ARC amps and KT150's

**Mike** · January 13, 2015, 10:30 AM

Audio Research finally clarified this morning in writing that the KT150's are electrically compatible with the following:

VSi60
VSi75
REF75
REF150
REF250
REF750

However, because the KT150 is physically larger than the KT120, technical compatibility has not been confirmed at this time. For example, they indicated there might be a "clearance problem" with the top cover of the REF75. MEP can you confirm?

There should not be an issue with the REF150 or REF250.

They made mention that the proper selection of the bias range and device matching of the KT150 tubes for each model is of critical importance for optimal sonic performance. They recommended customers purchase properly matched and biased KT150's from Audio Research for their particular product - when they become available from ARC - later in the first quarter.

They mentioned that KT150 tube sets will not be available for the REF750's for quite a while due to the tube matching requirements for a pair of the big 750's.

ARC made mention that they will NOT be held responsible for damages and/or repairs to a product if the KT150 tubes were installed that were NOT purchased as a set from Audio Research. Interesting.

**mep** · January 13, 2015, 11:21 AM

The cover fits on the Ref 75 with the KT-150s.

**mep** · January 13, 2015, 11:35 AM

I'm not sure I understand what ARC is saying about how to bias the KT-150.

**Dizzie** · January 13, 2015, 11:41 AM

How much space is required between tubes and the top cover?

**mep** · January 13, 2015, 11:48 AM

The cover is ventilated so as long as the tubes don't touch the cover I'm fine.

**Dizzie** · January 13, 2015, 11:49 AM

Originally Posted by mep

The cover is ventilated so as long as the tubes don't touch the cover I'm fine.

That is what I was thinking as well.

**joeinid** · January 13, 2015, 03:39 PM

Great news! Thanks Mike! Makes me feel a little better experimenting with my ARTsa amp.

**octadyndude** · January 13, 2015, 04:17 PM

Originally Posted by mep

I'm not sure I understand what ARC is saying about how to bias the KT-150.

I think they have a very tight tolerance for voltage gain and plate current. Then spec and test their tubes to a very high standard. Therefore they can command top dollar for replacements along with a guarantee.

**mep** · January 13, 2015, 04:24 PM

The problem is, ARC is not currently selling KT-150s to people who own their amps that can run them. They only have enough stock for their new amp that uses KT-150s. I bought my KT-150s from Uncle Kevin because he does a better job matching output tubes than anybody else in the U.S. that is selling them to my knowledge.

**octadyndude** · January 13, 2015, 10:32 PM

Of course none are sale right now. They have to get their inventories up of tested/certified tubes. They could also have a higher reject rate due to the ARC 'standard'. At any rate I personally would under bias them a bit just to be sure for now. I have never dealt with uncle Kevin yet - but I can say Jim McShane mentioned to me that Kevin was as good as himself. That says a lot. Jim said if he doesn't have a tube see Kevin next. Also my Octave V110 has a plate voltage of 620 and a grid of 330. Info like that helps when matching tubes. It's even better when the seller knows the amp. Unfortunately Jim doesn't have KT150's and he doesn't Cyro tubes.

**mep** · January 14, 2015, 09:45 AM

I'm not a believer yet in why we need to cryo vacuum tubes, but you can't buy KT-150s from Uncle Kevin that haven't been through the cryo process. The greatest sounding tubes ever known to man never went through the cryo process during the golden age of tube manufacturing. If you read the info on Uncle Kevin's website, you will see he has a high-rejection rate of tubes also. In addition, Kevin only buys tubes from Sovtek/Tung-Sol that test at the top 50% of production values in order to get better tubes to start with.

**Mike** · January 14, 2015, 09:51 AM

Thanks Mark. Kevin is definitely one of my go to guys. But geez is that dude busy.

**mep** · January 14, 2015, 10:16 AM

Originally Posted by Mike

Thanks Mark. Kevin is definitely one of my go to guys. But geez is that dude busy.

You're right, he is a busy dude. And people wonder why he does't have time for tire kickers.

**Harlequin** · January 21, 2015, 10:00 AM

Originally Posted by Mike

Audio Research finally clarified this morning in writing that the KT150's are electrically compatible with the following:

VSi60
VSi75
REF75
REF150
REF250
REF750
.

Mike , If I may inquire, where is/was this particular memorandum published ? Or is this a reference to the internet memo, rumoured to have been issued a while back, eyes only, to the Distributer network. If I recall correctly, up until very recently Customer services at ARC Central were in denial over any such Official sanction.

Jasper.

