I'm not sure if this is related to the RFT EZ-81, but I've experienced some sibilance with this tube and replaced it with the RFT EZ-80, and problem solved. I even prefer the EZ-80 sound contribution overall.

Having said that, I've never experienced any 'squeals' with the RFT EZ-81, just a loss of control on high pitch passages, which I presume may turn into a squeal if the particular tube involved is in worse shape than in my experience, or if your system tends to be on the bright side.

If you already replaced that tube with the same EZ-81 spec, I would urge you to try the EZ-80 (the tube sounds better anyway, IMO)

As far as I know, German made RFT's are great tubes. I got them from Tubemonger, at a good price.

The EZ-81 has shown to be a little sibilant depending on the amp and tube complement.  It may work well with smoother drivers, but with my Brimar 12AT7's, it tends to misbehave in some high frequency passages.

The RFT EZ-80, on the other hand, is quite neutral and does not overdo it at those frequencies. These seem to create better synergies with my tube setup.

Alternatively, try to determine if you have a tube with high microphony (ringing sound due to some elements within that tube which resonate with vibration), in which case any spec tube in your setup could be causing this effect.

I'd try the EZ-80 first. If not, then replace each of the other tubes involved, one at a time. You need to discard a likely microphonic tube in that case.

Good luck!

I have not yet experienced microphonic issues myself, so I don't know how these issues present themselves exactly, although a very microphonic tube (i.e., one that squeals), would probably still do it to a lesser degree, even at iddle, from vibrations coming from the trannies.

I understand the most common microphony scenario is the faulty tube's resonance with vibrations stemming from the sound waves created by the speakers, though. Also, the more the amp is under load, the more microphonic that tube should become.

Can you try to apply some dampers to both rectifiers and drivers, and see if the squeal issue improves?

I believe the official description on the Mini Torii keeps the old EZ-90 (6x4) rectifiers listed by mistake, since these have been replaced for quite a while now with the EZ-81's. Do not try those 6x4 (EZ-90's) in your recently revised model.

In case there is a more organic cause for this issue, I suggest you call Steve and ask him directly about it. I'm sure he will help you solve this in no time. In the meantime, get those EZ-80's, as one or both of your current EZ-81's seem at this point the most suspicious candidates for either spec sibilance (systematic) or microphony (non-systematic).

Keep us posted.

No problem, Tungsram rectifiers are reported as very good also.

I have a similar sound from the right side.  Its not the power tubes been swapping those around.  It will stop when i turn off that side and turn it on again.  And i have tube dampers on 2 tubes.

I suspect is a microphonic tube.  just havent had time to track it down.

Nice tube complement. I would go for the current production Tung-Sol 6V6GT's, unless you already have an overly bright system. These are better sounding output tubes than the JJ's, by far (pace, transparency.)

You did not specify if the RCA's are 12AU7 or 12AT7's. If the latter, these could tend to make the EZ-81's even more sibilant on high pitch passages.  I personally prefer 12AT7's in general, coupled with EZ-80's.

Discarding any more organic issues, the weakest link in Mini Torii's tube complement remains the rectifiers. These work hard, which explains some sibilance on EZ-81's when pushed too far (high frequency pitches), or when these tubes are not in top shape. Never use JJ EZ-81's in that position (don't last long).

I would stick to 6V6 output tubes for now. These sound the best in general (with some reported good exceptions out there), and won't press the rectifiers too much.

I'm sorry it looks like there is something organically wrong with your unit, after all. I'm glad you called Steve, who will fix it in no time.

12AT7's do increase the gain, but not dramatically. The end result is less range used on the volume pots to reach your sweet spot listening volume, but not by much.

I can't generalize given my limited exposure to the vast variety of 12au7/12at7's out there, but the benefits I perceive from 12AT7's in my system, in general, is the improved openness and pace.

Some forum members enjoy the 7062 (slightly less gain than a 12at7), a driver that I will be trying myself eventually.

I'm sure you will like the EZ-80 rectifiers.

I'm glad to learn your troubles are over. I'm very pleased with my RFT's, but I got them NIB from Tubemonger.  I agree with your conclusion about a possible bad RFT lot in your case.

Fireblade: I am loving the EZ80 rectifiers! Thanks again for the recommendation!

Thinking about popping the TungSol 6V6GT Reissue power tubes in there, have you used the TungSol 12AT7 Reissue, what about the svetlana? I know they are both made by the same company in the same factory.

Just trying to find a less expensive new production tube complement that I enjoy listening to.

I'm no tube expert by any means, but my current views about tubes in the Mini relate to either my own experience or testimonials from experienced Mini owners, whom I trust.

I currently favor 6V6 output tubes almost exclusively in the Mini, as in my view, the amp was voiced against those. There are alternative exceptions, of course, but these are less likely to beat a good 6V6 option, and more expensive.

I have two output tubes I prefer so far, and both are relatively inexpensive: The black glass Reflektor Plant, a Russian NOS 6V6, and the current production Tung-Sol 6V6GT's.

The first is my favorite, as it has all the transparency and pace I expect, and at the same time offer a warm flavor without high/low frequency roll off.

The second choice has more power (volume) and is very transparent, but with less pace and may tend to overdo the highs, when pushed. Depending on the recorded material, I interchange them within the same complement setup.

If it was not for the still very affordable black glass Reflektor 6V6, I would stick to current production 6V6's, as the sound differences, risks and investment are less evident. My only caveat here is the JJ 6V6, a tube lacking pace and volume and dull sounding to my ears.

I have not tried current production Tung-Sol 12a(?)7 alternatives yet, since my current preferred drivers (NOS Brimar 12 at7's) keep me happy. I suspect these new tubes may not make much of an impact, though. The driver position in this circuit is very important for sound tuning, and maybe here a good NOS is worth the risks. Some forum members really like the current production Psvane 12at7's, but these are really expensive.  YMMV, so if you are curious, check the Tung-Sol drivers and let us know.

This is a very cool thread!! A positive outcome for Ron I hope...Fireblade, I have a MT on order as we speak...it's "on the bench". My palms are sweating due to anticipation to hear this little beast! I will refer back to this thread for your tube rolling suggestions if I decide to try it. It's comforting that we have helpful members like you who have experience with these issues...
I once had a girlfriend with a "high pitched squeal"...no troubleshooting needed for that, tho