5E3 Rectifier Options?

[mfreqmaster]

Last year I built a 5e3 kit using mostly Triode Electronics parts. I had never played through a 5E3 before. I really enjoy it's light weight & portability, especially for the amount of volume it produces. Anyway about 3 weeks ago my old Sylvania 5Y3 rectifier gave out. This was the day of a band audition & I did not have any other large enough amps ready to go. I did not have a spare 5Y3 but did have a brand new 5AR4 tube I was saving for a future Deluxe Reverb or JTM build. I usually am not the gambling type but took a chance & really liked the sound, it seemed to increase the headroom a little. Volume is usually around 3-3.5 & stays pretty clean even with a humbucker equipped guitar. My question now is am I waiting for a disaster to happen or am I safe to continue with this rectifier tube? With the amp on standby I am measuring around 343V at the 5AR4, & with standby off I get around 375-380V on the plates of the 6V6s. Also my power transformer is rated for 2 amps on the 5V windings. I found some earlier threads that touched on this but I could not come up with a definitive answer.

Thanks in advance to all who answer.
Jon

[Bruce / Mission Amps]

See how hot the power tubes are running at idle.
Measure the DC resistance of the power tube's cathode biasing resistor with the amp off and all caps fully discharged....and then with the amp on, measure the DC voltage across that resistor.... divide the voltage by the DC resistance of the resistor to determine how much current is flowing through the tubes at idle.
It should be OK if the tubes re running under 13-15 watts each.

[mfreqmaster]

OK, I have measured the resistor at 245 ohms. The voltage across the resistor was measured at 23V dc. I did a V/R=I and got .09 amps. Multiplying .09A by 23V gets me 2.15 watts? Am I doing this right? Just wanted to make sure. Thanks.

[pdf64]

No, nearly there but you worked out the bias resistor dissipation.
Tube dissipation = V(plate to cathode voltage) x I(cathode current 0.09A)
The 'per tube' figure will be half that.
Then remove ~1 watt that the screen will be dissipating.
Pete.

[deci belle]

I tried to do the figuring too. I got almost 16w for each tube. Did i do it right?

[mfreqmaster]

Here is an update, not sure how my first measurements were way off but plate voltage is 414V on these jj 6v6s. Plate to cathode voltage is 390V. 390V * .09A gives me 35.1W. Divided by two this is 17.55 watts, subtract the 1v for the screen gets me to 16.55W. Should I just pony up & buy a new 5Y3?

[cminor9]

I would buy a new 5Y3. You are really punishing those tubes.

You could also check out something like a 5V4 which isn't quite as hard as a 5AR4 but will give you a bit more headroom than that 5Y3. I've used them before with good results.

[mfreqmaster]

Thanks Cminor, I will check those out.

[Bruce / Mission Amps]

For what it's worth... I've run JJ 6V6s at 15-16 watts each for months on end.... they seem to have a higher actual plate dissipation rating then real 6V6s.
You could buy a couple 12V@5 watt zener diodes and put them in series (cathode band pointed to ground) with your PT's, grounded center tap wired. That will drop the B+ down a bit and or you can lift your power transformer leads from the rectifier socket (lugs 4 and 6) and use a 5 watt resistor in each leg to slightly lower the AC voltage to the rectifier tube socket.
That uses power transformer high voltage current to heat the resistor but a 150-220 ohm resistor in each leg will drop a few volts AC off BEFORE rectification.
I prefer the 5 watt zener diode method myself.

[frus]

but wouldn't that be almost equivalent to putting a 5Y3? especially the resistor method
If he likes the sound, maybe he could just increase the cathode resistor a bit, so it would bias colder