[wushuliu]

I bought a used SP3. My very first tube amp purchase, having sworn to myself that I won't try to build anything for at least 6 months (ha ha, there's a SimpleSE pcb laughing at me in a drawer). I got it tuesday so as you can see it took me 4 whole days before I opened it up. No mean feat. Mostly because tubes are new to me. Anyway, I wanted to take a look inside because while researching the Onix I noticed that there were several variations since the MKII debut in 2004: the 6 moons, Audioholics, and current amp (sold overseas) have their differences and it seems to my eye that newer iterations appear more 'mass-market'. No P2P wiring of any kind, straight pcb. Maybe it's just increased efficiency... maybe not. I read something about the later version being originally intended for another design. In any case, I was happy to open this guy up and see that it's the earlier version. Chinese(?) PIO caps, silver or silver plated copper wiring, stepped attenuator with Dale resistors. Pretty darn nice! I'll probably just do some basic mods if possible - space is a little tight. Replace some of PS caps and maybe add a film cap if I can fit it. Replace the fuses (sorry if that offends, but they gotta go. Acme's are only $10 anyway.). Debating on the PIO caps. That's the real potential money pit. May just leave them. The real aim is to bypass the attenuator altogether so I can use the lightspeed. We'll see if that happens. At any rate, certainly seems well worth the money paid. Beautiful chassis to boot. Open to constructive thoughts and suggestions.

[JohnR]

You can just set the attenuator at max.

Are the tubes in it 5881s?

[wushuliu]

You can just set the attenuator at max.

Are the tubes in it 5881s?

Darn good point. The stock are 5881s. Mine came w/ 6p3c-e's and I managed to get a set of Valve Art 350B for cheap.

[bunnyma357]

Although it wasn't my initial plan, I'm running my SP3 as a Power Amp with a separate Meridian Pre-Amp.  I actually prefer the coin base 6p3c-e's to the Valve Art 350B's.  In my setup, I have numerous Subs, so having the volume control on the SP/3 gives me an easy way to adjust the bass/treble balance if I need to - the stepped attenuator makes it really simple to go back to the default calibrated level.  I set mine up with the SP3 attenuator at 12:00, which I figure gives me enough power without pushing the pre or power sections of the amp too hard.

In purist terms, it doesn't make sense to have 2 pre-amp stages but I like what the tube preamp section of the SP3 adds sonically. And the convenience/control features of a real preamp make using the SP3 more enjoyable and better sounding - since in my room I really needed to add bass management to get reasonable sound.

I've done a fair amount of tube rolling with the pre-amp tubes, and I'd be happy to provide any info I can. Although, I think what I prefer doesn't match up with a lot of the general consensus, based on the old AV123 threads.

Here's the breakdown on what I'm using with approx. eBay prices.

12AX7 slot - RFT ECC81 (12AT7 - 60% gain of a 12AX7) $10-$20 ea.
6922 slot - Voskhod 6N23P $10 ea.
12AU7 slot - RFT ECC82/12AU7 $20 ea.
5881 slot - Reflektor(?) 6P3S-E (Coin Base) $7 ea.

I'm really happy with the sound of these together, really musical and lively - haven't wanted to roll tubes in close to 2 years.


Jim C

[bunnyma357]

Also, most of the 6L6 variants want a higher bias than the 1.15 that the stock 5881's were set at.  As I recall people were setting the bias between 1.25 and 1.45 on the 350B's - I had mine at 1.35 when I had them in the amp.

Jim C

[wushuliu]

This got me curious, since I have the last Onix version sold by by AV123 the SP8/3, which was originally supposed to be a rebranded Melody SP7 (EL34 based)  http://www.usatubeaudio.com/melody-sp7.php  But when the actual amps arrived for sale at AV123 they ended up being another variant of the Melody SP3, from a practical stand point the main difference is the base bias is .4V rather than 1.15V. After opening the case, the construction looks very similar to your photos.

Cool. So coupling caps range from .1uf to .47uf., minimum of 250v. Good to know. Thanks for the tube info Jim!

[bunnyma357]

...while researching the Onix I noticed that there were several variations since the MKII debut in 2004: the 6 moons, Audioholics, and current amp (sold overseas) have their differences and it seems to my eye that newer iterations appear more 'mass-market'. No P2P wiring of any kind, straight pcb. Maybe it's just increased efficiency... maybe not. I read something about the later version being originally intended for another design. In any case, I was happy to open this guy up and see that it's the earlier version...

This got me curious, since I have the last Onix version sold by by AV123 the SP8/3, which was originally supposed to be a rebranded   Melody SP7 (EL34 based)   But when the actual amps arrived for sale at AV123 they ended up being another variant of the Melody SP3, from a practical stand point the main difference is the base bias is .4V rather than 1.15V. After opening the case, the construction looks very similar to your photos.




