Charred Resistors Coming off of V1 Tube on Gibson GA-20RVT Minuteman

[JosephF]

Hello,

My dad owns a vintage Gibson GA-20RVT Minuteman guitar amplifier. I've looked at the schematic, but my knowledge of such is limited and I'm unsure of what to do. I need replacements (part numbers or detailed information) for the two (carbon composition?) resistors that are attached to the V1 tube. Both are charred too badly (and split in half) to see the colors properly. Does anyone know of these, and what I need to get to replace them?

Thanks.

[52 Bill]

Welcome to the place. It sounds like you are inexperienced and will need either a lot of help or the advice of someone with at least some practical knowledge of guitar amps, as they contain things that can kill you if they are not handled correctly. Is there someone that you know that can help you?

First off, V1 is a 6EU7 tube that has two triode sections built into it. Each section acts as the input amplifier for the two channels of the amp. There are a number of resistors connected to this tube, and there is no way for anyone here to know which two resistors you are asking about unless you give us some more information, like which pin they are connected to, etc.

[JosephF]

We have experience soldering stuff, however, I don't know how much more he has.

To be specific, the two charred resistors were connected directly to the tube's socket within the amplifier. Out of all the tube sockets, that was the only one with resistors connected directly to the pins on the socket, and the two charred ones are the only resistors connected to that socket.

[52 Bill]

Sorry, I haven't memorized what that chassis looks like, so I still have no clue as to which resistors you are asking about.

Maybe somebody else here has it memorized and can help you. Or maybe you could post a photo of the parts.

Best of luck.

[Enzo]

Do you know how the socket pins are numbered? SO then you could maybe tell us the resistors both go to pin 3 or one to pin 4 and one to pin 5 or whatever?

[JosephF]

Here is a picture of the tube socket from inside the amplifier. The one resistor is still there, the other my dad removed.

[Jazz P Bass]

Need better lighting.
And focus.
I have attached a 6EU7 tube pinout diagram.
This is to be viewed as the underside of the tube.
Which is the view of the tube that you have.
Note that between pin 1 & 9 is a space.
Use this space to orient the drawing.
Rotate the drawing until the space is where the tube in the amp is the same.
Draw what you can see in the amp.
Indicate the burnt (broken) resistors.
Post back the drawing.
Or indicate what pins we are dealing with.
(now that you know there numbers)

[JosephF]

That PDF is broken.

[Resonator Guy]

According to the schematic in the Gibson Service Book, which is known for inaccuracies due to the constant change in amp specs, both Pin 9 and Pin 4 have 1.5k resistors on them.

[Jazz P Bass]

That PDF is broken.

Hmm.
Blank.
Link:http://www.mif.pg.gda.pl/homepages/f...093/6/6EU7.pdf

[52 Bill]

OK, that looks like R38 and R39: 100 ohms 1/2 watt. They connect to pins 1 and 2 and the chassis ground.

These set the heater virtual center tap. Without them, the amp will hum like crazy.

[Enzo]

I think you are right, and chances are V1 is not at fault. Miore likely a power tube shorting to heater.

[JosephF]

Thanks for the help, guys. I asked my dad, and he said pins 1 and 2 (he's not 100% and he'll check, but from memory, yes). The replacements would be 100 ohms 1/2 watt resistors? Can someone link me to one, please? Thanks.

[52 Bill]

If you are looking to purchase just the 2 replacement resistors, you may have a hard time. While the resistors cost maybe 5 cents a piece, most places have minimum order requirements that will make it impractical to order them that way.

I don't know where you are located, but in the US there are stores called Radio Shack. They still carry a small assortment of electronic parts including 1/2 watt resistors in small packages of 5 pieces. They will have the 100 ohm 1/2 watt resistors that you need. If you are in some other part of the world or in an area that has no Radio Shacks, you could try contacting someone in your area that services consumer electronics like TVs and stereos. They may be willing to sell you two resistors.