advice for mono cartridge

Chakster, To answer your questions:(1)  I am not really sure your assumption about compliance applies to ALL true mono cartridges.  The fact is that vertical compliance in a mono cartridge is irrelevant, since the motor does not respond to vertical motion at the stylus by producing an audio signal.  Ideally, the cartridge is totally inert to vertical movement of the stylus. I don't know whether that is always true in practice. "Modern" mono cartridges are nearly always stereo cartridges that have been internally bridged to produce a mono signal; therefore those typically do have vertical compliance.  (Bridging ideally cancels signal voltage due to vertical motion of the stylus tip.)
(2) I have read that fancy stylus tip shapes are irrelevant for mono.  JCarr has argued otherwise, I think.  Miyajima seem to think conical is fine for mono in their true mono cartridges.
(3) In my opinion, the definition of a "true mono" cartridge is that it has one set of sensors that work only to respond to lateral motion of the stylus tip, and often they have only one pair of output pins.  Compliance or no compliance.  There is no bible for this.

@lewm  Yes, the Miyajima MC is a true mono in total oldschool way (japanese style), but this is not the only cartridge on the mono market, especially if we will add some nice vintage true mono MM.  

I've been reading so much about serious advantages of the LineContact styli over the Conical/Elliptical to play vintage vinyl, so i believe same principle applied for mono records played for decaded with conical needles only. Quality must be better with LineContact type simply because this part of the groove wall is untachable by Conical tip. If the mono record is from the 50's and in used condition then it must be played with LineContact (or MicroRidge) for better sound quality. I thinks it's obvious for old records. No?   

I don't think it is quite that simple Chakster.

As I see it, all things being equal (which they never are unfortunately) there are simply more compromises to be made with mono cartridges than with stereo as a result of the 3 different types of grooves to be played with mono (very early 33 RPM pre-microgroove mono, microgroove mono and "modern" mono cut on a stereo head) as opposed to the one groove formation to be played with stereo cartridges.

With very early pre-microgroove I think it is quite possible that a larger 1 mil conical may actually give the best performance in terms of dealing with the wider groove. On the other hand, the line contact or microridge (on a mono cartridge with adapted vertical compliance) would be very likely to provide optimal performance with more modern monos and recent reissues cut using a stereo head.

I'd be reluctant to play the latter using a so-called "true mono" cartridge with no or very limited vertical compliance; Miyajima does not recommend playing "stereo" records with their mono cartridges and I see no reason to take a chance playing a modern mono reissue cut using a stereo head with a cartridge like that even though some say they have done it successfully (some also say they haven't if you search the net).

And JCarr admits himself that a LC or MR is more likely to drag along the bottom of the groove in earlier wider groove monos and/or hit dirt or damage in that area leading to more noise in playback.

I think one should also distinguish between modern stereo cartridges that simply bridge the channels to provide "better" mono playback vs. modern mono cartridges with adapted vertical compliance purposely designed with 2 coils that are oriented to both grossly reduce and/or eliminate (the purists will always argue) reproduction of any vertical info/noise while at the same time eliminating the chance for hum/noise issues when used in a typical 2 channel setup.

In my experience, the 2nd (whether it has a line contact or decent conical) is much better at mono playback than the first whether it is regarded as "true mono" or not and these mono cartridges are really the swiss army knife of monos for users wanting one mono cartridge to play all their mono records.

As most of my mono vinyl is in very good shape and I have only a handful of monos from the pre-microgroove era I am tempted to retip my AT 33 Mono (aluminum cantilever and nude conical stylus) with a boron cantilever and MR stylus at some point. I think the results would be positive on most of my collection, but not necessarily all.

But I don't really find it wanting with the conical and still prefer it on the same table on an inferior arm (with both cartridges gain optimized also using the same phono stage) compared to my much more expensive/prestigious stereo cartridge when playing both vintage monos (to be expected) and modern mono reissues (some would argue or take the position not to be expected).

For the super hardcore purists wanting to extract the most from large mono collections, I can see the need for 2, maybe three different mono cartridges.

You could take the same position on stereo cartridges but the argument would be much more about subjective preference as opposed to technical merit in terms of actually retrieving the info from the grooves.

I see your point for 78s and late 1940s and I don’t know about 45s of the 50s, but I own nothing in any of those categories. 0.7 mil or exotic nonconical stylus is fine for my needs. And I do insist upon 2 channels of mono output, however it’s achieved. That’s how I approach the mini-dilemma. Plus my preamp must have a mono switch.

From what I've read, hdm raises a good point about matching stylus size with the vintage of the LP and thus the grooves.  Apparently all the cutter heads are now stereo (no surprise) so even remastered mono LPs will have a narrower groove than the originals.  That may be why Mr. Carr recommends modern styli, if he tests with reissue pressings?