This is my first time replacing tubes for my ToriiMK5 or any other amplifier. I have a loud hum coming from the left channel that I would like to fix. I spoke with Steve and he indicated that it is most likely a bad rectifier, input, and/or tube regulator. I have a few very basic questions:

1) For the tube rectifier, does it matter if it is a 5U4G or a 5U4GB instead of a 5u4? I noticed that Decware has the 5AR4 available but the 5U4G is out of stock. Should I buy a 5AR4?

2) For the input tubes, are there any alternative to using 6N1P or a 6922 tubes?

3) For the input tube regulation, are there any alternative to using the VR75 or VR150?

I know that these are very basic questions. This is my first tube amplifier and the first time I buy any tubes on my own. I would really appreciate the assistance of the more experienced members in this regard. Thanks!

Both of those rectifiers will work properly in the amp.

There are a number of input tubes that will work as far as I know (I never have had a Torii Mk V, I did have Torii Mk IIIs).In general, in my experience the 6N1P and 6922/6DJ8 types worked best. But 7DJ8, 6N5P and others can work.

You can also use VR90 (0B3) or VR105 (0C3) I believe. I found VR90 (0B3) to be my favorite in the Torii Mk III.

Hopefully Torii Mk V owners will chime in and correct any erroneous information I posted and offer more opinions.

Hello Lon and GroovySauce,
I ordered a pair of OA3's and a pair of 5U4G's from Decware. I will try replacing the OA3's first and see if that solves the problem. If not, I will replace the 5U4G's. I will consider replacing the input tubes if those two changes do not solve my problem.

Once again, thanks so much for your help!

Another way you can get a hum on one side is if an IC has a weak ground connection. I have one I need to replace the end on that is a KLE sort of design with a little ground connector on one side. It has gotten loose, so the IC needs to have a little tension on it to get that little ground nub to connect well and not cause a hum. But I agree, it is often a tube. Why is it good to have spares of each type, for troubleshooting and maybe fixes, but as much for me, having a little variety can be really nice for shaping the sound. This led me to having a ridiculous number of many types gathered over time. And they all sound different, making refining a room's sound by mixing and matching a pretty powerful tool.

I have not heard a MKV either, using a MKIV now that I modified over time to be more resolving, fast, complex. It allows the signal through so easily, I most often prefer less potent tubes, easier/cleaner flow, more powerful tubes can be overstated. Also, my preferences are for a little tube euphonic quality, but more about speed, resolution... lack of smearing, so going for euphonic "warmth" more as subtle musicality enhancement than an obviously "tube sound."

With the MKV design changes, improving stock parts and wires, more resolving output transformers, inverter tubes, lower capacitance rectifier power... guessing yours sounds faster, more spacious and resolved than my MKIV did stock, but not having heard it, and tubes so affected by the amp design, I can only point to tube characteristics you might apply to whatever sound changes in your setting you might prefer.

As I recall, 5U4GBs are generally a little denser and more powerful feeling than STs, while the nice ones (to me) can also be a little more obviously textured, and the signal contrasting spaciousness and a little denser sound more...But some are really close to good 5U4G-STs also, so it is always interesting to see what a tube actually sounds like once in hand.... and all tubes affected by each other, so can't say conclusively what would be best there.... But GB's tendencies for a little more powered sense of signal can be really good, or it can be overstated. In my warm leaning setup, and with the remaining low bass issues I have here, that extra push is more obvious in the bass than elsewhere. So when I was using GBs a lot, I took care to compensate with more open and fast tubes, or the extra bass could off balance with the rest, becoming strong enough to thicken, slow and reduce definition some. Good sound still, but not my thing, needing fast and complex bass that blends smoothly with resolution and speed everywhere else. But if you need a little more weight, bass, density, nice NOS GBs can be pretty cheap, and it might be fun to pick up a few to try and see how you like them.

Nice 5U4G-STs are not all that different in the broader sense, but to me, being a little less powerful feeling in general, they tend to be a little more neutral, and a little less obvious in all they do, nicer ones balanced and more nuanced, which can also be really nice. But this is really general, every tube having its own sound influences.

5AR4/GZ34 generally make the signal faster and more dynamic with a similar signal push as 5U4G types. GZ32s were my preference here, a less forceful, even faster and more open version of the GZ34s sound-wise. But again, they helped here by opening things up, where in a leaner setup, they could be too open, fast, and lean. I have tried some of the new GZ34s, and did not think they were great, but I have a lot of nice tubes I picked up over years, and many of them really pretty exceptional sounding. The last new ones I tried Psvanes, were decent, but, compared to NOS versions, they were a little held back, slightly masked, and flatter the way the system sounds these days. But NOS have gotten really costly, and again it all depends on everything else. So if a punchier sound that sets up contrasts between signal and space might help you get a sound you prefer, trying a pair of new 5AR4s that people rate well could be a fun experiment.

I like, but never loved 6N1Ps in my Toriis, again, preferring less warmth, and more fine detail, speed and space in my setup.  And E88CC/6922s, though many love them, were always a little too forceful for me. So I used nice NOS euro ECC88 types a lot. And before opening up the sound using more resolving and fast amp parts and wires, I tended to use PCC88s, sort of like the GZ rectifiers... tending to be punchier, more open, faster. Lately I am leaning toward using either pretty neutral 6CG7s or transparent, dynamic, and resolving Linlai E-6SN7s with adapters. With the more powerfully expressive and transparent DAC I am working on, those tubes tending warmer, fuller, and smoother (though nicely resolved and complex) compared to the ECC88s types I tend to prefer (early 60s Heerlin made, or Siemens both being notably open, transparent and nicely balanced here). But I go back and forth.

GS pointing out VR ratings, those numbers are voltage drop. So an OA3 drops the voltage before the other tubes less, making it the one that gives the signal most power, which could be right with all else, or overstated. Where an OD3 drops the voltage the most, reducing signal power and giving the most open, nuanced, and delicate sound, which could be right, or too lean depending on all else. But if you need stronger signal power... a more pushed, dense and big sound with more bass power, OA3s are a good choice. And those too all sound different, so if you prefer them, not a bad idea to try other makes if you can find them. I like all VRs with the right company, but OA3s are generally too much here, and though I can get them all to sound really good, so far, I always end up back with OB3s in this setting.

Tubes can be fun, and daunting, especially in a resolving system/room that shows even the finest subtleties of so many different sonic characteristics between types, and with all the tubes within the types. And with practice and luck, finding synergy that takes the whole beyond their individual qualities can be enlightening.... how they blend together enhancing our sonic experience as much as the tubes themselves.