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Old 5th November 2019, 10:23 AM   #111
Mark Tillotson is online now Mark Tillotson
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Use transparent solder mask perhaps?
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Old 5th November 2019, 11:55 AM   #112
JeffYoung is offline JeffYoung  Ireland
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Quote:
Originally Posted by Iain McNeill View Post
... Copper is a fairly active metal and will corrode quite quickly...
Even without a solder mask the copper still has a protective coating of tin.

I've repaired a bunch of little amplifier circuit boards for the coolant level and outside temperature sensors in 1960s and 70s RR/Bentleys that have been sitting around in British Isles humidity for nigh on 50 years. 90% of the time it's the diodes that fail, with the odd transistor or rivet that attaches the pins to the board. But I've never had an issue with oxidation on the board itself. (I do spray the entire assembly with cellulose lacquer after replacing the diodes and transistors, but that's just because they're going back out in the weather again.)

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Use transparent solder mask perhaps?
Yeah, I actually tried that, but sadly it kicks you out of the pooling and the board cost goes way up.
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Old 5th November 2019, 12:10 PM   #113
JeffYoung is offline JeffYoung  Ireland
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Originally Posted by avtech23 View Post
Would it be worth opening a dedicated group buy thread?

I'd be interested in 2 amp and 2 inverted regulators but dependant on price.
I didn't originally because I didn't want to get flooded with 70 subscriptions like with my J2 boards. But this appears to have much less interest, so I think I will put up a GB thread....

[Edit: thread is up: NAP250 amp boards & regulator boards ]

Last edited by JeffYoung; 5th November 2019 at 12:19 PM.
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Old 7th November 2019, 01:08 AM   #114
gary s is offline gary s  Australia
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Hi Jeff,

Any clues as to where to source the BC239C input transistors and either of the output TO3 metal can types you have on the schematic. Not stocked at Mouser. All the other transistors are in stock in qty at Mouser , so no problems with those.

Or, have you further alternatives, should not be too hard for the inputs TR1 and TR2. Maybe the output stage TR11 and TR12 need to be as close to original design semi's as possible.

Look forward to your thought on these devices. Also posted this in your GB thread.

Also, have you posted the schematics for both regulator design's?

Gary..

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Old 7th November 2019, 01:17 PM   #115
JeffYoung is offline JeffYoung  Ireland
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Hi Gary,

I replied on the device questions in the GB thread.

I probably posted both regulator schematics, but it's easier to do it again than to find them.

Julian's regulator:

NAP250 clone-youngreg_schematic-pdf


My inverted version:

NAP250 clone-youngreginv_schematic-pdf

Cheers,
Jeff.
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File Type: pdf YoungREG_schematic.pdf (73.0 KB, 280 views)
File Type: pdf YoungREGINV_schematic.pdf (80.0 KB, 202 views)
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Old 7th November 2019, 08:35 PM   #116
gary s is offline gary s  Australia
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Thanks for the schematics again Jeff.

Regards,

Gary..
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Old 8th November 2019, 02:12 AM   #117
Iain McNeill is offline Iain McNeill  United Kingdom
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Quote:
Originally Posted by JeffYoung View Post
Even without a solder mask the copper still has a protective coating of tin.
OK, good - you have a protective layer.

I did a lot of home etch boards back in the day and they did not hold up well, even with good post etch cleaning. Maybe city air quality has an accelerating effect but bare copper isn't a longevity play.
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Old 8th November 2019, 12:17 PM   #118
JeffYoung is offline JeffYoung  Ireland
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I have some cold tin plating solution for home etching, but I got on so poorly with the iron-transfer part that I've never tried it.

City air definitely greatly speeds the oxidation of copper roofs, but I'm not sure how much of a part rain plays in that.
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Old 8th November 2019, 01:23 PM   #119
stanislav1957 is offline stanislav1957  Russian Federation
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I don't understand why you don't use the Darlington amplifier voltage or kaskadno connection !
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Old 8th November 2019, 03:01 PM   #120
JeffYoung is offline JeffYoung  Ireland
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Hi Stanislav1957,

Did you mean to post that to a different thread? It doesn't look anything like a NAP250 (other than the LTP and VAS current sources sharing the same reference)....

Cheers,
Jeff.
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