And here's an example of the kind of chassis-mountable, integral-heatsink resistor i was mentioning:
THS50820RJ TE Connectivity / CGS | Mouser
Looks maybe a little doubtful that there is a good spot on the existing chassis, but maybe you can add a bit of sheet aluminum to attach it to.
THS50820RJ TE Connectivity / CGS | Mouser
Looks maybe a little doubtful that there is a good spot on the existing chassis, but maybe you can add a bit of sheet aluminum to attach it to.
If anode voltage is 425V and cathode on 70-71V (you have fixed biased 300B, R//C in the cathode), 300B operated at about 355V, 85mA, -70V operating point, which is a little on the hot side, but enough safe for 300B.
The 820R cathode resistor dissipation is about 6W, so minimum 25W -aluminium body- resistor required, with adequate heatsinking. If you use these resistor without heatsink, the recommended maximum wattage is only 40% (at about 100C)!
If impossible to use -for example box side as- heatsink, I prefer Welwyn W24 enamelled wirewound resistor (up to 200 C). It will be very hot, and if you don't have conventional airflow, the whole box heating up inside.
The 820R cathode resistor dissipation is about 6W, so minimum 25W -aluminium body- resistor required, with adequate heatsinking. If you use these resistor without heatsink, the recommended maximum wattage is only 40% (at about 100C)!
If impossible to use -for example box side as- heatsink, I prefer Welwyn W24 enamelled wirewound resistor (up to 200 C). It will be very hot, and if you don't have conventional airflow, the whole box heating up inside.
I am not sure if I should make the resistor touch the metal case and dissipate through it. I am worried there may be glued pieces on the case which may unglue if the case is too hot. I have to have a look at it better...
What does it mean "R/C in the cathode"? And what makes you say this is fixed bias?
I mean, usually Dared amps are fixed bias and I guess this one is too, but what about those two potentiometer?
Can I change the bias through those pots, and is it something I should try do to optimize the amp based on the tubes I'm using?
What does it mean "R/C in the cathode"? And what makes you say this is fixed bias?
I mean, usually Dared amps are fixed bias and I guess this one is too, but what about those two potentiometer?
Can I change the bias through those pots, and is it something I should try do to optimize the amp based on the tubes I'm using?
Tyco aka T/E Connectivity and Vishay are very reputable brands. You can see from the link i posted that aluminum-body power resistors are not so expensive in the great scheme of things.
It looks to me like the board is mounted in sort of a metal pan, right?
If those amps were mine, i would figure out if i could attach some 'wings' of sheet aluminum to the case, right next to where the resistors go, and would get the 50w aluminum cased resistors and attach them to those wings.
Might use pop rivets.
You can get pre-cut aluminum from onlinemetals.com or from numerous ebay vendors. Alloy doesn't matter here - and thicker is better if you can make it fit.
.:Sent by pneumatic tubes
It looks to me like the board is mounted in sort of a metal pan, right?
If those amps were mine, i would figure out if i could attach some 'wings' of sheet aluminum to the case, right next to where the resistors go, and would get the 50w aluminum cased resistors and attach them to those wings.
Might use pop rivets.
You can get pre-cut aluminum from onlinemetals.com or from numerous ebay vendors. Alloy doesn't matter here - and thicker is better if you can make it fit.
.:Sent by pneumatic tubes
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