5150 Bias Resistor

[Bardagh]

So check this out. I got this 5150 in a trade a little bit ago and the headshell was not in good shape so I was swapping it into the one I have from an old dead 6505, so I took a moment to look at the insides. I had noticed it ran tubes a lot hotter than a 5150 normally would, so I was expecting maybe to see an adjustable bias mod, but instead the stock 15k resistor is still there but another resistor has been piggybacked on the adjacent capacitor.

Based on the stripes, is that a 16k resistor? If so, the resistance is dropped to around 7.7k if I'm thinking right?

 

[griff10672]

Brown stripe is ( 1 ) Grey stripe is ( 8 ) that third band ...the multiplier .... can't tell if it's orange or yellow

and the gold band means it's a 5% tolerance

if it's yellow it's a 180K if it's orange it's a 18K

 

[Bardagh]

The multiplier band has to be orange or it wouldn’t make sense, but I’m not sure if the other one is grey or blue. Either way the value wouldn’t be too far off and the original resistor has to still be in the circuit and working or the bias would be even colder than stock.

Basically I want to remove or replace that extra resistor and go back to stock or a resistance value that will get the tubes out of this mush territory it’s in now with them way too hot. I didn’t pull the board to make sure everything is normal underneath so I was a little concerned to just remove the extra resistor in case I missed something, but like I said given it’s value and how hot the tubes are running, the original resistor has to be in circuit and functioning so I assume it should be good.

 

[Bardagh]

Clipped that dude out and the TAD Redbase tubes I was running dropped way down to 15mA. Now the amp sounded like the familiar fizzy garbage at lower volumes and great cranked up. Swapped in a set of EHX 6L6 I knew would run hotter and they’re at about 24-25mA which seems like a sweet spot. Sounds much less fizzy at low volume and just sounds better as you turn it up. Doesn’t fall apart and get mushy at any point on the dial I can ever imagine needing to turn up to.

I think in the future I’m going to either have to add the adjustable bias or see if any place will reliably sell me sets that run hotter like these EHX. You used to be able to buy Mesa branded sets or Ruby or Groove Tube sets in graded categories for how hot they would run, but it looks like they all stopped doing that.