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Kendrick's 11-winding interleaved Output Trans' - hype or real?


 
4/20/2000 4:05 PM
Mark
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Kendrick's 11-winding interleaved Output Trans' - hype or real?
In looking around for OPT options for a Princeton Reverb, I came across Kendrick's 'Special 11-winding Interleaved OPT' that claims to make 2 x 6V6 amps as loud as a 50 watt Marshall. Selling at a hefty $225, it had better hold up to its claim! It's too much $'s for me but I am curious if anyone has any experience with this trans and if they can share any comments.  
 
BTW, no one yet has been able to tell me whether or not the stock OPT's in PR's and DR's are interleaved. Anyone know this one?
 
4/20/2000 4:14 PM
R.G.
quote:
"claims to make 2 x 6V6 amps as loud as a 50 watt Marshall"
 
 
Huh? To the best of my knowledge, interleaving has nothing to do with output volume, everything to do with frequency response.  
 
Interleaving reduces leakage inductance, which increases high frequency response. It has some side effects, but that is the primary effect. It's mostly got nothing to do with "loudness". Power output is affected primarily by impedance matching (get it right and get the most power) and a little bit by distortion (some distortions sound like more loudness to the human ear), and perhaps a little bit by extended frequency response - if you hear more highs and lows, there actually is more power going out, but this effect should be trivial compared to matching.  
 
I think Gerry's getting the techie stuff wrong again. Interleaving *is* our friend, but it doesn't make EL84's into KT90's. Speakers might.
 
4/20/2000 4:37 PM
John Stokes
This is yet another example of Gerrie using hype and bullshit to justify his insane pricing. In interleaved transformer is a good thing, but it won't make a 20 Watt amp as loud as a 50 Watt amp driving the same speakers.  
 
As far as I know, DR and PR transformers were not interleaved.  
 
Like I told the other guy, take everything Gerrie says with a grain of salt. He's trying to sell his stuff.
 
4/20/2000 4:33 PM
Ray Ivers
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Mark,  
 
I've had a couple of Kendrick transformers in the last few weeks (I had to send them back because my customer didn't want to drill the holes for the four-bolt mount in his brown Vibrolux) and I can tell you they looked really well-made to me. In the process, I also have 'tech/dealer' status with Kendrick for the next 5 months or so and can get parts for 40 percent off, if that's of any interest.  
 
I do believe the original Fender transformers WERE interleaved, although not with 11 windings (did I read 7 somewhere?). Interleaving is done to reduce leakage inductance and improve high-frequency response (thank you, Randall Aiken) and is generally a feature of higher-quality output transformers, although I don't know about interleaving with toroidal transformers, which are some of the highest-quality output transformers around.  
 
It's possible that an upgraded transformer, in a 2-6V6 amp with a sufficiently beefy power supply (not a Princeton Reverb, in my opinion), could cause enough of a midrange power boost to sound almost as loud as a 50-watt Marshall using the same speaker. I would NOT want to be those 6V6's, though, as they will probably be trying to supply the maximum current their cathode coatings will allow, way above the 'design maximum' ratings in the tube manual. The expression 'burning a candle at both ends' comes to mind.  
 
 
I just recently put a Hammond 1645 transformer in a tweed Deluxe (I've also put in 3-knob reverb, B/M/T tone controls, overdrive, and an effects loop, with NO VISIBLE DRILLING! - hey, it's what the customer wanted) and I think it's a nice unit - power went from about 15 watts up to a solid 30, using the original Triad PT. The unit is small, about the size of an AC30 OPT, and rated conservatively for 30 watts. The 1650F (25 watts)is more of the 'correct' plate load for 6V6's, and will probably sound more original. The nice thing about Hammonds - you've got all the secondary impedance options available, although the arrangement of the multiple secondary windings can make 3-way impedance switching a pain.  
 
Hope this helps!  
 
