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Post subject: Re: Replacement Tube Suggestions
Posted: Sun Oct 07, 2012 12:02 pm
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cedarblues wrote:
I've used the taller TADs in my SR and loved them!

http://thetubestore.com/tad6l6gc.html

"The new 6L6 GC-STR has a tight low end and has all the guts and bite to perfectly accomplish all the rocking sounds from SRV to modern NU-Metal. They have powerful deep bass and a clear, airy top end."

That is a very accurate description.


Yes, I saw that review. Thanks. It seems the TADs are getting good reviews.
I'd like to experiment with different tubes but buying 4 at a time takes a bite out of the wallet. May have to roll the dice on a set and keep the originals for backup.


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Post subject: Re: Replacement Tube Suggestions
Posted: Sun Oct 07, 2012 12:34 pm
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dshalfstack, when you bias an output tube, it's the idle wattage that is important. Not simply the measured voltage or calculated current across the cathode. What Fender did was "assume" (and we all know what that means) that the plate voltage would remain constant.

Wattage is calculated as: (anode plate voltage) times (idle current).

And yes, plate voltages can vary from amp to amp. And is not easily adjustable. So, you can see if you don't take this voltage into account, you could be running a tube way over or under the desired wattage range (as you are only adjusting the idle current, measured as voltage drop across the cathode --- as using Ohm's Law to find current draw from voltage reading).

FWIW... if you read the voltage drop across a one-ohm resistor, the measured voltage is equal to the current draw across said resistor:

(Voltage) = (resistance) times (current)

If the (resistance) = one ohms. Then, (voltage) = (current)

Back to that crazy "W" designation. Russian military specifications rarely placed over 450 VDC plate voltage for their 6L6 use. Therefore, most relabeled Russian made tubes can't handle this type of voltage, esp if you are pushing the tube in an amp that is running them at 25+ watts per tube. Like some ultra-linear amps.

You can run these tubes in your Evil Twin --- but keep the output wattage to 20-25 watts per tube. And I'd be sure those screen resistors (which keep keep the screen grid voltage BELOW the anode plate voltage) are in good shape. This helps avoid runaway tubes & damaged amps.

Really, most Twin Reverbs I've worked on seem to be most happy & long lived with good quality US made 6L6GC or 7581A. Or 1990-2000's vintage Svetlana (=C=) SV-6L6GC. I've used 7581A in amps that place way over 500VDC onto the plates & all is well (running them well over 30 watts) .

I know this is all kinda confusing. But, there are many good sites on the Net which explains concept of idle biasing better than me.

Anyhow, good luck with amp! Sorry for the "tech talk."

http://www.geofex.com/tubeampfaq/tube_amp.htm#Section11

http://www.aikenamps.com/Biasing.html


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Post subject: Re: Replacement Tube Suggestions
Posted: Sun Oct 07, 2012 1:06 pm
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BMW2002Ti wrote:
dshalfstack, when you bias an output tube, it's the idle wattage that is important. Not simply the measured voltage or calculated current across the cathode. What Fender did was "assume" (and we all know what that means) that the plate voltage would remain constant.

Wattage is calculated as: (anode plate voltage) times (idle current).

And yes, plate voltages can vary from amp to amp. And is not easily adjustable. So, you can see if you don't take this voltage into account, you could be running a tube way over or under the desired wattage range (as you are only adjusting the idle current, measured as voltage drop across the cathode --- as using Ohm's Law to find current draw from voltage reading).

FWIW... if you read the voltage drop across a one-ohm resistor, the measured voltage is equal to the current draw across said resistor:

(Voltage) = (resistance) times (current)

If the (resistance) = one ohms. Then, (voltage) = (current)

Back to that crazy "W" designation. Russian military specifications rarely placed over 450 VDC plate voltage for their 6L6 use. Therefore, most relabeled Russian made tubes can't handle this type of voltage, esp if you are pushing the tube in an amp that is running them at 25+ watts per tube. Like some ultra-linear amps.

You can run these tubes in your Evil Twin --- but keep the output wattage to 20-25 watts per tube. And I'd be sure those screen resistors (which keep keep the screen grid voltage BELOW the anode plate voltage) are in good shape. This helps avoid runaway tubes & damaged amps.

Really, most Twin Reverbs I've worked on seem to be most happy & long lived with good quality US made 6L6GC or 7581A. Or 1990-2000's vintage Svetlana (=C=) SV-6L6GC. I've used 7581A in amps that place way over 500VDC onto the plates & all is well (running them well over 30 watts) .

I know this is all kinda confusing. But, there are many good sites on the Net which explains concept of idle biasing better than me.

Anyhow, good luck with amp! Sorry for the "tech talk."

http://www.geofex.com/tubeampfaq/tube_amp.htm#Section11

http://www.aikenamps.com/Biasing.html


Ugh! I thought setting the bias was going to be easy. I suspect if I saw the proper technique demonstrated I could do it myself but trying to follow instructions off the Internet is difficult. Do most people bring their amps to a tech when changing tubes? Seems excessive but I would prefer not to zap myself noodling around inside my amp I suppose.


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Post subject: Re: Replacement Tube Suggestions
Posted: Sun Oct 07, 2012 2:19 pm
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It's not that bad.


viewtopic.php?f=13&t=72470

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Post subject: Re: Replacement Tube Suggestions
Posted: Sun Oct 07, 2012 2:19 pm
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dshalfstack wrote:
Do most people bring their amps to a tech when changing tubes? Seems excessive but I would prefer not to zap myself noodling around inside my amp I suppose.


Those with the wisdom to understand their own limited level of comprehension about electronics do (the truly foolish throw caution to the winds and usually end up hosing a perfectly good amp or killing themselves or both).

:lol:

While biasing after every power-tube change may seem "excessive" in terms of the amount of time a chassis spends on a competent tech's bench, bear in mind that a quality set of tubes will last a decade or more if installed correctly. Thus, a small price to pay for the peace of mind that regular servicing provides.

HTH

Arjay

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Post subject: Re: Replacement Tube Suggestions
Posted: Mon Oct 08, 2012 8:26 am
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Retroverbial wrote:
WTF is "NU-Metal"......some type of isotope alloy made from Nitrogen and Uranium?

:lol:

Arjay



I didn't know either... http://en.wikipedia.org/wiki/Nu_metal :roll:

I'll 2nd the EHX recommendation.

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Post subject: Re: Replacement Tube Suggestions
Posted: Fri Oct 19, 2012 6:05 pm
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I love my JJ tubes from Eurotubes. Sound great and are reliable. Guys there are very knowlegeable.

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