**Mike** · January 21, 2015, 10:12 AM

Originally Posted by Harlequin

Mike , If I may inquire, where is/was this particular memorandum published ? Or is this a reference to the internet memo, rumoured to have been issued a while back, eyes only, to the Distributer network. If I recall correctly, up until very recently Customer services at ARC Central were in denial over any such Official sanction.

Jasper.

Jasper, this was a letter from ARC to their dealers that I transcribed.

As a side note, I see other sites have taken upon themselves to post my summary without the proper credit.

Sent from my iPhone using Tapatalk

**Rscotth** · May 11, 2015, 03:14 PM

Any updates from users who have upgraded to the "SE" KT150?

**Dizzie** · September 9, 2015, 07:30 PM

Has anyone changed the standoffs in a Ref-75 to give more clearance for KT-150s? I assume that is the physical change alluded to by ARC as part of their upgrade to the SE version.

If so, how hard was it. Does anything have to be unsoldered? What size did you use--thread and height? If anyone has an SE version could they please tell me how tall the standoffs are?

**Bifwynne** · October 10, 2015, 03:00 PM

@Dizzie, I believe the answer to your Ref 75 SE Q is YES. Based on A'gon posts from one or two other members, ARC dropped the main circuit board as part of the 75 SE upgrade. The top can now be screwed down with the new KT-150 tubes. But call Kal at ARC to confirm. Or, if you wish, I'd be happy to contact an A'gon buddy who owns the 75 SE for you via a PM and ask him directly.

@Rscoth, I did the SE upgrade to my Ref 150. The mods are done at the factory and at the time (earlier this year) cost $5000. The upgrade includes a complete re-tube, which ain't cheap if you source tubes at ARC ... e.g., KT-150s cost $200 per.

As for results, very real, palpable improvement in SQ across the board. Bass is tighter. More open sounding. Better sound stage and imaging. Augmented detail. If one can afford the $$$, IMO, it's a worthwhile investment. Unofficially, Kal said he thought the Ref 150 SE came pretty close to the new QS 150 amp. Most if not all the circuits are the same. Tube are the same. If interested, give Kal a call.

**mep** · October 10, 2015, 08:28 PM

The top can be screwed down on a regular Ref 75 with KT-150s. I know because I have an ARC Ref 75 running KT-150 tubes.

**Dizzie** · October 11, 2015, 11:30 AM

Originally Posted by mep

The top can be screwed down on a regular Ref 75 with KT-150s. I know because I have an ARC Ref 75 running KT-150 tubes.

Bifwynne, mep, Thanks. I know that because I was able to put the cage back on mine. Clearance is very small and that bothers me. I was exploring the feasibility of replacing the standoffs myself or having a tech friend do it. That was why I asked about thread sizes and standoff height and whether or not de-soldering was required.

I am on the fence ($$$) regarding having ARC do a full upgrade.

**Bifwynne** · October 11, 2015, 01:06 PM

Originally Posted by mep

The top can be screwed down on a regular Ref 75 with KT-150s. I know because I have an ARC Ref 75 running KT-150 tubes.

@Mep, I PM'd my A'gon pal about the Ref 75 (not SE) and KT-150 tubes. Here's what he wrote:

"If I remember correctly, I think the lid will just barely fit ... but my friend at ARC advised me to keep it off for proper cooling purposes. And yes ... the new SE's circuit board was lowered in the chassis."

I think the take-a-way is that technical questions about ARC products are best directed to ARC. I have always found Lenard (now retired) and Kal (his successor) to be extremely helpful and knowledgeable.

BIF

**mep** · October 11, 2015, 03:40 PM

The top cover does just barely fit, but the point is that there is clearance from the top of the KT-150 tubes and the top cover. The other thing is that the top cover is ventilated and the Ref 75 does not run very hot. You only have two output tubes per channel and they are being operated very conservatively. So for me, it's a "Don't worry be happy" issue. I normally run my tube amps sans covers because I think they look better that way. The Ref 75 looks ugly without the top cover in my opinion and so it stays on.

**Bifwynne** · October 11, 2015, 04:04 PM

Originally Posted by mep

The top cover does just barely fit, but the point is that there is clearance from the top of the KT-150 tubes and the top cover. The other thing is that the top cover is ventilated and the Ref 75 does not run very hot. You only have two output tubes per channel and they are being operated very conservatively. So for me, it's a "Don't worry be happy" issue. I normally run my tube amps sans covers because I think they look better that way. The Ref 75 looks ugly without the top cover in my opinion and so it stays on.

Go for it!

**mep** · October 11, 2015, 05:49 PM

Originally Posted by Bifwynne

Go for it!

I did, months ago.

**Rscotth** · February 23, 2016, 02:03 PM

For anyone who has done the upgrade, what was your turn-around time? Who pays for shipping?

Thanks,
Scott

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