[R-390] Arising from the dead: Again

[Perry Sandeen]

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