White carbon composite resistor? - UK Vintage Radio Repair and Restoration Discussion Forum

icecreamterror · 3rd Apr 2010, 3:19 am

Iv noticed in a few British guitar effects pedals from around 69 White carbon composite resistor, were these a forerunner of the brown carbon comps I know and love, or a brand issue.

(its intriguing as the company used brown ones in both early and later models)

Lucien Nunes · 3rd Apr 2010, 8:58 pm

The resistors shown in your pics are from different makers. The brown ones are Morganite, the white ones Erie. The pedal makers probably used whatever was most readily available, as nothing in a guitar pedal requires any particular characteristics of resistor, it just has to work. There are similar-looking brown-bodied resistors with a glossier surface, these were made by Allen Bradley and often found in imported gear. They are still available new and I use them for replacement purposes to keep the authentic appearance. Nothing looks quite like the Erie although cream-bodied 2W carbon film resistors aren't too far off.

Lucien

icecreamterror · 3rd Apr 2010, 10:03 pm

Thank you so much Lucien, much appreciated!

David G4EBT · 3rd Apr 2010, 11:01 pm

The white ones are actually ceramic tubes with a puny carbon composition resistor inside, terminated with metal end caps and wires. The resistor was secured in place in the ceramic tube with a hard 'cement' substance at each end.

They commonly go way out of value, even if unused. I have scores of NOS ones which bear no relationship to the marked values. They were a cheap impulse buy at a rally - I'd hoped I might get at least a few within spec, but should have known better. Even when new, they were +/- 20% tolerance, so a 100k for example could have ranged from 80k - 120k.

Oddly enough, the little Erie resistors designed for PCB use seem not to suffer to quite the same extent, even though (apart from the absence of the ceramic tube) they were of similar construction - a carbon rod with metal end caps.

If I'm restoring rather than simply repairing a radio, I measure and record the values of resistors and replaced any that are more then 20% out of tolerance, so that the set is as near as possible to what it was when it went through the factory gate.

I've just renovated a little Pye R33 (1957 vintage) which has 18 of the little PCB type Eries. Of those, only three were worse than +20% - namely, 35%, 40% and 53%, which I changed.

David,
G4EBT

3rd Apr 2010, 3:19 am	#1
icecreamterror Retired Dormant Member Join Date: Apr 2008 Location: Hastings Posts: 8	White carbon composite resistor? Iv noticed in a few British guitar effects pedals from around 69 White carbon composite resistor, were these a forerunner of the brown carbon comps I know and love, or a brand issue. (its intriguing as the company used brown ones in both early and later models) Attached Thumbnails Last edited by Brian R Pateman; 3rd Apr 2010 at 9:55 am. Reason: Embedded images converted to thumbnails.

3rd Apr 2010, 8:58 pm	#2
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: White carbon composite resistor? The resistors shown in your pics are from different makers. The brown ones are Morganite, the white ones Erie. The pedal makers probably used whatever was most readily available, as nothing in a guitar pedal requires any particular characteristics of resistor, it just has to work. There are similar-looking brown-bodied resistors with a glossier surface, these were made by Allen Bradley and often found in imported gear. They are still available new and I use them for replacement purposes to keep the authentic appearance. Nothing looks quite like the Erie although cream-bodied 2W carbon film resistors aren't too far off. Lucien

3rd Apr 2010, 10:03 pm	#3
icecreamterror Retired Dormant Member Join Date: Apr 2008 Location: Hastings Posts: 8	Re: White carbon composite resistor? Thank you so much Lucien, much appreciated!

3rd Apr 2010, 11:01 pm	#4
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,761	Re: White carbon composite resistor? The white ones are actually ceramic tubes with a puny carbon composition resistor inside, terminated with metal end caps and wires. The resistor was secured in place in the ceramic tube with a hard 'cement' substance at each end. They commonly go way out of value, even if unused. I have scores of NOS ones which bear no relationship to the marked values. They were a cheap impulse buy at a rally - I'd hoped I might get at least a few within spec, but should have known better. Even when new, they were +/- 20% tolerance, so a 100k for example could have ranged from 80k - 120k. Oddly enough, the little Erie resistors designed for PCB use seem not to suffer to quite the same extent, even though (apart from the absence of the ceramic tube) they were of similar construction - a carbon rod with metal end caps. If I'm restoring rather than simply repairing a radio, I measure and record the values of resistors and replaced any that are more then 20% out of tolerance, so that the set is as near as possible to what it was when it went through the factory gate. I've just renovated a little Pye R33 (1957 vintage) which has 18 of the little PCB type Eries. Of those, only three were worse than +20% - namely, 35%, 40% and 53%, which I changed. David, G4EBT