Power Up; Time to push some electrons!

[gearhead]

I'm 99% sure they're shorting jacks. I now recall thinking about that (one output jack without a cord plugged in), way before wiring them in. Completely slipped my mind and just aped the common layout.

[gearhead]

Hmm, that wasn't it. Volume is extremely low, like the life is squeezed out of it.

I am getting this constant hum though, with or without the instrument jack inserted. Same, constant volume.


Still checking for continuity. If I do check for voltages with the standby off, by the time I hit V2 plate, and don't switch off first, there is a LOUD pop. There seems to be plenty of juice at that point, and it's getting thru the power amplifier to the speakers. Guess my prob is between the input and V2?

Do have a q from the Francesca pics: what are those extra wires running from the impedence selecter lugs? The secondaries from the OT connect to three lugs(4, 8, 16) but there are some extra wires that are on each lug and wrap around out of site beneath the selecter pot?

[Allynmey]

gotta scope?

Try to take some close up hi def pics going right across the preamp then the power board, them the output tubes and then pot connections. The pot connection pics should be straight on to see correctly. It should be easy!

[gearhead]

Wish I did.

Pics of controls and preamp/PI:

[Bob-I]

I don't see any ground connection on the pots. Maybe it's the angle of the pics but you need to make sure that's got a solid ground connection.

[Allynmey]

Check to see if your tonestack pots leads are touching the pot covers. A few look very close. Measure the ground side of your Cathode resistors and the chassis for resistance make sure it's zero on your preamp tubes. A lot of those solder joints could be reheated. Loud hum can come from a heater wire touching a plate on a tube socket and injecting a 60 cycle signal.

[gearhead]

The ground buss, like the way Ken built them, isn't connected to a drilled, grounded lug. Each of the pots does have a lug that the lower buss bar connects to. I will probably eventually do the drill thing, but I assure you each and every one has continuity to chassis. Since I fired this one up, have spent at least 6 hours just checking for shorts to ground.

[Bob-I]

Your best troubleshooting is to build a stethoscope and listen.

Get a 1/4" in line jack, a .1uF 600V cap and 2 alligator clips. Connect the cap to the hot lead of the jack, the other end to an alligator clip. Connect the other alligator clip to the ground of the jack.

Now connect the jack to a working amp's input, the ground clip of the stethoscope to the chassis and plug a sound source into the input of the amp. I use a CD player as a sound source, and my stereo as the listening amp.

Take the hot lead of the stethoscope, the one with the cap on it and touch it to points along the signal path ....

1) Grid of V1a... sound? go to....
2) plate of V1a ... sound? go to...
3) Grid of V2a ....
4) plate of V2a
5) PI input
6) Each PI grid
7) each PI plate

When you hit the location where there's no sound or low volume sound there's your trouble spot.

[gearhead]

WHOO HOO, it's up and running!

I redid a couple dozen joints in the preamp section, and one of them must have been it! It was not a short to ground, but an open. Doh.

Am going to redo a whole number of joints tomorrow. Especially near components, I was far too hesitant in applying heat, not wanting to damage them. Harkens back from my stompbox days where it was easy to fry low power components.

Considering all the efforts for noise reduction folks seem to pursue, mine is quite acceptable.

Thanks all!

Edited to add: I have the parts for a stethoscope, and will put it together soon. There are some things that I already want to change (volume and voicing).

[Firestorm]

GREAT! I was hoping it would turn out to be something benign. Of course, since you shotgunned it, we'll never know which solder joint we've all been staring at was the culprit.
Do build that "stethoscope." Incredibly useful tool.
Congrats.

[Bob-I]

Great news. Congrats on finding the solder joints, they'll get you every time.

[gearhead]

Spent a good deal of time on it this weekend, fancy that!

Better tubes do make a -Huge- difference. Have a mix of Brimar and NOS JAN Phillips 12AX7s in there now, along with a set of EL-34 Tesla's. Gonna pop in the Xf3 Mullards soon. Still dialing in the tone/sound; haven't gotten to changing any components because wanted to try everthing else first.

One thing that's got me a bit puzzled is that mine seems a bit too much under control. It definitely roars and would never think this about any other amp than a trainwreck. I can get feedback, but have to wrestle the neck a bit to get it. Was expecting to have to quiet the beast down, but that's not the case so far.

Is there anyway to make it LESS stable? LOL.

Thanks all!

[Ron Worley]

Not to hijack the thread at all... but I am following what I see in Franny, and installed shorting jacks in both outputs....

Is this incorrect? Why does it work on the real Wreck?

Ron

[gearhead]

Yes, you are hijacking my thread.

Go ahead, I'm gonna start a new one anyway.

[Ron Worley]

Sorry, I will start a new one. Mea Culpa...

Ron