HRP_50

[Steveo]

Hello, does the fx loop work good when coming from the master volume instead of the treble pot into the fx loop then back out to the master volume pot? Ive always wondered.

[maint_tech]

@PDF64 - 3K2 xfmr, I just thought having the safety resistor on the main spkr out switched pole made sense i case forget to plug spkr in or bad cable.
@ Steveo - I dunno. I have never tried a passive fx loop either way and this is how Mark Fowler did it on the units he built, so that is what I went with. He has said in the past it works well, so I'll find out and report.

[maint_tech]

Well got the chassis done just in time for a present to myself. Wow, this thing does just grab you by the yaya's! I'll be suffering (more) hearing damage, no doubt. I don't want to change a thing in it, thanks for the encouragement Mark. Yes it is bright, but not ice pick bright, just easy to get out a screecher bright. And if the axe isn't in tune, its gonna let you know it ain't happy!
Damn, more woodwork, gotta build a box.
FX loop works great coming off the Volume, have not tried to relocate it to the treble pot yet, having too much fun.
Presence and depth controls are a treat.

[ChopSauce]

Congrats for your build and merry Christmas: that's something of a present!

[M Fowler]

Looks great and enjoy that beauty.

Mark

[dcribbs1412]

Nice build!
Have to ask
What's the Neon bulb on V2 for?
Like Diode clipping?

D

[Auke]

Very nice build indeed.

When I was watching your pictures I looked like you placed the 100 pF cap on the 220K resistors as per schematic it is placed over the plate resistors off the PI.

With regards,

Auke

[tmknight]

...What's the Neon bulb on V2 for?
Like Diode clipping?

http://www.valvewizard.co.uk/dccf.html

[dcribbs1412]

...What's the Neon bulb on V2 for?
Like Diode clipping?

http://www.valvewizard.co.uk/dccf.html

Gottcha
I think Jim Kelley used something similar using diodes for "clamping"

Regarding the diodes, they're really not clippers as much as they're voltage clamps - to keep the grids from going too far negative. That causes a shift in duty cycle at lower frequencies (asymmetrical), gives a flubby, compression-like effect. It's more of a DC thing than an AC thing. A grid stopper is the latter-day method of dealing with the issue.

[martin manning]

The neon bulb or diode/resistor from g to k on a direct-coupled CF is purely a protective measure, not for sound. From the Valve Wizard page linked above:
"...on start up, the grid will immediately rise to HT potential while the cathode is still cold, at ground potential. It is not unknown for this to cause arcing between the electrodes, and rapid destruction of the valve, even when a standby switch is used..."

[maint_tech]

Thanks for all the comments!
Ya the neon glows for a bit when everything is warming up keeps the CF from an early demise. I think this one flashes at about 67 volts or so.

you placed the 100 pF cap on the 220K resistors as per schematic it is placed over the plate resistors off the PI

Ya I gotta move that, thanks. Fixed Skat and layout to reflect in original post.
Haven't had any signs of oscillation tho...
Man this thing does wail!