SWR SM 400 burned resistors on power amp

[The Dude]

......The only difference being the amp was supplying 60V +/- while the power amps required up to 55V +/- with 50V ideal......

Is 55V the max spec on the new amp, or is there a plus or minus spec? In other words is it stated as max supply = 55V, or is it supply = 55V with a 10% tolerance or something of the sort. It would help to see the actual amp specs.

[g1]

Dropping the power amp supply rail voltage is more involved with a solid-state amp due to the higher current compared with a tube amp. How you achieve this depends on the space inside the cabinet and the method used. The problem with regulating the voltage down, or using a MOSFET dropper circuit is the heat dissipation - such methods effectively convert the voltage drop into heat and require a lot of heatsinking to prevent the regulator from burning up at full output. I can't think of a really easy way to do this that doesn't require a lot of space.

I was wondering about a bucking transformer on PT primary. I guess it might depend on how the low voltage rails for the preamp are derived. I guess VA rating for the bucker and space requirement would factor in as well.

[chrisdski]

Is 55V the max spec on the new amp, or is there a plus or minus spec? In other words is it stated as max supply = 55V, or is it supply = 55V with a 10% tolerance or something of the sort. It would help to see the actual amp specs.

thanks for the reply. Here are the new amp specs. I was speculating that the max voltage of 55 stated in the specs would handle a bit over. The power coming to the amp is 60v, and when hooked to the amp my VM reads it at 56.

[The Dude]

Specs here indicate max 55V, but I don't think a single volt over spec will make any difference.

https://www.aliexpress.us/item/32568...andl_shipto=US

[chrisdski]

Thanks all for the help. As I read elsewhere- does it work? Yes. Then quit fixing it.