New build startup issues

[geetarpicker]

Could a partial short on the filaments (tube, wiring, ?) saturate the power transformer enough to also sag the separate B+ winding?

Seems all the voltages are low, which could still point to the PT itself.

I remember Allyn talking about having odd low voltages on a build and it turned out to be a lamp in the house pulling his workbench area down!
It wasn't even the amp at fault.

Just for grins, what is your wall voltage with the amp plugged in and turned on?

[Ron Worley]

Dan-

I will get on this tomorrow (busy tonight). Thanks for the great walk through.

BTW, ditch the bulb limiter???

[Firestorm]

Guys, all of Ron's voltages were taken with the light bulb limiter in series with the power cord. That will knock 'em all way down. The pics are a little fuzzy, but I can tell that he's got three spike protection diodes in series, oriented correctly, between the plate and chassis ground on each tube. I also can't see any other obvious error. If it was me, I'd install the preamp tubes, leave the power tubes out for the moment, and power it up without the limiter. Check the heater voltages (they might be little high with no output tubes in), and check the B+ at the center tap, check the bias voltage on the grid pins, and if everything looks okay, power down, install the EL34s and see what you've really got.

[Moose]

Dan-

I will get on this tomorrow (busy tonight). Thanks for the great walk through.

BTW, ditch the bulb limiter???

If it wasn't glowing full on, you didn't have a dead short. You're fine without the limiter, now.

[skyboltone]

Dan-

I will get on this tomorrow (busy tonight). Thanks for the great walk through.

BTW, ditch the bulb limiter???

I'm with firestorm and others. You're done with the light bulb. The point is to be methodical here. Firestorm may well be correct that the only thing standing between you and a fully functional Express is the limiter. But I doubt it. Just for the sake of education, lets take it one step at a time. Take the darn spike diodes out for now. Make sure that the 6.3 volt winding is working properly. If so, then reconnect the HV and plug in all the pre tubes. If you're good, then add the power tubes. If you get to where you've got -30VDC on the grids and 410VDC or so on the plates you can move to a signal.

[Ron Worley]

It's ALIVE.... The limiter was the culprit.. note to self and all reading..

I powered up with the limiter and added B+ to charge the caps- thought being to not have that big bump when I did it without the limiter.

Powered down, ditched the limiter. Added power, no smoke... waited 2 minutes to make sure the heaters did their thing, then added B+...no smoke, etc.....

It was humming some, so I turned up the volume a bit which added more hum, but tolerable. Twiddled with the tone pots... man they add hum / gain..

Here's the good news:
Bias V -36.37V Max Neg, -29.5V Min Neg
Secondaries= 616V in standby, 613 ON
B+1- 417V
B+2- 407V
B+3- 326V
B+4- 307V
B+5- 291V
Heaters- 6.8V (seems a little high actually)

At this point, I'm thinking "play the damn thing".... So I grabbed a Strat (that's what was handy) and plugged in...

HOLY SHIT... It had a fair amount of hum (but got much better when I backed away from it). I cranked it all the way up.. and my God what a tone... almost uncontrollable..but in a good way.

I peaked under the amp and now I have a different issue- V4 was red plating pretty bad- V5 looked OK. The bias was max negative..

At this point, I have an amp, but further issues... Really happy though.

I suspect either a bad Tube (I may have hurt it in my initial power ups), or (hopefully not) maybe other tranny issues????

I imagine I am going to have to do some hum reduction measures... But it did have the chassis cover off and a 2 shop lights above it...

Progress is progress.... and I think that I am going to have a Martini just to pat myself on the back... thanks mostly to you all....

Moose.... you sell one tough tranny.. I think I pushed the limit on the poor thing...

Ron

[Ron Worley]

The obvious next step is to swap V4 and V5 to see if the red plating follows the tube.

That's on tomorrow's punch list..

[Bob-I]

Congrats on the working amp.

With the red plating, I'd measure the C- right at pin 5. It's possible that it's not getting to the tube itself.

[geetarpicker]

Don't forget you might want to rewire the polarity of your preamp filaments so that only v1 is opposite polarity. This may also help the hum issue.

Cool that it's playing!

GK

[Ron Worley]

Glenn-

I rewired the heaters so that all is in phase.... I know that Franny is "mis-wired", but my Fender training says that this is not right....

I may be missing an important KF subtlety, but I'm not sure that he did not perhaps make a mistake... only you could verify with Annie...

Ron

[Moose]

Congrats on the working amp.

With the red plating, I'd measure the C- right at pin 5. It's possible that it's not getting to the tube itself.

+1


As for the high heater V -- did you check the wall voltage? I bet you have 125V or more. I tend to see 6.5V on 121V wall voltage here in the house, and 405 B+ on the plates, depending on the tubes used.

If the bias voltage IS getting to the tube, you might just need a little more for that set. I've had perfectly "good" tubes be far enough mismatched that one would be way out. I've also seen tubes that took 5V more or 5V less than their contemporaries, meaning I had to bias one quite cold. And with the slightly higher wall voltage, you'll need to be 3mA colder on the bias -- all things being equal.

As for hum, at least now you're looking for normal problems!

[geetarpicker]

"Annie" also has the reversed phase V1 filament just like Francesca.

I just looked at two pics I have of original Liverpools and they both also had some swapping of the phase in the preamp filaments, albiet one also on V1 and one on V2 instead.

Who knows if it makes ANY difference in the hum. When you use the same color to wire up the filaments it's easy to cross them up.

My original Express was originally miswired on the output tubes. Ken originally had the screen feeds coming in on the wrong side of each of the 5 watt 1k resistors. This effectively put them totally out of the circuit. Must have been that way for the first several months before I caught it and corrected it. I first noticed it because they were always cold even after running the amp a while. Funny, it sounded great either way but was probably a bit more of a tube eater the first way. Ken confirmed with me he didn't intend to wire it that way, ooops.

I sometimes wonder if my original GP Soundpage recording track was before I caught the wiring mistake, since that was the first recording I did with the amp when I got it. Can't remember.

[Noel Grassy]

Congrats on the functional "1st build" Ron. I hope tube swapping and minimal fidgeting will getcher toddler motating. It you do flip yer filament phases on V1, let us know if any eggregious noises are cured or created.

[skyboltone]

Well hallelujah Ron. I'm not in the least bit stunned that I had it wrong. Thanks Firestorm. I'm used to using a variac for startup. I had a hard time believing that the lamp could drop that much V. In any case, count me as a winner in the "smarten up" category too!

Dan

[Ron Worley]

Nah, I think I have you all beat in the dumb shit category... I'm a Engineer, but learned almost all digital stuff...... I am coming from dead zero on this analog tube / tranny stuff