So has anyone replaced the 6550s in their Ref 10 with KT88s?

**joeinid** · May 28, 2018, 08:23 PM

I’m thinking about doing it. But curious what you guys think.

**La Dolce Vita** · May 28, 2018, 08:26 PM

Originally Posted by joeinid

I’m thinking about doing it. But curious what you guys think.

Joe...so funny you should ask!! I had this conversation with Roger Gibboni of Rogers High Fidelity two weeks ago. He explained the KT88 is generally s better sounding (and testing) tube...

He encouraged me to change from a 6550 to a KT88 in my Ref 3. Honestly...I have yet to do so...but I am very tempted!!

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**Jack** · May 28, 2018, 08:46 PM

Joe

Order a pair of Gold Lions and give it a try. The Tube Store is experienced with tubes for ARC.

**joeinid** · May 28, 2018, 09:57 PM

I think it’s worth a try.

**Jack** · May 28, 2018, 10:03 PM

I agree and also extremely popular tubes you can flip if you don't like it. I always thought the KT-88's had a smoother and more even tonal balance.

**Randy Myers** · May 29, 2018, 12:14 AM

The Gold Lion KT88s sounded much better than the 6550s in the ARC VT-50 amp, for what it's worth.

**joeinid** · May 29, 2018, 12:46 AM

Thanks Randy.

**nc42acc** · May 29, 2018, 01:58 PM

I think this is a completely different application of the 6550 or a KT88 in the ARC REF10. It used in the power supply in a capacity I am not sure of. Anyone know how this tube is used?

**La Dolce Vita** · May 29, 2018, 02:01 PM

Originally Posted by nc42acc

I think this is a completely different application of the 6550 or a KT88 in the ARC REF10. It used in the power supply in a capacity I am not sure of. Anyone know how this tube is used?

I think you just stated it - it’s used in the power supply not the signal or output stage.

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**microstrip** · May 29, 2018, 02:39 PM

Originally Posted by nc42acc

I think this is a completely different application of the 6550 or a KT88 in the ARC REF10. It used in the power supply in a capacity I am not sure of. Anyone know how this tube is used?

I periodically post this warning in audio forums - the 6550 it is used as a serial element in the HV voltage regulator. One of the characteristics of the 6550 tube is VG1max = -300V. Unfortunately the very similar KT88, 120 or 150 have VG1max = -200V. This means that during the warm up or power down phase your KT xxx in power supplies can break. For this same reason some of their amplifiers using 6550's having driver cathode coupling to the grid one coupling had to be modified to use the KT120's or KT150's.

**nc42acc** · May 29, 2018, 02:56 PM

Thank you.....I think I remember you or someone else making this statement in the past. Could be an expensive swap especially for a ARC REF10.

Originally Posted by microstrip

I periodically post this warning in audio forums - the 6550 it is used as a serial element in the HV voltage regulator. One of the characteristics of the 6550 tube is VG1max = -300V. Unfortunately the very similar KT88, 120 or 150 have VG1max = -200V. This means that during the warm up or power down phase your KT xxx in power supplies can break. For this same reason some of their amplifiers using 6550's having driver cathode coupling to the grid one coupling had to be modified to use the KT120's or KT150's.

**Barry** · May 29, 2018, 05:37 PM

Originally Posted by microstrip

One of the characteristics of the 6550 tube is VG1max = -300V. Unfortunately the very similar KT88, 120 or 150 have VG1max = -200V.

Micro, are you sure? If I look at data sheets for a SED Winged C and a Svetlana KT-88, the VG1 max for both are -300V. It appears some KT88s have a higher rating.

Have you acutally measured the power up / down voltage for the regulator circuit?

**Mike** · May 29, 2018, 06:05 PM

I asked Warren at ARC and he said using KT88’s is fine instead of the 6550. You may or may not like the sonic change.

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**Billion$Baby** · May 29, 2018, 06:22 PM

Originally Posted by joeinid

I think it’s worth a try.

You have my vote to be the Guinea Pig. Let me know how it works out will ya?

**joeinid** · May 29, 2018, 06:39 PM

Absolutely. I'll place an order this week.

