Orange OR80 Combo Repaired!

[OffYourFace]

are you sure it's not orange? If so, that would be 15k and 15k is probably correct for EL34s. In Marshalls it's 15k or 27k. But I forget which one is better for modern day EL34s. I think 27k is... but Pop in the tubes and see what happens.

If the amp sounds good and the tubes aren't red-plating, you'll be fine. But watch for red-plating. If you're not sure what that is, that's when the main metal plates inside the tube start to glow red from over-heating. Turn it off immediately if so and take it to a pro.

[HNB]

are you sure it's not orange? If so, that would be 15k and 15k is probably correct for EL34s. In Marshalls it's 15k or 27k. But I forget which one is better for modern day EL34s. I think 27k is... but Pop in the tubes and see what happens.

If the amp sounds good and the tubes aren't red-plating, you'll be fine. But watch for red-plating. If you're not sure what that is, that's when the main metal plates inside the tube start to glow red from over-heating. Turn it off immediately if so and take it to a pro.

It looks red. The one near it has an orange stripe. Maybe it is the wrong value? I don't know what it should be. I will try to see if I can figure out the schematic, but I have a hard time reading those things. LOL

2023-04-26_04-00-47 by Christopher Louck, on Flickr

[HNB]

Maybe it was changed to 1.5 instead of 15? I see an area by the bias pot that shows 15k. Is that this resistor?

Untitled-1 by Christopher Louck, on Flickr

[HNB]

LOL I am in the weeds. The one next to it is 15k. The other one in the pic looks brown brown yellow gold which should be 110k?

[HNB]

Another diagram I found? No idea on what one is good or if they are the same.

Untitled-1 by Christopher Louck, on Flickr

[HNB]

The one that has the wire over it is 15k.

[JSett]

The jumpered one is 15k and is this one on the schematic...



Pretty sure the one with the messy solder (1k5) is part of, or attached to, the NFB loop going to ground on V2

[sal paradise]

This is amazing. I’m learning stuff about amps just by reading this. This forum is the best.

[OffYourFace]

Well what are you trying to do? Do this yourself? Do you know how to drain the voltage so you don't kill yourself?

[HNB]

If it is just those two resistors, I feel like I can change those myself. It is a bunch more that is needing to be changed, I would probably take it to someone. I know how to drain capacitors from videos online, but I don't know enough about schematics to know if I need to change that one resistor and remove that jumper to get it so it can work as stock again tube wise.

[panoramic]

UF, yeah those KT88s (or 66s?) should not be in there. That noise might even be caused by one tube making intermittent connection because the glass envelope is keeping it from seating correctly.

look like kt88's to me, time to get the right tubes

[JSett]

Yeah, be super careful in there...my OR120 gave me the biggest shock of my life so far (many many hundreds of volts).

[OffYourFace]

Well let's start from the top. You only need to change the bias range resistor if you don't have enough range in the bias trimmer. For all we know the current component selection in your amp is fine. You won't know until you try to bias it. If you don't have the equipment, I'd take it to a pro.

[HNB]

I do have a multimeter to check the bias. I was planning on setting it far left to the lowest end to see what it reads in case any mods have made it run hotter than it should and to avoid blowing the tubes to start off and then turning it up depending on the reading.

[HNB]

This is the method I have used before. Were you use the pin on the tube resistor to get your reading. It should work fine right? I also have a voltage tester that tells me if there is current to make sure I don't shock myself. I have adjusted bias before when installing new power tubes. I just didn't know if those potential mods might make the EL34 not be compatible anymore.

https://youtu.be/yg0SoUrF-X8