Jim C

[wushuliu]

Ok. so far I have:

Replaced coupling caps with Ampohm Aluminum PIO
Replaced Aux jacks w/ Vampire CM1FB or whatever, the copper body one
Replaced signal wire with Neotech UPOCC teflon
Replaced all fuses w/ Acme Audio
Bypassed the attenuator, replaced it with Optical Volume Control (lightspeed)
12BH7A tubes for driver and preamp stages
Valve Art 350B Power Tubes

There was some drama when some unseen solder shorted a wire beneath the board, causing redplating and bias issues, but that's been sorted. I also used some Jantzen Superior caps for coupling briefly and they also came off better than the stock caps to
my ears. The Ampohms have similar performance but do add that extra something as far as texture.

The amp now sounds outstanding. Lots of settling in to do yet with the tubes and caps, but I am very happy. Also some shielding needed for signal wire. Pics later.

[eclein]

Good stuff!!!!

[johnzm]

theres quite a few of these out in the wild with some problems, since av123 sold a bunch of "for parts only" units.

i have gone through mine a bit, and was wondering if your input wiring goes through the bias board, and through those relays on there. if so did you replace the wiring before and after the relay,or did you just bypass the relay all together and make it a 1 input unit?
also, did your attenuator bypass create a large amount of noise in the output? i noticed with mine at full vol, its rather noisy even with nothing plugged in.

also, on my previous sp3, i did sonicap platinum bypass on the .47's and .1 platinums on the coupling caps for the preamp tubes if i can find them ill post a few pics

[wushuliu]

theres quite a few of these out in the wild with some problems, since av123 sold a bunch of "for parts only" units.

i have gone through mine a bit, and was wondering if your input wiring goes through the bias board, and through those relays on there. if so did you replace the wiring before and after the relay,or did you just bypass the relay all together and make it a 1 input unit?
also, did your attenuator bypass create a large amount of noise in the output? i noticed with mine at full vol, its rather noisy even with nothing plugged in.

also, on my previous sp3, i did sonicap platinum bypass on the .47's and .1 platinums on the coupling caps for the preamp tubes if i can find them ill post a few pics

The short was on me, though the inconvenient wire placement did not help. I replaced the wiring before and after. There's some low level noise, not much but I'm hoping shielding the new wires will help with that. Are you using low gain tubes for the pre section?

[eclein]

wushuliu- How did you know what values to change to?? Did you have a schematic of your amp or was it just open'er up and look around?

[wushuliu]

wushuliu- How did you know what values to change to?? Did you have a schematic of your amp or was it just open'er up and look around?

Both in the end. The stock amp uses smaller value than shown in the schematic (which is somewhat outdated), and since the smaller ampohms are cheaper, went with that. I also used the larger .47uf indicated in the schematic with no issue.

[eclein]

Whats an "ampohms"??? A brand? Thanks Wush!!! Ain't tubes cool!!!

[wushuliu]

Whats an "ampohms"??? A brand? Thanks Wush!!! Ain't tubes cool!!!

http://thetubestore.com/ampohmpioal.html

http://www.audiocircle.com/index.php?topic=54218.msg627556#msg627556

[johnzm]

The short was on me, though the inconvenient wire placement did not help. I replaced the wiring before and after. There's some low level noise, not much but I'm hoping shielding the new wires will help with that. Are you using low gain tubes for the pre section?

i was using 5751's i believe and amprex 6922's. 350b's as well. i think upgrading the rectifiers might make a huge improvement in the sound quality, but they were relatively difficult to get to because of the terminal strip and caps.  i dont think shelded wires will get rid of that extra background noise on this amp, but let me know if it does.

[wushuliu]

i was using 5751's i believe and amprex 6922's. 350b's as well. i think upgrading the rectifiers might make a huge improvement in the sound quality, but they were relatively difficult to get to because of the terminal strip and caps.  i dont think shelded wires will get rid of that extra background noise on this amp, but let me know if it does.

Hm. Two of the rectifiers are pretty accessible (+B2, B-). What would be a good replacement rectifier?

[johnzm]

Hm. Two of the rectifiers are pretty accessible (+B2, B-). What would be a good replacement rectifier?

ill let some of the other more knowledgable members help, all i know is a hand built one with premium components will work better.

[zappasan]

Hello

Do you know any data about the resistor across the 1 and 6 pin of the power-tube?
The big resistor with colorcode looking like red, black (or dark blue), black (or dark blue) and gold ?
On my SP3 one of the resistors seems to be destroyed and measuring 410 M ohm while the other three measure 34 ohm each.
Can you please help me out with this.

Regards,
Zappasan

[wushuliu]

Hello

Do you know any data about the resistor across the 1 and 6 pin of the power-tube?
The big resistor with colorcode looking like red, black (or dark blue), black (or dark blue) and gold ?
On my SP3 one of the resistors seems to be destroyed and measuring 410 M ohm while the other three measure 34 ohm each.
Can you please help me out with this.

Regards,
Zappasan

I believe that resistor connects cathode to ground. Mine measure 33ohm, so yes you will want to replace that resistor. Should be very easy. I would guess 3 or 5 watts carbon film resistor type.