Help identify and replacement of ? resistor - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th May 2012, 02:08 AM   #1
diyAudio Member
 
devilsindetails's Avatar
 
Join Date: May 2011
Location: 100th Meridian
Default Help identify and replacement of ? resistor

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
Attached Images
File Type: jpg resistor.jpg (261.7 KB, 53 views)
File Type: jpg scott schematic.jpg (92.6 KB, 49 views)
__________________
"A problem left to itself dries up or goes rotten. But fertilize a problem with a solution--you'll hatch out dozens." (N.F.Simpson)

Last edited by devilsindetails; 19th May 2012 at 02:14 AM.
  Reply With Quote
Old 19th May 2012, 02:28 AM   #2
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
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.
__________________
Eli D.
  Reply With Quote
Old 19th May 2012, 02:45 AM   #3
diyAudio Member
 
devilsindetails's Avatar
 
Join Date: May 2011
Location: 100th Meridian
Quote:
Originally Posted by Eli Duttman View Post
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.
__________________
"A problem left to itself dries up or goes rotten. But fertilize a problem with a solution--you'll hatch out dozens." (N.F.Simpson)

Last edited by devilsindetails; 19th May 2012 at 02:55 AM. Reason: clarification
  Reply With Quote
Old 19th May 2012, 02:47 AM   #4
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Quote:
Originally Posted by Eli Duttman View Post
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.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 19th May 2012, 03:32 AM   #5
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Quote:
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.
__________________
Eli D.
  Reply With Quote
Old 19th May 2012, 03:40 AM   #6
diyAudio Member
 
devilsindetails's Avatar
 
Join Date: May 2011
Location: 100th Meridian
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?
__________________
"A problem left to itself dries up or goes rotten. But fertilize a problem with a solution--you'll hatch out dozens." (N.F.Simpson)
  Reply With Quote
Old 19th May 2012, 03:53 AM   #7
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Quote:
Originally Posted by devilsindetails View Post
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.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 19th May 2012, 03:59 AM   #8
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Quote:
Originally Posted by Eli Duttman View Post
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.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 19th May 2012, 04:00 AM   #9
diyAudio Member
 
devilsindetails's Avatar
 
Join Date: May 2011
Location: 100th Meridian
Quote:
Originally Posted by HollowState View Post
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.

Quote:
Originally Posted by HollowState View Post
Using a multi section device was a cheaper way of doing things.
Jeez...must have saved at least .2 cents doing it that way.
__________________
"A problem left to itself dries up or goes rotten. But fertilize a problem with a solution--you'll hatch out dozens." (N.F.Simpson)
  Reply With Quote
Old 19th May 2012, 04:08 AM   #10
diyAudio Member
 
devilsindetails's Avatar
 
Join Date: May 2011
Location: 100th Meridian
Quote:
Originally Posted by HollowState View Post
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?
__________________
"A problem left to itself dries up or goes rotten. But fertilize a problem with a solution--you'll hatch out dozens." (N.F.Simpson)
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Replacement for 200 Ohm variable resistor? maurycy Parts 5 8th April 2012 01:22 AM
Is a Vitreous Enamel wirewound resistor a good replacement? erkess66 Parts 1 8th December 2006 09:26 AM
Resistor popped...need help for replacement in Yaqin amp nubbins Tubes / Valves 8 4th July 2004 03:19 PM
screen-plate resistor and grid leak resistor metebalci Tubes / Valves 4 26th February 2004 03:18 AM


New To Site? Need Help?

All times are GMT. The time now is 01:37 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2