[6BQ5]

I've noticed on some pictures I've seen of the RM-5 Mk IV that these were available with grey/silver faceplates in addition to black.

          Question 1: Is it possible to update an oder black RM-5 to the newer grey/no rackmount faceplate?



Speaking of updating the RM-5, the Mk III and prior versions would be at least 15 years old now.

         Question 2: Is it advised to send in an older RM-5 to have the capacitors (and for that matter resistors) checked at this point in time?

[rbwalt]

i had my RM5-Mk2 for over 15yrs without nary a problem. it went through gain stage tubes quite often. i know with some of the newer ones roger did away with the adjustable gain switches. I have heard that it improved the sound. might be something to look into. Great little pre-amp for the money when it came out .

rob.

[6BQ5]

The issue with caps and resistors aging (and going out of spec) is not specific to Music Reference, but any type of electronic gear.

On most discussion boards, people advise that after 15 years, there is a very good chance that they will have drifted, dried up, etc... You may not necessarily hear or notice this changing over time, but it happens. You've still got people using gear from the '70s untouched, but I highly doubt the kit sounds anymore like intended or to potential.

[Roger A. Modjeski]

This reply is applicable only to electrolytic capacitors. Mylar and other film caps do not deteriorate with age as long as no moisture gets in. The infamous bumblebee capacitors all went bad because their moulded case cracked. Mc Intosh and Tektronix gear of that period suffer greatly. I had to replace 30 capacitors in my curve tracer to get it to stop drifting.

In my experience capacitors last a lot longer than the belief in them does. I do careful research (I have my own methods) for selecting the capacitors I use and very, very few have been replaced. I therefore disagree with the blanket replacement policy now in vogue.

When I work on older equipment I am careful to first form up the capacitors for several hours before making any assessment of them. I have worked on many amplifiers from the 70's which need no capacitors at all. We have added a "capacitor forming" function to the RM-200 MK II mostly for sonic benefits but it helps in the long run too.

If you don't have a variac here is a simple procedure for any amplifier. This can save a perfectly good capacitor from blowing up.

Turn the amp on for 15 seconds. Leave it off for 30 seconds. Turn it on for 30 seconds leave it off for 60. Keep the series going always doubling the time. Don't leave the amp on for more than 30 minutes till you have cycled it there 10 times.

Temperature is the killer of electrolytics. For every 10 degrees C  that you can cool them down they last twice as long. My equipment is known to run cool, so maybe there is a reason for my capacitors lasting longer.

[6BQ5]

So, unless I see (or hear) something weird with an RM-5, I should assume that its OK Dokey?

[Roger A. Modjeski]

Yes, that's right. The stuff just keeps on going I designed it that way. These blanket recommendations of replace this replace that do not apply here. My electrolytic caps last longer because my gear runs cooler. My regulators don't fail because they are short protected. I have looked at many preamp and have yet to find one with short circuit protection.

Consider this: A well known and respected manufacturer made a preamp with 3 regulator transistors. To make a long story short, I slipped with the probe and shorted the regulator for just a moment. The pass transistor failed because the regulator was not short protected. I put in another of the same part but a different maker. It failed on turn on. Then I took a serious look at what was going on in the circuit, consulted my data book on the transistor and found that every time the unit was powered up that pass transistor was being exposed to conditions outside it's rating. A perfect example of an accident waiting to happen. This preamp was made in large numbers and by the time it was discontinued it had gone from it's original designation through the alphabet to "e", counting on my fingers, that's 5 revisions.  The first 4 revisions were  band-aids. The final revision replaced the main regulator transistor with a tube which could easily handle the turn-on conditions. Of course it was marketed as a "sonic" improvement.