Interesting. What in your opinion are the sonic differences between the two rectifiers. I find the SP-14 very smooth and dark. But a little bit wispy. I have another tube pre that runs a 5u4g and it sounds fuller. Maybe I'm just splitting hairs. Maybe the rectifier doesn't do all that much. I know different designs yield different results. But It's a rabbit hole I must go down.
It's been a while since I used the 6BY5 but IIRC it has a fuller sound than the 6X5. It's also been a while since I used my SP-14 board, which got a bit battered up from experimentation. ;-) How "souped up" is your SP-14? What attenuators does it use? Are there film caps or electrolytics in the power supply? What output caps does it use?
I used 100K Eizz pots. A five-way Elma rotary switch. Electrolytics are stock. However, I'm thinking I would put pure films in it? But not sure about any sonic improvements? Using the Mundorf caps in one channel and the stock Russian caps in the other. I can't tell the difference between the two. My next move is to put a defeatable tone stack in it. Three band or a Baxandall. I know tone knobs are sacrilege. But it's my preamp so who cares. Plus, I can switch it out if I want, I love to Eq my stuff.
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I have considered different output caps. But the cost starts to get crazy. But I would if encouraged.
I tried these PSVANE CV181 MK2 tubes. They had a wider sound stage but lost the vocals in the background. The Tung sol 6sn7 has been an all-around good tube. I managed to snag some old Sophia 6sn7 tubes for a song. They're the best 6sn7s I've heard so far. I haven't put much time on the CV-181'S though. I was pretty turned off right away. I've herd they really need to bloom. Any upgrades worth doing??
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That looks nice. Is that your own build? What's that rectifier in there now?
Replacing all electrolytics with film caps will help. What size are the output caps? Roy used .22uF caps, which are way too small and don't supply enough heft. Try a pair of these, they're what John Broskie originally sold with his Aikido kits and they're a very good cap, rich and full-bodied, with a very clean top:
https://www.mouser.com/ProductDetail/Cornell-Dubilier-CDE/942C6W1P5K-F?qs=oi6qnwyrdkyl1aeuIRk6dA==
I also use the Bendix 5852 rectifier, which gives the Aikido a lot more body. The 6X5 is really kind of a crappy tube. For 6SN7s I use GE 6SN7GTA or B. I've never cared for those big Chinese-made 6SN7s, they sound thin to me. I like a very solid, palpable midrange. These are the best 6SN7s IMO:
https://www.ebay.com/itm/135750761523?_skw=sylvania+6SN7wgt&itmmeta=01JT5W60Y8Z0JCZG09F9TJ06NN&hash=item1f9b603c33:g:XtQAAOSwbhpoEr1f&itmprp=enc:AQAKAAAA0FkggFvd1GGDu0w3yXCmi1ckaU4oxnske0+evPPaMMhTGyu0yF9fRIFNyV0aBVlB1eygClkd4Fdd0tZfOgFRhsXiVaOe6Va3hxyet7B4+g1t8pmQDSf8bqbdAADbIa9UauCBnq6b3KHG2aJvK4on56g59fvV1JHe1tFEpFr5HutjytDYKL1gNRk+njN1xpfYKe3+CBNhocIo6W/flAfLIFXkFognJyljUdBQG4q1zQq8El9VcIdw0Goa1Obad1/ycVjZ5y5SEhfAMTXO6NUEeTU=|tkp:Bk9SR6KPmLzRZQ
Those have the back-to-back plates, not the angled ones. But IMO just about any NOS 6SN7 is better than any made today. Those new-made Tung-Sols are better than most, though.
