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previous: kg randall aiken has already taken thi... -- 3/31/2003 8:31 PM View Thread

Re: transformer options

4/4/2003 10:18 PM
Re: transformer options
Salesman Kevin here!  
Our QRK Quad Relay Kit easily controls up to four channels using very simple circuitry - the kit costs more than the book where the circuit was published originally (TUT2) - but its notes show how to cascade for more channels, or how to daisychain for multiple control positions.  
The advice given thus far should be heeded. You really really should build this thing as a separate amp and preamp if you absolutely must have eight output tubes. It will be much easier to transport and much simpler to change as you use it.  
As for the 200W design, if you want to keep costs to a minimum, then the audio path is best built with Hammond's 1650T. You can use it with the 5881s at the voltages required, as long as you heed the usual advice of individual 1k-5W screen resistors. You can use UL or pentode mode - UL will be cleaner and less stress on the tubes.  
Six 5881s will be sufficient but you can use eight if it makes you feel good. Similarly, you can use four 6550s/KT88s. Determining how many tubes of a given type are required for a given output stage is covered in both TUT2 and TUT3.  
If you take the fewer tubes approach, you will have easy room for an integrated amp even with three preamp channels. In any of these amps, you definitely DO NOT want regulated supplies for the any portion of the power amp. You _might_ play with such things in the preamp, but even there, the benefits are very tiny.  
As a further note, TUT3 has a simplified design for an SVT using all off-the-shelf parts, nothing custom. It sounds better than any SVT and is built all as one unit. The chapter also discusses the alternative approaches to the power supply - transformer mixing to get voltage/current, regulation or not, all-toroidal, custom. The issues of each approach are discussed so the builder can make his own choice.  
On another note: 200W as MI power goes is just not an easily marketed building block of power. 50W and 100W are. Big amps jump to 300W just because it was to be the "ultimate". Modern power plays happen at 400W. My 700W amps have been around forever and were just a numbers game as more than twice what an SVT accomplishes. I used two tubes.  
The reason 160W is so easy to do is because there is a cheap available transformer set. Four tubes of any type will get full power and the whole thing fits onto a 10x17" chassis. If you want more power, build a second PA. You can also boost power by adding a second small Tx to raise Va. That will get you 200W if you really need it.  
Numbers games can be expensive. The return rarely justifies the cost. Getting 1dB more power is harder to do with tubes than by simply re-orienting your speaker cabinets. That is an area not addressed in this thread, and most players are limited by convention in this regard. They could get more sound and better tone using almost anything other than the usual cluster, and using cabinets like those depicted on our site. (you can visit our site totally for FREE)  
Have fun  
Kevin O'Connor

andy btw, what is the url for your websi... -- 4/6/2003 9:24 PM