Help me NOT blow my 5150

[SpaceShipOne]

I'm working on the bias and wanted some info. I see the max wattage for 6l6's is 25 watts about. Ok that's nice. I have it biased for such with the volume on 1. But as you turn it up, it goes well out of that range. I'm confused by this. Can someone explane?

 

[Virtual Kevorkian]

Re: Help me NOT blow my 5150

Not sure what you're talking about... You shouldn't be measuring the wattage when taking a bias reading - measure in mA's.

 

[JB_From_Hell]

Re: Help me NOT blow my 5150

C'mon... watts, miliamps.... what's the difference?

 

[80's_Metal]

Re: Help me NOT blow my 5150

C'mon... watts, miliamps.... what's the difference?

Oh man! thank you for that, I haven't laughed hard all night!

 

[SpaceShipOne]

Re: Help me NOT blow my 5150

Not sure what you're talking about... You shouldn't be measuring the wattage when taking a bias reading - measure in mA's.

Ok well, fill me in. I followed a thing at Duncanamps. What do YOU do to measure the bias. You have more experience than me.

 

[Virtual Kevorkian]

Re: Help me NOT blow my 5150

I had a little thing I stuck between the tube and its socket, fed it into a multimeter. Set the thing to measure mA and tweaked it until it read between 30 and 35... not much to it, IIRC.

 

[subanots]

Re: Help me NOT blow my 5150

turn it up all the way and play an Emin7f9sus/aug5 chord, thats how you bias an amp.

 

[Gearjoneser]

Re: Help me NOT blow my 5150

I had a little thing I stuck between the tube and its socket, fed it into a multimeter. Set the thing to measure mA and tweaked it until it read between 30 and 35... not much to it, IIRC.

Yeah, it's a good idea to buy a bias tool, like the one I have in my Vault thread on biasing the Jubilee. I paid $15-$20 for it off Ebay. Also, own a volt/amp/ohm meter.

Sometimes, when biasing an amp, the amps starting fluxuating when you're turning the bias pot on a live amp. If that happens, turn off the amp for half an hour, and start again. The goal is to get a steady reading of about 32 mA, no matter where the volume is set on the amp. 32mA for 6L6's and 36-38mA for EL-34's. With E-34L's, you can get away with a bit more, like 30-40mA.

The problem with a stock 5150 is that it doesn't have a bias pot, so just pop the tubes in, and they should be within range, as set by the factory, using a resistor instead of a pot.

 

[theodie]

Re: Help me NOT blow my 5150

Dont put your mouth anywhere near it.

You must really love that amp????

 

[Oudy]

Re: Help me NOT blow my 5150

turn it up all the way and play an Emin7f9sus/aug5 chord, thats how you bias an amp.

LOL

 

[sosomething]

Re: Help me NOT blow my 5150

Dont put your mouth anywhere near it.

You must really love that amp????

I'll admit it... I LOL'd.

 

[SpaceShipOne]

Re: Help me NOT blow my 5150

I had a little thing I stuck between the tube and its socket, fed it into a multimeter. Set the thing to measure mA and tweaked it until it read between 30 and 35... not much to it, IIRC.

AT what volume level? Or should it always be at 35 ma no matter where it's set?

 

[Pierre]

Re: Help me NOT blow my 5150

It makes no difference bro. Power supply isn't influenced by volume is it? The signal path is seperated from the power rail.


Basically what you're doing is controlling the current coming into the tube (VERY simplified). The same current will come in regardless of volume (it basically comes from power transformer -> rectifier -> tubes).

For the purists I know this is uber simplified but bear with me

 

[theodie]

Re: Help me NOT blow my 5150

I'll admit it... I LOL'd.

ROTF!

 

[SpaceShipOne]

Re: Help me NOT blow my 5150

Thanks a lot for the help guys, I've had the 5150 a while, but gotta learn the tube stuff. It was biased for 23 mA, now it is at 34.3 mA and running beautifully. Big big difference in sound. It's not got that wierd buzz that happens on sustained notes. Much more natural sounding as well!

 

[Pierre]

Re: Help me NOT blow my 5150

23MA????? That is COLD man. Glad it's going ok. How did you do it?

 

[SpaceShipOne]

Re: Help me NOT blow my 5150

23MA????? That is COLD man. Glad it's going ok. How did you do it?

No kidding, what do YOU set 6l6's to usually? As you see, i was told 35 max, but my dad does this stuff for a living and the math came out to a max of 40ish mA, based on the max watt rating of the tube. It was easy, just a pain to be very sure of everything.

 

[crusty philtrum]

Re: Help me NOT blow my 5150

in a class AB amp, the bias is set at idle. The current flow will rise a lot as the amp is wound up. This is the big difference compared to class A amplification, in which the power stage runs full current all the time, regardless of how it is being used. If the original post refers to he current measurement (in MilliAmps) going 'well out of range' when the amp is turned up, that is perfectly normal.

The figures usually given are for the idle state. Think of it like tuning a car engine....the tune-up specs would probably say to set the idle speed at 1,000 RPM or something similar. When you drive the car, the accelerator pedal allows you to adjust the RPM anywhere you want for the speed you want, but when you release the pedal, it should return to it's 1,000 RPM idle speed. That idle speed sets the foundation for all other performance.

Bias on a class AB amp is the same. Dial all the knobs to zero. Set the bias then play for a while and keep an eye on the tubes. Maybe re-check the bias after that. Bake in a moderate oven for 35 minutes and serve with a side salad.

 

[Mr 9finger]

Re: Help me NOT blow my 5150

Dont put your mouth anywhere near it.

You must really love that amp????

As soon as I seen the thread title I knew.....

 

[theodie]

Re: Help me NOT blow my 5150

As soon as I seen the thread title I knew.....

Raunch!

HOLLA!