I'm going to order the Stereo 70 driver board. Can anyone give me a rundown of the differences between stock vs the Russian cap upgrade? I've decide to do the upgrade to 306uf, but can't decide on the coupling cap upgrade.
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Bob Latino
Brent70
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Cap upgrades on VTA boards
Brent70- Posts : 5
Join date : 2009-12-08
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Brent70 wrote:I'm going to order the Stereo 70 driver board. Can anyone give me a rundown of the differences between stock vs the Russian cap upgrade? I've decide to do the upgrade to 306uf, but can't decide on the coupling cap upgrade.
Hi,
The Russian K40-Y paper in oil (PIO) caps are military caps that were made in Russia during the cold war. They are very well made caps and IMHO are as good sounding (or better) than much more expensive coupling capacitors available from Mundorf, Hovland, Auricap etc.. I have used over 700 of these capacitors in my own amps and in kit amps shipped to customers. Everyone has been pleased with the sound and AFAIK not one of the 700+ caps has ever failed. They do take maybe 200 - 400 hours of play time to completely break in but if you stick with them you will be rewarded with a very smooth and effortless sound with a large soundstage.
Bob
Brent70- Posts : 5
Join date : 2009-12-08
Sounds like the way to go.
Thanks!
Thanks!
Tube Nube- Posts : 707
Join date : 2008-12-06
Age : 61
Location : Calgary, AB
Their hulking size and the fact they seem to weigh about a pound each only enhances ones confidence that the things are robust!
;-)
;-)
vegaseddoc- Posts : 12
Join date : 2009-11-21
I've been using the K40y caps that Bob sent in my ST-120 kit. They are fantastic. I have some 0.1 mfd 1000V K42 PIO caps laying around and I was wondering if there would be any "sonic improvement" by placing these in the C1,2,3,4 positions. They are large but I can make them fit. Anyone have any experience doing this or other cap modifications?
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vegaseddoc wrote:I've been using the K40y caps that Bob sent in my ST-120 kit. They are fantastic. I have some 0.1 mfd 1000V K42 PIO caps laying around and I was wondering if there would be any "sonic improvement" by placing these in the C1,2,3,4 positions. They are large but I can make them fit. Anyone have any experience doing this or other cap modifications?
Hi,
Of the 4 caps that you mention (C1, 2, 3, 4) on the VTA driver board only C1 and C2 are really directly in the signal path. These are the two .10 @ 400 volt orange drop caps usually placed on the top of the driver board. I have tried Russian PIO caps here (C1 and C2) and they didn't seem to make much of a difference over the stock 716P caps normally used here. You could TRY the Russian caps that you have in this position and let us know what you think ? I honestly have never tried changing out C3 and C4 which are normally installed on the bottom of the driver board.
Bob
RockyAM- Posts : 26
Join date : 2008-12-14
I have a VTA driver board on my ST-70. When I bought the amp from a guy on Audiogon last year it had the stock orange coupling caps. I pulled these and tried some other caps in their place. In order, I tried Auricaps, Jensens and some REL Audiocaps. They were all OK sounding with the REL's seeming to sound the best of the three. As a last resort I ordered some of the K40-Y Russian PIO caps from a Russian seller on Ebay. I ordered 10 of these because I wanted to try four of them in another amp. I believe these are the same caps that Bob has as an option with his kits. They were a little larger than the other caps and I had to insulate the leads when I installed them. Immediately I noticed that the soundstage seemed larger with the Russian K40 caps and the sound seemed more focussed. Since they seemed (initially) the best of the four, I left them in there and let them burn in over many listening sessions spanning 3 or 4 months. I never believed much in this burning in thing but sure as hell they seemed to get better as the weeks progressed. There was a guy on the Tube DIY Asylum who made the comment that with more and more play time these Russian caps "sneak up on you like buzz on good weed" 
and I think he was right. They do seem to get better with more playing time. The bottom end seems to go deeper and the top end has better extension and the sound itself is more holographic. RockyAM
and I think he was right. They do seem to get better with more playing time. The bottom end seems to go deeper and the top end has better extension and the sound itself is more holographic. RockyAMLast edited by RockyAM on Thu Dec 20, 2012 10:29 am; edited 1 time in total
vegaseddoc- Posts : 12
Join date : 2009-11-21
Thanks for the input. Since I have them I will give the mod a try. I'll let them run for at least 100 hours before I give my impression. I don't have the greatest ears in the world, but I will try to be as objective as possible.
Brent70- Posts : 5
Join date : 2009-12-08
Bob,
What EL34s do you like in the Stereo 70? I've been partial to the Winged Cs, but they are getting fairly pricey. I've tried JJs, but felt they really colored the sound.
