Finally installed speedball

[Bloozestringer]

I think I built this Crack in 2017 IIRC. Been sitting on the speedball since then and finally decided I might as well, even though my hearing sucks.

The only real trouble I ran not was the 12AU7 filament wire would not go between the terminal strip and the standoff, so I unsoldered it from the 12AU7 tube socket and was able to bend it more toward the socket. Looks like shite and I may redo the heater wiring to the 9 pin with some 18awg ptfe wire I have that’s about 1/4 the thickness of the stock stuff. But for now all the voltages look good and it plays music. There was a slight low level hum in the left channel independent of  the volume pot and rcas being disconnected. It did lower a little more over the first  30 minutes but I’m wondering if it’s just WiFi everywhere, the severely microphonic 6080, or possibly that heater wire that’s now sitting near the output pins on the 12AU7?

[Bloozestringer]

Some other pics.

[Paul Birkeland]

The back side of the panel is painted/powder coated.  This needs to be scraped off for the volume pot, terminal 3 where it touches the chassis, and the safety ground by the IEC power entry module.

It is a little alarming to see that your safety ground looks to be insulated from the chassis, which is far from safe.

[Bloozestringer]

The back side of the panel is painted/powder coated.  This needs to be scraped off for the volume pot, terminal 3 where it touches the chassis, and the safety ground by the IEC power entry module.

It is a little alarming to see that your safety ground looks to be insulated from the chassis, which is far from safe.

I used a dremel and every terminal strip mount and the safety ground  and the volume pot had the powder coating removed. I just didn’t take any more off than the size of the washers. If you look closely at the terminal strip mount/socket mount tab between pins 1 and 8 of the octal socket you can see where  the spot is slightly larger than the tab. Safety ground always concerns me more than anything. I verified them all this afternoon as I was adding the speedball.

Edit: I just went and double checked because. With a clip on the ground prong of the IEC jack every bolt head, and the volume pot all are at zero ohms.

Here’s a pic of the safety ground which has the same size as the internal tooth washer removed and of terminal 3. 

[Paul Birkeland]

 It could be helpful to post your Speedball voltages just to double check things.

[Bloozestringer]

I was planning on checking all voltages throughout the amp tonight for my records, if I can find the time. I will report back all of them for your review.

[Bloozestringer]

Voltages:

Mains: 123.9VAC

OA: 75.2V
IA:  187.0V
B: 0.4mV
IB: 187.0V
OB: 72.5V

OA: 104.0V
OB: 105.1V
G: 0.5mV
B+: 187.0V

Resistance checks all check out as well.

[Paul Birkeland]

With stuff like this, you can poke around the circuit with a wooden chopstick and a cheap pair of headphones plugged into the amp to see if you can actuate the noise by putting pressure on a certain part of the amp, and this can help narrow down where the problem is.  It would also help to listen to a 60Hz and 120Hz tone (or 50Hz/100Hz if you're in a 50Hz mains country) to see which noise is what you're hearing.

[Bloozestringer]

I e poked around with a chopstick to no avail. The 6080 tube is highly microphonic and just barely touching it makes all sorts of humming and ringing noises. The 12au7 is slightly microphonic, but no worse than any other I’ve used. I’ll try swapping tubes as well as I have a stack of 6080’s now and this hum has always been there since the beginning. It’s not a very loud hum and once the music is playing I don’t even hear it  even I. The quiet passages. I have to really concentrate to hear it much at all. The benefits of getting old!  I’ll continue to peruse it as I get time and ask questions. Thanks Paul for all  recommendations.