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Author Topic: OTS with KT88?  (Read 6191 times)
JD0x0
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« on: March 31, 2009, 10:38:44 PM »
Can an OTS use KT88 power tubes? With biasing ofcourse.

Are there any simple mods to makes this work?
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JohnE
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« Reply #1 on: March 31, 2009, 11:55:37 PM »
I don't think it would be a good idea.  The KT88 is designed to operate with a plate voltage of 600-800 max. I believe the OTS is 425-450. The current output transformer, etc. would not support KT88s.

Also my personal experience is that there is little reason, other than to satisfy your curiosity, to do a conversion. Several years ago, I did a fairly major overhaul of a '66 Super Reverb (this is before I knew that they would be such a collectors item). Since I was replacing most of the components I decided to upgrade the output transformer (50W vs. 40W),  etc. to support EL34s. The net result was a much louder amp, that still sounded like a Super Reverb. Contrary to what most people think, output tubes do not change the tone of an amp that much. On the Super Reverb, changing brands (e.g., JJ to Sovtek) seems to change the tone as much as 6L6 to EL34.     
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JD0x0
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« Reply #2 on: April 02, 2009, 04:41:04 AM »
hmm i was just thinking the added headroom would be nice plus KT-88s get awesome bass response.

How about 6550's or other higher headroom tubes?
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JohnE
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« Reply #3 on: April 02, 2009, 09:32:13 PM »
Quote from: JD0x0 on April 02, 2009, 04:41:04 AM
hmm i was just thinking the added headroom would be nice plus KT-88s get awesome bass response.

How about 6550's or other higher headroom tubes?
6550s and KT88s are equivalent. Also after sending the post above I read the link for Eurotubes in one of Hywel's posts on biasing. In there, Bob was talking about substituting 4 KT88s for 6L6s in a Twin and how good it sounds. I think if you email Bob at Eurotubes and give him the amp specs he can probably provide some  valuable guidance on this subject.

I think I mentioned that I set up my super reverb to run EL34s. If I want clean headroom at high volume with that amp I use JJ KT77s (amazing tubes) and a 12AT7 in the PI. The amp breaks up at about 4 with a 12AX7 and humbuckers, but stays clean up to 8 with the AT7.
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JD0x0
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« Reply #4 on: April 04, 2009, 02:57:47 AM »
I found this on the webber site

6550 - 35W  Hot (70%) Avg (60%) Cool (50%)
400V            61mA         53mA         44mA
425V            58mA         49mA         41mA
450V            54mA         47mA         39mA
475V            52mA         44mA         37mA
500V            49mA         42mA         35mA
525V            47mA         40mA         33mA
550V            45mA         38mA         32mA
575V            43mA         37mA         30mA
600V            41mA         35mA         29mA

for reference heres EL34 and 6L6

EL34 - 25W  Hot (70%) Avg (60%) Cool (50%)
300V 58mA 50mA 42mA
325V 54mA 46mA 38mA
350V 50mA 43mA 36mA
375V 47mA 40mA 33mA
400V 44mA 38mA 31mA
425V 41mA 35mA 29mA
450V 39mA 33mA 28mA
475V 37mA 32mA 26mA
500V 35mA 30mA 25mA

 


--------------------------------------------------------------------------------

 

6L6GC - 30W  Hot (70%) Avg (60%) Cool (50%)
300V 70mA 60mA 50mA
325V 65mA 55mA 46mA
350V 60mA 51mA 43mA
375V 56mA 48mA 40mA
400V 53mA 45mA 38mA
425V 49mA 42mA 35mA
450V 47mA 40mA 33mA
475V 44mA 38mA 32mA
500V 42mA 36mA 30mA


« Last Edit: April 04, 2009, 03:00:11 AM by JD0x0 » Logged
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JohnE
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« Reply #5 on: April 04, 2009, 03:57:33 AM »
I am familiar with that chart. I built a Weber Bassman kit about 3 years ago. I would still check with someone knowledgeable before I started running KT88s in my OTS. 
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JD0x0
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« Reply #6 on: April 04, 2009, 05:54:09 AM »
i'll probably bring it to a tech when i get my hiwatt recapped
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hywelg
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« Reply #7 on: April 04, 2009, 09:58:42 AM »
Quote from: JD0x0 on April 04, 2009, 02:57:47 AM
I found this on the webber site

Immensely useful thanks.
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