"Fiddy" 50-watt build log

[martin manning]

I understand elevating the heater voltage above ground to reduce hum but I have never heard of connecting the heater center tap or artificial center tap to the output transformer secondary.

Not sure where youi saw that Tom... in this case the heater voltage was temporarily connected to the OT secondary as a source of AC voltage to use in testing the OT.

[ToneMerc]

I am feeling kind of dense about this.

I understand elevating the heater voltage above ground to reduce hum but I have never heard of connecting the heater center tap or artificial center tap to the output transformer secondary.

What is the theory behind that?

Testing the integrity of the OT by inserting an AC voltage on it's secondary and comparing voltages at each end of the primary winding.

TM

[Structo]

Yes, that 6.73vac was with the filament winding (both legs) connected to the OT secondary.

I did indeed reconnect 100R resistors as an artificial CT last night, and successfully booted up and played for over an hour, quietly, with no trouble. Baby is still quiet as a mouse in terms of hum and hiss.

I

Oh OK, that makes sense that he was just using the heater voltage to test the OT.
I thought I was missing something there.
My brain is not fully functioning but without the pain killers, my shoulder pain would be unbearable.

[xtian]

Hey, man, we share parts around here; don't see why we shouldn't share drugs...

[Structo]

hehehehe, sorry but the percocets barely touch the pain I am in.

What's weird is that I didn't injure my shoulder, it just slowly happened.

Physical Therapy starting Monday, god I hate that.

[xtian]

Now building Fiddy #2 using 100-watt Weber iron. Had my first date with the drill press as my turret staking machine. Awesome. So easy. So fast, the fun only lasted about three minutes.

Turret board populated. Aren't you always tempted to quit at this point, when it's just beautiful artwork, and who's to say you made an error?

[ampmike]

Wow!!!Very nice clean build.Did I say tidy?Looks like a keeper Bro,Good Luck,Mikey

[Reeltarded]

Turret board populated. Aren't you always tempted to quit at this point, when it's just beautiful artwork, and who's to say you made an error?

lmao.. ME!

You didn't even dab the exit end of the PI to V5 coupler.

[Colossal]

I like the board layout. Very economical. Yes, it's always good when the boards are made and you can step back and look at your handiwork! There is art in the process for sure.

As said of Zen, the journey is in the Way not the destination.

[xtian]

You didn't even dab the exit end of the PI to V5 coupler.

Dude--hold your tongue! Left some unsoldered for attaching to chassis wires! I'm sure my errors are far more subtle.

[Reeltarded]

Just poking! I love it!

[xtian]

Wondering about this, from Paul Ruby's startup guide <http://www.paulrubyamps.com/info.html#FirstPowerUp>:

You can use this pre-choke cap to adjust B+ under load to some point between the 90% and 140% of the VAC.

In the 1987 schematic, the pre-choke cap is 100uF. How can adjusting this value affect the B+ DC under load?

[martin manning]

This is messing with the RC time constant where the R is the equivalent load resistance drawing current from the reservoir. See: http://www.valvewizard.co.uk/psu.html

[xtian]

Finished the build. Voltages look good; a bit lower than my last build. Plates are at 402v and bias is set to 38ma (about 60%). Sounds great, but has too much hum when you turn up the volume much. Chopsticking didn't reveal anything.

Gonna rest my brain for a while.

[M Fowler]

I missed something along the way, what kind of amp is this?