I have had some great results from some 40's RCA 6v6g st.  got some bass punch and nice extended range.  I agree about the Amperex 7062 good tubes.

I tried some Art Valve 350's, very nice sound sweet airy but light on the bass.

got some OC3's b/c i liked the blue glow  not much tone change from the stock OA3's

I've been very happy with my preferred driver tube these days, Philips SQ 7062. These have the ideal combination of openness, warmth and intermediate gain which do not  drive fast and sensitive output tubes (like the current production Tung-Sols), into sibilance on very high frequency passages. As opposed to 12AT7's, these drivers need an open, big sounding output tube to sound their best though.

So far my first choice combo for the M-T is the Phillips SQ 7062 paired with the excellent RCA 6V6 G ST (1940's production, big, coke shape).

The next preferred pairing is Brimar 12AT7 along with said G ST's.

On third place, the Brimars with the Russian Reflektor Plant black glass 6V6's. The usually dark but sweet sounding Russians need to be opened by a powerful, commanding driver, and the Brimars are just the ticket.

The Tung-Sol 6V6's are good tubes but can be ridden to far on high frequency passages by 12AT7's in the M-T. My Phillips SQ 7062's do not show special synergy with these (like with my G ST's), although the combination sounds fine nevertheless.

In all the above suggested combos, I use the RFT EZ80 rectifier rather than the stock JJ EZ81 (not only due to reliability issues).

Some time ago, I decided to skip any output tube outside the 6V6 family due to potentially excessive stress on the circuit and because IMO the original voicing enhances the 6V6. YMMV.

My next test will be a pair of 6414's paired with my tour de force RCA's G ST's. I've heard good things about these drivers and according to the literature, these are very similar to the 7062's.

In general, I prefer to go for drivers offering an intermediate gain between 12 AU7's and 12AT7's, as the former are somewhat dull-sounding in the M-T, whereas the latter tend to be edgy in the high frequency ranges.

The 6V6 G ST's sound big, with wider soundstage, PRAT and transparency, and as has been mentioned here, its bass is better than the rest of my other combos with the ubiquitous OA3's in place. My OD3's, on the other hand, flatten that sound, killing some of the presentation depth.

Yet, the biggest sound improvement from my system came from the installation of 7 DIY absorption pannels, critically placed in the room. There's no question reflections kill the soundstage and naturalness of the sound, and increases listening fatigue. Today, at close to near field, my system behaves neatly and timbres and imaging are again in focus, while bass lines are deeper and well defined (as opposed to boomy).

My system uses an active subwoofer with a crossover at 65Hz and thanks to the absorption pannels now the bass really enhances the nice low-mids, mids and highs of the DM945's when placed on monitor stands and away from walls.

Interested in anyone's experiences with 6414's and the corresponding best output tube pairing.

Jim McShane sells the RFT EZ81.

From Brent Jessee's summary on the 350 B tube:

"For most applications calling for a 7581, KT66, or 6L6GC these tubes will work fine and sound great. They do have different filament current draw specs and other slight differences, so you should always check with the amp manufacturer, dealer, or a tech before subbing these tubes in place of the stock tubes."

The 350's (A & B) seem to be considered the best sounding in this tube family. I just wonder if we can use the KT66's safely in the Mini Torii and if the amp's voicing is consistent with their characteristics ... I assume the latter holds as per the recommendations.

Individual good tubes may or may not be special, depending on the accompanying complement set. SQ 7062's are not that special if paired with Tung-Sol, JJ or Reflektor Plant 6V6's, in my experience. YMMV.

Hi PK,

Can you describe the sound differences you get with the substitutions that you recommended?

Thanks,

Pete

Hi Others here

I found the difference btw the RCA 6v6g st and the VA350's to mainly one of bass.  Your description of the 350's is right on, we differ only the lower end.  The 6v6g's just seem to have more punch in relationship to the 350's

It may be that i'm new to low watt and more used to bigger pumpier tubes like kt88's and el34's

Grinnell,

Can you tell me where to find the 1940's RCA 6V6G ST coke bottle tubes and how much should the cost be.

Thanks,

PK

I got lucky on ebay and got them for about 30.00  
$50.00 is more like it although if labeled cunningham they could be cheaper  RCA made

Jessie brent is probably the best source for the best price i have bought a number of tubes from them

It is true that we can profit from the self-biasing feature, but I prefer to be on the safe side, as there's less chance of getting a weaker tube that way and the price difference (in relation to, in my case, customs, logistics and all) is not that significant.

Any experiences with 6414's on the driver seat?

Well, I still think when they go about the matching process they have to discard the weaker ones which you will get in a singles purchase (weaker=more probable of early failures). Plus, replacing a tube is a logistics hazzle for me, so it is cheaper to be more on the safe side in the long run. These may still fail but at least there's that first screening on my side.

I'm hoping the 6414's are similar to the 7062's, that's why I would like to try them. I liked the Phillips SQ 7062's so much when paired with the G ST's.

The price is very good BTW. Store?

Happy holidays to all!

Mine are Radiotron labelled and gray glass, with a round halo getter. RCA made.

You shouldn't mix brands. The RFT sounds better than the JJ's.

Anyone try a 6F6 output tube in the Mini Torii?

PK,

One is labeled Radiotron the other Cunningham  both identical, grey glass, not sure about the getter (not expert enough to tell)

"(white lettering with a cartoon of a tube playing a flute)"
Ah, ze famous `Bugle Boy`brand.

Well maybe i will drop in my VA 350's and give it another try

probably need some burn in