Speedball upgrade fail - please help

[Paul Birkeland]

Those are 75K and 33K resistors, yes. 

[vincentquy]

I just finish the large board speedball upgrade. Sounds really awesome.
However, the measurement is as follow:
OA 90V
OB 105V
G 0 V
B+ 180V

OB is a lot higher than OA, is that normal?

Also: are these capacitor similar to those come with the stock Crack?
https://www.partsconnexion.com/NICHICON-76189.html

[Deke609]

are these capacitor similar to those come with the stock Crack?

Those are snap-in capacitors for pcb boards. The very short leads will make installing them very difficult. But electrically they should work like any other good 220uF 250VDC cap.

PB may want to chime in here to confirm, but generally BH specs capacitors (and other parts) with long operational life. The following link will take you to a search page on Mouser showing in stock options for Nichicon radially leaded (what you want) 220Uf 250VDC caps: http://www.mouser.com/Nichicon/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/Aluminum-Electrolytic-Capacitors-Radial-Leaded/_/N-75hqwZ1yzvvqx?P=1z0zlbmZ1z0wrjqZ1yzs9nv 

If you scroll to the right you'll see the "Life" column showing how long the various caps are expected to perform within spec at their max rating. The figures range from 1K to 10K hours - i.e., some caps will last 10 times longer than others.

cheers, Derek

[Paul Birkeland]

OA 90V
OB 105V
OB is a lot higher than OA, is that normal?

You'll probably find that OA and OB on the small board are a little different, and that difference is carried over to the 6080 and reflected in the operation of the big PC board.  Some variation here doesn't make much of a difference.

Also: are these capacitor similar to those come with the stock Crack?
https://www.partsconnexion.com/NICHICON-76189.html

We would try not to use a part with such a low life rating.  I would consider those a downgrade from what we usually provide. As Derek also mentioned, mounting snap-in capacitors on terminal strips isn't always the easiest thing to do either.

[vincentquy]

@Deke609: Thank you for the information!

@Paul: I see. Do you think the Voltage difference is the reason why my left channel is louder than right channel? I used APO to correct the imbalance and find that left channel is about 3dB louder than right channel.

[Paul Birkeland]

What are the OA/OB values on the small board? 

How much rotation are you using on your volume pot?  They can be a bit imbalanced at low volume levels, and a mod for this is provided in our FAQ.

[vincentquy]

I just measure again:
Small board;
OA: 63V
OB: 77V

Large board:
OA: 107V
OB: 99V

I use the volume pot at around 10 - 2 o'clock. The imbalance is consistent throughout the range.
My headphone is ZMF Aeolus, rated at 300 ohms.

[Paul Birkeland]

Yeah, there's a reasonable difference on the plates of the 12AU7, and since the circuit is directly coupled, this also appears on the 6080.

These are DC differences though, the AC performance of the circuit will not show such large differences.

[vincentquy]

I use the volume pot at around 10 - 2 o'clock. The imbalance is consistent throughout the volume range.
My headphone is ZMF Aeolus, rated at 300 ohms.

It's really not a big deal since I can use APO equalizer. However, if needed what can I do? Do you think the volume pot mod can correct it?

[Paul Birkeland]

If the pot is all the way up, is the channel imbalance still there?  If so,  I would be most suspicious of a solder joint issue in the amp. 

Can you post a photo of your small Speedball board installed in the amp?

[vincentquy]

Here it is, I checked all the solder joints.

[Paul Birkeland]

Other than the LEDs, those joints could use a bit more solder and more heat.  You want to see the solder wick through the holes to the other side if possible.  The LEDs have such low thermal mass that the soldering process is really quick, and that's why they look good compared to the other joints.

If you look at the photo you posted, notice that the solder joint on Q1A closest to the 237 ohm resistor looks like it has no solder in it.  You'll want to heat up that joint till the solder flows through the hole. 

As far as the channel imbalance goes, if it's present with the volume pot all the way up and it's more than a dB or two, then there's likely a solder joint in the amp that's not behaving.  You could also try different tubes, though a bad tube will usually make itself known with problematic voltages.

[vincentquy]

I see. I will give it a try.

[Deluk]

I always solder the top side as well as the bottom. From other pictures around the forum this doesn't seem to be the norm. The topside usually only needs a very small amount of solder to make a good meniscus around the component leg to finish the joint. The wire connections here look as if the solder has hardly flowed at all, very dry and dirty. You can prop up the wire with a folded up tissue , or anything really, to stop the wire dropping out when you heat the joint.

[vincentquy]

I have check and re-solder to make sure the joints have enough tin. The problem still persists.
However, I wonder if a blown capacitor can affect voltage. One of my capacitor looks like this.