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07/25/21 at 19:38:06 


       


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Question about tube replacement (Read 368 times)
pineman
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Posts: 15
Question about tube replacement
04/04/21 at 22:54:55
 
I have been enjoying the ZMA for over six years now and recently replaced all 4 output tubes when one of them began to fail.  Is it generally advised to replace the input and regulator tubes at the same time, or do those typically last much longer?
Thanks!
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VPI Classic w/ Ortofon 2M Black, ZP3; PS Audio DSD & PST; ZMA, Zenstyx; Bösendorfer VC-7
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HockessinKid
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Posts: 699
Re: Question about tube replacement
Reply #1 - 04/04/21 at 23:06:15
 
You don't need to replace the input tubes if your output (power) tubes are getting noisey. The stock input tubes usually last a long time.

I suggest you get a new matched quad of output tubes. There are several very decent sounding new production tubes - TungSol, Gold Lion (New Sensor), etc. I really like the sound of TungSol 7027a substitute tubes for the KT66 tubes. A matched quartet can be purchased online for ~$120. Easy swap out, I bias these at ~58 mV.

HK
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Nottingham Interspace TT w/ Dynavector 20x2 cart + Modwright PH 9.0X phono pre OR Modwright modded Cambridge CNX V2 streamer/DAC > CSP3-25th mods preamp > ZMA-25th mods amp > PI Audio UberBUSS > Omega SAHO XRS or Caintuck Lii15+ speakers > various cables & tweaks.
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Archie
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Posts: 2294
Re: Question about tube replacement
Reply #2 - 04/04/21 at 23:32:45
 
I concur about the Tung Sol 7027As.  I bias at 64 to 68mA though.  My last quad seemed short lived but I only got 8 to 9 months out of the quad before that.  Maybe my high bias is the issue?  How long are yours lasting?  I pull mine when one or more starts to drift.
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
ZMC1
ZP3 (25th A Mods)
ZR2 (25th A Mods) -- currently not in use
CSP3 (25th A mods)
ZMA (25th A mods)
Homemade Big Betsy Speakers (F15s)
Silver Cabling
DIY Isolation platforms under amps & TT.
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HockessinKid
Seasoned Member
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Posts: 699
Re: Question about tube replacement
Reply #3 - 04/04/21 at 23:59:48
 
Archie,

I've been getting about 18 months on a quad, guessing 1600-1800 hours. I calculated bias at 58mV using the plate voltage. I think your biasing a bit high which will lead to shorter power tube life.

Happy Easter.

HK
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Nottingham Interspace TT w/ Dynavector 20x2 cart + Modwright PH 9.0X phono pre OR Modwright modded Cambridge CNX V2 streamer/DAC > CSP3-25th mods preamp > ZMA-25th mods amp > PI Audio UberBUSS > Omega SAHO XRS or Caintuck Lii15+ speakers > various cables & tweaks.
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Archie
Seasoned Member
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Posts: 2294
Re: Question about tube replacement
Reply #4 - 04/05/21 at 00:12:11
 
I'm in the "Class A" range which is a 90%+ so I think you are right.  I think I'll back it off and see (hear) is there is much difference.  I didn't realize there might be a 2X effect on tube life.
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
ZMC1
ZP3 (25th A Mods)
ZR2 (25th A Mods) -- currently not in use
CSP3 (25th A mods)
ZMA (25th A mods)
Homemade Big Betsy Speakers (F15s)
Silver Cabling
DIY Isolation platforms under amps & TT.
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