Well I had a good start with the 70 finding hammered coins on the first and second trip out,both from pounded to death sites,yesterday I was out again on the same sites and found a pocketful of non ferrous of this site,best finds were a George III penny and a gold plated ladies watch,what amazed me was that I found them in a small tennis court sized area I had grid searched countless times before,also the signals were were loud and clear which had me scratching my head as to how they had missed before.
Here are some things I've noticed
Depth is very good with sensitivity in the high twenties,I usually run mine at 28-30,above 28 the machine gets nice and sparky but the signals come in loud and clear.In trashy areas I went down to 20 but going below this looses a lot of depth.
The 70 with the 10 inch DD 18.75 Khz coil fitted likes iron(on pasture),especially any round iron,holed iron or large flat iron,coming from a Sovereign this was a bit of a shock as the GT never digs iron but there are several good ways to id it as described in the "tips and tricks" article by Des Dunne,however the method I found best was to switch to prospect mode and sweep the coil over the target,if it screams it's iron,if it's loud it's probably iron,if it gives a quiet signal it's probably good.
The stock coil is good on iron and will only dig the trickiest type of signal,on an iffy signal where you are not sure if it's a deep target or deep iron here again the prospect mode will come to your aid,if it screams or is loud or fairly loud it's iron,it the signal is a quiet quick rise in then it's probably good.
Now we come to the prospect mode,should you use this or the C&T mode for general searching,well it depends on how high you can get the sensitivity on your site,if you can get it into the high twenties or even 30 then I would say no as the C&T mode only looses a little depth to the prospect mode at these settings and is far quicker to use,in fact at 30 it's hard to find a signal in prospect that won't also give at least a faint signal in C&T,this also goes back to what I said above about identifying iffy deep signals,since the difference in depth in not so great there is no way an iffy deep non ferrous signal in C&T can scream or be loud in prospect.
All this changes on a heavily mineralized site,let's say you can only get your sensitivity to 15 in C&T mode,here the prospect mode will have the C&T mode for breakfast,it will be much deeper ,try this put a coin in the bottom of an empty flower pot or something,now using C&T mode keep sweeping the coil over the top of the pot and reduce sensitivity until the signal disappears,on my six inch deep pot this happened at 15-16,now switch to prospect and sweep over the pot,loud and clear!
Also of course prospect mode will find far smaller items than C&T,and is usefull on worked out sites to find some extra targets missed by C&T.
Now to tones,I use 2 tones nearly all the time,I love the non ferrous signal in this mode,really sharp and unmissable,the iron tone is also not annoying like some other machines,as you go up to 3,4 and 99 tones the audio response on signals gradually gets worse and more confusing,also the recovery speed seems to suffer,I'd use 4 tones on the beach or a very clean field and I do like the high pitch in the silver area but it's not for me,however on an iron laden or trashy site no way.
Ok now we come to a problem with the tones,-2 on the meter is NOT IRON,or I should say almost never iron,in fact if you are sweeping over an iffy signal and see -2 flash up in the meter just start digging,usually the meter will jump from -2 to plus numbers,often low digit numbers and I have dug these signals to find small non ferrous targets.
The reason this is a problem is that the 70 will of course give a low iron grunt on -2,so if you are sweeping along happily in all metal and hear an iron grunt you will not know it's -2 unless you look at the meter,this is a pain and the only way around it is to use one tone and disc out -8,-6,-4,then if you get a tone it will be -2 or above,this sucks however as I hate to use anything but all metal and I don't like the low pitched tone on one tone mode.
Now when hunting in an iron laden site trying to find targets next to iron ther are only 2 choices for me,one tone or two tone mode,two tone mode is good but one tone is better,in fact with a HF DD coil on and using one tone mode in all metal the 70 is very good at finding next to iron,however 2 tone mode is also good but you'll get the iron and non ferrous tones sounding together which sounds a bit mushy but still very usable.
I only use all metal mode,this allows all the signals to come through and doesn't strangle the audio response on signals,also the recovery speed is better,if you choose to use disc then don't disc out -2 !!! ,in fact don't disc out -4 either.
