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** All-tube KT88/6550 head **

R

REDLAWMAN

Jun 14, 2010
257
1
59
Cornwall, England, UK
#1
Imagine an all-valve head that's designed for four 12AX7's and four KT88's. Let's assume stock tubes are JJ.

1. Can you simply take out the KT88's and replace with 6550's (eg. Svetlana 'Winged-C's')?


2. I appreciate the evolution of both of these tubes on different sides of the Atlantic and I've read that there are different voltages, etc. in relation to certain parts of the tubes, but my current knowledge ends there.

What are the principal differences?


3. I see that you can buy 'Winged-C's' in KT88 (both regular and Cryo'-treated) and 6550 format:

Do the Svetlana KT88's sound largely similar and exhibit largely the same characteristics as the 6550's?



4. What's the real-world difference between the regular Svetlana KT88 and a Cryo'-treated one and is the latter really superior?



5. What changes am I likely to hear if I switch from the JJ's to the Svetlana?


Thanks everyone.
 
#3
You should be able to use 6550/KT88 interchangeably.

Stock JJ's should be pretty solid. At $200+ for a power tube swap, I'd just keep them. They are both pretty high end tubes. For more impact, play with your preamp tubes, start with V1.
 
#4
You can use 6550 instead of KT88 in most amps, but some might have too high plate voltage for the 6550 to take. Most amps, especially modern ones won't, the gap between the two types has closed up. There is a risk from putting KT88 into an amp designed for 6550 because the KT88 draw more heater current which can cook your transformer, but again, the gap isn't as large as it was so you'll probably get away with it. Basically, compare spec sheets for the valves, which vary between manufacturers, you'll see the heater current draw and safe maximum voltages across various parts on there.

The actual sound difference between valves is dependent on the amp, so you can't really generalise, some amps work in entirely different ways and the differences between valves will vary accordingly.
 
#8
B-string said:
By the way "Svetlana" has not been Winged "C" for a while now, they are now New Sensor/Sovtek.
Click to expand...

Uh, no. The company formerly known in the US as Svetlana lost its use of the Svetlana trademark when New Sensor bought the mark. They were forced to use "SED USA" initially, and switched to the Winged C name because the logo had been used on the tubes for decades.

(edit) See this link for the history: Invalid Link Removed (end edit)

IMHO New Sensor bought the Svetlana trademark specifically to confuse unsophisticated tube buyers.

There is a BIG difference between the tubes made in the actual Svetlana factory in St. Petersburg and the Sovtek/"Svetlana"/"Mullard"/etc. tubes made in the Reflektor factory. Unfortunately for musicians, the Svetlana factory primarily makes big radio power tubes (like 15KW of RF big!), and the audio tubes are a sideline that they only dabble in on occasion. So availability of the Winged C tubes is poor.
 
#11
KT88's can take both higher plate and screen voltage than the 6550. An amp designed for KT88's can destroy 6550's if the voltage ratings for the 6550's are exceeded. For example, a Hiwatt running KT88's with 650-700 V on the plate would probably not like 6550's in the long run.
 

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