Biasing a 1959HW

[greengriff]

Hi,

I just picked up a 1959HW. The valves are all 7 years old and the previous owner is a guitarist in an internationally known hard rock band, so the amp has been played hard and regular. Accordingly I want to replace the power valves.

The only method of biasing I'm comfortable with is the cathode current method but this amp has pins 8 and 1 of every power valve wired straight to earth with no 1ohm resistor in the way. I'm not really keen to put resistors in and then remove them straight afterwards, so I'm wondering what - if any - effect they would have on the tone of the amp if I put them in and left them in?

Alternatively is there a trick for performing this method of biasing without the 1ohm resistor, or perhaps another simple, safe biasing method that can be done with just a multimeter?

[acorkos]

i use one of these:
Bias Tester Probe (mV) Version for Vacuum Tube Guitar Amplifier by AMP-HEAD

[Gtr_tech]

You can leave the 1 ohm R's in there. Just be sure to use good quality 1%, and I'd use 1w rated as well. I've noticed them getting warm and drifting (half W), so 1w should be more reliable to leave in.

When you install them, be sure to leave pin 1 connected straight to gnd. The K resistor goes in line with pin 8.

[greengriff]

Cool, thank you. Does anyone know if something like this is available in the UK? I'm still also curious as to what tonal effect a permanently connected 1ohm resistor between 8/1 and earth will have?

[greengriff]

So send them to ground separately??? I just need to double-check that I've understood this correctly, as when I've seen 1ohm resistors inserted as a permanent fixture on other amps (from the factory) pins 1 and 8 have still been joined in the usual way and both go to earth through the resistor.

[Gtr_tech]

Pin 1 is the suppressor grid. It needs to be straight to gnd. Pin 8 is the cathode.

[greengriff]

Many thanks.