Amp Bias Match Meter--MKllC Bias HELP is 70ma too hot

Bought a Quad Tube Amp Bias Match Meter on e-bay. After receiving it I think I bought a meter to bias amps. I have all boogies (fixed bias) so is this of any value to me at all. Just what am I testing, tube ma- amp ma-tube in the amp ma. Also When I bought THIS mark 2 c+'s I was told NEW POWER TUBES, CORRECT BIAS INSTALLED BY LOCAL BOOGIE TECH How High is too high in tube MA for a plus. I've got a set running 69ma + or - 1. IS THIS TOO HOT CAN I POSSABLY DAMAGE MY AMP. :shock: Been running them for 6 months with out problem and they sound great ( WINGED C's) THANKS FOR RESPONDING !!!

I haven't a clue, but the =C= Quad I bought for my Mark III are 21.5 ma. and they sound awesome. Sounds outrageously high to me, but I can't tell you what ma. is let alone what is high. I told the place I bought the quad from what amp I was putting them in and that's what they sold me.

http://www.webervst.com/tubes1/calcbias.htm

A great page to calculate tube amp bias. 8)

I wonder why my amp works, according to the chart, my 21.5 ma 6l6's aren't even in the ballpark?! The amp rules as far as I'm concerned.

JOEY B. said:

http://www.webervst.com/tubes1/calcbias.htm

A great page to calculate tube amp bias. 8)

Click to expand...

Thanks for the info !! I don't know how to calculate plate voltage but looking at the schematic at what I think is plate voltage it says 479v which would make tube ma 43.8. Dose that sound right for a c+ ? Some of you are running your tube bias much lower it seems. What's the reason for that- Tube life?


Never mind, I spent more time with B/B tube archives and got all the info I needed

I'm not an expert but I think the mid 40 MA range is right for IIC+. I have a coliseum and it had mixed tubes but one Mesa 415 left and it read 44-46 ma so I matched around that. I think some new 6L6 measure in the high 60's but the safe zone for IIC+ in mid 40's? I hate the mystery of it someone needs to make a list of all the boogies and acceptable MA readings so we don't have to buy only mesa rebranded tubes!

So I'm assuming each tube is running @ 34.5 mA to 35.0 mA...

Based on that reading and your estimation for the plate voltage, you're running the tubes @ 55% of their max plate dis. Many Boogie owners claim that sweet spot is @ 60% of the max plate dis. Seems to me like you're right in the ball park with no danger to tubes.

Buster Leggs said:

JOEY B. said:

http://www.webervst.com/tubes1/calcbias.htm

A great page to calculate tube amp bias. 8)

Click to expand...

Thanks for the info !! I don't know how to calculate plate voltage but looking at the schematic at what I think is plate voltage it says 479v which would make tube ma 43.8. Dose that sound right for a c+ ? Some of you are running your tube bias much lower it seems. What's the reason for that- Tube life?


Never mind, I spent more time with B/B tube archives and got all the info I needed

Click to expand...

Which power transformer is in your C+ ? Also, which power section do you have? 60 watt, 60/100, Simulclass, or Coliseum. My original C+ Simulclass has a plate voltage of around 480V DC. I have seen Coliseum amps in the 520-530 range. 60 watt amps will be near 450.

HRG orig with a 105PT
HR orig with a 105PT
DR orig with a 105 PT
DRG upgrade with 100PT

I've read that some of you more knowledgeable than I, run about 22ma to 35 ma which is cool according to the 70% (rule)? Then again I just got my DR back from shop, had a blown a screen grid resistor from running hot tubes, hence my new found interest in tube MA. My HR had new winged c's in it when I bought it and they are running about 70MA.(which I pulled) I'm assuming my c+'s all have pretty close plate voltage so I'm using any thing I have that's under 35MA and shooting for 30ish on new tubes. IS THERE ANY DISADVANTAGE TO INSTALLING ADJUSTABLE BIAS IN THESE AMPS?

Plate voltage can be measured at pin#3 of the power tube socket, bias voltage can be measured at pin #5. The combination of these two will determine tube current draw in mA. The upgraded DRG C+ should have 450-460V Plate voltage, and the 105 PT models will have close to 480V. With the STR-415 Sylvania tubes, the 105 PT 60/100 models should be in the mid-40's mA range. The 105 PT Simulclass models will be in the mid 20's for the inner pair and high 40's to low 50's for the outer (Class-A) pair. I do not remember exactly the current draw range for a 100 PT Simulclass amp, though.

Ok Joey B me too
Mark IIC+ Coliseum (no simul)
Mark IIC+ 60 Export

JOEY B. said:

Plate voltage can be measured at pin#3 of the power tube socket, bias voltage can be measured at pin #5. The combination of these two will determine tube current draw in mA. The upgraded DRG C+ should have 450-460V Plate voltage, and the 105 PT models will have close to 480V. With the STR-415 Sylvania tubes, the 105 PT 60/100 models should be in the mid-40's mA range. The 105 PT Simulclass models will be in the mid 20's for the inner pair and high 40's to low 50's for the outer (Class-A) pair. I do not remember exactly the current draw range for a 100 PT Simulclass amp, though.

