kt88s or 6550s in a ad200b

Orange Amps Technical Q&A's

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Jane Starship
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Post by Jane Starship » Mon Jan 28, 2008 4:06 am

I have a ad200b on the way and was wondering if anyone suggests using kt88s instead of the 6550s? I assume the amp would need to be re biased, is there anything else that would have to be done?

markjazzbassist
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Post by markjazzbassist » Mon Jan 28, 2008 6:42 am

you can use either. and like you said if you did switch to kt88's you have to get it re-biased. other than that, that's it.

good luck.

what kinda tubes you looking to put in it?
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boroman
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Post by boroman » Mon Jan 28, 2008 10:28 am

Mark, if you put another set of 6550's you must bias it too. Everytime you put any power tube on it you must bias it.

I would like to switch to kt88's but noone told me what it will sound like...

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Post by bassdrop » Tue Jan 29, 2008 7:24 pm

There was somebody that posted about installing KT88's in the AD200 a couple of months ago (I believe they were JJ's). He seemed to like them. I replaced the original tubes when they were 1 year old and they still had a good bit of life in them. The replacements were early 90's GE 6550A's which are the least expensive NOS of the 6550 variant, although the price continues to go up. The sound improved but nowhere near as much as when I replaced the preamp tubes with NOS types.

According to Doug from dougstubes.com, the best new production KT88's are the Sovtek reissued Gold Lion and the Penta Labs.
mmmmmm drop

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Jane Starship
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Post by Jane Starship » Wed Jan 30, 2008 3:18 am

I need to use the amp with the 6550s first and decide I was thinking it might give it a lil more headroom/wattage using the KT88s??
I have another question my MkIII head has 3 speaker inputs 2-4 ohm and 1-8 ohm, I have 2, 8 ohm cabs....do I need to daisy chain the two cabs (cabs have 2 inputs each) together, then run a chord from one cab into one 4ohm output??
thanks

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Post by bassdrop » Wed Jan 30, 2008 7:52 pm

Re: speaker outputs. You can daisy chain the 8 ohm cabs together and run from the 4 ohm output on the amp as you mentioned. You could also hook each 8 ohm cab directly to the 4 ohm outputs on the amp.

KT88's will sound different than 6550's. How much, I'm not sure since I've never A/B'd them. If you wish to improve the clean headroom after hearing the amp and experimenting you could always try what I did. Get a 5751 tube to install in either V1 or V2 to lower the gain slightly. I found that with the stock tubes the overdrive came on incredibly early. You can read my review of the AD200 on Harmony Central to read about all of the tube rolling I did.:D
mmmmmm drop

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Jane Starship
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Post by Jane Starship » Thu Jan 31, 2008 2:08 am

is there any difference in plugging each cab to its own input on the head or is it basically the same daisy chaining?
doesnt 4 6550 tubes only put out 100 watts? I have had Marshalls 100s with 4-6550 and my old Sound City 200 had 4-kt88s.

I like a lil break up but if its too much Ill have to change them.

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Post by boroman » Thu Jan 31, 2008 11:58 am

every 6550 tube has about 50 watts
6l6/el34 - 25 watts
el84 - 7-10 watts

bassdrop
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Post by bassdrop » Thu Jan 31, 2008 7:09 pm

Correct. In an amplifier that can provide full plate voltage, and operates the tubes in fixed bias Class A/B each pair of 6550s will produce 100 watts.

There is little difference in sound that I can tell between daisy chaining or connecting directly. Another user here seemed to think it would be more reliable connecting directly.
mmmmmm drop

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Post by boroman » Thu Jan 31, 2008 9:18 pm

bassdrop, yeah, i always wondering how it;s possible eg. that some of the amps with 2xel84 are 14watts, and some other operating on the same tubes is 20 watts... is there a rule here? does kt88 has the same power as 6550's?

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Post by bassdrop » Sat Feb 02, 2008 8:15 pm

It is possible to get more wattage out of a KT88 due to its higher rating, but it comes at the expense of reliability. Since modern tubes are made with weaker vacuums and cathodes of lesser purity, due to the lower numbers of production and limited competition in the tube market these days, pretty much all amp designers play it safe so that you don't have to install new tubes every couple of months. So one of the advantages of a KT88 should be better reliability due to that higher rating. Some would also say better tone, but as we all know that is subjective.
mmmmmm drop

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Modified Fender Custom Shop Jazz, Warmoth P/J clone,
Orange AD200 MkIII, Barefaced Compact

Jane Starship
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Post by Jane Starship » Sun Feb 03, 2008 5:35 pm

would a kt88 be more reliable than the 6550?

bassdrop
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Post by bassdrop » Mon Feb 04, 2008 4:06 pm

Notice my use of the word should. This is because all other variable would have to be equal and considering that modern tube manufacturing tolerances are nowhere near as tight as they were it is not possible to say with any certainty that any KT88 would be more reliable than any 6550.

However, based solely on the ratings of the KT88, running that same KT88 in a 6550 circuit should make it more reliable- again all things being equal.
mmmmmm drop

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Modified Fender Custom Shop Jazz, Warmoth P/J clone,
Orange AD200 MkIII, Barefaced Compact

ardent
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Post by ardent » Fri Feb 08, 2008 4:04 am

this post might be a little late but i switch to kt88's and love them i run my master at 8 and just roll in the gain to get a warmer tone. the kt88 have a bit more headroom then the 6550 that i ran before. but then again i prefer cleaner amps, i just switched my first preamp tube to a ge 12au7 and love the cleaner tone i now get.
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Post by boroman » Fri Feb 08, 2008 7:54 am

Are KT88's warmer in sound than 6550's? Are they lasting longer than 6550s?

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