Boully88

Hello to all

This is one of my 2003 designs , since 2002 Single ended is in fact become boring because its allways the same and people are getting used to it.

So back to push pulls, as EL34 and EL84 i allready made many before and the KT88 family is one of my favourites i choose for a KT88 design.

The other tube that would run without to many changes is the KT66, in fact the KT66 may sound better, compare the KT88 to a 300B and the KT66 to a 2A3 and you get the picture.

The reason why KT88 was chosen is because many tube companies make them and the KT66 is only made by the chinese.

The circuit :

What is so interesting in this design ?

Its apparent simplicity, its build as a stereo integrated amp, however the power output is limited as the driver cannot drive the outputstage to the limit.

The first triode 2C51 western electric and only half of it is used to produce all the gain ( mu of 35 ) and uses no feedback, the load is the Lundahl LL1660/10mA interstage tranny, also used for fase splitting.

Negative bias is added for each output tube and the inter stage is loaded to avoid ringing and other side effects.............

The output stage is connected Ultra lineair or triode using a switch to change coils on the Lundahl LL1679PP tranny.
I used 1/4 watt resistors in the cathodes to act as a slow blow fuse in case something goes wrong.

I also added a timer and a relay for the high voltage as this circuit is choke regulated and therefore cold tubes that draw no current are quite a hazard for the powersupply capacitors.

Its so simple it really comes down to the quality of the components and power supply it sounds beautifull.

For the first time i used a spectrum analyser because it tells the nature of the beast much better then a distortion meter

first row : triode connected 1.8volts , 5.6 volts ,18 volts and 20 volts on a 8 ohm load

2nd row : Ultra lineair connected 2.81v , 16v , 24v , 25v

please note that distortion of frequency generator has to be discounted, a little bit of 3rd and 5th at higher outputs,

offcourse triode connected requires more drive from generator then Ultra lineair and therefore has more distortion but if discounted the right harmonics are added and this makes this amp really good, the customers who bought it are very happy indeed.

Frequency chart measured at 2.81volts triode connected. ( the GE5670W sounded worse but measure almost identically )

Please note from 7Hz to 46Khz perfectely lineair, this is without feedback.

The kit can be obtained from stock including all you need.

Public sale price is 4999 euro build, in the shop.( we work with dealers nowadays as well )

To dealers we export as well and for DIY contact us for a quote. ( its offcourse affordable )

some pics of the inside :

Copywright @ 2004 BG webdesign for info email sales@diyparadiso.com