KT88s ain't cheap

NickS · Post by **NickS** » Mon Mar 03, 2008 1:18 pm

Matched set of 4 GEC KT88s on eBay - Â£375 with 2 days to go?!
There's a pair of 200W Sowter OPTs from the same seller at Â£102. Seems arse about face to me. (Hmm, what are those old bottles in the workshop drawer? I bet they're only KT66s)

Post by **Mike** » Mon Mar 03, 2008 1:21 pm

Matched quad of those should be Â£80-90 since they're Â£20 each.

I don't like them anyway really, way too much clean headroom.

Bacchus · Post by **Bacchus** » Mon Mar 03, 2008 1:22 pm

Perhaps this is a really obvious question, but I know fuck all about tubes, so here goes:

How would he know that they're not microphonic if he's never used them?

Post by **Mike** » Mon Mar 03, 2008 1:24 pm

Generally Power Tubes don't go microphonic.

NickS · Post by **NickS** » Mon Mar 03, 2008 1:26 pm

BacchusPaul wrote:Perhaps this is a really obvious question, but I know fuck all about tubes, so here goes:

How would he know that they're not microphonic if he's never used them?

..apart from sticking them in his monster hifi amp to check they still work..I know what you mean.

Bacchus · Post by **Bacchus** » Mon Mar 03, 2008 1:27 pm

Oh. Why is that?

It's just that he answers a question mentioning microphony in the answer, and it got me thinking.

Post by **Mike** » Mon Mar 03, 2008 1:30 pm

BacchusPaul wrote:Oh. Why is that?

It's just that he answers a question mentioning microphony in the answer, and it got me thinking.

I dunno, it's just one of those things, I'll do some digging.

There is always the possibility he's a dick.

Post by **Mike** » Mon Mar 03, 2008 1:35 pm

http://www.mesaboogie.com/US/Dealers/FAQs/faqs.html

Suggests that Power tubes only blow (short) or are noisy. Preamp tubes (especially V1) are susceptible to noticeable microphonics because they are the start of the chain, their output is amplified by the preamp and power amp tubes following, amplifying any microphony.

This belongs in Effects.Amps, I'm moving in there now.

NickS · Post by **NickS** » Mon Mar 03, 2008 1:38 pm

Mike wrote:This belongs in Effects.Amps, I'm moving in there now.

My bad, I keep posting "Ripleys Believe It Or Not" posts in the Pub 'cos I think the other forums are for serious discussion. Then the discussion turns serious, I guess.

jcyphe · Post by **jcyphe** » Tue Mar 04, 2008 12:17 am

KT-88's think Billy Corgan Marshall tone, that's what he put in alot of his marshalls. hendrix too, who used 6550s which i think is basically the same type of tube, they are interchangeable.

What Mike says is true, lots of Marshall players that use strats and are looking for "more cleans" do this mod, hence Hendrix and Corgan.

filtercap · Post by **filtercap** » Tue Mar 04, 2008 12:25 am

Ampeg SVT + KT88's = tasty. Also expensive, because you need six of them, matched.

Ninja Mike 808 · Post by **Ninja Mike 808** » Tue Mar 04, 2008 4:10 am

Ok, so in mics, you get matched sets so that they're as close to sounding like each other as possible.

Is this still true with tubes? I think the answer might be obvious...

filtercap · Post by **filtercap** » Tue Mar 04, 2008 8:41 am

Ninja Mike 808 wrote:Ok, so in mics, you get matched sets so that they're as close to sounding like each other as possible.

Is this still true with tubes? I think the answer might be obvious...

It's true with the power tubes for most "push-pull" amps. Though it isn't exactly because they sound alike. It's more that they pass a similar amount of electrical current through when provided with a given control voltage. In other words, with microphones you might want two that respond to a given sound the same way, and with tubes you want two (or whatever number) that respond to electrical voltages the same way.

In a "push-pull" amplifier, one tube (or set of tubes) amplifies the top half of each sound wave ("push"), and another tube (or set of tubes) amplifies the bottom half ("pull"). If the two tubes (or sets) are very similar in performance, the two halves of the wave are amplified in a very similar manner, and the resulting sound wave is a good reproduction of the input signal. If the two tubes (or sets) perform differently, with one amplifying more than the other, the resulting wave is lopsided and not an accurate reproduction of the input signal.