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Joey thank you for the info. Obviously my goal is to dial in the best sound and at the same time not damage anything. When you talk about what the plate voltage SHOULD be, it this something that can wonder out of specs? And if so, how far out is an issue. Also you refer to STR 415's when recommending tube MA. I recently bought a set I heard a substantial tone improvement. (both 46MA I got lucky). But would those MA'S apply to any brand tube? The 415's are getting hard to come by and they cost a small fortune. THANKS

Buster Leggs said:

JOEY B. said:

Plate voltage can be measured at pin#3 of the power tube socket, bias voltage can be measured at pin #5. The combination of these two will determine tube current draw in mA. The upgraded DRG C+ should have 450-460V Plate voltage, and the 105 PT models will have close to 480V. With the STR-415 Sylvania tubes, the 105 PT 60/100 models should be in the mid-40's mA range. The 105 PT Simulclass models will be in the mid 20's for the inner pair and high 40's to low 50's for the outer (Class-A) pair. I do not remember exactly the current draw range for a 100 PT Simulclass amp, though.

Click to expand...

Joey thank you for the info. Obviously my goal is to dial in the best sound and at the same time not damage anything. When you talk about what the plate voltage SHOULD be, it this something that can wonder out of specs? And if so, how far out is an issue. Also you refer to STR 415's when recommending tube MA. I recently bought a set I heard a substantial tone improvement. (both 46MA I got lucky). But would those MA'S apply to any brand tube? The 415's are getting hard to come by and they cost a small fortune. THANKS

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I am NO amp tech for sure, but am just sharing some of the info that I have gained over the years. I do highly recommend the original Sylvania STR-415 or STR-416, based on longevity alone. You can pay much upfront for these tubes, or a little many times over for the Russian or Chinese copies. The SED =C= is the best among the copies, if you had to go that route. I would shoot for the same current draw as the Sylvanias, if you can.

Thanks Joey, that info is very valuable to me. Much rather put my money towards tubes than techs. I notice an improvement in tone with the STR415's, to MY ear nothing compares. I like 6l6's a little more than el34's (class a). I'm wondering if I would like STR416's. I've never tried them in fact, I don't think I've seen them for sale. I've got a guy on e-bay that's been straight with me so far. I'll see if he can get them. He doesn't advertise them though so I'm thinkin they ain't gonna be cheap. If I can even get them.

JOEY B. said:

Plate voltage can be measured at pin#3 of the power tube socket, bias voltage can be measured at pin #5. The combination of these two will determine tube current draw in mA. The upgraded DRG C+ should have 450-460V Plate voltage, and the 105 PT models will have close to 480V. With the STR-415 Sylvania tubes, the 105 PT 60/100 models should be in the mid-40's mA range. The 105 PT Simulclass models will be in the mid 20's for the inner pair and high 40's to low 50's for the outer (Class-A) pair. I do not remember exactly the current draw range for a 100 PT Simulclass amp, though.

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Just got a multi meter. Do I test plate voltage and or bias voltage with the tubes in? Also just to make sure, these voltages are DC not AC correct? I'm probably making you a little nervous at this point with my inexperience but I assure you I WON'T fry myself in the process. Thanks for the info.

DC voltage for sure. If I remember correctly the pin #5 voltage can be measured with the amp in "standby" mode. The pin #3 voltage has to be measured with the amp in operating mode. I would leave the tubes installed , just to make sure that they are not the source of any problem. 8)

Hey Joey thanks for all your help. This will get me started. The more I learn the more I realize how little I know. But at least I can properly tube my amps. Now I've got SED winged =C='s and some old Sylvania and Philips tubes that don't fall in the proper MA range. It there any draw back to having a tech put bias adjustment pots in one of my amps so I can use those tubes? Dose it devalue the amp by much?

All the C+ PT's have a different fixed bias ma and the simuclass models have two different fixed biases.
Class A bias and Class AB bias. The 60/100 are obviously the same but different to their PT. I have all the bias specs (thanks Mike) if interested.

kippiejr said:

All the C+ PT's have a different fixed bias ma and the simuclass models have two different fixed biases.
Class A bias and Class AB bias. The 60/100 are obviously the same but different to their PT. I have all the bias specs (thanks Mike) if interested.

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Yea if you don't mind hit me with the info you have. 1 of my C+'s is a simulclass upgrade with a 100 power transformer if that makes a difference. The other simulclass (factory) has the 105 PT and no eq if that matters. Then I have 2 60/100 factory, both 105 PT one with and one without eq. Any info even if it's duplicated info from the past I would still appreciate hearing it. Thank you for your time !!!!

Nice post !