As to coils well I like the stock coil best so far,the 10 inch HF DD might be great on ploughed but likes iron on old pasture,still is has great see through iron ability and finds very small items,I have a DD 7.5 Khz on the way so looking forward to using that.
That's my thoughts at the moment,hope it helps other new users
Here are some things I've noticed
Depth is very good with sensitivity in the high twenties,I usually run mine at 28-30,above 28 the machine gets nice and sparky but the signals come in loud and clear.In trashy areas I went down to 20 but going below this looses a lot of depth.
The 70 with the 10 inch DD 18.75 Khz coil fitted likes iron(on pasture),especially any round iron,holed iron or large flat iron,coming from a Sovereign this was a bit of a shock as the GT never digs iron but there are several good ways to id it as described in the "tips and tricks" article by Des Dunne,however the method I found best was to switch to prospect mode and sweep the coil over the target,if it screams it's iron,if it's loud it's probably iron,if it gives a quiet signal it's probably good.
The stock coil is good on iron and will only dig the trickiest type of signal,on an iffy signal where you are not sure if it's a deep target or deep iron here again the prospect mode will come to your aid,if it screams or is loud or fairly loud it's iron,it the signal is a quiet quick rise in then it's probably good.
Now we come to the prospect mode,should you use this or the C&T mode for general searching,well it depends on how high you can get the sensitivity on your site,if you can get it into the high twenties or even 30 then I would say no as the C&T mode only looses a little depth to the prospect mode at these settings and is far quicker to use,in fact at 30 it's hard to find a signal in prospect that won't also give at least a faint signal in C&T,this also goes back to what I said above about identifying iffy deep signals,since the difference in depth in not so great there is no way an iffy deep non ferrous signal in C&T can scream or be loud in prospect.
All this changes on a heavily mineralized site,let's say you can only get your sensitivity to 15 in C&T mode,here the prospect mode will have the C&T mode for breakfast,it will be much deeper ,try this put a coin in the bottom of an empty flower pot or something,now using C&T mode keep sweeping the coil over the top of the pot and reduce sensitivity until the signal disappears,on my six inch deep pot this happened at 15-16,now switch to prospect and sweep over the pot,loud and clear!
Also of course prospect mode will find far smaller items than C&T,and is usefull on worked out sites to find some extra targets missed by C&T.
Now to tones,I use 2 tones nearly all the time,I love the non ferrous signal in this mode,really sharp and unmissable,the iron tone is also not annoying like some other machines,as you go up to 3,4 and 99 tones the audio response on signals gradually gets worse and more confusing,also the recovery speed seems to suffer,I'd use 4 tones on the beach or a very clean field and I do like the high pitch in the silver area but it's not for me,however on an iron laden or trashy site no way.
Ok now we come to a problem with the tones,-2 on the meter is NOT IRON,or I should say almost never iron,in fact if you are sweeping over an iffy signal and see -2 flash up in the meter just start digging,usually the meter will jump from -2 to plus numbers,often low digit numbers and I have dug these signals to find small non ferrous targets.
The reason this is a problem is that the 70 will of course give a low iron grunt on -2,so if you are sweeping along happily in all metal and hear an iron grunt you will not know it's -2 unless you look at the meter,this is a pain and the only way around it is to use one tone and disc out -8,-6,-4,then if you get a tone it will be -2 or above,this sucks however as I hate to use anything but all metal and I don't like the low pitched tone on one tone mode.
Now when hunting in an iron laden site trying to find targets next to iron ther are only 2 choices for me,one tone or two tone mode,two tone mode is good but one tone is better,in fact with a HF DD coil on and using one tone mode in all metal the 70 is very good at finding next to iron,however 2 tone mode is also good but you'll get the iron and non ferrous tones sounding together which sounds a bit mushy but still very usable.
I only use all metal mode,this allows all the signals to come through and doesn't strangle the audio response on signals,also the recovery speed is better,if you choose to use disc then don't disc out -2 !!! ,in fact don't disc out -4 either.
As to coils well I like the stock coil best so far,the 10 inch HF DD might be great on ploughed but likes iron on old pasture,still is has great see through iron ability and finds very small items,I have a DD 7.5 Khz on the way so looking forward to using that.
That's my thoughts at the moment,hope it helps other new users