07-12-2016, 01:45 PM
(This post was last modified: 07-12-2016, 01:49 PM by Valvebloke.)
I normally start with the cold value of the resistor and bring that back to nominal. Its value was originally specified cold of course, so any resistance changes due to the original temperature coefficient should have been built into the equipment's design. There may be an additional 'new' tempco arising from ageing effects, but if there is then, as the above posts show, people's experiences of that do vary. If the new tempco is negative then padding 'too low' will at least provide some future-proofing against continued upward drift. I did some measurements on a single resistor set over a five year period and, broadly speaking, the drift which had got them to their initial value seemed to be continuing at about the same rate over the five years. So it's not that the resistors drift and then settle.
As folks have said, the long term reliability of a Quad II might well be better if its innards were stripped out and modern components were substituted. Fortunately Quad have met that need for people who want it. The Quad II Classic is exactly that http://www.quad-hifi.co.uk/product-detail.php?pid=20, made very nicely in China. I own a pair and they are lovely, and I never worry about them. My customers don't want this though. They want original. Many of them buy classic vinyl and old stock valves and a few even drive classic cars. If you're going to suggest that they should drop the original engine out of the latter and fit a modern one then you might want to do that from a safe distance
.
I do draw the line at leaving Hunts Micamoulds in critical positions though !
Sorry, I forgot to say, I don't use hidden micro types Gary, I just tack ordinary half-wattish metal films underneath the original Eries. That way people can see what I have done and remove it if they don't like it. They can also swap the resistors out for new ones in a decade or two if the drift requires it.
VB
As folks have said, the long term reliability of a Quad II might well be better if its innards were stripped out and modern components were substituted. Fortunately Quad have met that need for people who want it. The Quad II Classic is exactly that http://www.quad-hifi.co.uk/product-detail.php?pid=20, made very nicely in China. I own a pair and they are lovely, and I never worry about them. My customers don't want this though. They want original. Many of them buy classic vinyl and old stock valves and a few even drive classic cars. If you're going to suggest that they should drop the original engine out of the latter and fit a modern one then you might want to do that from a safe distance
.I do draw the line at leaving Hunts Micamoulds in critical positions though !
Sorry, I forgot to say, I don't use hidden micro types Gary, I just tack ordinary half-wattish metal films underneath the original Eries. That way people can see what I have done and remove it if they don't like it. They can also swap the resistors out for new ones in a decade or two if the drift requires it.
VB
Ampregen Ltd http://www.ampregen.com