Originally Posted by Billion$Baby

You have my vote to be the Guinea Pig. Let me know how it works out will ya?

**microstrip** · May 29, 2018, 07:55 PM

Originally Posted by Barry

Micro, are you sure? If I look at data sheets for a SED Winged C and a Svetlana KT-88, the VG1 max for both are -300V. It appears some KT88s have a higher rating.

Have you acutally measured the power up / down voltage for the regulator circuit?

Yes, it depends on brands - I was referring to Tungsol datasheets, see page 2 www.tungsol.com/specs/kt120-tung-sol-specs-curves.pdf

**microstrip** · May 29, 2018, 08:01 PM

Originally Posted by Mike

I asked Warren at ARC and he said using KT88’s is fine instead of the 6550. You may or may not like the sonic change.

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Then it is possible, many thanks. Good news for ARC owners, NOS 6550 are terribly expensive. Did you ask it specifically for the REF10 or also for older power supplies using the 6550 in series? The advice I got was also from ARC, but about older models - about 10 years ago, I think I owned a REF3.

Anything about using the KT120?

**nc42acc** · May 29, 2018, 08:02 PM

Joe please let us know when the planned swap will happen. I will look for a mushroom cloud to my north.

**microstrip** · May 29, 2018, 08:23 PM

Probably they have changed their opinion, but in 2013 we debated this issue about the REF5 in another audio forum and ARC were clear https://www.audioaficionado.org/show...6&postcount=34 - the KT88 should not be used as serial element in the power supply.

**joeinid** · May 29, 2018, 08:23 PM

Hahahahahahha, look for the fire sale.

**Barry** · May 29, 2018, 09:11 PM

In the REF 10 Phono, I much prefer the Shuguang Treasure KT88 Zs over both the SED "C" and the Sovteks.

Of couse YMMV, but may be worth trying.

**XV-1** · May 30, 2018, 01:59 AM

Originally Posted by joeinid

I’m thinking about doing it. But curious what you guys think.

didn't take long Joe

what are you not liking in the Ref10 in order to look at changing tubes?

**joeinid** · May 30, 2018, 05:44 AM

Honestly, there’s nothing I don’t like about it. I absolutely love it. Mike said ARC recommended the change to him. I’m not even sure what the difference will sound like.

I am trying to find it again, but somewhere I read that the 6550 tubes ARC preamps should be changed at 2K hours, not at the 4K hours like the rest in the preamps. I can’t remember where I saw that.

ps. Don’t tell me GAT owners never roll their tubes

Originally Posted by XV-1

didn't take long Joe

what are you not liking in the Ref10 in order to look at changing tubes?

**Harlequin** · May 30, 2018, 07:28 AM

Some food for thought.

http://psvanetube.com/wordpress/psva...-mullard-kt88/

**Harlequin** · May 30, 2018, 07:31 AM

Originally Posted by joeinid

ps. Don’t tell me GAT owners never roll their tubes

Cannot see that helping Joe

**joeinid** · May 30, 2018, 07:39 AM

Thank you so much for that link. Very interesting.

Originally Posted by Harlequin

Some food for thought.

http://psvanetube.com/wordpress/psva...-mullard-kt88/

**joeinid** · May 30, 2018, 07:42 AM

As a former GAT owner x 2, I realize we all can’t leave well enough alone. I know someone who uses 2 different tubes in his GAT so that the “mix” of the music finally hitting him sort of blends into a custom signature. Very interesting concept.

Originally Posted by Harlequin

Cannot see that helping Joe

**Harlequin** · May 30, 2018, 07:55 AM

A few more comments.

http://www.audiokarma.org/forums/ind...s-kt88.241929/

**nc42acc** · May 30, 2018, 08:18 AM

I think they are running the tube hard in whatever capacity it is being used in the POWER SUPPLY!!!

Originally Posted by joeinid

Honestly, there’s nothing I don’t like about it. I absolutely love it. Mike said ARC recommended the change to him. I’m not even sure what the difference will sound like.

I am trying to find it again, but somewhere I read that the 6550 tubes ARC preamps should be changed at 2K hours, not at the 4K hours like the rest in the preamps. I can’t remember where I saw that.

ps. Don’t tell me GAT owners never roll their tubes

**Barry** · May 30, 2018, 10:36 AM

Originally Posted by joeinid

I am trying to find it again, but somewhere I read that the 6550 tubes ARC preamps should be changed at 2K hours, not at the 4K hours like the rest in the preamps. I can’t remember where I saw that.

Ah... in the Owners Manual....

**joeinid** · May 30, 2018, 05:22 PM

Originally Posted by Barry

Ah... in the Owners Manual....

The vacuum tubes inside your Reference 10 are quality tubes and with
normal use should not need to be changed for approximately 4,000 hours
of use.

That's from the manual but I don't remember where I saw that the 6550s needed changing at 2,000 hours. Still looking ...

**joeinid** · May 30, 2018, 05:25 PM

http://www.tonepublications.com/revi...f-6-linestage/

To get the most from the REF 6 tube complement, one menu option allows the user to see the number of hours on the current tubes. According to AR, new 6550WE tubes should serve their owner for about 2,000 hours, and the 6H30 tubes offer roughly twice that life span. When the tubes eventually wear out, ARC offers carefully matched replacement tubes. As there are not a lot of variations on the 6H30 tube, just giving the factory a call is the easiest way to roll. To maximize tube life, owners will delight in another REF 6 feature. The owner can set an automatic preamp shutdown to engage at a one to eight-hour interval. This feature can be disabled if you prefer fully manual control.

**joeinid** · May 30, 2018, 05:32 PM

https://soundstageultra.com/index.ph...0-preamplifier

The 6H30 tubes ARC supplies with the Ref 10 have an estimated life of 4000 hours, though word on the street recommends that they be replaced after 3000 hours (2000 hours for the two 6550s).

http://www.theaudiobeat.com/equipmen...ference_10.htm

The 6H30s are spec'd for 4000 hours of use and the 6550s for 2000 hours. A built-in time counter makes it easy to follow tube usage and know when replacement is nigh.

**Barry** · May 30, 2018, 08:03 PM

Originally Posted by joeinid

The vacuum tubes inside your Reference 10 are quality tubes and with
normal use should not need to be changed for approximately 4,000 hours
of use.

That's interesting. I checked the Ref10 preamp manual too & it's not in there. It is in the REF40 and Ref 10 Phono manuals under the "Servicing" section (the 2 units I have).

Another tube to try in the PS besides the Psvanes are the newer Shuguang Treasure KT-88 Z CBs. They are supposed to have an extended top and bottom end v. the earlier KT-88 Zs.

In my system, the Ref10 Phono seems to respond a little more positively to tube rolling KT-88s than the Preamp where I was completely happy with the SED Winged Cs. I liked the Sovtek in the Phono better than the SED Cs as there was a little more clarity and immediacy. Dropping in the Shuguang Zs removed a bit of mist/fine grain evident with either of the 6550Cs.

They're all different sonically so YMMV of course.

**Mike** · May 30, 2018, 08:05 PM

Hey guys - I got a box of these gems today:

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**Mike** · May 31, 2018, 02:44 PM

The test system.

Tried a NOS 1960’s GoldLion KT88.

Results:

More body.
Sweeter on top.
Overall, muddier, less transparent sound.

Conclusion:

The stock 6550 was preferred in this shootout.

Will try a Winged C, current GL KT88 and the new KR Audio later.

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**joeinid** · May 31, 2018, 02:46 PM

Awesome Mike, thank you so much.

**Harlequin** · June 2, 2018, 08:53 AM

How did your Ref6 fare with the " Winged C, current GL KT88 and the new KR Audio later " Mike

**Mike** · June 2, 2018, 09:12 AM

Originally Posted by Harlequin

How did your Ref6 fare with the " Winged C, current GL KT88 and the new KR Audio later " Mike

Haven’t tried yet.

**Harlequin** · June 4, 2018, 07:25 AM

Originally Posted by Mike

Haven’t tried yet.

what could possibly be more important

**Barry** · June 7, 2018, 04:35 PM

So I tried a pair of Shuguang Treasure KT-88Z CBs (burned in 150hrs) in the PS of my ARC REF10 phono and think I like them best of all (v. Sovtek WEs, SED Cs, Shuguang KT-88Zs). Started to compare them directly, back-to-back, to the earlier Shuguang KT-88Zs, but one of that pair went dead after only 125 hours of use. Not exactly enthusiastic endorsing these, as I've never had a PS big tube failure. I have ordered another pair anyway. Thankfully, no damage was done.

