14" Sierra Gold Max for GMT - DD or Concentric?

[steve herschbach]

Here is a rare tidbit for you. The Sierra 13.5" x 7.5" Sierra Gold Max coil comes in two versions. The older white housing units, discontinued last year, are concentric coils. The new black housing coils are DD units. This kind of just quietly happened. There are still some new concentric versions sitting new on dealer shelves but White's is no longer making them. In theory the concentric will get you a bit more depth in low mineral ground and the DD will better handle high mineral ground.

[attachment 255922 goldmaxloop2.jpg] [attachment 255923 801-3204-1-s.jpg]

Both versions of the coils work on 48 kHz - 50 kHz White's Goldmaster II, Goldmaster V/SAT, Goldmaster 3, Goldmaster 4/B, GMT and GMZ.

Part number for the white concentric was 801-3204 and part number for the black DD is 801-3204-1


Steve Herschbach

 

[SNOWMAN.]

Interesting Steve. It never occurred to me that the original would be other than a DD. On a slightly different note, have you ever asked anyone at Fisher why the GoldBug 2 has no optional DD coils?

That's not a criticism of Fisher by the way.... just a curiosity more than anything.

Jim.

 

[steve herschbach]

I have seen hints that detectors can be specifically tuned to run best with either a DD or a concentric coil. The Teknetics T2 and Fisher F75 are often mentioned as "being the same detector". They are not. Well, no more than most detectors are a variation of another. The biggest difference is the T2 is wired specifically to work with DD coils made specifically for it. F75 coils will not work on a T2. Any detectors that cannot share coils are by my definition different detectors. There are no concentric coils for the T2. A change was made in the F75 to make it compatible with concentric coils.

There have never been DD coils for the Gold Bug 2 though I would think it would be a good idea. However, the unit does what it does fabulously well, and it may be concentric coils are a part of that. DD coils are not better than concentrics, they are just different. See http://www.fisherlab.com/hobby/davejohnson/searchcoils%20essay%20revised.htm Mention is made in the essay to DD coils falling out of favor for the period of time in which the Gold Bug 2 was developed.

I am very interested in coils and will seek more information on this. Thanks for the question!

Steve Herschbach

 

[Dave J.]

To a minor extent a detector design can be "tuned" for the response pattern of a DD vs. concentric.

The T2 transmitter circuit is designed specifically for driving a DD, and it'd be very difficult to make a concentric to run on it. Don't expect it to ever happen.

The F75 has a completely different transmitter circuit that doesn't care whether a searchcoil is concentric or DD, but in any case the searchcoil has to be wired to work on the F75.

The T2 searchcoil is wired specifically for the T2 transmitter circuit and is completely incompatible with the F75, and vice versa.

The GB/G2 series transmitter circuit was designed specifically to drive "Fratbros" ("Greek series") DD's, but some individual concentrics from that series will sorta work on the GB/G2 sometimes if you get lucky.

The Gold Bug II searchcoils (71 kHz) are concentrics. Marketing dept. has been beating me over the head for a lot of things that we really do need, but DD's for the GB2 aren't on that list. So I doubt it'll ever happen.

--Dave J.

 

[steve herschbach]

Hi Dave,

Thank you very much for the response and rare tidbits. It is an open secret that the Gold Bug 2, as an analog design, is living on borrowed time. It makes no sense to put any more development money into a machine whose days are numbered. I have two, just in case!

Steve Herschbach

 

[SNOWMAN.]

Thanks Steve, DJ