HarmonyoftheSpheres wrote:
I have about 370V on my EL84 pins 7, as I've noticed is also the case with a few others commenting on the forum. The TC-15 literature gives a significantly lower value, 295 I think. I've been running JJs with no issues at my 370V.
IIRC that's only slightly higher than the Vox and Matchless amps that the TC-15 is closely related to. Somewhere around 330V to 350V is probably a good voltage range to aim for. 370V is a little high in any case.
HarmonyoftheSpheres wrote:
But I'm wanting to replace my JJ EL84s with some NOS Amperex, which are recommended to not be used at more than about 340V. Am I destined to burn out my nice Amperex tubes?
Don't forget that all the voltages given in tube specs are
relative to the cathode. So let's say you bias your amp with the cathode at a fairly typical 12V. That means you can run those tubes safely up to 352V on the anodes.
HarmonyoftheSpheres wrote:
Could I decrease that voltage to say 340 without losing the great sound of the TC-15?
In my experience most EL84s will sound richer at the slightly lower voltage. You don't want to go too far lower than that, or the amp will start to lose crispness and headroom.
HarmonyoftheSpheres wrote:
I am using a JJ rectifier, so another option might be to replace that with a NOS 5AR4.
I thought that trick only applied to NOS 5Y3s vs Sovtek 5Y3s. I might be wrong about that though...
HarmonyoftheSpheres wrote:
Since I can't easily reduce my house voltage, would it be worth trying a NOS rectifier before adding a Zener to the circuit?
What's really important is that your heater voltage shouldn't be more than + or -10% out from 6.3V AC, or your tube lifetime will be reduced. In other words it should be below 7V AC. FYI you can in effect reduce your house voltage, by putting in a Vintage Voltage Adapter -
www.geofex.com/Article_Folders/vintvolt/vintvolt.htm Just bear in mind if you use one of these, your heater voltage still mustn't be allowed to go more than 10% below the 6.3V AC norm.
coco wrote:
A 5W zener is quite cheap in comparison.
+1 However, I would feel safer with a 10W or 12W zener (placed in line with the B+ rail after the first filter cap). Either that or divide the voltage drop between a couple of 5W zeners. So for example you could have two 9V zeners in series for an 18V drop.
HTH