I still have SED Winged "C"s in the ARC REF 40 preamp and really have little desire to swap them out for now as I liked them better than the Sovteks, but who knows....

May buy a pair of Psvanes to try later. More to follow if I don't get too lazy and the weather is also perfect for cycling these days. Got 640 miles in last month.

**Harlequin** · June 8, 2018, 08:50 AM

Most interesting Barry, pleased to read that you survived that valve fail unscathed.

**Mike** · August 8, 2018, 06:48 PM

Originally Posted by Barry

So I tried a pair of Shuguang Treasure KT-88Z CBs (burned in 150hrs) in the PS of my ARC REF10 phono and think I like them best of all (v. Sovtek WEs, SED Cs, Shuguang KT-88Zs). Started to compare them directly, back-to-back, to the earlier Shuguang KT-88Zs, but one of that pair went dead after only 125 hours of use. Not exactly enthusiastic endorsing these, as I've never had a PS big tube failure. I have ordered another pair anyway. Thankfully, no damage was done.

I still have SED Winged "C"s in the ARC REF 40 preamp and really have little desire to swap them out for now as I liked them better than the Sovteks, but who knows....

May buy a pair of Psvanes to try later. More to follow if I don't get too lazy and the weather is also perfect for cycling these days. Got 640 miles in last month.

I swapped out the Sovtek 6550’s today and installed my NOS, matched SED Winged C 6550’s (from here: https://rover.ebay.com/rover/0/0/0?m...2F283069212072)

Much fleshier sound, slight increase in sweetness, just a touch of warmth. Vocals were the most improved. Vocals and instruments had a greater 3D presentation. I would consider the improvement quite significant.

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**Mike** · August 8, 2018, 08:20 PM

Still listening. Loving this change. HIGHLY recommended.

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**Audio 1** · August 8, 2018, 09:43 PM

I just ordered a set for my Ref.6 pre and Ref.3 phono-pre.

**Bobvin** · August 8, 2018, 10:48 PM

There were some problems I remember with the later winged C valves, can anyone speak to when the production began to be sketchy? I know I had purchased some and they caused me some round trip repairs to ARC, but I don't know how old "NOS" needs to be?

**Barry** · August 8, 2018, 11:25 PM

Originally Posted by Bobvin

There were some problems I remember with the later winged C valves, can anyone speak to when the production began to be sketchy? I know I had purchased some and they caused me some round trip repairs to ARC, but I don't know how old "NOS" needs to be?

I have a few dozen of the SED Winged "C"s including newer ones. You should try to avoid anything 2011 or newer (11XX). I've bought new production from reputable suppliers that have very low plate current as measured on my Amplitrex tester using fixed bias that tested as low as 40-80% of spec. They also may have a very poor vacuum. I've had ones gas out even before I used them. The best quality SEDs were sourced from ARC and were well worth the additional cost. They'd test north of 100% even after 1,000 hours of use.

It's not critical that the tubes be exactly matched as ARC REF PS 6550 tubes are autobiased, but I match mine anyway.

**Elberoth** · August 9, 2018, 07:50 AM

Some 10+ years ago, when I still had my ARC Ref 3 preamp, I had great success with NOS Tung-Sol 6550 Black Plate from the 50s. Those tubes got hard to get nowadays AFAIK.

**Mike** · August 9, 2018, 10:22 AM

Originally Posted by Elberoth

Some 10+ years ago, when I still had my ARC Ref 3 preamp, I had great success with NOS Tung-Sol 6550 Black Plate from the 50s. Those tubes got hard to get nowadays AFAIK.

Found a matched quad of these this morning. Going to try them.

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**mep** · August 9, 2018, 11:42 AM

Geez, I have a NOS GE 6550 that came from ARC as a spare for a D-79 I used to own. I wonder how that would sound in the Ref 6?

Thread: So has anyone replaced the 6550s in their Ref 10 with KT88s?

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