SITE UPDATE: Subscriptions are now available, for image uploads and no ads. Check the sticky thread in Recent Discussions for more info.

AC30 with 2 el84s pulled - Rectifier options?

Measured voltages & bias with 4 el84s, came out as 15.4 watts/ valve, 128 %

Pulled 2 el84s, so now I guess it's an ac15, and changed the cathode bias scheme to accommodate - it's now two pairs, each biased with a 120r/100uf pair.

I've switched from a 5AR4 to a 5V4G to stop the B+ rising too much, it's gone up by 15v (thought I think 3 of those were the wall voltage going up in the time it took me to re-wire the cathode bias scheme) which puts the 2 el84s at 16.9 watts/ valve, 140%. And that feels a bit reckless.

Is there another rectifier that'll drop in and sag things a little more? 5Y3? I've also got a voltage bucking transformer that'd knock 12v off the mains, but I wouldn't mind a bit more sag anyway....

As to the "why" of it... I want to put a celestion blue in, it's a 1x12 combo...
0reaction image LOL 0reaction image Wow! 0reaction image Wisdom

Comments

  • ICBMICBM Frets: 61637
    A 5Y3 should do what you want - with only two EL84s the current draw is within the correct range.

    16W is a bit reckless, but that's what Vox always biased them at, and they do seem to hold up OK.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • CirrusCirrus Frets: 7349
    Great, thanks @ICBM ;

    There's a few fair priced NOS ones on eBay, I see there are different glass shapes and also read that the modern production might not drop as much voltage. I'll pick one at random and slightly lament that the Brimar 5v4g that has been waiting in my drawer for the last 6 years is going to go back in the box.

    I'm also reading that the old ac15s connected the OT centre tap after the choke, which would drop a few more volts, but have my doubts about the ac30 choke holding up even with only 2 el84s...
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
Sign In or Register to comment.