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More on capacitors http://dcaudiodiy.com/phpBB3/viewtopic.php?f=5&t=1734 |
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Author: | ArthurOtt [ November 2nd, 2020, 1:30 pm ] |
Post subject: | Re: More on capacitors |
Hello, I also own a BAT VK3i preamp but I don't have it in my system currently. I was actually thinking about selling it. It was recapped in 2019 with the stock Jensen 1uF 400 VDC caps. I see that you've done some mods on your VK3i in regard to the caps. Can you tell me more about what you've done and how it's changed the performance of the preamp? Thx......Arthur |
Author: | SoundMods [ November 2nd, 2020, 3:56 pm ] | ||||
Post subject: | Re: More on capacitors | ||||
ArthurOtt wrote: Hello, I also own a BAT VK3i preamp but I don't have it in my system currently. I was actually thinking about selling it. It was recapped in 2019 with the stock Jensen 1uF 400 VDC caps. I see that you've done some mods on your VK3i in regard to the caps. Can you tell me more about what you've done and how it's changed the performance of the preamp? Thx......Arthur I discussed the end result when I announced the discovery of the Russian Hybrid caps. As far as global upgrades are concerned -- the question is -- what didn't I do? All of the power supply caps were replaced with industrial-grade products having a 105-degree C or better rating and designed for long life and low ESR. The 1-ufd power-supply bypass caps were replaced with 20-ufd polycarbonate caps bypassed with .27-ufd CRC hermetic Teflon caps The 1-Kohm grid-stop resistors were replaced with RN-65 Vishay bulk-film resistors. The input resistors were candidates but "buried" under the four volume control boards (disassembly is not recommended). The Jensen output couplers were replaced with hermetic 2.2-ufd K75-24 Russian hybrid capacitors bypassed with .25-ufd Tex-Cap hermetic Teflon caps. Output buffer resistors were added as the pre-amp was designed without any. ??? I installed Vishay RN-90 bulk-film resistors. Past mods included shielding to limit RF contamination from the digital volume level controller. I also added 2-ufd capacitors across the filament supply to the 6V6 current sources Tube complement is Eastern Block Amperex ECC88s and mil-spec RCA metal jacket 6V6s. Teflon damping rings were installed on the ECC88s and Pearl Coolers on the 6V6s. Case work included extensive constrained layer damping where-ever possible using ceramic tiles and RTV silicone. Since I am obsessive (no surprise there) I blinged-up the cosmetics. Was all that WORK justified and worth it? DAMN RIGHT!!! I had no interest in any other pre-amps either new or used. For me -- this baby is a keeper!
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Author: | ArthurOtt [ November 2nd, 2020, 4:18 pm ] |
Post subject: | Re: More on capacitors |
Wow! I thought you just changed out the output caps and that made all the difference. I could handle that. I didn't know you had done extensive mods. I bought the Beckert Labs Rhumba 1.2 tube preamp because I wasn't happy with the VK3i. Some good NOS tubes helped but I just wasn't able to get the transparency and openness from it that I wanted. Sounds like you've been able to do that with the mods you've implemented. It's not a bad preamp but it's not great in its stock configuration. Thx for the info. |
Author: | Pelliott321 [ November 2nd, 2020, 4:23 pm ] |
Post subject: | Re: More on capacitors |
he is avid and I mean avid crazy man |
Author: | Roscoe Primrose [ November 2nd, 2020, 4:31 pm ] |
Post subject: | Re: More on capacitors |
Pelliott321 wrote: he is avid and I mean avid crazy man Who here isn't |
Author: | SoundMods [ November 2nd, 2020, 5:24 pm ] | ||
Post subject: | Re: More on capacitors | ||
ArthurOtt wrote: Wow! I thought you just changed out the output caps and that made all the difference. I could handle that. I didn't know you had done extensive mods. I bought the Beckert Labs Rhumba 1.2 tube preamp because I wasn't happy with the VK3i. Some good NOS tubes helped but I just wasn't able to get the transparency and openness from it that I wanted. Sounds like you've been able to do that with the mods you've implemented. It's not a bad preamp but it's not great in its stock configuration. Thx for the info. I've tried numerous tubes in the BAT. What works best are either Eastern Block Amperex ECC88s, Valvo ECC88s, or Tesla Gold-Grid ECC88s. The only 6V6 current-source tubes that really gave the pre-amp the breath of life were the metal 6V6s. BTW -- you can't change tubes without re-setting the bias and balance -- otherwise it's a fools' errand. The coupling caps I used provided most of the improvement -- but since I had to do a full disassembly to replace them I went after anything and everything. Like I said, the BAT is a keeper and I wanted to extend its expected useful life.
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Author: | ArthurOtt [ November 2nd, 2020, 6:24 pm ] |
Post subject: | Re: More on capacitors |
My VK3i seemed to sound best with a quad of Philips Miniwatt ECC88 tubes and a pair of Mazda 6V6GT from the 1950s. I wasn't aware there were user-accessible bias and balance adjustments on the VK3i. |
Author: | SoundMods [ November 2nd, 2020, 7:48 pm ] |
Post subject: | Re: More on capacitors |
ArthurOtt wrote: My VK3i seemed to sound best with a quad of Philips Miniwatt ECC88 tubes and a pair of Mazda 6V6GT from the 1950s. I wasn't aware there were user-accessible bias and balance adjustments on the VK3i. Yep. That's what has to be done when changing tubes. And BTW -- no glass envelope 6V6s work as well. Why? The metal enclosure of the metal tubes is tied to ground and shields the critical current source from the self-generated RFI of the display and volume control electronics. |
Author: | DaveR [ November 3rd, 2020, 1:05 pm ] |
Post subject: | Re: More on capacitors |
Roscoe Primrose wrote: Pelliott321 wrote: he is avid and I mean avid crazy man Who here isn't Indeed. |
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