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Post subject: Economy Biasing
Posted: Tue Mar 06, 2018 1:55 pm
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How many others here use a single bias probe to bias your amp? I got one from Eurotubes, and must say I couldn’t be happier with the results.

My amp has two 6V6s, and all you have to do is pull one out, and plug it back in through the single bias probe with your volt meter, turn on your amp, and it shows you your bias in milliamps.

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Post subject: Re: Economy Biasing
Posted: Tue Mar 06, 2018 4:12 pm
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You need to know the plate voltage to correctly set the bias, and the eurotubes probe doesn't do that. You have to open up the amp to measure that.

I bought dual Amp-head bias probes wich can read both. It is not available anymore :(


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Post subject: Re: Economy Biasing
Posted: Wed Mar 07, 2018 12:13 am
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I’m just going with the good experience, and advice from the guys at Eurotubes.

This is where I learned all I need to know.

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Post subject: Re: Economy Biasing
Posted: Wed Mar 07, 2018 1:36 am
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This is a average bias and for a Fender Deluxe Reissue, it may not be the best bias.
And it is only for the reissue, may not work for a original vintage one.

Plate voltage reading is alway a must.

Amp-Head makes a plate voltage probe too just for this purpose!
For instance with a 30 watt 6L6GC divide the max wattage dissapation by the plate voltage
My fender Supersonic-
30watts/470 volts=.064 max dissapation . Then take 60% ( you can go to 70% ) of that for a conservative idle setting .064 X .6 = 38ma


A correctly biased amp will run efficiently and maximizes the life of your tubes.

Under - biased (hot ) amps will lack of punch and tubes will run hotter , shorter tube's life .
Overbiased amps ( cold ) will sound thin and brittle. with tubes running too cool for proper performance .
A correctly biased amps will sound clean and tight a moderate volumes, than at higher volumes breakup and distort musically .


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Post subject: Re: Economy Biasing
Posted: Wed Mar 07, 2018 3:08 am
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Ummmmm.

Fender has made several amps with external bias test points and external bias pots. So has Marshall. And a dozen other manufacturers. Where you just assume the plate voltage is fairly close to the design spec.

If you're just aiming for a safe range between 60 to 70% plate dissipation it's an ok way to do it. You may end up a couple percent high or low, but that's not really a big deal.

If you're biasing a vintage amp that was designed back when line voltage was lower, measuring plate voltage is more important.

If your goal is to set it exactly for 70% plate dissipation, you have to measure plate voltage.

But to get it somewhere in the safe range, you don't really have to.
--------------------
On other forums there are techs who say you need to use an oscilloscope when setting bias.

There are other techs who say the transformer shunt method is the only proper way to do it.

And then there's Mesa that says not to measure anything on their amps -- just buy Mesa-branded tubes and never use anything else.


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Post subject: Re: Economy Biasing
Posted: Wed Mar 07, 2018 3:27 am
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strayedstrater wrote:
Ummmmm.

Fender has made several amps with external bias test points and external bias pots. So has Marshall. And a dozen other manufacturers. Where you just assume the plate voltage is fairly close to the design spec.

Your wall outlet voltage should be same as Fender say , many time is not
And you must use same tube


If you're just aiming for a safe range between 60 to 70% plate dissipation it's an ok way to do it. You may end up a couple percent high or low, but that's not really a big deal.

Yes it is safe, just safe, don't you want the best tone too ?

If you're biasing a vintage amp that was designed back when line voltage was lower, measuring plate voltage is more important.
Yes

If your goal is to set it exactly for 70% plate dissipation, you have to measure plate voltage.
Many Fender amps work as good a t lower plate dissipation

But to get it somewhere in the safe range, you don't really have to.
--------------------
On other forums there are techs who say you need to use an oscilloscope when setting bias.
Gerald Weber,did you know him ? ( and many other ) write scope is not accurate


There are other techs who say the transformer shunt method is the only proper way to do it.
Shunt method is accurate but too dangerous for unqualified person. Result is the same as cathode reading

And then there's Mesa that says not to measure anything on their amps -- just buy Mesa-branded tubes and never use anything else.
Try to find Mesa Tube , For other brand , new bias is needed



Cathode bias reading is the best way with plate voltage reading


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Post subject: Re: Economy Biasing
Posted: Wed Mar 07, 2018 4:05 am
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I wasn't endorsing using an oscilloscope. Nor the transformer shunt method. I was implying that you're being a little dogmatic in saying that people have to measure the plate voltage and do the calculations, like those techs who say their preferred method is the only proper method and every other method is wrong.

Idle current alone will reliably get you into the 60~70% range, give or take a bit.

If we all demanded the "best" instead of "good enough", we'd all have Buzz Feiten nuts and use strobe tuners. We'd all use RCA Blackplates or NOS Mullards. Nobody would buy a TRRI or Marshall JTM45 -- they'd only buy originals. Squiers and Epiphones wouldn't exist.


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Post subject: Re: Economy Biasing
Posted: Wed Mar 07, 2018 3:17 pm
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I actually just us a multi meter on the BIAS point of my Hot Rod Deluxe. I do not need BIAS probes for that amp. I guess if I had some other model amp, I would have Eurotubes BIAS probes for that. I do have an Egnater Tweaker 15 watt head but that one does it's own BIASING somehow. No need for me setting the BIAS on the Tweaker.

