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Vintage threads from the first ten years

Deluxe 5E3-clone

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5/31/1999 3:48 PM
Nils	Deluxe 5E3-clone Hi, I just wanted to check some values on my clone, I have 370 on the plates and 20 volts on the 250 ohm resistor, both measured to ground are these ok or too high. Any advice Nils

5/31/1999 4:31 PM

Benjamin Fargen

Nils,
That's 350VDC plate to cathode.....That's a good voltage if you plan on running modern tubes(sovtek,ruby ect.)If you are running NOS stock you could be a little more risky and up the plate voltage if you were looking for more output power. If you do ever decide to up the plate voltage, make sure to check your dissipation on the tubes to make sure not to fry them. 12 watts is the max for a 6V6-GT. If the dissapation it is to high you need to up the cathode resistor accordingly to achieve the correct rating.
The formula to figure the dissipation is plate to cathode voltage x bias current.
I.E.(example. 350vdc X .032amp. = 11.2 watts (sweet!)

Have fun rocking out!
Benjamin.

6/1/1999 1:01 AM
Nils	Thanks Benjamin, I will try a GZ34, I'm sure it will give 30-40 more volts. But I don't really get the formula, if I have 20 volts on a 250 ohms resistor isn't that 81 mA, and 350VDC plate to cathode isn't that 28,4 Watts, care to enlighten me? Nils

6/1/1999 7:12 AM
jason	Nils, Isn't that 81mA for the pair of 6V6's. Assuming matched tubes should yeild around 40.5mA per tube. 40.5mA X 350vDC=14.1w per tube. jason

6/1/1999 7:30 AM
Nils	Jason, That's what I meant, the earlier comments were that I could increase voltage, that I was a bit on the safe side. I just wanted to point out that as far as I can gather the tubes are quite pushed already, but then again I'm far from really understanding this technology. Nils

6/1/1999 7:58 AM

Benjamin Fargen

Nils,
I should have clarified my post. your Plate voltage is safe (under 400vdc on a NOS 6V6-GT is good)But just because the plate voltage is safe doesn't mean you are not over dissipating the tube. This has to be controlled by the cathode resistor value in conjunction with the plate voltage. My calculation was just a quick example(sorry for the confusion!) and Jason's 14.1 figure was the real wattage. 14.1 watts is a little high but right in the ballpark.(ask Bruce how hard he runs those bad boys!!!) I would leave in the 5y3 and DO NOT put in the 5AR4. This would be a little to much on those 6V6's. If you were converting to 6L6's....that would be OK.

Benjamin.

6/1/1999 11:35 AM

Just as a fwiw

The current you read across the Rk is a sum of both the idle plate & screen current. So that 14W rating isn't really dead on, as you have more than just ip there.
(yeah, the screen doesn't pull down that much @ idle, but..) Do a xfmr shunt measurement to see the actual screen draw.
I usually run 6V6GTA's in these apps when I can, and they have 12W plate & 2W screen max ratings, and so 14W is just right IMO. I've never had a problem with them (knock wood!)
Remember to play the amp hard to keep the tubes cool!!

I'm with Benjamin: I'd stay away from the 5AR4 as well. You will _not_ get rid of the "sag" (if that's what you're going for). The sag is built into the cathode bias setup. Try fixed bias if you want a tighter sound (and a 12AY7 in front).

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