Help identify and replacement of ? resistor

[devilsindetails]

The Patient: HH Scott Model 223
P/P Mono Amplifier

2X6L6
1X12AX7
1X 5U4G

(schematic attached)

After checking and replacing caps and resistors on my old Scott...I found one resistor (notated as R21 on schematic) that has me stumped.

See Pic: It appears to be some kind of multi-stage resistor with definite signs of distress (some kind of oily substance oozing from the seam with that definite acrid smell! (resistance readings confirm this thing is toast)

So is this some sort of multi-gang resistor?

I doubt that a replacement is still available given the age of this thing. How would I wire in individual replacement resistors of the same value. As this thing was mounted flush on the inside and flush to the frame itself I'm a little confused by that orientation. Was it attached to the frame as part of the heat dissipation factor?

Any advice greatly appreciated...Leo

[Eli Duttman]

It's several resistors in a single package. They go in the PSU. The schematic gives the values, positions, and wattage ratings. Belt and suspenders says increase the wattage ratings over OEM, if space and air flow permit. Low cost metal oxide parts should be suitable for this job.

[devilsindetails]

Originally Posted by Eli Duttman

It's several resistors in a single package. They go in the PSU. The schematic gives the values, positions, and wattage ratings. Belt and suspenders says increase the wattage ratings over OEM, if space and air flow permit. Low cost metal oxide parts should be suitable for this job.

Thanks Eli...I figured I could go that route. It's just that I just haven't run into one of these before and was wondering why this type of mult-stage resistor would have been used (wouldn't it actually increase the thermal wattage in this area making it more susceptible to breakdown/failure) instead of individual resistors with a lot of airflow and space around each one?...and why would it be mounted flush against the case?

Anyways...just my curiousity.

[HollowState]

Originally Posted by Eli Duttman

Low cost metal oxide parts should be suitable for this job.

Eli, I'm shocked. Metal oxide resistors can't take much overload. I say use 5 and/or 10 watt wire wound types. They're much more reliable. The original is probably wire wound. And if it wasn't, it should be.

[Eli Duttman]

Eli, I'm shocked.

I did say increase the wattage ratings over OEM. WW or MO, increased wattage over OEM is the belt and suspenders way. The replacement should hold up, "under fire", longer than the OEM stuff.

[devilsindetails]

I'm still interested as to why HH would place a resistor flush against the frame...seems to go against the notion of dissipating the heat generated, doesn't it. And why a multi-stage resistor instead of singles? Anyone care to hazard a guess?

[HollowState]

Originally Posted by devilsindetails

I'm still interested as to why HH would place a resistor flush against the frame...?

Doing so lets the chassis act as a heat sink. Using a multi section device was a cheaper way of doing things.

[HollowState]

Originally Posted by Eli Duttman

I did say increase the wattage ratings over OEM.

Yes, you did. I just have a dislike of metal oxide/film resistors in power applications unless there's a real good reason for them.

[devilsindetails]

Originally Posted by HollowState

Doing so lets the chassis act as a heat sink.

That was my guess too but seemed kind of goofy to me and I hadn't seen this employed in similar Fisher, Leak or even cheap console amps of the same period.

Originally Posted by HollowState

Using a multi section device was a cheaper way of doing things.

Jeez...must have saved at least .2 cents doing it that way.

[devilsindetails]

Originally Posted by HollowState

Yes, you did. I just have a dislike of metal oxide/film resistors in power applications unless there's a real good reason for them.

So what's your objection to using MO/F Rs in power applications HollowState?