Humdinger question

[passfan]

I was just wondering if it had the varnish coating on it and if so did you sand it off before soldering ? It is also a good idea to scuff up the copper so it holds solder better. If one of those vibrates loose from sitting on top of a speaker cabinet you'll be doing all this again.

[surfsup]

I cut the copper and ran each run down into the turret from both sides so there's quite a bit of contact.

Also, I'm not opposed to dropping the EL84 socket (I don't really plan to use that tube much). I can use that to wire up a FX loop possibly later. do you think it would help just dumping that socket entirely and running only the octal?

[martin manning]

...I'm not opposed to dropping the EL84 socket (I don't really plan to use that tube much). I can use that to wire up a FX loop possibly later. do you think it would help just dumping that socket entirely and running only the octal?

Running parallel sockets with only one in use at a time means that you either have longer leads than necessary, or you have shorter leads with a small antenna attached to each tube pin. In both cases the leads to the unused socket pierce the shield created by the metal chassis. The worst case is the grid, so after you reroute the grid wire from the board directly to the octal socket, you might try removing the leads to the 9-pin, beginning with the grid lead, and see what effect that has.

[surfsup]

Okay I haven't dropped the EL84 socket (yet)...still thinking about it. I have an update:

I installed a "humdinger" as per the second pic (updated):

http://chicagocadcam.com/ChrisHahn/amp.html

The hum/noise is now significantly less. I can crank everything and speak at normal level without having to yell above this massive wall of humming/static from the amp.

The hum/hiss has subsided, but still too much. My main concern now, however, is the voltages are low. Here are some readings:

WITH ALL TUBES (EL34 bias=54)
B0 - 207.2 AC
B+ - 238.0 DC
B1 - 232.2 DC
B2 - 225.7
B3 - 212.4

WITH NO PT but both 12ax7s are inserted
B0 - 215.5 AC
B+ - 269.3 DC
B1 - 268.7 DC
B2 - 264.4
B3 - 248.9

I also swapped the 12ax7s for new ones, both. So I don't understand how B can drop 7V like that...

Regarding static/humming: If I have all the knobs at noon with MVol at 3pm it is basically fine. The moment I turn MV past 3pm toward max the static and hum start to become prevalent. Way better than before but I'd still like to get it less but totally playable now. Thanks for looking!

[martin manning]

If you are comparing voltages against the schematic, those values are for an EL84; perhaps that is some or most of the difference. In fact tubes of the same type will vary enough in their characteristics to cause noticeable voltages changes.

There is nothing surprising about an increase in supply voltage with the power tube removed. The decreased load reduces the voltage drop through the transformer secondary and the first dropping resistor.

Re your hum, why don't you try routing the heater wiring more like the published layout, against the back of the chassis as shown below (twisted, of course). Keep the purple wires elevated for a bit so they are well away from the heater wires.

I have to say, the original layout is known to work well without the artificial center tap, so I think it's a pretty good bet that your non-standard layout is causing the problems you are having here.