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Post subject: Tung-Sol new production 7581A
Posted: Wed Jul 01, 2015 10:21 am
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Another tube question for my Deville power tube search.
This is a new production drop in for 6L6GC, but rated at 35 watts. ...yet I believe the same heater draw as a 6L6GC.
Does'nt the heater draw limit the plate dissipation? Could this really be a 35 watt tube?


http://www.dougstubes.com/power-tubes/6 ... 581-a.html


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Post subject: Re: Tung-Sol new production 7581A
Posted: Wed Jul 01, 2015 4:16 pm
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In this tube, the heater is separate from the Cathode and the heater current draw does not limit the Plate dissipation. You might be thinking of tubes that have a directly heated Cathode, called a "filament", in which the filament (heater) is the Cathode, and therefore the Plate is limited by the Cathode current draw capability.

According to the spec sheet for this tube, the max Plate dissipation is indeed 35 watts at a max Plate voltage of 500 VDC when connected as a Pentode.

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Post subject: Re: Tung-Sol new production 7581A
Posted: Wed Jul 01, 2015 5:32 pm
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shimmilou wrote:
In this tube, the heater is separate from the Cathode and the heater current draw does not limit the Plate dissipation. You might be thinking of tubes that have a directly heated Cathode, called a "filament", in which the filament (heater) is the Cathode, and therefore the Plate is limited by the Cathode current draw capability.

According to the spec sheet for this tube, the max Plate dissipation is indeed 35 watts at a max Plate voltage of 500 VDC when connected as a Pentode.


OK- Good. Then it's the iron that governs power output.
Pair on order. Will try out for awhile and report.
thanx


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Post subject: Re: Tung-Sol new production 7581A
Posted: Wed Jul 01, 2015 8:21 pm
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ckmckool wrote:
...Then it's the iron that governs power output..


The tubes govern the power output. The tubes have a max Plate watts rating, use lower wattage rated tubes, less power out. The iron might be a limiting factor, as in how much can it handle, and is typically sized for the amps rated output. Trying to throttle more power out with higher wattage tubes might not be the best idea. :idea:

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Post subject: Re: Tung-Sol new production 7581A
Posted: Thu Jul 02, 2015 3:04 am
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Actually i'm not trying to throttle more power, i'm hoping it would be a more robust tube and last longer at moderate volubes of 4-5.


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Post subject: Re: Tung-Sol new production 7581A
Posted: Thu Jul 02, 2015 5:24 pm
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Let us know how they sound, your bias current, etc. :)

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Post subject: Re: Tung-Sol new production 7581A
Posted: Thu Jul 02, 2015 6:02 pm
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I have used the TS (Russian) 7581 tubes. They are very good. More headroom than the 6L6GC. 7581 is rated at 30 watts max per tube. I set the idle dissipation to around 20-22 watts/tube.

Be interested in hearing about the 7581A. The old US made variety are very good tubes.


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Post subject: Re: Tung-Sol new production 7581A
Posted: Fri Jul 03, 2015 2:27 am
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Just came in the mail - have'nt tried them yet.
The plate is unlike other russian 6L6GC's in that they are non ribbed.....and have extensions folded out from the corners, increasing overall plate area. Very neat welded plates.
Will evaluate this weekend at 480 plate volts.
For being a NEW ....new production, the price was about the same as the Tung-Sol 6L6GC-STR's..

I recently put a quad of russian Svetlana 6L6GC's into another amp (69 silverface twin reverb) and was sonically underwhelmed with them. I swore off russian power tubes after that.
Hope I was wrong.


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Post subject: Re: Tung-Sol new production 7581A
Posted: Fri Jul 03, 2015 3:30 am
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Tung Sol are Russian, as are EH, Sovtek, Mullard RI, and more.

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Post subject: Re: Tung-Sol new production 7581A
Posted: Fri Jul 03, 2015 4:15 am
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shimmilou wrote:
Tung Sol are Russian, as are EH, Sovtek, Mullard RI, and more.


Yep i knew these were russian. .......just pointing out that these are'nt other existing russian relabeled tubes.

Since my PTP Deville is wired for very conservative bias, I just threw them in w/out biasing for the moment.
Compared to the JJ's at same bias, the volume was (lower) at the same initial setting.....likely due to JJ's being so conductive at higher bias voltages.
But the power IS there at higher settings. Can't turn it up real loud yet due to unaddressed cabinet vibrations, but these ARE cleaner at comparative volume to the JJ's.
I was pleased with the mids and highs compared to other 6L6GC's i've tried so far. As to the bass, i've got to address my cabinet issues before commenting.....,but i suspect that the bass will also be cleaner at comparative volumes to the JJ's.

Will follow up on numbers.


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