Advice needed- best way to lower plate voltage

[Prairie Dawg]

Oh, well if you still want to use the choke, I'd put it ahead of the first filter caps, and add another filter cap in there. But that's starting to get more complicated and take up more space.

450V still seems awfully high. Even if you bypassed the droppers, there shouldn't be any voltage above 400 in there... What's your line voltage? Or maybe Mesa bumped up the plate voltage for the Rev.B and that's why they increased the dropper resistors, to keep the screen voltage under control.

I tend to agree-even 400v is stretching the envelope out of shape with today's EL84s....now, if you had a dandy set of new old stock 7189s you probably could run them that hard but they're pretty much made of unobtainium these days-at least for people who ain't J. Paul Getty or Donald Trump.

[jutsin]

Okay an update:
I've replaced the 5440 ohms worth of resistors in series and moved the choke to just after the standby switch. I now have: (all measurements to ground)
Plate- 420V
Screen- 315V
The plate is still a bit high, so I may try the zener diode. any thoughts/input?

[tubeswell]

The plate is still a bit high, so I may try the zener diode. any thoughts/input?

Try a string of (say 4-6 x) 12V 5W zeners in series mounted on a tag strip - banded end(s) pointing to ground.

[ThermionicScott]

Okay an update:
I've replaced the 5440 ohms worth of resistors in series and moved the choke to just after the standby switch. I now have: (all measurements to ground)
Plate- 420V
Screen- 315V
The plate is still a bit high, so I may try the zener diode. any thoughts/input?

That might be good enough, I think. How hot are they biased at this point?

- Scott

[Prairie Dawg]

Okay an update:
I've replaced the 5440 ohms worth of resistors in series and moved the choke to just after the standby switch. I now have: (all measurements to ground)
Plate- 420V
Screen- 315V
The plate is still a bit high, so I may try the zener diode. any thoughts/input?

If you've got the real estate, go for it.

[imaradiostar]

I wrote a reply the other night and deleted it before posting because I didn't wanna sound mean...but what are you doing? I think you may be overestimating the effect of a choke on the sound.

I think the DC series amps were some other better mesas for your dollar- decent clean sounds, not as crunchy as a dual rect but most people wouldn't want that anyway! I've recorded them on a number of occasions and have known many people that love them in recording and live settings.

It sounds to me like you're trying to make it into a different amp entirely. There's nothing wrong with that of course...I'd just start with a different amp if I wanted a different amp.

I modded a friend's DC-5 so that the lead channel more closely resembles a dual rect or bogner- put the gain after the first stage, changed cathode and plate resistor values, etc- the result was pretty great, much more what my friend was looking for. It was neat to have a "dual rect" style lead channel while retaining a more fendery clean channel than most mesas are capable of.

If you want lower plate voltage the zener suggestion was excellent. Keep in mind it'll lower voltages throughout the amp and you may or may not like the effect. You could also add a variable plate voltage circuit- lots of those out there now sold as little easy to use kits.

If it were my project I'd mildly mod the mesa or keep it stock and build a different amp to achieve my goals. Of course I have a lot of parts to use up before I'm old and grey so I'm not afraid to build a new amp.

Of course don't let me tell you what to do! Have fun!

jamie