Looking for a C&G Bobcat 2 schematic

[Dr Vel]

As the title indicates I need a schematic for a C&G Bobcat 2, and scans or a PDF of the operation manual. I have searched hundreds of pages online and so far all I have learned is I think this may be a rare model judging from the absence of anything useful about it online. I can say after using it (by guesswork as to operation) for a while and getting a feel for how it seems to work compared to many others I have used, I think I love this old machine. Even a little knowledge about the design and theory of operation would be useful. Simply amazing how much information is conveyed by sound alone after you get the feel of it in operation. This one has the push button auto tune function.

[Carl-NC]

Tesoro might be willing to provide these.

[Dr Vel]

Thanks for the advise Carl, I sent a short letter to [email protected]. I read their history page and learned what you must have already known, they created the model.

On a side note do you have an avatar with the Darth helmet on in the junkyard scene? Just thought it would look cool.

[Dr Vel]

Since it appears they will not send me the diagram for the C&G Bobcat 2, I started studying their later models under the Tesoro name. I am almost certain the Tesoro Bandido II schematic I have been studying is simply a resurrection of their old 1970's C&G Bobcat 2. With one exception, in the very area I have been trying to understand. The old C&G has a momentary switch in the handle which re-adjusted the circuit whereas the newer Tesoro uses an SPST switch for 'auto' (which only works in the all metal center position since to either side the same closure as the auto function is made). My purpose in this was trying to understand how the auto function is implemented electronically as in the push button in the handle on my Bobcat 2. What little tracking down of the circuit I have done on the C&G seems to indicate very similar design. If you can suggest any threads here which give good instruction on the push button auto control I would appreciate it since as I said I do not think Tesoro is going to provide the Bobcat 2 diagram. My goal is knowledge in depth on how the momentary push button on my Bobcat 2 works from an electronic theory viewpoint.

I have a Pioneer 101 I am going to use as my framework by replacing the old control box with a box I build and was desiring to replicate the Bobcat 2 circuit with a little redesign. It seemed this would be a good model to sacrifice since it is a not very good design. I proved to myself how poor the discriminate function was by finding an old tin can 6 inches deep with the 101 where the sound and indication was identical to a silver coin of moderate size. Likely an old food can from the 50's or earlier long before they learned how to plastic coat the inside of modern Al cans. I did some experimenting with the 101 and you can tell the difference in discriminate at 6 inches deep between an Al and Sn can easily. Yet a silver dollar 3 inches deep gave a nearly identical signal on full discriminate 60% sens. as the deeper but larger Sn can. Meaning this 101 cannot tell the difference between real tin metal and silver from all the tests I have done. But it is a nice handle with 8 inch coil to use to build something else using my own electronics and was fairly cheap to obtain.

[Reg]

I haven't verified this schematic but it says it is for the Bobcat 2.

Reg

[Dr Vel]

Thank you for posting this. Looking at the IC's I think this is a very good candidate for being the right one. Will have to take it back apart to be sure.

One question from careful study of this schematic is do you know if possibly there are errors in this drawing?

[Dr Vel]

Does anyone have the construction data for the coil on this model and does anyone know the proper operating frequency?

[Dr Vel]

To answer my question I took my Bobcat 2 apart and hand traced out the complete circuit. What I found was the schematic posted above is correct, and not only is this the correct schematic for the Bobcat 2, but also the C&G model 200-1G is completely identical in every detail. What I do not totally understand is why the ground balance and discriminate are the same, single pot. How does this work? Hoping Carl will explain as I have never found the operating book for either model. The C&G TECHNOLOGIES Bobcat model 200-C is completely different internally. No idea why they gave it the same '200' series designation. I did not bother tracing it out as it's heart is a big black rectangle potted plastic block. As it has the same controls all I can think of is possibly it is the same circuit with 3/4 of it encased in a block of plastic. No desire to deal with methylene chloride to depot it and see. I can say however for anyone interested the coil is identical for all three models. A 6 inch coplanar, very standard design. TX coil is 15.5 ohms, 8.7 mH. RX coil is 8 ohms, 1.4 mH. Just in case someone decides to build or repair one of these models. Out of some 20 different models I own I still keep coming back to my Bobcat 2, I love this machine. So much so that I decided to give it a new life mounting the box and coil on the remains of a BH Tracker 4 I did not care too much for. Makes it much less stress using the MD out in the field and gave it a more modern look.

Only other thing I might point out is the values of the pots in the schematic above do not match what is in the MD in reality. Isolating and carefully measuring each gave 3K for the disc pot and 6K for the tune pot. No idea where C&G came up with 3 K and 6 K pots, yet this is what they measure. All other part values are identical except for some reason some use an LM301 instead of a CA3130 after the Gnd Comp/Disc pot. Unsure why C&G chose to randomly use one opamp over the other unless it is based upon what year the model came out, possibly a later design change? Leaving me with only one question to figure out. Is the Disc pot only Disc in Disc mode and becomes Gnd Bal in normal mode?

[Merc]

Ground balance and discrimination are very similar. Ground balance is just a way of discriminating out the ground signal.

Merc

[Dr Vel]

The C&G TECHNOLOGIES Bobcat model 200-C does not have the push button retune, I forgot to mention this above. All other controls are identical leading me to think they may be closely related (reason for same '200' designation?). I reverse engineered both in the hopes of adding retune but it appears all parts of the chopper circuitry are inside the plastic block making this idea not worth doing.

Thanks for your reply but it does not help. While Disc and Gnd Bal are similar they are not identical. What I was wondering was how did it become one or the other, since it is labeled both on the box. As near as I can tell it is changed by selecting Disc or Normal mode by selecting one opamp output or the other. Still not being completely up to speed on Disc and GB theory I had thought the only difference was the phase of the return signal. Yet inversion is the only difference I see between the two (study the diagram above). Meaning the difference between Disc and GB is 180 degrees whereas I thought it was less like say 10 or 20 degrees. Guess I still need to study.