Sometimes a certain amount of lopsidedness sounds good when amplifying a guitar, but generally the idea is to match the performance of the tubes on the "push" side with the tubes on the "pull" side. Some amps provide a balance control to do this. However the most common way is to measure the performance of each tube, and gather together a bunch of tubes with very similar characteristics. Tube dealers often do this, and sell the matched groups.

NickS · Post by **NickS** » Tue Mar 04, 2008 8:41 am

Ninja Mike 808 wrote:Ok, so in mics, you get matched sets so that they're as close to sounding like each other as possible.

Is this still true with tubes? I think the answer might be obvious...

Yeah, in a push/pull (Class AB or B) amp you want them with the same bias and gain so the negative and positive halves of the waveform have the same characteristic.
KT88s do 100W/pair, I have a GEC application note for a 400W amp using 8 KT88s.

Ninja Mike 808 · Post by **Ninja Mike 808** » Tue Mar 04, 2008 9:36 am

Ok, cool. I love learning!

Post by **Mike** » Tue Mar 04, 2008 9:51 am

I only use two tubes in my amp and have a bias control for each, I basically don't worry about matching at all. I think it's a bit snake oil.

jcyphe · Post by **jcyphe** » Wed Mar 05, 2008 3:36 pm

Mike wrote:I only use two tubes in my amp and have a bias control for each, I basically don't worry about matching at all. I think it's a bit snake oil.

The funny thing is nobody routinely did any of that stuff until the 70's when the dudes from Groove Tube came along and started labeling and matching replacement sets of tubes. I read stories about old blues guitar players stealling each others tubes, but that was more out of jealousy.

The tones of the late 40's, 50's, 60's and early 70's I consider to be the best guitar wise, but people didn't really pay attention to any of the stuff we do now. So i do thinka big part of it is snake oil, and people should just shut up and play what sounds good.

Post by **Mike** » Wed Mar 05, 2008 3:43 pm

jcyphe wrote:
Mike wrote:I only use two tubes in my amp and have a bias control for each, I basically don't worry about matching at all. I think it's a bit snake oil.
The funny thing is nobody routinely did any of that stuff until the 70's when the dudes from Groove Tube came along and started labeling and matching replacement sets of tubes. I read stories about old blues guitar players stealling each others tubes, but that was more out of jealousy.

The tones of the late 40's, 50's, 60's and early 70's I consider to be the best guitar wise, but people didn't really pay attention to any of the stuff we do now. So i do thinka big part of it is snake oil, and people should just shut up and play what sounds good.

Totally. Also, when you think about it, since when has symmetrical waveforms ever been a concern of anyone involved in MAKING music not REPRODUCING it. I hate it when Hi-Fi science gets in the way of Music. I had a mess about with the bias on my head recently and guess what? You can't hear a noticeable "badness" when the two side of the push-pull are out by even 10%. Get that thing out of crossover distortion and that's all that matters. Hotter bias doesn't necessarily mean better either, bias really only affects the compression and attack as far as I can tell. I set mine a little higher than stock but not insane.

The "big" guitar sounds were, as you say, being made by people breaking the rules, doing all the wrong things. The AC/DC crunch is a JTM45 on fullwhack basically destroying Greenback 25W speakers. The Money For Nothing sound was a small Laney amp and some hokey mic/baffle placement that they could never recreate. Apparently they were going for a ZZ Top sound and when Knopfler wanted to retrack they couldn't get that sound again, in the same room with the same setup and tools. That's music.

Post by **Doog** » Wed Mar 05, 2008 4:31 pm

And the good ol' Kink slashing his speaker for furzeeee.

euan · Post by **euan** » Wed Mar 05, 2008 5:59 pm

Mike wrote: Apparently they were going for a ZZ Top sound and when Knopfler wanted to retrack they couldn't get that sound again, in the same room with the same setup and tools. That's music.

Cocaine.