What EL34s do you like in the Stereo 70? I've been partial to the Winged Cs, but they are getting fairly pricey. I've tried JJs, but felt they really colored the sound.
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Brent70 wrote:Bob,
What EL34s do you like in the Stereo 70? I've been partial to the Winged Cs, but they are getting fairly pricey. I've tried JJs, but felt they really colored the sound.
Hi Brent,
My favorite tube in the VTA ST-70 is presently not an EL34. I use the Genalex Gold Lion KT66's in my own ST-70. They are also pricey at about $150 a matched quad but IMHO are probably worth it if you want to extract the best out of your ST-70.
These KT66's are exact copies of the original Genalex tubes with gold plated grid wires, carbonized screen grids, and a tri-alloy plate structure. The outer glass seems thicker and the tubes weigh more than an EL34.
For an inexpensive EL34 tube any of the Chinese Shuguang made EL34B tubes are excellent for rather low bucks. Sometimes these are sold under the Ruby or Valve Art name. These are only about $12 each or $48 a matched quad and are a good buy. Check out the reviews on modern EL34's at the link below ...
The Tubestore's EL34 reviews
Bob
Brent70- Posts : 5
Join date : 2009-12-08
Any mods needed to run the KT66s in the 70? I'm installing the VTA board. I agree, those are great tubes. I've used them in guitar amps.
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Brent70 wrote:Any mods needed to run the KT66s in the 70? I'm installing the VTA board. I agree, those are great tubes. I've used them in guitar amps.
Hi Brent,
Just plug in the KT66's in place of the EL34's and up the bias setting a little. I bias them at .450 volts DC per tube and IMHO they seem to sound better at this setting than the normal .400 VDC setting that you would use for an EL34.
Bob
Brent70- Posts : 5
Join date : 2009-12-08
Sounds like a plan. I have the VTA board on the way. I just received the 80/40/30/20 cap from Dynakit parts (they seem to be the only people to have them.) I'll get the Gold Lions next week too. Should be up and running within 2 weeks. I'll enjoy the last of the stock Stereo 70 this weekend.
Bugs- Posts : 90
Join date : 2009-04-17
Another EL34 option is the Tungsol EL-34B. You can find them at a lower cost the the Winged-C. I've been going back and forth between the Genalex KT-66s and the Tung-sols and switching back and forth between triode and pentode mode. To my ear, the Tun-sols in pentode sound pretty close to the KT-66s rounded-off in triode and Tung-sols are even more rounded-off in triode mode. In pentode the KT-66s give better highs and bass.
vegaseddoc- Posts : 12
Join date : 2009-11-21
Took a while to make sure the k42 caps in the c1-4 were broken-in before I made a critical assessment. I honestly here no difference (even though psychologically I want to). The caps Bob sends with the amp are a perfect size and sound great. I wouldn't bother changing the caps in these positions. Most other caps (like the K42s) are difficult to fit on the board so I don't think is worth the expense or the hassle for an "upgrade" in these positions.
kost- Posts : 35
Join date : 2009-05-12
Age : 60
Location : athens
hi
the k-42 are not as good as the k40,they are completely diferent.
Good capacitors are the k40,k75 and teflon ft3.
The k75 and the teflons are hudge and it is very tricky to fit.
I ill try and let you know
the k-42 are not as good as the k40,they are completely diferent.
Good capacitors are the k40,k75 and teflon ft3.
The k75 and the teflons are hudge and it is very tricky to fit.
I ill try and let you know
Bob Latino- Admin
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kost wrote:hi
the k-42 are not as good as the k40,they are completely diferent.
Good capacitors are the k40,k75 and teflon ft3.
The k75 and the teflons are hudge and it is very tricky to fit.
I ill try and let you know
Hi Kost,
Some say that the K42-Y are not a true PIO cap. People have taken these apart and some have found metallized paper with some kind of "grease" but no oil. I am not sure whether they are even a true "paper in oil" capacitor even though they continue to be advertised as "PIO capacitors" by Russian sellers. It was thought that the K-42's were a later series and an attempt by the Russian's to make a cap for less money than the K40-Y's. People have taken K40's apart and they do have a heavy oil inside. All the K42-Y's that I have seen were green in color. The K40-Y's usually have a gray metal case and are true PIO capacitors. Some K40-Y's have a metal case but the case is painted a brownish tan color.
IMHO > There is a big difference in sound quality between the K40-Y and the K42-Y's. The K40's are more tonally accurate and smoother sounding. I still have a bunch of K42's here but I won't use them in my amps or put them in anyone's amp that I am working on. K40-Y caps are excellent main coupling caps in Dynaco or almost any tube amp. When used in earlier stages of a tube amp's circuitry, the K40's don't seem to have as much impact on the sound of the amp.
Bob