[R-390] Arising from the dead: Again

[Cecil Acuff]

Well I have no proof of it at this point but it's been mentioned in the past 
that some metal film resistors are deposited in a spiral and it stands to 
reason that inductance would be created in that design.  Only at RF 
frequencies I would guess.  That being said I can see how metal film 
resistors would be highly recommended for audio circuits.  They are superior 
for sure.

Guess I'll have to throw a few on the sencore cap/inductor tester and see 
how they test against the same value carbon comp.

I've also heard that baking the moisture out of NOS carbon comps will bring 
them back to their original values too but I've not tried that either...

Oh well...that' one of the good things about the list...you can learn 
something new each day if you go looking for it...:-)

Cecil
----- Original Message ----- 
From: "Perry Sandeen" <sandeenpa at yahoo.com>
To: <r-390 at mailman.qth.net>
Sent: Monday, September 13, 2010 9:45 PM
Subject: [R-390] Arising from the dead: Again


> Gents,
>
> Wrote: Also yes...resistors should be checked.  It's easy enough to do 
> most of the time with the tubes pulled out.  Try to put carbon resistors 
> back in their  place.  The modern metal film resistors do have inductance 
> and can cause  problems in some cases.
>
> I leap up upon my Soap Box.
>
> Arise Igor!  Sound the alarm and man the parapets.  Get the Crucifixes and 
> Garlic! The urban legend that refuses to stay dead and buried returneth to 
> haunt us.
>
> Our great contributor from the past, Dr. Jerry, covered this extensively 
> in previous posts.  His tests showed that there was NO measurable 
> inductance until up into the GHz range.
>
> If you try to buy Art’s Original’s from Mouser and others, they are almost 
> unobtainium and very expensive?  Why, you ask?  Because they are very 
> inferior to both metal film and carbon film resistors.  Because of this 
> almost no one buys them.
>
> Over the years list members have made numerous posts  concerning value 
> shifts they had found in their R390As with carbon comps.  Also they change 
> value during operation with the high temperatures in BA receivers.  Also 
> remember that the OEMs are 50 plus years old.  Just because they look good 
> does not mean they are good.  Even if a radio is operational that does not 
> validate the old parts.  It simply means that the parts have not become so 
> bad that some circuit will not operate.
>
> Never forget the difference between OPERATIONAL and OPTIMINE.  They are 
> worlds apart.
>
> Several years ago I sold to the list members about 30 complete resistor 
> replacement kits for both the R390A and SP 600.  99 percent were metal 
> film.  No one has said to me or to the list that they had any problems. 
> Nada, zilch, zero.
>
> No list member that I can recall has posted any problem where a metal film 
> replacement caused a problem and had to be replaced by a carbon 
> composition type to operate properly
>
> Wrote: I do NOT see the need to shotgun 390s or 390As, except for the 
> several critical and failure-prone caps -- they do not have the same 
> record of unreliability as SP-600s.
>
> Both Chuck Ripple and Dallas Lankford have published audio circuit 
> improvements for the R390A.  In his audio improvement circuit for the SP 
> 600 chuck specifically advises to use metal film resistors for improved 
> performance.
>
> I tend to agree about doing a shotgun approach on some of the R390A 
> modules as it is a real chore.  But if you have to go into a module to do 
> caps I believe one should do resistors at the same time.
>
> As for the SP 600, since the underside is relatively open, one should 
> replace all the carbon film resistors as well as moving the power dropping 
> resistors to the top side of the chassis.  Especially if one is replacing 
> any BBODs.
>
> If you ever have to take out and repair the RF deck of a SP 600, by the 
> time you get it removed you will want to put in the best, most reliable. 
> resistors, capacitors, and new wires money can buy.  For  further proof 
> Read The Fine Manual or ask someone who has none it; it will make you a 
> believer.
>
> Not mentioned in the previous series of posts.  Use DISK CERAMICS for RF 
> circuits only and FOIL CAPS AKA ORANGE DROPS of audio only.  Beware, THIS 
> NOT what Hammarlund did with most SP 600’s.
>
> I now descend from  my Soap Box and return you to your normal postings. 
> Refreshments are available in the lobby for a modest charge.
>
> Regards,
>
> Perrier
>
>
>
>
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