So has anyone replaced the 6550s in their Ref 10 with KT88s?
- Thread starter joeinid
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La Dolce Vita
New member
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
Active member
Joe
Order a pair of Gold Lions and give it a try. The Tube Store is experienced with tubes for ARC.
Order a pair of Gold Lions and give it a try. The Tube Store is experienced with tubes for ARC.
Jack
Active member
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
Well-known member
The Gold Lion KT88s sounded much better than the 6550s in the ARC VT-50 amp, for what it's worth.
nc42acc
New member
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
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I think you just stated it - it’s used in the power supply not the signal or output stage.
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microstrip
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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
New member
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.
Barry
Member
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?
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
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You have my vote to be the Guinea Pig. Let me know how it works out will ya?
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microstrip
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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
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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
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Joe please let us know when the planned swap will happen. I will look for a mushroom cloud to my north. :hey:
microstrip
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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/showpost.php?p=518986&postcount=34 - the KT88 should not be used as serial element in the power supply.
