2 track stereo with 1/4 track heads

[steveidosound]

I have been wondering what is the nature of the loss of playing a 2 track stereo tape with a 1/4 track stereo head.
Some of my classic (ahem...relic) tape machines have a mechanical lever or switch that actually shifts the 1/4 track head downward to center it on  the tape rather than covering positions "1 & 3" as it normally would. This as opposed to an electrical switch for another head as some newer decks have. Aside from the wisdom of designing a mechanism that physically moves the head, pretending it all works correctly, how much is lost by playing 2 track tapes with the narrower gap head properly centered? I understand there must be some loss, but is it signal to noise? Frequency response should be OK IF the head is in alignment. I know it does not work so well to play one with  a 1/4 track head in it's normal position. I think that would lead to high frequency loss from not being centered on the track, even if azimuth is spot-on, but I am not sure of that.
Anybody ever do any critical evaluation of this?  I would think that those lucky enough to have 2 PB  heads with a switch could simply change it and hear what changes in the middle of playback.
When I change my 1/4 track head to the 2 track position, I hear a slight balance change and it gets a bit louder, but frequency response seems to be unaffected. 

[ironbut]

Hi Steve,

I would think that (in theory at least) you'd get some "fringe effect" from the wider track of the 1/2 track tape with a 1/4 track head set in the middle.
Aside from that, just getting a mechanism to "slide" the playback head and still retain proper alignment from one position to another would make getting optimum playback a tough row ta hoe.
It is a pretty clever set up though.

[steveidosound]

Here is one example of such a deck from the beginnings of The Tape Project -
http://www.bottlehead.com/et/adobespc/Seduction/bottleheadtapeheadpreamp.htm
I have about 3 Ampex machines, two with transports similar to the one in the picture and one 600 series transport based stereo playback only deck, plus a Wollensak, and a Roberts/Akai that have this mechanical shift scheme. I believe I once owned a Viking as well that had a little H/Q knob on it's head block. Probably was fairly common through the mid 60s when there were a large # of both mono and stereo machines around. The same feature would theoretically allow you to play mono 2 track tapes properly.
Here is an image of that Viking knob I just lifted from eBay -
http://i.ebayimg.com/t/VINTAGE-VIKING-88-STEREO-TUBE-REEL-REEL-TAPE-RECORDER-1965-/00/s/MTIwMFgxNjAw/$(KGrHqZ,!ooE8c7KNIHNBPVihP(Khg~~60_57.JPG