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Townshend EEI 600C
Townshend EEI 600C
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Old 17th July 2019, 08:14 PM   #1
ferret is offline ferret  South Africa
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Default Townshend EEI 600C

I am looking for the schematic diagram for a Townshend EEI 600C preamp.
I have contacted Max Townshend, but evidently the original schematics were destroyed during a flooding of the factory/offices many years ago.

I got mine back from my brother, but it is not powering on. I will first try powering it with two 12v 7.2 A/h batteries, by-passing the onboard adjustable regulator - RC4194DB (+& - 42V @ 200mA.) The BJTs are ZTX214s and 384s. There are also two potted discrete ICs (5 resistors, 3 caps and a BJT.)

I will put two 150mA fuses into the power lines, just for safety sake. Picture of a variant is attached.

Kevin
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Last edited by ferret; 18th July 2019 at 07:03 PM.
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Old 18th July 2019, 05:04 PM   #2
Mark Tillotson is offline Mark Tillotson
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7.2mAh batterys? Really? They would be microscopic! I suspect you mean 7.2Ah


Never do this. High current batteries will burn the entire board if something is badly wrong, fuses or not. Semiconductors will fail far faster than any fuse, fuses are there to stop the wiring or transformer catching fire.

A current limited supply is needed, could be as simple as some 100 ohm resistors in series with the rails to start with (changing to 10 ohms if nothing drastically wrong).

A bench supply would be better of course, but dual tracking supplies aren't cheap or commonplace...
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Old 18th July 2019, 07:01 PM   #3
ferret is offline ferret  South Africa
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Default Uhm, oops!

Quote:
Originally Posted by Mark Tillotson View Post
7.2mAh batterys? Really? They would be microscopic! I suspect you mean 7.2Ah


Never do this. High current batteries will burn the entire board if something is badly wrong, fuses or not. Semiconductors will fail far faster than any fuse, fuses are there to stop the wiring or transformer catching fire.

A current limited supply is needed, could be as simple as some 100 ohm resistors in series with the rails to start with (changing to 10 ohms if nothing drastically wrong).

A bench supply would be better of course, but dual tracking supplies aren't cheap or commonplace...

Hi Mark,

Indeed, did not check properly what I typed in. They are 7.2 A/h batteries.

Thanks for your advice; I do have a small LM317/337 PSU which I can use and have a 500mA 2*12V trafo somewhere. I will of course put in the limiting resistors, as you suggest. I fortunately have a selection of 5W ceramics in my stash of resistors.

Kevin
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