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Post subject: Re: Economy Biasing
Posted: Thu Mar 08, 2018 3:40 am
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strayedstrater wrote:
....Where you just assume the plate voltage is fairly close to the design spec...


Uuuummmm, yeah, about assumptions.....you know what that means? :roll:

By actually checking the Plate voltage, you can be sure that your power supply is good, so that maybe you save yourself from looking like an idiot who assumes that everything is ok. :wink:

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Post subject: Re: Economy Biasing
Posted: Thu Mar 08, 2018 3:48 am
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desertbluesman wrote:
I actually just us a multi meter on the BIAS point of my Hot Rod Deluxe. I do not need BIAS probes for that amp. I guess if I had some other model amp, I would have Eurotubes BIAS probes for that. I do have an Egnater Tweaker 15 watt head but that one does it's own BIASING somehow. No need for me setting the BIAS on the Tweaker.


Cathode biased is pretty much “self biasing”.

as for the test point on the hrdlx, it cant tell you if the tubes are evenly matched, as the test point measures current draw of both tubes combined.

So the lesson of this thread can be:

Use bias probes on each tube, and check the Plate voltage. This is the best way to be sure of what you have. :wink:

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Post subject: Re: Economy Biasing
Posted: Thu Mar 08, 2018 7:59 am
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Bias current:
The comments were about idle current (* plate voltage) being 60-70% of what, the tube's rated spec of Maximum Plate Dissipation (Watts)?

Is that an exact value. I may be wrong about this. But we agree about saying a certain tubes MaxPlate Dis is a blanket 25 Watts or did I read 30 Watts. What about the original Blues Deluxe which has 5881 tubes at a 23 Watts? dissipation or is it 24 W. It's not a measured number, but a mfg. given spec value. It's probably correct. A rounded off value. One way to find out is to red plate the tube and calculate the max-diss, no thank you.


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Post subject: Re: Economy Biasing
Posted: Thu Mar 08, 2018 10:48 am
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shimmilou wrote:
desertbluesman wrote:
I actually just us a multi meter on the BIAS point of my Hot Rod Deluxe. I do not need BIAS probes for that amp. I guess if I had some other model amp, I would have Eurotubes BIAS probes for that. I do have an Egnater Tweaker 15 watt head but that one does it's own BIASING somehow. No need for me setting the BIAS on the Tweaker.


Cathode biased is pretty much “self biasing”.

as for the test point on the hrdlx, it cant tell you if the tubes are evenly matched, as the test point measures current draw of both tubes combined.

So the lesson of this thread can be:

Use bias probes on each tube, and check the Plate voltage. This is the best way to be sure of what you have. :wink:


Of course I buy my tubes from a vendor who does check the capability of each tube, and sell them in matched pairs, or 2 matched sets of matched pairs for those amps needing 4 power tubes, so far so good (although I do not do amp repair for a living)

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Post subject: Re: Economy Biasing
Posted: Thu Mar 08, 2018 2:08 pm
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I took this thread in the wrong direction and I want to apologize. Especially to Stratele52.

Of course I agree that it's best to measure plate voltage first.

But when Blue Notes proudly posted about dipping his toe into the murky waters of biasing, St52's response struck me as harsh and discouraging. Instead of saying, "a good start, congratulations -- much better than only buying Groove Tubes with the same hardness rating as your stock tubes, and infinitely better than just slapping different tubes in and praying they don't redplate", his answer made it seem like Blue Notes had done it terribly wrong.

Of course that's just the "english as second language" thing. St52 is a great guy -- always helpful, always glad to share his vast knowledge. Sometimes he phrases things in a way that seems harsh to me, but I know he doesn't mean it that way.
--------------------
However, I stand by my opinion that just checking idle current isn't an absolutely terrible way to do it. Not the best way, but adequate.

Fender Evil Twin, Marshall DSL, many other mainstream amps and even some boutique amps have external idle current test points and external bias pots. The manufacturers facilitate, recommend, encourage simply checking the idle current on those amps.

Hot Rod Deluxes and many other amps have internal 1 ohm resistors to facilitate simply checking total idle current.

Like 99.9% of the population, I've never checked the wall voltage anywhere I've lived. I just assume and trust that it's within +/-10% or so of what it should be.

Perhaps it's foolish of me, but I've always assumed Fender, Marshall, etc used the correct power transformer and the correct component values when assembling the amps I've bought. And so felt safe in assuming the plate voltage was reasonably close to the schematic value.

Maybe my ears aren't good enough, or maybe it's the amps/tubes I've had, but I've never encountered a "bias sweet spot" where an amp sounded dramatically best. A little different when it's a little hot or cold, but somewhere around 70% is good enough for me.
------------------
Of course a professional tech should do every job the best way possible. And even as an amateur hack, if a friend asked me to bias his amp I'd either check the plate voltage or decline to do the job. But on my own amp? I have no idea what plate voltage my Evil Twin ran. It sounded great and it didn't eat tubes -- good enough for me.


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Post subject: Re: Economy Biasing
Posted: Thu Mar 15, 2018 6:18 am
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Idle current is all you need.


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Post subject: Re: Economy Biasing
Posted: Thu Mar 15, 2018 6:52 am
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Yep, just like I never check the oil in my car when I only need gas. :lol: :lol: :lol:

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