Replacing all electrolytics with film caps will help. What size are the output caps? Roy used .22uF caps, which are way too small and don't supply enough heft. Try a pair of these, they're what John Broskie originally sold with his Aikido kits and they're a very good cap, rich and full-bodied, with a very clean top:
https://www.mouser.com/ProductDetail/Cornell-Dubilier-CDE/942C6W1P5K-F?qs=oi6qnwyrdkyl1aeuIRk6dA==
I also use the Bendix 5852 rectifier, which gives the Aikido a lot more body. The 6X5 is really kind of a crappy tube. For 6SN7s I use GE 6SN7GTA or B. I've never cared for those big Chinese-made 6SN7s, they sound thin to me. I like a very solid, palpable midrange. These are the best 6SN7s IMO:
https://www.ebay.com/itm/135750761523?_skw=sylvania+6SN7wgt&itmmeta=01JT5W60Y8Z0JCZG09F9TJ06NN&hash=item1f9b603c33:g:XtQAAOSwbhpoEr1f&itmprp=enc:AQAKAAAA0FkggFvd1GGDu0w3yXCmi1ckaU4oxnske0+evPPaMMhTGyu0yF9fRIFNyV0aBVlB1eygClkd4Fdd0tZfOgFRhsXiVaOe6Va3hxyet7B4+g1t8pmQDSf8bqbdAADbIa9UauCBnq6b3KHG2aJvK4on56g59fvV1JHe1tFEpFr5HutjytDYKL1gNRk+njN1xpfYKe3+CBNhocIo6W/flAfLIFXkFognJyljUdBQG4q1zQq8El9VcIdw0Goa1Obad1/ycVjZ5y5SEhfAMTXO6NUEeTU=|tkp:Bk9SR6KPmLzRZQ
Those have the back-to-back plates, not the angled ones. But IMO just about any NOS 6SN7 is better than any made today. Those new-made Tung-Sols are better than most, though.
.22 stock value in mine. 6x5g currently. Cornell Dubliner 1.5uf? The price is way cheaper than those Mundorfs!! That Bendix is pretty expensive? Not a bad price on those NOS tubes either. Luckily, I ended up getting those PSVANES for free.
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The chassis work took a while!! I did the whole thing myself. I really like building chassis. I do have a quad of vintage GE 6sn7s that sound really good but lack in the top end sparkle. Very smooth though. Good bass definition. I just got These Klipsch Cornwall IV''s. They seem to be all over the place sonically. What I mean to say is they are finnicky. Of course, I don't have many hours on them.
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.22uF is too small. For the average amp input impedance of 100K it's just not sufficient. The Bendix is pricey but you only need to buy one, once. ;-) I don't think that 6X5G is helping things any.
The SP-14 doesn't seem to drive that hard. So, I see what you mean. Putting my parts list together now! Ha... Thanks for the help by the way.
You're welcome. The Aikido is a great preamp, IMO one of the great inventions in audio, along with the Williamson, the Mullard and the Dynaco. ;-) I won't show you mine because it's a point-to-point job I did to really experiment, and it's a mess. ;-) I use a Neurochrome Maida regulator board for the power supply and some 6V regulated filament boards made by a fellow here named v4lvelover. It wouldn't tell you anything about the SP-14 board. But I spent a lot of time with the SP-14, for a friend and for myself. My SP-14 build was laid out like yours, just not as nice looking.
I did all the mods you recommended. Wow!!!! Much more weight!! It brought all the missing music in the background forward. The vocals are killing it now. I feel like it's a lot less fatiguing to listen to now. Very even across the spectrum. Totally different preamp now. My Cornwalls are very happy now. Do you feel like there's noticeable difference between the bendix 5852 and the 6BY5? Now I'm tempted to get one.
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Excellent! It's a terrific circuit and the SP-14 board is well designed but it needs a little help. ;-) The Bendix has a richer, more intense sound, not as "open" as the 6BY5 and a bit "darker" but with a deeper sound stage and more midrange energy. I think you might like it. For $100 I think it's a significant upgrade, but it depends on your taste, of course. Roy used to sell them either stock or as an upgrade, I forget which, but got tired of trying to source them. They're not that rare now.
Oh, and please note that the 5852 has a VERY slow warm-up time, like 45 seconds. If you want to avoid the notorious Aikido hum while the noise-cancelling kicks in, be sure you let the preamp warm up sufficiently.
I use ez81 in my version, no lack of power... and 1uf output caps. I find that it doesn't make any noticeable difference the type of caps... I tried 3 film caps ... zero difference, decoupling power supply caps too...
The only thing is that I will replace the choke which I removed , mine is a passive power supply, and it started to hum a bit more recently for no reason.
The only thing is that I will replace the choke which I removed , mine is a passive power supply, and it started to hum a bit more recently for no reason.
There are a lot of DIY versions of the Aikido. I'm helping 1973bronco improve the SP-14 kit version, which uses the octal 6X5 and variants, and needs a little help to be fleshed out, IMO. My own version is quite different and tuned to my preferences, but I've worked with the SP-14 board a lot. I'm surprised you don't hear a difference between output caps. I stick to the C-D 942 series in my amps and preamp as being the best all-around cap at an affordable price. But other caps certainly make a difference in my system.