Orange Thunderverb 200 bias current

[The Dude]

On the resistors: Resistors don't short, so if you measure a low resistance, my guess is that the "yellow" is faded gold.

[GainFreak]

This thread is like 6 years old and about a different unit.

It looks to me like the same amp - Orange Thunderverb 200. At least the power amp section has the same voltages and corresponds to the hand drawn schematic (less the 1+3/2+4 power tubes switch).

On the resistors: Resistors don't short, so if you measure a low resistance, my guess is that the "yellow" is faded gold.

Could be but I measure zero Ohms across and 3mVDC when the amp is on (bias volatge -47VDC) and output is ~170W RMS.

UPDATE:

R1 and R5 are really 100k but are shorted when the switch is in 200W mode. In both 100W modes alternatively one of the resistors is in circuit.
Upon further inspection I don't see any 1 Ohm resistors on the power tubes PCB.

[Enzo]

Gain Freak. May be same model, but different unit. We generally don't like to discuss repairs to two different units in the same thread. Threads don't cost anything to start.

R1 and R5 are really 100k but are shorted when the switch is in 200W mode. In both 100W modes alternatively one of the resistors is in circuit.

Then that sounds like the switch disables two of the tubes for lower power. The 100k just keeps the tubes in a circuit, but unable to amplify.

[Purgasound]

I know this is an old thread but I'm convinced this same amp wound up on my bench.
It had been messed with quite a bit. I opened the amp up and was surprised to see the bias trim pot maxxed out. The amp had blown the HT fuse for the power section so I tested the tubes and they all checked out ok but they would only bias to to around 23 to 25mA. My spare set of 6550's were well within range with the bias pot barely halfway up. This was an easy fix. There's a 68K resistor inline with the bias trim pot. I just piggybacked a 150K resistor over it and was able to get the tubes to idle at 34mA with room to go up.
It was popping fuses because whoever my client bought the amp from had the voltage set to 100V. That is no good for here in the U.S.
The amp was a mess. Input jack haphazardly repaired, looked like it was in a flood. Headbox poorly recovered and had staples all over it, guide pins on the tubes busted off... Sheesh.

After some TLC the amp sounded great though. Hated to see it leave.