Sparton 617

2/27/2008 2:18:22 AMSteve K

I have a Sparton 617 that I want to restore. I have been checking all the resistors and I have found that R4, R16 and R17 (all wire wound) are way above values. The only replacements I can find of the proper values (22K and 27K) are Ohmite ceramic composition resistors. Is this type of resistor a good substitute for wire wound?? I have seen where a 5 watt carbon composition resistor was used to replace a 3 watt wire wound resistor only to blister from the heat after about 20 minutes. I can't find any other "power resistors" in the right values. In case you can't tell, I'm pretty new at this, so any info would be appreciated. THANKS.

2/27/2008 6:58:31 AMTonyJ

Came across this surplus supplier showing they carry wire wound resistors - may want to check them out.

http://www.surplussales.com/index.html

:I have a Sparton 617 that I want to restore. I have been checking all the resistors and I have found that R4, R16 and R17 (all wire wound) are way above values. The only replacements I can find of the proper values (22K and 27K) are Ohmite ceramic composition resistors. Is this type of resistor a good substitute for wire wound?? I have seen where a 5 watt carbon composition resistor was used to replace a 3 watt wire wound resistor only to blister from the heat after about 20 minutes. I can't find any other "power resistors" in the right values. In case you can't tell, I'm pretty new at this, so any info would be appreciated. THANKS.

2/27/2008 11:07:10 AMEdd

Looking at the mentioned resistors functions in that sets circuitry, the one with the least to worry about is the R4---22k value….if you are sure of that being the resistor…. is functioning as a voltage drop to supply the oscillator for the unit, at that miniscule power level of that circuit, it is within the norm to be using an ~1/2 watt unit in that slot.

The pair of resistors…R16-17…. that you give, are used as a voltage divider bridge off the main B+ buss to drop that level on down to a lower value to feed the screen grids of the three frontal RF tubes.

As for those resistors….. R16---15k and R17---27K…. a set of modern day metal film resistors should hold up and stay in that function, with the selection of both of them being 2 watt rated units. They hold up as well as a wire wound…and I have seen them even be used up to the power level where a unit can take on a dull red glow . Much like a Cromalux heater element !
The 2 watt value…with your resistive values is a common , easily found item, with them also being available in 3 and 7 watt ratings also.

The only REAL power resistor unit that I see in the unit is that tapped Cand-ohm unit….R18-19…shown just above the rectifier tube on the schema.

Mouser has the units in 2-3-7 watt ratings and I probably would spring for the 3 watt unit at 53cents versus the 2 watt unit at 32 cents in the Vishay brand.
They have no minimum order, and could even ship in a bubble bag for that small of a parts order.

Hot linked catalog reference:

> http://www.mouser.com/catalog/633/628.pdf

The standard units are at the top of the page and the REAL premium units that I mentioned ...doing the glow...are shown at the bottom of the page.

73's de Edd

2/27/2008 11:24:18 AMEdd

A repeat of the hot link...it wasn't hot enough.... (after receiving an errant character hit in transmission)....

Looking at the mentioned resistors functions in that sets circuitry, the one with the least to worry about is the R4---22k value….if you are sure of that being the resistor…. is functioning as a voltage drop to supply the oscillator for the unit, at that miniscule power level of that circuit, it is within the norm to be using an ~1.2 watt unit in that slot.

The pair of resistors…R16-17…. that you give are used as a voltage divider bridge off the main B+ buss to drop that level on down to a lower value to feed the screen grids of the three frontal RF tubes.

As for those resistors….. R16---15k and R17---27K…. a set of modern day metal film resistors should hold up and stay in that function, with the selection of both of them being 2 watt rated units. They hold up as well as a wire wound…and I have seen them even be used up to the power level where a unit can take on a dull red glow . Much like a Cromalux heater element !
The 2 watt value…with your resistive values is a common , easily found item, with them also being available in 3 and 7 watt ratings also.

The only REAL power resistor unit that I see in the unit is that tapped Cand-ohm unit….R18-19…shown just above the rectifier tube on the schema.

Mouser has the units in 2-3-7 watt ratings and I probably would spring for the 3 watt unit at 53cents versus the 2 watt unit at 32 cents in the Vishay brand. They have no minimum order and could even ship in a bubble bag for that small of a parts order.
Hot linked catalog reference:

http://www.mouser.com/catalog/633/628.pdf

The standard units are at the top of the page, while the glazed units, at the bottom of the page, are of the type that I have seen used up to the "glow" threshold.

73's de Edd

2/27/2008 11:57:19 PMSteve K

Thanks Tony and Edd. I guess I used the wrong term, Edd. It seems so many of the high wattage resistors listed in catalogues are called power resistors,I assumed (there's that nasty word) that the term referred to just that (wattage) rather than the way in which they were used. How would you define the term and/or how/where it is used in a circuit.

2/28/2008 5:17:27 PMEdd

I guess that…… in my minds perspective..….. I want to think of anything above 5 watts as being in a power resistor category, while the very numerous ¼--½--and 1 watt units found in a radio would definitely be the normal, common resistor category , with the 2-3 watt units being borderline.

73's de Edd