RedB4Black
Well-known member
Yes. I’ve run 6550s in the KT150 amps. No issues. Differences not that big of a deal. Lose a little low end and gain a little more mids. Easier to just run an EQ in the loop
Yes. I’ve run 6550s in the KT150 amps. No issues. Differences not that big of a deal. Lose a little low end and gain a little more mids. Easier to just run an EQ in the loop
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braintheory
Well-known member
Nice, that sounds like it could be more up my alley and what I was hoping for with the swap. The amp has low end power to spare lol. Did the 6550’s need to be biased at different values or the same is fine?
RedB4Black
Well-known member
I just measured the PV and calculated the bias on the Weber site. But absent doing that, I’d bias like a kt88.
I used Svetlana 6550s if I recall. I was concerned about the high plate voltage. Generally use JJ in Wizards because of that. I’ve used gold lions too without issues
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braintheory
Well-known member
Yeah I’m no tech guy at all, just a little cautious since George said I can’t use 6550’s in his KT88 DAZZ model, but maybe he was also pulling a Rick on me LOL. For some of my 6L6 amps I was also told I can’t safely use KT66’s in them
Visually (maybe structurally) 6550’s & KT88’s look different to me as do EL34’s & 6CA7’s, but I don’t really know what I’m looking at lol
RedB4Black
Well-known member
I specifically asked….Rick said I could run 6L6s in my KT66 MTL.
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braintheory
Well-known member
Cool thanks! Any chance you remember what numbers (or range) you biased the 6550’s at? If not, I guess I’ll just match wherever the KT88’s in it are currently biased at
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braintheory
Well-known member
But can’t run KT66’s in a 6L6 model Wizard right?
RedB4Black
Well-known member
No. Sorry it was a while ago and have since sold that amp
mnemonic
Active member
What are the plate and screen voltages? Kt88 can often handle higher voltages on the screens than 6550, according to the data sheets I’ve seen. I don’t know enough to know when the datasheet maximums can be exceeded.
RedB4Black
Well-known member
I got the feeling it didn’t matter.
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harddriver
Well-known member
I read this description of 6550's versus KT88's once on some tube site and I find it is pretty accurate.
They described the KT88 as a larger big bottle EL34 that can handle higher plate voltages but still has some warmth and emphasis on mids like an EL34, supposedly it is why Marshall chose the KT88's for the Marshall Majors and why Jimmy Page had KT88's installed in his Marshall's at one point.
The same site described 6550's as a big big bottle 6L6 that can handle more plate voltage and more rugged, 6550's are quite linear and balanced in the sonic spectrum much like a 6L6 and my ears also agree with that description.
So if you like EL34's the KT88's might float your boat and if you like 6L6's then the 6550's might be your tube.
The only new production KT88 I did not like was the JJKT88 it was just too warm and undefined soft in the attack, but some people really love them. I like the Sovtek, SED, and EH KT88's all of those sound great and usually are reliable. As for 6550's try to find some NOS SED's or even GE6550A's but the new New Sensor EH's and Svetlana are pretty decent. I've been running older SED and Svetlana 6550B and C's for years and they are great sounding tubes and very reliable.
Here's the description of the JJKT88 from Doug's tubes and it is accurate and why I didn't care for them.
https://dougstubes.com/collections/6550-kt88-kt90/products/ruby-kt88-cz
"The Ruby KT88-CZ has a tightly compressed bottom end that is perfect for jazz and audio. Just like the JJ KT88, repackaged by Ruby Tubes."
If you like a compressed bottom end then you might like the JJKT88.
Stay away from the Valve Arts 6550 A tubes, they were supposed to be a copy of the GE6550A's and the couple of sets I tried went bad quickly and one or two started to red plate and or shorted completely out. I won't run another set of them. There are people selling old NOS new or tested used SED's/Winged C's on Ebay every now and then and they are my favorite.
KT88's and 6550 should bias in the same range.
