Rescued an HD 130 Reverb, Bias and Cathode Resistor Question

inertian

Recently rescued a real basket case '75 HD 130 Reverb head. Two previous owners had attempted (unsuccessfully) to repair it and made quite a mess. The amp had many issues, but thankfully they were fairly easy to sort out - no small part due to what I have learned from this site.

To my great surprise, the amp powered right up and passed good signal once all the major problems were addressed. Still some cleanup to do, but what a great sounding beast.

The original 10 ohm 1 watt cathode resistors have drifted about 20%, wanted a recommendation what to replace them with. Is 2 watt sufficient, or is higher (5 watt) safer? Carbon comp, carbon film, metal film, ceramic, or does it not matter?. What minimum voltage rating?

As for biasing it - is the .5v DC across the 10 ohm resistor adequate, or maybe a bit cooler to avoid any heat issues?

Thanks.

Music Man Equipment
MM 2-10-65

Member for

11 years
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mm210 Tue, 09/26/2017 - 06:38

Two watt is plenty. One watt is plenty. I like metal oxide where they are exposed to heat. I WOULD bias a little cooler. I usually look for around 22-23 which would be .42-.46 on that resistor. Mike

Full Name
Ian Azrikan

Member for

11 years

inertian Tue, 09/26/2017 - 09:26

Appreciate the good info. Ordered some 10 ohm 2 watt metal oxides with some other items I needed from Newark Electronics.