Ray Ivers  
R.A.G.E. Electronics
 
4/20/2000 5:34 PM
Carl Z
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This is such total and complete BS I don't know how the man keeps from getting his ass sued off! There is no way in hell any pair of 6V6's can approach a pair of 6L6's in any frequency spectrum or with any voltage. PERIOD!!!!  
 
As you raise your B+ voltage your power output is going to increase. However by the time you reach levels that would produce power equivalent to a 6L6 you will have burned up your tubes and/or your output transformer.  
 
The little experiment on the Deluxe is interesting but 30 watt still isn't even close to 6L6 power. Most of these will spec out at around 42 watts before clipping. You can get substantially more than that after distortion sets in. In the neighborhood of 60 watts!  
 
Granted you may be able to squeeze a few watts out of a pair of 6V6's by optimizing the transformer load but you won't get 60 watts or even 42 watts.  
 
Also at maximum power output you will also have minimized the life of the tubes. Double your power and cut your tube life in half. I don't like the idea of burning up a pair of 6V6's every 2 to 3 months for the sake of an additional 3 dB of output gain.  
 
Regards;  
Carl Z  
Summit Amplifiers
 
4/20/2000 6:37 PM
Ray Ivers
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Carl,  
 
I didn't mean to say in my posting that changing the output transformer could change the output power of a 2-6V6 output stage to equal that of a 6L6 stage. What I did say is that you could ALMOST equal the VOLUME of a 50 watt Marshall, at mid-band and at great expense to tube life. I stand by that statement. A 3 dB reduction in volume, which is really not audibly all that much, would correspond to an output power level of 25 watts RMS - or 17 watts RMS if you believe that a 50-watt Marshall puts out 34 watts, as I've seen repeatedly in print - which is well within the abilities of a pair of 6V6's in an optimized-for-power output stage. Personally, my '67 Plexi puts out almost 75 watts with a SS rectifier, about 65 with a 5AR4. I've seen 34 watt Marshall 50's, too. I've seen 140-watt Marshall 100's, along with 80-watt ones.  
 
I have seen two garden-variety Russian black-bottle 6V6's put out 29.6 volts RMS at (mild) clipping, into an 8-ohm speaker load, at 400 Hz - roughly 110 watts. I saw this - I did this. Details on request, and definitely NOT recommended, but I wanted to push the envelope, so I did. If I had had 9-pin sockets to play with, I would have plugged in EL84's. The 6V6's plates did not glow, nor did they short out or get especially hot to the touch, although I only did this for less than 30 seconds. The wonders of Class B!  
 
This Deluxe is actually running Groove Tube 6V6HD's, which are not a 6V6 at all but a weird Russian tube halfway between a 6V6 and a 6L6. Of all the tubes I tried in that amp, these tubes seemed to like the 5K plate load the best. High voltage dropped from 500+ no-load to about 390 volts at full 30 watt output. I don't mean to contradict you, and perhaps I misunderstood what you said, but I don't think any Deluxe will put out 42 watts clean. Perhaps by "most of these" you were referring to 6L6 amps?  
 
I hope the Kendrick statement was just hype, because I agree with you - pushing 6V6's that hard is not a good thing to do.  
 
Ray Ivers  
R.A.G.E. Electronics
 
4/20/2000 8:33 PM
Doc
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Interleaving, or sectionalizing the primary and secondary windings into multiple alternating layers, can increase coupling efficiency and thereby reduce the conversion losses.  
 
An output transformer can be built with say 1/2 the primary being layed down, then the entire secondary, then the remaining half-primary which will result in moderate coupling and power conversion efficiency. I suspect that this type of trans was built for many Fender amps. Steven Delft's AX84 output transformer is wound this way.  
 
A better grade transformer, having a better frequency response and higher power conversion efficiency can be built by breaking up the primary and secondary into many sections. Your better hifi transformers are wound this way. For instance, Peerless 20-20 Plus series transformers have a higher efficiency than the regular grade (albeit still high grade) Peerless output transformers.  
 
Using a better grade output transformer can make your amp noticeably louder, due to increased conversion efficiency, but we all know Gerald exxagerates a bit. He's a salesman.
 
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