kt120s) here soon.  
Thanks all. 
More to discover