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In Reply to: RE: It's Cary indeed. posted by ianm0 on December 17, 2014 at 15:18:00
I'd be happy to PSUD2 the supply, if you want me to. Have the schematic's URL ?
That ripple you quote is "off" in my opinion, without checking, simulating. Waht did Mike Samra post about HIS cary on the AA ?? !!!
jeff medwin
Follow Ups:
The ripple estimate is based on the following measured values:
Transformer secondary: 375-0-375 VAC; B+=495 VDC
Ripple = 1 - 495/(375 *1.414)=6.6%
Are you trying to say there is 32.67 VAC on the 495 VDC B+ line ??
.066 times 495 VDC ???
If so...no way !!!!! Put a multimeter on that spot and measure VAC !!
In any case, you do not need or want 600 uF effective there, way too large.
LOOK at the new technology WIMA DC LINK caps in the 800 to 1000 VDC range, maybe 100 uF or 150 uF !!!
Jeff Medwin
Perhaps my non-engineer perception of ripple is causing mis-communication. The "ripple" I mentioned was actually the voltage drop from peak to that at start of next charge cycle.
I have looked up datasheets of DC Link caps. They are too large to be used as drop-in replacement, being 85 mm in diameter & the existing caps are of 51 mm.
I agree that 600 uF maybe too large, but what would be the appropriate replacement value?
If you could tell me what the current draw is on the supply, ( current of tubes in each stage ) I could PSUD2 model it, and we could jointly figure out what uF values will be good to chose from. Maybe leave it up to others on Forum to comment, with YOU having the final choice.My rough "guess" would be to try 100 to 200 uF, but I prefer to MODEL/ simulate it. In my own tube amps, I never use over 50 uF, BUT, I also use multiple series chokes as in L1/C1/L2/C2. Let me see If I can look-up Mike Samra's post on what he did with a Cary to reduce it, it was a few years ago. We have better cap choices in late 2014.
Also, there are many makers of this new technology DC LINK cap, to name a few, WIMA, VISHAY, EPCOS, PANASONIC. The caps you use do NOT have to be round !!! You can " gut" the 1200 uF cans, and place the FAR FAR FAR better sounding DC LINKS inside, using GE Silicone 2 to hold them in place. These DC LINK caps are designed for pulsed response, which is exactly what an audio amp does, reproduces PULSED transients of the music.
I got a report today, of a St. Louis audiophile who replaced his Solen film caps banks with a 50 uF 800 VDC DC LINKS, and he said there was much more definition with the DC LINKS !! ( all DHT Type 45 amp ). No comparison. Its a bold new world in audio ...today !!
Jeff Medwin
Edits: 12/18/14 12/18/14
...the Cary amp he was referencing used a tube rectifier. 1200uF or 600uF immediately following the rectifier tube is WAY too much...overall, a very poor design. The primary purpose of reducing the value of those 1200uF caps was to eliminate rectifier tube arcing and excessively short life. With solid state rectifiers the input cap max safe value is much greater than with a tube rectifier.
I don't see a tube rectifier, do you see one ?
"Let me see If I can look-up Mike Samra's post on what he did with a Cary to reduce it, it was a few years ago."
Then you provide the following link: Mikes post about the Cary SLP90 .
If you read the entire thread, it will be clear Mike is working with a preamp utilizing a high-vacuum rectifier, NOT a SS rectifier. IOW, you're referencing a post where the primary goal is to reduce PS filter input capacitance to extend rectifier life. His report of improved sound is a nice side benefit. The PS you're working with uses SS rectifiers where the influence of the size of PS input filter capacitance on rectifier life is not the issue. Therefore, Mike's solution to his specific problem (arced rectifiers) may not be the optimum solution to your situation since you don't have vacuum rectifiers that are arcing.
I thought my post was quite clear about this but apparently it wasn't clear enough.
AOK. Good enough !! Happy Holidays to you and your family.
Jeff Medwin
Cary beat the living guano out of vacuum rectifiers. It's no small miracle that they found specimens that could survive the ABUSE , for even a short period of time. Those designs are hideous! :> ((
RTFM applies, "in spades", when dealing with vacuum rectifiers. Read the data sheets and take the info. provided to heart, seriously.
Eli D.
Thanks for the good advice.
First each KT88 is drawing about 35 mA (idle) at the moment. I would not go above 45 mA. Hope that the info you want.
As for gutting the 1200uF, I don't think I am skilled enough to attempt out of safety concern.
Looks like Mikey Samra used 140 uF total, which is about what I said...100 uF to 200 uF .Instead of "gutting" the big electrolytics ( Dremel tool, a messy job ), you can leave them in place, so the amp "looks" stock, and simply disconnect them. Place one to three 800 VDC rated DC LINK caps under the chassis, in parallel, to equal 140 uF, give or take 20 uF. Use good wire to connect them to the amp.
The REASON why I am pushing you on DC LINKS is because they will sound great, versus, say, an older style motor run cap. This is a new cap technology - much wider band, lower in ESR, and they are designed for PULSED operation, which IS our SE tube amp playing back music.
Jeff Medwin
Edits: 12/19/14
I'm very tempted to try out the DC Link caps too, but only if space permits. Not much room in the chaasis. If it comes to that, I suspect removing the electrolytics will give a better sound.
Allied handles Wimas and the less expensive Vishays, and has all the dimension specs in metric, for each uF / voltage. Just use 800 VDC rated for bullet-proof safety and reliability !!! I bet there is room, use GE Silicon 2 to attach caps, in a non-heavy field place.
We beat this to death. Any more, do through email, glad to try to help !!
Jeff Medwin
Owing to high B+ (~500VDC), my best option is to have 2 x Wima 700VDC, 190 uF (=380 uF) replacing the existing 600 uF. My main concern is about increased hum. Cary groundings are at convenient points on the steel chassis - not very nice. As suggested elsewhere on AA, I will connect all ground points to the -ve terminal of the filter cap and see if the amp will be more quiet. Even now, the hum is quite acceptable, but need extra margin for possible increase of hum.
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