VTA ST 70 - What are your favorite tubes?

Hi guys,

I am new to this forum, to DIY audio and have just completed one of Bob's ST 70 kits, that I ordered with the cap upgrades, KT 88 tubes and the TDR. The amp just sounds awesome and I am very excited. I am also looking forward to try different tubes. So I was wondering, which one's you guys like?

Hope to get lots of ideas from the community.

Link to my VTA ST-70 kit assembly blog > Michael's VTA ST-70 blog

Michael

Michael,

Welcome to the forum. I have one of Bob's ST120's that I built over four years ago. Great amp. As to the KT88 power tubes, I have tried Gold Lion, Elektroharmonics, JJ, and Penta Labs. All of the tubes made in eastern Europe had quality problems/failures in less than a year. Granted when they did work their sound was very good, (I think that Bob's amps are really what make the tubes sound their best). Gold Lion failed with two weeks, JJ made almost a year. The tubes from Penta Labs are their KT88SC version with solid plates and are made in China by Shuguang. These tubes have lasted the longest. They are going on 3 years now and they sound great. I have come to the conclusion that it is the luck of the draw regarding tubes now days. The old saying "don't buy a car made on a Monday or a Friday" surely would hold true in this situation if we could choose. Being that the ST70 uses lower voltages you may have better longevity with the KT88's. Hope you have many enjoyable years of listening, I know that I have.

ArlanB

Thank you for your reply. The number of brands and types is a bit overwhelming in the beginning. Also, the range in prices. And I found, that Ebay is not really a cheap place either. Lots seem to be cheaper here: http://www.btb-elektronik.de/de/endstufen_roehren.html
It would be interesting to know, if it is worth spending $500+ on 4 output tubes. KT 88 from PSVANE for example are in this range. Or will there be hardly any difference over the Sovotek that I have and that I like. Any opinions?

Michael

I have tried valve art ( supplied from bob), jj-kt77 ( very nice ) jj-e34l ( some crossing
distrorsion in spite of elevated bias ) jj-el34 ( nice full sound)

Will test jj-jt88 when time allows

( yes i have access to jj tubes, makes lifer both easier and more economical :-)

Now i have jj-6550 in my vta-70
it seems that bias between 0.42 0.45V is needed. Any experiences with
generic 6550 in vta-70 What bias is used and why ?

Bob Latino wrote:

peterh wrote:Now i have jj-6550 in my vta-70
it seems that bias between 0.42 0.45V is needed. Any experiences with
generic 6550 in vta-70 What bias is used and why ?

Hi Peter,

In the VTA ST-70 assembly manual it mentions that 6550 or KT88 output tubes should be biased at about .50 VDC. KT88 and 6550 tubes (IMHO) when used in the VTA ST-70 need a somwhat higher bias point than EL34's.

Bob

I know i have read it somewhere! Ok ill do that and hopfully they will get a bit hotter
( measuring the anodes with an ir-thermometer gives 125-135 degrees C right now)

< grunkgrunk>
Now i have .5V on all catodes. I also have app. 175 degrees C on alla anodes, about
the same as the anodes on the valveArt EL34 that got .4V Maybe anode temperature
is another good indicator on bias.

I have now put some Siemens NOS ECC82 (quite pricey at EUR50 a piece....) and matched quad EL34 Svetlana SED winged C into my VTA ST-70. Very nice sound. Compared to the Sovotek KT88 and JAN 5963, which I like btw., the sound is even more balanced. The soundstage seems wider and very stable. Biggest difference I find is in Triode mode. I did not like the KT88 in Triode mode due to a clear lack in the bass region. I always used them in Pentode mode. With the EL34 I have not yet made up my mind, which mode I prefer.

Best regards


Michael

Now i'm running jj kt-88 . And there is a difference, maybe it's the lower
tube lower impedans that makes the difference.

Now i have just what i want, clean brilliant high, clean voices and firm bass that goes all the way down. I think i'll keep it this way. I even mounted the cover to keep me from fiddling with the stuff :-)

Groove Tube EL-34Ms.

After trying several brands and types - EL34, KT88, etc. my hands down favorite are the new production Genalex Gold Lion KT66s.