Fender The Twin Resistors?

[DRH1958]

I edited my last post a few times to add more info and questions. Your snipet is from my original draft.

Good explanation, I understand the concept of going from 470 to 1k lowering the voltage and helping extend the life of the output tubes. However I am confused about going from 1 to 5 watts on these resistors. Wouldn't we want to stay at 1 watt so it acts like a fuse, at 5 watts it may never blow and don't we lose some protection?

thanks!

With going from 470 ohm to 1k ohm, the voltage drop will be higher, thus raising the wattage the resistor will dissipate, so the 5 watt rating is needed. This also add a safety cushon to not have the resistor dissipate too much wattage. You don't WANT it to burn up, only under abnormal conditions.

EDIT; Your article you read at the Aiken site is for grid stoppers, not screen grid resistors. They are completely different animals. The 1.5k resistors on your amp are the grid stoppers. These 470 and 1k resistors we are talking about are the screen grid resistors.

[misterc57]

OK so after digesting all of this, this is my latest thinking...

Replace the 470 1 watt with 1K 5 watt wire wound, to protect the output tubes. I need the higher wattage because the higher resistance will be dissipating more heat.

Replace the 1.5k 1/4 watt with 1.5k 1/2 watt, to protect the resistors from the heat. Install these close to the tube, inside the socket like the original ones are installed.

Replace the external fuse with a 4A slo blo to protect everything.

Thank you! MC

[DRH1958]

This is what I would do considering the situation you are in. Others might disagree. Personal preference is the factor.

[Jquijano]

This is the red knob The Twin LL 66385. Schematic I found says 470 ohms 1 watt.

Picture attached. I can see that someone had previously replaced the v10 1.5k resistor.

[ATTACH=CONFIG]34629[/ATTACH]

OK which are the Plate Grid Resistors in this amp? the 470 ohms vintage brown resistors on top of the power tube sockets? My red knob twin is generating an audible hum and intermittent pop and crackles. Still trying to troubleshoot but cant seem to figure this out. Has anyone experience this? Will removing one leg of the resistor help me diagnose which resistor needs to changed? All filter caps were changed in 2015.

[xtian]

"Plate grid" is confusing, and mashes up two concepts. There are control grids (the input, pin 5, 1.5K resistors), screen grids (pin 4, 470R resistors), and plate (anode, pin 3, no resistors).

Referring to this schematic: https://schematicheaven.net/fenderamps/the_twin.pdf

[Jquijano]

Ok experts in fender red knob twin asked me to change all plate resistors with metal film resistors for the preamp section to eliminate noise and hum. Where do i get these metal film resistors?

[Tom Phillips]

... Where do i get these metal film resistors?

It would be helpful if you add your location to your profile because the answer depends on where you are located. I buy my metal film resistors from Mouser.
Cheers,
Tom

[Jquijano]

Quite interesting info here for a new 2nd hand fendee red knob twin! Mine has all original carbon resistors. Just measured them and only one is 473 ohms.

I do have a set of five 470 0hms metal oxide resistors if needed! Guess its 1 watt

[Jquijano]

With going from 470 ohm to 1k ohm, the voltage drop will be higher, thus raising the wattage the resistor will dissipate, so the 5 watt rating is needed. This also add a safety cushon to not have the resistor dissipate too much wattage. You don't WANT it to burn up, only under abnormal conditions.

EDIT; Your article you read at the Aiken site is for grid stoppers, not screen grid resistors. They are completely different animals. The 1.5k resistors on your amp are the grid stoppers. These 470 and 1k resistors we are talking about are the screen grid resistors.

So the 1.5K resistors that go across the power tube sockets you would recommend 1.5k 1 watt or 2 watts?