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Post subject: deluxe vm biasing
Posted: Fri Oct 25, 2013 7:20 am
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I need info as to how to bias my deluxe vm.

I am getting into tube amps again, and got a good deal on a used vm combo. I want to be prepared when time comes to change the tubes. if there is a manual/diagram out there, or a video you could point me to I would appreciate it.

a few years back I sold my brownface early 60's amp. I was the owner for almost 45 years, if my math is correct. the amp never had a tube change. the new owner was pleased as could be.

one more question- if I put the same tubes in (currently jj 6l6gc) do I still need to re-bias? or is it just a good idea to do it anyway? I have a multimeter. any other tools I need?


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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 7:37 am
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phreddybee wrote:

one more question- if I put the same tubes in (currently jj 6l6gc) do I still need to re-bias? or is it just a good idea to do it anyway? I have a multimeter. any other tools I need?


You need to check bias each time and adjust if needed same tube or not. Tubes 's amp have lethal voltage and can kill you .

Bias ; on TP26 ( 6L6GC cathodes ) shematic said you must read 54 millivolts , IMO close to 48 mv if sound good is better ( save tube) . This is for 6L6GC not other 6L6 .

Schematic here , not sure if it is the right one ;

support.fender.com/schematics/guitar_amplifiers/Deluxe_and_Bandmaster_V.PDF

Owner manual here;
support.fender.com/manuals/guitar_amplifiers/Band-Master_and_Deluxe_VM_manual.pdf


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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 8:51 am
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sorry-link didn't work. thanks for the effort anyway


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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 9:03 am
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support.fender.com/schematics/guitar_amplifiers/Deluxe_and_Bandmaster_V.PDF

Link is good I don't understant why it do not work , must be in red to clic on.

It will work if you copy adress in the google window .


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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 10:04 am
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Here you go:

http://support.fender.com/schematics/gu ... ematic.pdf

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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 12:38 pm
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is it where I see the r71? on the tube pcb board it looks like. just need to know what steps to take, so I do it properly. is there a chart that tells me the proper bias for this amp,and do different power tubes require different bias settings?

many thanks for your patience and help. this is kind of foreign to me see any bits of advice are welcome.

any recommendations for tubes, power and pre-amp?


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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 1:14 pm
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First, be aware that there is high voltage in the amp, use caution.

It is R66. Measure the millivolts (mV) across the resistor. Since the resistor is 1 ohm, you can translate directly to milliamps (mA). This is the current for both tubes, so divide by two to get the current through one tube. Measure the Plate voltage, measured at pin 3 of an output tube. Multiply the current for one tube, times the Plate voltage measured, to get the wattage dissipated for one tube. Typically you want to shoot for a range of 50% to 70% of one tube max Plate wattage dissipation. Most 6L6 are 30 watts, so the range would be 15 to 21 watts, but always be sure of the rating for the tube used.

So, if you read 48 mV across R66, this is 48 mA for both output tubes, 24 mA for one tube. In this case, if the Plate voltage is approx 440 volts, times 24 mA (.024 amps), this will give approx 10.5 watts, which is way too cold. IMO, 16.5 watts would be much better, so 75 mA at the test point would be a good value, provided 440 volts at the Plate. Always measure the Plate voltage and recalculate every time that you make an adjustment, as the Plate voltage will change with change in current. At 75 mA across R66, the Plate voltage might be as low as 430 volts or less, measure to be sure.

When changing output tubes, using the same brand does not insure that the bias will be the same, unless the new tubes have the exact same ratings for current/transconductance. It is always a good idea to check the bias when changing tubes, even if the ratings are the same, as you might have a bad set even though new. :idea:

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Last edited by shimmilou on Fri Oct 25, 2013 1:22 pm, edited 1 time in total.

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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 1:20 pm
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Shimmilou beat me to it, but this thread of mine may be helpful:

viewtopic.php?f=13&t=88475

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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 1:26 pm
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People should learn to do searches. You and I have posted this same thing over and over, the forum has to have dozens of these same threads by now. :|

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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 1:28 pm
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shimmilou wrote:
People should learn to do searches. You and I have posted this same thing over and over, the forum has to have dozens of these same threads by now. :|


Truth is, I had forgotten I even posted that until I read your response. :oops:

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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 4:41 pm
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:lol:

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Post subject: Re: deluxe vm biasing
Posted: Fri Oct 25, 2013 4:44 pm
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shimmilou wrote:
:lol:


Its hell getting old. :(

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Post subject: Re: deluxe vm biasing
Posted: Sat Oct 26, 2013 1:49 pm
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bluesky636 wrote:
shimmilou wrote:
:lol:


Its hell getting old. :(


+1!

Tri-focals can help.

(a little)

:mrgreen:

Arjay

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Post subject: Re: deluxe vm biasing
Posted: Sat Oct 26, 2013 9:35 pm
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Yes, if you can remember where they are! Oh, here they are, on my head. :lol:

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Post subject: Re: deluxe vm biasing
Posted: Sat Oct 26, 2013 10:06 pm
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shimmilou wrote:
Yes, if you can remember where they are! Oh, here they are, on my head. :lol:



Truth is stranger than fiction.

I once found my sunglasses......in the refrigerator!

:wink:

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