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 Post subject: 807 to kt88 convertor
PostPosted: May 6th, 2020, 4:03 pm 
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Location: Baltimore MD
noodling around I found this
Attachment:
807_web.jpg
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https://www.amazon.com/JEMOSA-Convert-Socket-Electronic-Adapter/dp/B07NVN9B5R/ref=sr_1_11_sspa?crid=R8PINXWTQ3UW&dchild=1&keywords=kt88+tube&qid=1588793781&sprefix=kt88%2Caps%2C144&sr=8-11-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEySEJFT1AwVDBLNE0yJmVuY3J5cHRlZElkPUEwNDA0NTEyM002OERHWDcyRjZVRyZlbmNyeXB0ZWRBZElkPUEwNTYwNjI1M1M3TktZQkU0WDJQRiZ3aWRnZXROYW1lPXNwX210ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=
807 are alot cheaper than kt88
does make any since or is it stupid


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PostPosted: May 6th, 2020, 11:16 pm 
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Pelliott321 wrote:


What the hell -- it's worth a shot. You know me -- I tube-roll until I puke -- but it has paid dividends with improved sound.

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PostPosted: May 7th, 2020, 6:59 am 
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I have a KT88 SET coming in soon and this will be a good place to test


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PostPosted: May 7th, 2020, 9:37 am 
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Pelliott321 wrote:
I have a KT88 SET coming in soon and this will be a good place to test


Who knows? With a plate-cap to further separate the plate from other internal wiring it just may sound better.

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PostPosted: May 7th, 2020, 10:42 am 
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not really the plate cap wire still goes through the tube socketi


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PostPosted: May 7th, 2020, 10:49 am 
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When Walt mentioned internal wiring I'm pretty sure he was referencing the inside of the tube not necessarily the wiring of the amp


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PostPosted: May 7th, 2020, 10:52 am 
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Pelliott321 wrote:
not really the plate cap wire still goes through the tube socketi


Yes -- but that's where it ends. It's still isolated to some extent -- although I expect that would only matter when handling RF.

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PostPosted: May 7th, 2020, 12:05 pm 
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Those work very well. I use them in my Williamson amps. But I would strongly caution against replacing a KT88 with an 807, unless your circuit is adjusted for much lower plate voltage and current limits. Even replacing a 6L6GC could be more than an 807 can handle. They are rated for 400Vp max and 25 watts of plate dissipation. Some of the multi-tube SE amps, like Dennis Had's Inspire, can take advantage of the sub. My friend Jim used 807s in his Inspire with very nice results. The 807 is about as close as you can get to a 300B in sound, without the hassles or expense. ;-). It's definitely a more "vintage" sound, warm and a bit rolled-off on top, very pretty if that's what you want.

ETA: To be more clear, if the KT88 amp you ordered is triode-connected, be sure to follow the 400VDC plate maximum. If it's an "ultralinear" design I would still observe that limit. If it's a true "pentode" design with a separate screen supply then you can go higher, up to 600Vp, with a screen voltage limit of 300VDC. But I wouldn't push these very hard. My point is that these are in now way a direct substitute for a KT88. ;-)


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PostPosted: May 7th, 2020, 2:23 pm 
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Grover Gardner wrote:
Those work very well. I use them in my Williamson amps. But I would strongly caution against replacing a KT88 with an 807, unless your circuit is adjusted for much lower plate voltage and current limits. Even replacing a 6L6GC could be more than an 807 can handle. They are rated for 400Vp max and 25 watts of plate dissipation. Some of the multi-tube SE amps, like Dennis Had's Inspire, can take advantage of the sub. My friend Jim used 807s in his Inspire with very nice results. The 807 is about as close as you can get to a 300B in sound, without the hassles or expense. ;-). It's definitely a more "vintage" sound, warm and a bit rolled-off on top, very pretty if that's what you want.

ETA: To be more clear, if the KT88 amp you ordered is triode-connected, be sure to follow the 400VDC plate maximum. If it's an "ultralinear" design I would still observe that limit. If it's a true "pentode" design with a separate screen supply then you can go higher, up to 600Vp, with a screen voltage limit of 300VDC. But I wouldn't push these very hard. My point is that these are in now way a direct substitute for a KT88. ;-)


The tube data ([i]here is the link to the tube data -- http://tubedata.milbert.com/sheets/049/8/807.pdf[/i]) is not conclusive because the 807 seems to be de-rated for continuous commercial service [(CCS*)(24/7)], but for intermittent commercial and amateur service (ICAS**) the ratings are far more liberal and allow for a plate dissipation of about 72-watts at a plate voltage of 750-volts for class AB1 operation. For triode mode I am sure you can diddle with the tube bias because the data allows for a maximum of 120-ma DC plate current in triode mode. It seems this tube was designed more for rigorous commercial/industrial use than the kind of duty experienced with home stereo so in my opinion those ratings may be played with. Granted the KT-88 is "the BIG DOG" when comes to beam-power tetrodes, but a lot depends on the amplifier Paul is getting and if the designer was conservative or has tried to push the KT-88 to it's limits (not recommended).

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PostPosted: May 7th, 2020, 2:33 pm 
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If it's going to be used in any circuit that's class A, use the CCS limits....

Roscoe

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