|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
In Reply to: Sovtek KT66 posted by hurdy_gurdyman on May 18, 2002 at 10:38:42:
i've been using them in my gt se-40 for about two months. i can't tell you anything about their longevity yet, but i thonk they sound great. in my amp thay are a huge improvement over the 5881s that i was using before; more air, more open sound stage, improved bass and treble control. while i'm sure they probably don't sound as good as nos gec, gold lions, osram or mullards, they also don't cost $100 each. i got two pairs of matched quads for $180, which left me two for b/u.
Follow Ups:
It may be amplifier dependant, but, I have a mathced quad Sovtek KT-66s in my Leak TL-25 Plus amps and don't like them at all. The Svetlana EL-34s sound much better.
I also like EL34's a lot, but my amps transformer heater windings won't handle the extra current. Unless I add a small transformer just to handle the heaters, I'm stuck with a 6L6 type tube.
Dave
Dave,If you are going to add auxilliary heater power, I think you can do better by using the internal 6.3 VAC winding to power the O/P tubes and buy/build a DC supply for the small signal tubes. DC on the small signal tube heaters will lower the residual hum in the amp.
Eli D.
Thanks Eli. That is one of the options I'm considering. This amp is already absolutely dead quiet. All transformers are covered with mu-metal, plus grounded 6CG7's. You can't even tell if it's on or not with your ear 6" in front of the speaker.
Havn't decided yet if I'm switching from KT66 to EL34's. I'm going to solisit more opinions yet.
Dave
I would be very careful using KT66 type tubes if your transformer cannot handle the current requirements of EL34 tubes. KT66s require about the same current as EL34s. 6L6GC & 5881 type tubes, if my memory serves correct, draw around .6 A. whereas EL34 and KT66 filaments draw around 1A. Although KT66 tubes are similar to 6L6GC, there are differences.
Good luck
Alan Gallacher
KT66 heater current = 1.3A, EL34 = 1.5A, 6L6(any version)= 0.9a. If you've got concerns with KT66, you've got bigger concerns with EL34.
Actuall, my amp, Heath W5-M, is designed for KT66's. However, since I've changed the drivers from 12AU7's to 6CG7's, the 4 amp filliment winding just handles it with KT66's. Using EL34's will exceed the 4 amps a bit.
Dave
Well, memory didn’t serve me to well on the specific filament current ratings. I am glad that this forum is sharp enough to catch it!
I own a pair of w-5m’s also. As you know that power transformer is the weakest link of the amp. Mine run HOT!
In what areas did the 6CG7 mod improve the amp? Mine have a trick power supply with 400 v B+ and fixed bias output. The correct voltage to the front end has been maintained, but myself and some of my friends feel the existing setup of the voltage amp/ phase splitter runs out of steam before it can drive the output to full potential. I am interested in learning what you did.Alan Gallacher
I rewired the filiments for 6CG7 tubes. These have their own shields (ground pin 9) and are closer to a 6SN7 in build and sound than a 12AU7. The sound is fuller and richer with these. The difference is very noticable. It lowered my opinion of 12AU7 tubes.
I also inserted a resistor (150 ohms) following the filter choke to lower voltage just a bit. Easier on the power transformer. I use a cooling fan at reduced speed. The transformer never gets real hot anymore.
I only have one W5-M at this time. Am looking for another at a realistic price. Using a UA-2 for the other channel. It doesn't sound to bad.
Dave
Did you change any of the passive components when you changed fron 12AU7 to 6CG7 or did you just rewire the sockets? I'm contemplating a W5 tube swap out like yours but am looking over the passive values used in the original Williamson and those used in the W3 both of which used 6SN7s in the input/inverter/driver stages. As I'm sure your aware, the 6CG7/6FQ7 is the 9 pin version of the 6SN7.
I haven't changed anything but heater wires yet. The sound is very good as is, though I'm always open for expeimenting.
Dave
Alan,The mu of a 6GC7 is 20. That is set part of the tube's design. The only thing which I find helps is an good oversized power transformer with a hefty filter supply.
I find that a lot of newer units kinda skimp on the PT and electrolytic filter caps. What this can do is starve the tubes during heavy bass and strong transients. This pushes them into a non-linear region, where a lot of distortion and weak response is displayed.
Voicing the 6GC7 for more bass will only expose a weak power supply even more.
What you may want to do is setup a seperate power supply for the phase inverters and gain stage. And another PS just for the power tubes.
The extra current saved from the present power supplying all of tubes, will act as a reserve for the front end tubes. And also will give the power tubes a bit more reserve.
steve
That's an interesting idea, but it may get crowed on that chassis real quick. Also, the extra tranny's could cause hum to enter what is now the quietest tube amp I've ever heard. Life is full of compromises, isn't it. I'll give all this some thought.
Of course, the ideal solution is to find a pair of heavier power transformers. I'm keeping my eyes open.
Dave
This post is made possible by the generous support of people like you and our sponsors: