Author Topic: Restoration of a Leak Stereo 60 Valve amplifier  (Read 3268 times)

Offline Ampdog

Re: Restoration of a Leak Stereo 60 Valve amplifier
« Reply #30 on: August 28, 2018, 07:56:05 PM »
As an aside:

The necessity for strict non-inductive resistors as loads for audio amplifiers is often overrated. (One must not confuse requirements for r.f. with that for audio.) The impedance of normal w.w. resistors is hardly up to some 2% inductive at 20 KHz, and as such not a  factor. Such inductances become meaningful only at >1 MHz, where audio amplifiers are not or should not  be operative, and where the impedance of loudspeaker leads becomes dominant anyway.

For high output (hot resistor), increase in load resistance can be more important.  Keep heat down, or immerse the resistor in a bowl (not metal!) of water. That will be good for many minutes.

(But caveat: Tap water also has a finite resistance, so not practicable at high-voltages/high-resistances!)
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline fredeb

Re: Restoration of a Leak Stereo 60 Valve amplifier
« Reply #31 on: August 31, 2018, 03:54:00 AM »
Some of the audio watt-meters measures from 300 micro watt up to 50 watt with its own internal loads. Different impedance's can also be selected.   

I use Vitreous enameled wire-wound resistors with corrugated ribbon types with values of > 100 watt @ 8 Ohm
I never even knew one gets such a thing as an audio-watt meter - I'll keep an eye out for those .
I use a couple of these on a heatsink. They are non-inductive. https://za.rs-online.com/web/p/panel-mount-fixed-resistors/7890718/

Thanks for pointing that out handsome , good to know of the existence of these resistors .

As an aside:

The necessity for strict non-inductive resistors as loads for audio amplifiers is often overrated. (One must not confuse requirements for r.f. with that for audio.) The impedance of normal w.w. resistors is hardly up to some 2% inductive at 20 KHz, and as such not a  factor. Such inductances become meaningful only at >1 MHz, where audio amplifiers are not or should not  be operative, and where the impedance of loudspeaker leads becomes dominant anyway.

For high output (hot resistor), increase in load resistance can be more important.  Keep heat down, or immerse the resistor in a bowl (not metal!) of water. That will be good for many minutes.

(But caveat: Tap water also has a finite resistance, so not practicable at high-voltages/high-resistances!)

Good to know , thank you Ampdog .
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts