Don Tarbell's computer

From: dave dameron <ddameron_at_earthlink.net>
Date: Fri Sep 25 01:41:26 1998

Hi Sam and all,
At 11:34 AM 9/9/98 -0700, you wrote:
>
>If you're not aware of this, Don Tarbell, of the famous Tarbell Cassette
>standard, died earlier this year. Someone posted about this on the list
>around the time he passed on.
>
I called Don about 18 months ago asking if he could give me some information
on his earlier homebrew computers. I know he started in the mid 1960's with
a RTL (resistor transistor logic) system. He didn't know where to locate any
at that time. I also said I'd be interested in other earlier computer
literature.
I knew a little about his cassette interface from BYTE ads. He and his wife
Brenda took my mumber.

Well this week she called, She had taken care of most things and was moving
this Sat. She had a small box of literature that I could pick up if I wanted
it. I said Sure!

The box has several of the Micro 8 newsletters, some IMSAI stuff, some 1977
Bytes, source code listings for Processor Tech Basic-5 and Software package
No. 1, +...
I was happy to have found it. Her last trash pickup would have been the next
day.

Why I'm writing is thrown out at the street was his (their) last homebrew
computer, "PUTER". Brenda said I was welcome to it. She had spent many hours
soldering the boards, they had dropped all work on it when the Altair came out.

I would like to get it to do at least something. The problem which makes it
(maybe too) difficult is that ALL documentation is lost. Many wires are broken.

I have 3 units:
1. the rack "mainframe" which include 16 address lights, 8 data switches, 4
"file address" switches + about 10 others. The main power supply is 5V, 15 Amp.
The backplane has space for 16 cards. There are 8.

2. A spare? cardcage with 7 misc I/O cards? The edge connectors are wired
partially, but it looks like a card storage unit.

3. A "GA" logo core memory card, 15 x17 inches (38x43cm). Not sure if it was
connected. Brenda said Don collected all types of computer surplus for his
projects.

I left behind a hard disk unit in a rack in very poor condition. The single
platter had been exposed for over 10 years...

Most of the cards are Douglas Electronics 11DE5.
(They are in San Leandro in N. Ca. and still sell these. You can see their
line at www.douglas.com. they also sell DEC, S-100 and other form cards at
attractive prices, in my opinion, if anyone needs them.)

The cards 11DE5 hold up to 36 16 pin dips. They are soldered together with
vari-colored telephone wire. (AWG 24, about 0.5mm). Am example of what I
have is a serial card (from the DB-25S) which contains 20 IC's.

3-7401
2-7402
2-7404
1-7421
1-7427
1-7430
1-7442
2-7474
2-7496 5 bit shift reg.
1-74163
1-74180 parity gen.
2-9602 (T. and R clocks)
1-8273 10 bit shift register.
This was in the "spare" cardcage.

Have not traced this board circuit or any other yet! May start with a simple
one with only 8 IC's. Have not recognized any computer function yet, such as
a ALU, address latch, etc. Should I start by finding the data and address
busses on the backplanes? Or does this sound like an impossibly long task???

Brenda said this system was used to start development on a cassette system
before S-100 came along. It is really amazing that he interfaced a hard disk
to it and wrote an operating system for it. She said one output devicer was
an X-Y recorder. If anyone has any of the Amateur Computer Society issues
that have any descriptions, I would be very interested.
-Dave
Received on Fri Sep 25 1998 - 01:41:26 BST