Don't forget the load of the input capacitance of the grid of the preamp tube.

I appreciate your experience and knowledge in hi-fi and tubes.Very professional. I have a question: I want to replace the kt88 stock tubes in my Willsenton R8.What do you choose between Genalex gold lion kt88 and Electroakustik black diamond KT88 nade in USA ? Kind regards

@tubelab194

Жыл бұрын

First off nobody has made vacuum tubes in the USA, in any quantity, since about 1982. Genalex is an old brand name and is being used to rebrand a Russian power tube made in Saratov Russia by New Sensor of New York. They make all kinds of reissues (rebrands) including Gold Lion, mullard, Tesla and Svetlana - none of them are anywhere close to the original vintage tube. Electroakustik is an old brand name, for what is probably a rebranded Chinese power tube - stay away - far far away from Chinese power tubes. The very best KT88's i've ever heard were true vintage Svetlana's (St. Petersburg) - a rare and hard to find tube these days - I make 2 or 3 quads up a year and they sell instantly. CAUTION! many Fakes and Reissues for this tube - none of them sound the same. One good option for the R8 is the true vintage Svetlana 6550c, a lower powered KT88, which is perfect for the R8. The R8 is basically an EL34 amp that can play KT77, 6550c and KT88 tubes - but because it doesn't have the voltage required by a KT88 to come close to max power, they are mostly wasted on the amp. And of course the R8 sounds amazing with vintage EL34's.

Good quality capacitors are quite expensive. Can c4 and c5 be replaced with small capacity?

@tubelab194

Жыл бұрын

Yes you can with some guidelines below. I use these high quality Solen "Fast Caps" in all of the Kit Amps, so we just standardized the voltage rating at 400v to cover a wide range of circuits. C4 needs to be rated for about 287vdc (239x120%) and C5 197vdc (164 x 120%). That's if your B+ is close to the design value of 402vdc. I use a minimum of 120% rating to give room for startup voltage surge, variations in household mains and to increase the lifespan of the coupling capacitors. Going cheap on coupling caps is never a good idea, if sonics are important to you!

I really love GU-50 I made wonderfull amps with it. The only thing that seems odd is that you put the G2 to plate voltage. Since I read Russian, they are really specific about not exceeding 250V. The plate can go to 1000V I made a push-pull monoblock with 500V plate and 250V on G2. It sounds wonderfully and it is shy of 20W rms.

@tubelab194

Жыл бұрын

Agreed! sound and durability of GU50 is very good. We of course work from Russian data sheet, but are not afraid to try different configurations and voltages. In many cases mil spec Soviet era tubes can operate safely outside of firm specifications under certain conditions and with careful testing and trials to confirm. We had a maximum 400vdc to work with and found in various quasi triode mode tests that the GU50 had more power (0.25w) and sounded better with G2,G3 strapped to the plate. We have 100's of hours on our original tubes and they still work perfectly and sound amazing.

@vextenoch

Жыл бұрын

@@tubelab194 thanks. Since you love triodes, you should try 6S19P (6С19П) it's about 5watt wonderfully sounding cheap tube.

Can you find a cheap deal on some GM-100 tubes?

@tubelab194

Жыл бұрын

Haha no such thing as a cheap GM100! Are you seriously thinking of working with 1,000 to 1,500v (1.0 - 1.5kV)? Other than the novelty of working with something that will kill you if you make one mistake, why not work with tubes like the GU-50 that are readily available, affordable and sound amazing. We have 5 bench supplies and one of them goes to 1kV and even though I know what I'm doing, my hands start to shake when i need to use it at max power!

@josepheccles9341

Жыл бұрын

@@tubelab194 When I first found them they were on ebay as cheap as 100 dollars each. After the war started the cheapest I have found is like 300 each. I have an eimac 3-1000Z that I have been messing with. You just know that you will only ever make one mistake. There are some commercially sold monoblocks using them. But I wanted to make one before finding that one.