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Old 29th August 2011, 08:06 AM   #1
mdm102 is offline mdm102  Russian Federation
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Default exceeding plate voltage of the output tube

Hi,

I want to try 6p3s in my guitar amp, which originally uses 6l6gc. The amp has an almost 500v anode voltage, but 6p3s rated for 400v, I found here 6L6 and 5881...identical tubes, right? [Archive] - The Gear Page one guy said, that is possible to use tubes, which has a lower voltage rating, if the current will be reduced to avoid exceeding power dissipation of the tube. Is it really possible and works good?

Thanks!
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Old 29th August 2011, 10:04 AM   #2
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Best to abide by manufacturers ratings, and if needed reduce the voltage to the anode to suit other valves. Various circuits can be used for reducing voltage, and the easiest is to use an appropriate transformer. High Voltages need a lot of respect and safety. Always power down by turning the equipment off and allow 30 mins for capacitors to discharge.

Reducing current is achieved with series resistance. Remember do not work on High voltage circuits whilst they are powered on.

Cheers / Chris
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Old 29th August 2011, 11:12 AM   #3
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A guitar amp is not often designed for longevity, and it's more of a rule than a deviation to exceed output tube voltage ratings (see for example all the old Fenders with 6V6's).

It'll be ok if you keep under max plate dissipation. Probably sound a bit better too, to push it.
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Old 29th August 2011, 12:00 PM   #4
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Make sure your tube is the 6p3s-e. If it's the -e you'll be fine. The 6p3s is not the same tube and may arc over on you.

Because of the lower voltage ratings the 6p3s is sometimes sold as a 6V6.
6V6
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Old 29th August 2011, 12:00 PM   #5
TG is offline TG  Ukraine
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Quote:
Originally Posted by mdm102 View Post
Hi,

I want to try 6p3s in my guitar amp, which originally uses 6l6gc. The amp has an almost 500v anode voltage, but 6p3s rated for 400v, I found here 6L6 and 5881...identical tubes, right? [Archive] - The Gear Page one guy said, that is possible to use tubes, which has a lower voltage rating, if the current will be reduced to avoid exceeding power dissipation of the tube. Is it really possible and works good?

Thanks!
New life of the old tubes (in Russian)
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Old 29th August 2011, 12:01 PM   #6
SY is offline SY  United States
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Max voltages often have to do with distances between electrodes, how their wires are run to the base, and electrode shape. Arcing is not fun (well, except for the shirtless guy from Florida). Respect the ratings.
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Old 29th August 2011, 12:17 PM   #7
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Quote:
is possible to use tubes, which has a lower voltage rating, if the current will be reduced to avoid exceeding power dissipation of the tube. Is it really possible and works good?
In case of 6L6-family, there are different types, but with quite similar construction.
For old metal 6L6 the max. specified plate voltage was 375 V whereas for 807 it was 750 V and both tubes share same internal construction.

An other example could be EL-34 tubes used by Geloso G 280 A. This amplifier operated at AB1 and rated output power was 100 W (from two tubes).
The used plate voltage was 1000 V. The max. specified plate voltage was 800 V.
In spite of that, Geloso sold this model for years.

My opinion is that 500 V for any 6L6-version is fully safe, but the max. plate dissipation must be in control.
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