[R-390] R-390 restoration

[Jordan]

Seeing as the 6080 tube is readily available, wouldn't a simpler solution be to use them with a separate filament transformer ??
With proper ventilation, the original design is a very good one... and removing the 6082 filament drain would also allow for less strain on the power transformer..even though I don't think it is exceedingly stressful on the transformer in
the first place...jmo....73 de Jordan...

"Veenstra, Lester B." wrote:

> Yes, of course, a regulated external 180 VDC supply is what I meant to say. Brain drifted out of phase lock. sorry!
> I have been accumulating these at the local fests, to be dedicated to the (non As in the) receiver rack. Some day real soon I will actually get it done along with the general overhaul of the receivers now backed up waiting my attention.
>
> -----Original Message-----
> From: Barry Hauser [mailto:barry@hausernet.com]
> Sent: Friday, August 09, 2002 8:11 AM
> To: Veenstra, Lester B.; DAVID MEDLEY; r-390@mailman.qth.net
> Subject: Re: [R-390] R-390 restoration
>
> Les wrote:
>
> >I lean toward the use of an external 300 VDC lab supply rather than trying
> to modify the internal regulator. Keep in mind no matter what you do
> internally, you still have to get rid of the IR drop heat. Instead, present
> the regulated bus with the right voltage from an external unit that can be
> disconnected to restore to the OEM design.
>
> That sounds like a good idea -- with the reg. supply set to 180 vdc.  If you
> need the P/S for other work, just won't be able to listen to your non-A at
> the same time.
>
> However, the heat dissipated by the SS VR circuit is much lower than what is
> given off by the 6082 pair and Dr. J. offers some heatsinking suggestions in
> the HSN article which get the heat out of the chassis altogether -- e.g., by
> mounting the heatsink on the outside of the chassis using existing holes
> alongside the audio deck area.  Warning on that -- the transistor that needs
> the heat sink will probably have a "hot" case or tab, so needs a mica
> insulator and heat sink grease -- plus an insulated cover over the
> transistor itself so as not to have a very oversized, external and dangerous
> B+ "test point".  If you don't like the idea of an outboard heat sink, one
> can be positioned inside and a small fan can be used to draw the heat out
> through a nearby "porthole".  BTW -- this is a good idea when running the
> 6082's.  The heat buildup is aggravated by the fact that they are upside
> down and the heat otherwise rises to cook the deck and warm up the whole
> chassis on that side.
>
> However #2:  The '391 I have (that sparked the article) has no heat sink.  A
> tab mount style transistor is just "floating" on the perfboard.  It looks
> like the guy originally had it mounted to the shield that encloses the 6082
> area, as there is a small hole and a residue of heat sink grease there.
> Maybe he had trouble isolating the tab, I don't know.  But it's the coolest
> spot in the rig and the mod was probably done over 15 years ago, judging
> from some of the components used.  I should point out that this was done
> irreversibly and the audio was solid stated out using one of those handy
> dandy ECC modules.  There is only one tube remaining on that audio deck.
> The rest of the radio is stock "tubular" and the solid state VR is supplying
> B+ to all of that.  Yet, no heatsinking and not much heat.  So ... I dunno.
>
> Barry
>
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