They described the KT88 as a larger big bottle EL34 that can handle higher plate voltages but still has some warmth and emphasis on mids like an EL34, supposedly it is why Marshall chose the KT88's for the Marshall Majors and why Jimmy Page had KT88's installed in his Marshall's at one point.
The same site described 6550's as a big big bottle 6L6 that can handle more plate voltage and more rugged, 6550's are quite linear and balanced in the sonic spectrum much like a 6L6 and my ears also agree with that description.
So if you like EL34's the KT88's might float your boat and if you like 6L6's then the 6550's might be your tube.
The only new production KT88 I did not like was the JJKT88 it was just too warm and undefined soft in the attack, but some people really love them. I like the Sovtek, SED, and EH KT88's all of those sound great and usually are reliable. As for 6550's try to find some NOS SED's or even GE6550A's but the new New Sensor EH's and Svetlana are pretty decent. I've been running older SED and Svetlana 6550B and C's for years and they are great sounding tubes and very reliable.
Here's the description of the JJKT88 from Doug's tubes and it is accurate and why I didn't care for them.
https://dougstubes.com/collections/6550-kt88-kt90/products/ruby-kt88-cz
"The Ruby KT88-CZ has a tightly compressed bottom end that is perfect for jazz and audio. Just like the JJ KT88, repackaged by Ruby Tubes."
If you like a compressed bottom end then you might like the JJKT88.
Stay away from the Valve Arts 6550 A tubes, they were supposed to be a copy of the GE6550A's and the couple of sets I tried went bad quickly and one or two started to red plate and or shorted completely out. I won't run another set of them. There are people selling old NOS new or tested used SED's/Winged C's on Ebay every now and then and they are my favorite.
KT88's and 6550 should bias in the same range.
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harddriver
Well-known member
Good advice....especially regarding new production tubes.
thegame
Well-known member
When I buy an amp it’s 100% mine to do with as I please and I’ll put my dick in it if I want to.
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braintheory
Well-known member
So this is Rick’s response… Thoughts?
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braintheory
Well-known member
I had the same issue with the Valve Arts 6550A’s, but actually thought they sounded good while they worked. My Winged C and pre-Winged C Svetlana 6550’s sound good, but my older US ones sound a level above in my amps (GE, RCA, Sylvania, JAN Philips and Coke bottle US Tung-Sol’s). KT88’s sound sort of like a higher powered KT77 to me. KT90’s I find sound more EL34-like
thegame
Well-known member
Just order several more Hell Razors with every power tube option there is. You know you will eventually.
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Racerxrated
Well-known member
Well, I'd keep it at 88s only then. I was reading up on the KT88 and IF you design a circuit for the maximum allowed current for a KT88, the 6550s may not be able to handle it. This is where you'd somehow measure how high the current is, and look for the spec sheet on 6550s and see if maybe certain ones can handle it, like the GE.
But it's probably better to be safe and just use 88s.
The VHTs probably run at a lower voltage than the Wizards, by a good enough margin that one can use all those types...KT88, 6550, KT90 and not sweat it.
glpg80
Well-known member
6550’s cannot handle a large screen grid voltage. You have to supply a second supply voltage as it’s too much of a drop to triode strap with just a resistor at the rated power levels.
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Racerxrated
Well-known member
Really?? Well, maybe if you've never tried GE 6550s. They are as '3D' as any EL34, or 6L6...fantastic. Winged Cs are good too, but take a back seat to the GEs.
6550 is not an "audio" tube. It was created for servo amps in B-52 Bombers.
They're not bad in 50 watt JMP's but are sterile, brittle & harsh in 100 watt guitar amps.
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Racerxrated
Well-known member
I found this on an Audio site...
M-O KT88
Va -------800V max
Vg2 -----600V max
gm ------11.5mA/V
Pa+G2-- 46W max /40W rated
GE 6550A
Va--------660V max
Vg2------440V max (450V UL)
gm-------11mA/V
Pa+G2---42W/42W
The 6550A has a higher rated voltage max then the regular non A 6550. I'd imagine Rick has the Wizard close to the max rating of the 88.