PSU Pre2 - R6 (15k)

[Johno210]

Hi there,
did my 1st service on this unit the other day.
Pretty good given PSU & Pre-amp have had daily use for the past 12 years.

The only resistor I found heat stressed was R6 (15k) this feeds the phono stage.

Resistor was still in spec. It's function is to drop the B+ from 325V back to 250V for the phono stage, which I use adhoc. My mains supply is typically +10% high so that 325V will also be higher.

The kit resistor for R6 is rated at 1W appears to be metal film ?
The dissipation for this resistor should be around 0.6W assuming a 100V drop due to elevated main supply. It does sit pretty close on PCB to R4 (22k / 6W ) which feeds the 100V Zener for the line stage.

Anyone else had problems with the resistor ?


Feedback appreciated,
Cheers Johno.

[John Caswell]

Hi Johno
I haven't had any problems with this component, however it will not harm to up its rating to 2Watts. It is all to do with the surface area of the component and the fact that a modern 1 Watt resistor has the equivalent size to a 1/4 Watt resistor of 50 years ago when I were young

John

[Johno210]

Hi John,
Agree 2W is better suited & there's plenty of room to accommodate the larger size.

All the best,
Dave Johnson

[pre65]

I try to allow at least double, and preferably triple resistor ratings compared to the actual need, so 2W should be good.

[david]

I calculated the power dissipation for a large sample of the resistors on my 300b pp clone with interesting results. The small resistors are generally massively over-specced, eg by a factor of 10, whereas the power resistors are more like a factor of 2 and they are the ones that get hot!
David