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In Reply to: Re: UPC 78M05 HF?(DATA?)168 degrees! I think I do need a higher current voltage regulator. posted by Mike Stehr on February 23, 2001 at 20:31:36:
Apparently a typical 78M05 can operate to a temp. of 150 deg. C, or ~300 deg. F. So you should be OK, but the cooler the better. Replacing the M version with a higher current rating plain 7805 (and still using the heat sink) would help. Yes, I meant Radio Shack by RS. I personally wouldn't buy electronic parts there except in an emergency, and wasn't recommending it, just using it as an example of how ubiquitous the 7805 is. Actually, that should be "was", since not too many people make them any more. Is the 7805 blown? I have tons of 7805's, all graded to voltage output, and can send you one if you want.
Follow Ups:
Interesting, the 7805 will not necessarily be able to handle much more power than the 78M05. The higher current rating has more to do with the ability of the internal pass transistor to handle the current without saturating with input voltages close to the output voltage (drop out voltage). The thermal resistance rating of both the 7805 and 78M05 is 5 °C/W from junction to case for a TO-220 package. This means that the transistor junction, where the heat is generated, will be 5° hotter than the case for each watt of power that the IC is dissipating. 168°F is 75°C, and if the regulator is delivering 500mA with 10V input, the regulator is dissipating 2.5W, and the junction temperature will be 12.5°C hotter than the case, or 75° + 12.5° =87.5°C. This is hotter than I would normally run things for best reliability, but probably OK. By the way, the projected lifetime of a semiconductor device running at 150°C is much, much less than when running at 70°C. Most of this information is available on the data sheets at manufacturers web sites.
Thanks for you info.I took a chance at doing some upgrading on this unit.
Replaced the larger caps in the power supply areas. (I guess.)
Replaced 2 2200uf 25v rubycons with 2200uf 35v Nichicon muse FG's,
and the 4 diodes around these, (2amp diodes)with 4amp 600v Harris diodes.
This is the circuit that is right after the transformer plug
on the main board.
A 3300uf 25v rubycon was replaced with a Nichicon muse FX 3300uf 50v.
This appears to be a rectifing circuit,(I wish I changed the 4 diodes
here but I set a 40 dollar limit upgrade.)
Then I changed 2 470uf 100v rubycons to 470uf 100v Nichicon muse
FA's.
These are most likely powering the tube circuit or relation.
This 7805 I.C. is in this area.
Threw in some sockets, and put a couple of op275's next to the
output jacks.I'll quick fix this with radio shack option, because this regulator
seems a little warm for me, and I would feel more safe.Maybe get a few more hours out of it.
I wonder if this regulator is blown?
This thing had some tracking/slowness glitches.
Upgrade seemed to cure it, though I never would have thought in million years that this would have happened.The player sounds kind of raspy, but a little better than it did.
The bass seems alright, but the high ends kinda nasty.I plan on purchasing a new player soon.
It basically boils down this:
''A Turd is a Turd''.
Thanx for the help!
Mike Stehr
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