Any infos are hard to find over the web, any chance that could be change is count, so let's try 
I have Audio Institute VR-70E (widely known as Dynavector VR-70E) where originally a pair of 6F2 is on board. Not bad Chinese Valves, but there's always could be better. I've tried 6U8A RCA, but ECF82 Polam goes much better. Those Polish Tube Valves sounds better in overall, but there is a annoying problem with vocal sibilance (especially "S" syllable).
Is there any good sounding ECF82, 6U8A, or 6F2 known by anyone? Preferably with good dynamics, good bass control, smooth mids and without overbright hi-end?
I have Audio Institute VR-70E (widely known as Dynavector VR-70E) where originally a pair of 6F2 is on board. Not bad Chinese Valves, but there's always could be better. I've tried 6U8A RCA, but ECF82 Polam goes much better. Those Polish Tube Valves sounds better in overall, but there is a annoying problem with vocal sibilance (especially "S" syllable).
Is there any good sounding ECF82, 6U8A, or 6F2 known by anyone? Preferably with good dynamics, good bass control, smooth mids and without overbright hi-end?
Neither of this - issue remains after speaker change, and not remains after back to Chinese tubes.
Amplifier is deeply modified, including small Caps addition to 400V diodes - that helps quite well, but not resolve the problem.
Apart from the above problem I love them! As a Polish guy I grow up surrounded by Polam Tube Valves - very underestimated today, also very rare. But with this issue I wont missed them if I found something better in this matter
6U8A definitely are compatible, I'll double check tomorrow, if 6EA8 have the same pin-out and are electrically the same, and let you know. That would be good to know if there is more choice on the market
I think I've seen both codes: 6U8A & 6EA8 together on some website today, but I am not 100% sure. Defo I am not not using eBay titles or descriptions as a verification, so don't worry - I wont leave inaccurate statement here
I think I've seen both codes: 6U8A & 6EA8 together on some website today, but I am not 100% sure. Defo I am not not using eBay titles or descriptions as a verification, so don't worry - I wont leave inaccurate statement here
It look like this is issue of in Dynavox VR-70E not Audio Institute VR-70E. All numbers and many values are different in mine. There is even no R35 / R36 on the board.
Nice to know. But do check that the cathode resistor has the same value as the plate resistor in the triode driver.
Changed out 6F2 for Jan Philips 6U8A in ChiFi PP schematic below...
6U8's have better brilliance up top w/ no loss of mid/lows into my Cambridge Minx XL's... But they're getting noisy after 150ish hrs of use- hum and hiss @ 0 vol that wasn't there initially.
So I weeded thru few data sheets of tri/pent equiv's in this searched thread...
Takeaway Q was construction of pentode first grid to cathode distance which garnered an app warning of arcing- does this relativity have any effect on sound? range? would seem so to me, but I'm always in 'learn' mode here.
Ordered matched 6AX8's to try, since there wasn't anything on this variant here, so we shall see.
Another Q-
Conventional wisdom here that plate and cathode resistors on PP triode inverter much match.. although they don't on current design (30k 27k). What does this imbalance do?
Thanks,
Jim
6U8's have better brilliance up top w/ no loss of mid/lows into my Cambridge Minx XL's... But they're getting noisy after 150ish hrs of use- hum and hiss @ 0 vol that wasn't there initially.
So I weeded thru few data sheets of tri/pent equiv's in this searched thread...
Takeaway Q was construction of pentode first grid to cathode distance which garnered an app warning of arcing- does this relativity have any effect on sound? range? would seem so to me, but I'm always in 'learn' mode here.
Ordered matched 6AX8's to try, since there wasn't anything on this variant here, so we shall see.
Another Q-
Conventional wisdom here that plate and cathode resistors on PP triode inverter much match.. although they don't on current design (30k 27k). What does this imbalance do?
Thanks,
Jim
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This seems to be a clone of dynavox where they also err with the cathodyn
resistors, The result is increased second overtone : distortion. Make the
resistors equal !
Instead of trying to tweak ChiFi circuit, I've designed retrofit PCB w/ proven audionote schematic. I'll be testing Chifi v audionote designs w/ same transformers & chassis. Board will also have capability to be expanded to UL mode (Rev E & F) in future. I'm sure curiosity will have me testing the different AN design's also.
Parameters aren't set yet, but thinking of using some or all of the following:
http://lcweb2.loc.gov/master/mbrs/r...ektronix Cookbook of Standard Audio Tests.pdf
Parameters aren't set yet, but thinking of using some or all of the following:
http://lcweb2.loc.gov/master/mbrs/r...ektronix Cookbook of Standard Audio Tests.pdf
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