Amp questions?

[Trouble]

With all the tube swapping and amp builds going on around here I've been doing a little research. I've never done any real work on an amp but I've been reading up on biasing and tube changing and seems fairly straightforward. My Super hasn't been biased in a very long time and has been running on the same tubes for years, of course it is only used on special occasions.

I'm thinking it's a good candidate for me to practice on. I have a good multi-meter, but I don't have one of those socket things to hook up to. They look pretty simple but the prices are like 60 to 80 bucks for them. Does anyone know a good cheap place to get one?

 

Also, everybody starts somwhere and I've worked with wring and some electronics before just not amps, am I okay starting here are I'm I getting over my pay grade? I'm thinking one day I might like to tackle building a little low watt head, maybe just from a kit, and that's about as far as I would want to go with building but it would be nice to be able to service my own amps.

 

Thanks in advance guys!

[Steiner]

You don't have to have a socket reader to bias. Normally you measure across pin 1 and 8 - I think. You might want to verify that.

[kbp810]

Well, there is always the DIY bias check kit: http://tubedepot.com/bt-biasrite.html

 

Otherwise, to measure with a multimeter - the easiest method to measure is to read the cathode current; reading from cathode (pin 8 on a 6v6/6l6) to ground, across a 1ohm resistor (so essentially putting a 1ohm resistor from pin 8 to ground, and then measuring the voltage drop across the 1ohm resistor). Set the meter to read volts (set to 100mV range); since you are measuring across a 1ohm resistor, whatever value you read in millivolts is the same number in milliamps. (standard disclaimer/reminder - very high and potentially lethal voltages exist inside the chassis!)

 

The socket is still by far the easiest and safest method for measuring

[Trouble]

Well, there is always the DIY bias check kit: http://tubedepot.com/bt-biasrite.html

 

Otherwise, to measure with a multimeter - the easiest method to measure is to read the cathode current; reading from cathode (pin 8 on a 6v6/6l6) to ground, across a 1ohm resistor (so essentially putting a 1ohm resistor from pin 8 to ground, and then measuring the voltage drop across the 1ohm resistor). Set the meter to read volts (set to 100mV range); since you are measuring across a 1ohm resistor, whatever value you read in millivolts is the same number in milliamps. (standard disclaimer/reminder - very high and potentially lethal voltages exist inside the chassis!)

 

The socket is still by far the easiest and safest method for measuring

Thanks, I think I'll try that. I know about the high voltages present and I've worked with electricity a lot. I'm okay with keeping myself safe just worried about potential damage to my amp.

 

That said, I gotta go to bed!

[Trouble]

Oh how do you know which one is pin 8?

[kbp810]

There is a small gap (and the postioning key) in between pins 1 and 8 on the socket; if looking at the socket from the bottom, pin 8 is the first pin counter-clockwise from the small gap. Some sockets also have them labeled with small numbers near the pins, there not always easy to read, but still well enough to make out which is pin 1 and which is pin 8, and count them out from there.

[kbp810]

Thanks, I think I'll try that. I know about the high voltages present and I've worked with electricity a lot. I'm okay with keeping myself safe just worried about potential damage to my amp.

 

That said, I gotta go to bed!

I always feel obligated to add some sort of warning/reminder for any post elduing to working inside an amp chassis; you never know who might come across the post and feel like giving it a try on their own amp

[DetroitBlues]

I always feel obligated to add some sort of warning/reminder for any post elduing to working inside an amp chassis; you never know who might come across the post and feel like giving it a try on their own amp

 

Heed the warnings or suffer some SHOCKING results...

[Trouble]

There is a small gap (and the postioning key) in between pins 1 and 8 on the socket; if looking at the socket from the bottom, pin 8 is the first pin counter-clockwise from the small gap. Some sockets also have them labeled with small numbers near the pins, there not always easy to read, but still well enough to make out which is pin 1 and which is pin 8, and count them out from there.

I need to do a little more studying I think. I was thinking the reason for the socket was because the tube had to be in place and the amp powered up to check the current, do you power up the amp without the tube to check the voltages?

[kbp810]

I need to do a little more studying I think. I was thinking the reason for the socket was because the tube had to be in place and the amp powered up to check the current, do you power up the amp without the tube to check the voltages?

Yeah, you need the tube in and on to check this; to check using standard meter leads you would be working inside the chassis from the other side - hence the socket does make this a whole lot easier

[Trouble]

Thanks Brian. When I get ready to give it a shot I'm going to get the bias rite first, lot better price than anything else I"ve seen. Might get 2 for that price. I don't know why I didn't think of Tube Depot, just ordered tubes from them!

[212Mavguy]

A double socket bias tool is a very good thing to own!