My DOD 250 Preamp-Gray

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memphis mike

Member
Messages
15
I noticed somewhere that someone metioned the different forms of this 250. I have an original gray I bought new many years ago. I can say that there are 2 different gray ones. I have never seen another like mine. It has no place for a power supply, 9 volt battery only. Anyone else run across one of these. Fortunately, the batteries last a long time.
I figure I must have the original "original". Kinda feel like the proud papa, lol...
 
Steve Mavronis

Steve Mavronis

Member
Messages
751
You have a very rare one, probably a 1976 or 1977 gray before the PC power jack was added. Also your DOD logo probably has a repeating 3D effect and is on the left side vs the solid right side logo as on the later gray 250's. Can you take large sharp pictures of the PCB board? I'd like to see it. I'm compiling a list of all the parts from all versions of the 250 you can see here:

http://sites.google.com/site/snmavronis/neoclassic/741overdrive/research

Your info would be very useful. Also if you temporarily unscrew the knobs and pots from the case, you can see a 7 digit date code starting with 137 for CTS brand under them, the next two numbers are the year the pot was made, and the last two numbers are the week of that year. That will tell you when at "least" your gray 250 was made. If you look for this also tell me any other writing on the two pots. The data code on the 741 chip will also be a good clue.

I built a very nice 'gray spec' clone of a 1979-1980 era last gray 250 model you can learn more about here:

http://sites.google.com/site/snmavronis/neoclassic/741overdrive
 
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memphis mike

Member
Messages
15
I'm not sure how to post pictures yet. I took pictures on a 3 1/2" Disk. How do I upload to thread? I may have to send pics to you by email. I don't have a site for my photos.
 
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memphis mike

Member
Messages
15
I am considering selling this. Any idea what it's worth? I may have to get one of Steve Mavronis' 741 O/D before I sell though.
 
Steve Mavronis

Steve Mavronis

Member
Messages
751
Based on ebay sales of other grays I've seen bidding between $400-$700. Make sure you advertise that yours is a rare gray from 1976 or 1977. Some purests prefer those first ones using germanium diodes for distortion verses silicon diodes in later years. Myself I prefer the late 70's grays marking the end of the series development just before evolving into the first yellow models.

Do me a favor though before you sell it: Maybe to help fill in missing info on my 250 parts chart you could list the resistor color bands and markings on the capacitors and other parts? You can use this simplified diagram of a later model gray as a general guide to point to a part code list, etc.

Here is a handy resistor color code calculator to help. Just enter the resistor band colors and it will tell you the value: http://www.hobby-hour.com/electronics/resistorcalculator.php

The photos you showed me were small and a bit out of focus so I couldn't tell anything by looking at them. You could try holding your camera at least 3 feet away and 'zoom' in for a clearer shot with daytime lighting like outdoors on your porch. If your zoom indicator bar has a line down the middle separating it into two halves, try to keep the zooming in the left half so it's an optical shot. Continuing the zoom into the right side of the indicator bar will throw the camera into digital zoom mode which isn't as sharp. Note that most camera lens cannot focus within 3 feet of the subject, unless you have a digital camera that you can set to macro mode for close-ups without zooming.

Note that early 76-77 grays were missing the extra 10uF capacitor at the bottom left and you won't have the 100 ohm resistor at the bottom right either:

dod250grey-pcb-layout.jpg
 
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memphis mike

Member
Messages
15
ok, I'll try and get a better camera shot. I'm using one of those old Sony's that carries a 3 1/2" diskette.. I have a lot of trouble with it saying disk error. Anyway, I'll be sure and get a picture with my sister's camera which takes excellent pictures.
 
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