2. amps-preamps
  3. 170890-112556

New spec calling for 5AR4 instead of initial 5Y3 rectifier in CA-906

Linestage is stereo dual 6SN7 (New Tung_Sol). Power stage is 5Y3 to dual 6V6 to 6SL7. I like the sound of the newly recommended 5AR4, except that with my NOS (Mullard, RCA, Ken-Rad, respectively) tubes it emits low (-60-70dB) scratchy sounds (noisy). Subbed the Mullard with a new Sovtek--same noise. Factory recently says use all JJ in power stage (just ordered, they're built sturdy I know, for guitar amps). If I use my CBS Hytron JAN 5Y3GT, no noise at all. (I tried another NOS JAN 5Y3 and it DID develop noise, so I'm guessing it's just bad.) Ugh! I wonder if the increased plate voltage and doubling of current from 5AR4 rectifier is creating noise somewhere else (6V6s? 6SL7?) Unit was totally re-capped last month, so I don't think caps are acting up. I can't find a schematic, so I'm asking for anyone who knows tube amp power sections... The 6SN7s aren't the culprit (I subbed them). The intermittent scratchy sounds that appear are independent of volume selection. Doesn't exist on mute of course, but appears on first notch up in volume, and stays the same at any level. I've asked the factory, no response yet.

128x128laughingrabbit
laughingrabbit's avatar
laughingrabbit OP
12 posts
 

Thank you

noske
783 posts
 

On a quick search I found some comments about new production 5y3 tubes. I’m not sure if you will be able to open this link coz it was a search, so I copy what one person says, in part -

As far as I know these are the only authentic 5Y3 tubes being made anywhere in the world.The Sovtek and Chinese variations are not quite the same thing - though they are safe for most all amps that use a 5Y3 - the JJ supplies the correct B+ (LOWER). I haven’t had any issues with the two i’m using. One can get a bad tube once in a great while

What seems to be important is that even within the 5Y3 family there are differences. To jump to a 5AR4 seems rather odd, not something I’d do without quite some thought. It hadn’t been previously blowing smoke or busting fuses and associated tubes?

 

laughingrabbit's avatar
laughingrabbit OP
12 posts
 

On numerous guitar amp posts, I've noticed that inserting the lower voltage drop tubes, 5V4 up to 5AR4 'tightened up' the sound, or 'reduced sag', and 'increased headroom', so maybe that perception drove the change. I have not heard confirmation (after asking the factory, and having the factory upgrade and replace all electrolytics,) that my unit though, from ~2008 has had any (needed?) upgrades other than the re-cap (more than doubling the output cap voltage capacity.) in order to handle the 5AR4. I mean, I suspect it CAN, but it may go thru tubes faster, thus the noise. ..

dekay's avatar
dekay
5,385 posts
 

The 5ar4 will increase the plate voltage quite a bit (over 5y3).

Does the amp have user adjustable bias for the power tubes?

DeKay

noske
783 posts
 

I don’t take any notice of what is said on guitar forums - they are on another planet and do some things to their amps that horrify me.

That the change in caps changed the specs - you are on your own with that. Assume nothing - I’m not even sure Canary will want to comment if it has altered things beyond what they designed.

edit - having said that, some of those comments from that link may have come from guitar amp people.  Dunno.  Probably.

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