Crack - installed Speedball, now balance to right, higher hum, distorted vocals

[cavedriver]

Hi everyone,

Ok, everything went fine with the base crack build, spent a day listening, embarked on Speedball.  Boards soldered up fine, except had to clean leads to one heat sink-mounted transistor where I used too much solder and had to clean some off.  Voltages all checked out, but when I moved on to listening it was clear that the right channel is louder and there is a new level of hum when no music is playing, still inaudible at low volumes but then the hum is audible when you crank up the volume.  The base Crack had zero hum.  It is also apparent that the vocals in music are buzzy and distorted.  Finally, I went back and checked the voltages for the end of the Speedball build and now they are no longer in spec.  Where 12U to OB was initally right at 100 V, as was OA, now OB is at 157 V (!) and OA has dropped to 97 V.  G is still at 0.7 mV, which is what it was initially, and B+ has now dropped to 166 V.  This was all after less than an hour of listening.  I also think that the heat sink on the transistor by OB is hotter than the one by OA, but I have not checked the temperature yet.  The OB transistor is not the one I had to clean the solder off the leads- that was OA.  Ok, have at it!  What could it be?

On a positive side note I raided my grandfather's Scott tube equipment that I have awaiting rebuilds and found two good Telefunken 12AU7 tubes in a Scott 350 FM receiver that isn't getting rebuilt, one each of the smooth plate and the ribbed plate.  Both are working great, along with a Genalex Gold Lion that I got with a Bravo amp.  At least this partially offsets the trouble with the Speedball. 

[cavedriver]

I should add that the Crack is a 1.1 and the Speedball is a 1.1, however mine does not look like the current pictures on the website.  On mine the boards for the preamp tube are a single smaller board.  I suppose there are two different "1.1" versions?

[Paul Birkeland]

This is the kind of behavior we would expect from a solder joint that isn't 100%.  It's not necessarily a solder joint on the Speedball though, as often we find the installation of the Speedball itself can disturb connections in the amp that weren't quite 100% prior to starting that work. 

Can you give me OA and OB on both the large and the small boards?  You have given some voltages, but it's not 100% clear which are from where.

[cavedriver]

oh right, I forgot the small (input tube) board also had an OA and OB.  I was giving voltages for 12U to the large board OA, G, B and OB.  I will let the amp warm up and re-measure both the large and small board voltages later today.  Thanks Paul!

[cavedriver]

ok, after visually re-inspecting all the welds I can't find the bad one, but here's what's strange- now I have balanced stereo sound but the amp sounds like it's literally on crack.  Where the base amp was relatively flat and accurate and didn't impart a lot of "headphonics" to the music, now I have all the trademarks of tube amplification- everything is whoopy and very dynamic and a bit distorted and more fun to listen to, but also not what I expected an OTL amp to sound like.  Some of it's good but I'm worried I still have a weak connection.  The voltages have also changed and I'm not happy that this could mean that I'm going to have a very hard to find bad solder joint.  Also, the hum has changed.  With nothing playing the amount of hum has decreased, but is still more than with the base amp and now I've noticed a faint ringing that sounds like a clanging if I tap on the amp anywhere.  Here are the voltages:
Small board:
OA        73.7
IA    173.2
B-A/B  0.5 mV
IB  173.0
OB   77.9
Large board:
OA   100.0
OB   103.1
G    0.6 mV
B+  172.5
So, it seems the OB voltage on the large board has come down some in correspondence with the more balanced sound.  Apparently whatever bad joint I had is now working a little better?  Is the 3V out of range error enough to still be worried, and assuming I would still want to make sure I don't have a borderline weld that could fail, where would I look?  Mostly of my welds look ok.  I've been doing soldering since I was a kid but I tend to overdo it so more joints have too much solder than too little.  If there are any joints I'm specifically worried about it would be terminals 1 through 5 where all the resoldering resulted in excess solder accumulating on the lower connections that I didn't bother to remove.  Yesterday after I posted the voltages I did go poke around under the large board looking for bad connections and maybe I pressured a wire in a good way.

[Paul Birkeland]

You need to reflow all of the solder joints in your amp.

[cavedriver]

did I do something to offend?  that will take hours with no sense of priority and I will have to disassemble some components to get to welds that are buried, further risking damage to those components.  I didn't see any mention of easily damaged components other than the transformer, which I am absolutely not going to reflow because the base amp was working fine and none of those welds were touched by the speedball.  Won't i risk damaging the transistors if I put too much heat into them?  i would think I would want to start with the grounds and everything on the left (OB?) channel??

[Paul Birkeland]

did I do something to offend?  that will take hours with no sense of priority

I timed myself and I can do it in about 12 minutes.  I think you are talking 30 minutes tops.  The symptoms you have are typical for a flaky solder joint, hence my recommendation to just reheat them all and to be sure that the solder flows out well.

and I will have to disassemble some components to get to welds that are buried, further risking damage to those components. 

Yes, you will need to unscrew the boards to reach the solder joints on the bottom side of each board anyway, so this will afford you ample opportunity to get to the joints on the 9 pin socket and terminal strips underneath the boards.

I didn't see any mention of easily damaged components other than the transformer, which I am absolutely not going to reflow because the base amp was working fine and none of those welds were touched by the speedball. 

Yes, you touched most of the solder joints installing the Speedball.  Things move around and solder joints that weren't 100% solid avail themselves after being jostled during the installation procedure.  What you are experiencing is relatively common and is 90% of the time resolved by reflowing the solder joints in the amp.  The power transformer will definitely tolerate reflowing of the solder joints.

Won't i risk damaging the transistors if I put too much heat into them?  i would think I would want to start with the grounds and everything on the left (OB?) channel??

The transistors? No, and in fact it's very common that the TIP50C dumps the heat from a soldering iron into the heatsink well enough that it's difficult to solder, especially on the middle leg.  The LEDs are about the only components that aren't tolerant to a ton of heat, so if you want to skip on any solder joints, those would be the only ones.  The issue that you are having absolutely does not indicate any issues with the LEDs themselves, which is something we often find folks focusing on.

[Doc B.]

You have not offended anyone. We are simply offering advice based upon 25 years of experience giving tech support for these kits. I invite folks to go back through the Crack tech support posts on this forum. I think you will find reflowing a pretty consistent item in the resolution of issues. Reflowing every joint takes just a few minutes. This saves you time vs. trying to guess which specific connection (or connections) is the problem, and solves the issue in 99% of the cases we see.

[cavedriver]

Aren't you going to ask me which tube I have installed since I've mentioned that I have a total of 4 different 12AU7's, including two vintage Telefunken tubes?  I was swapping these tubes and checking voltages and I am seeing that one of the Telefunken tubes always shows the higher voltages at both OB pins (~103 V on the large board and ~78 V on the small board).  When I put in the GE, Gold Lion, or the other Telefunken tubes the voltages on the two channels are almost equal.  I found another thread in this forum discussing how these voltages will rise as the 12AU7 tube wears out.  Doesn't this suggest that one of the Telefunken tubes that I recovered from my grandfather's 1960's Scott FM receiver might be wearing out?  I may still have a bad solder connection as well, but also could the one time the OB voltage jumped to 150 V be because I had not installed one of the tubes fully, since it has not happened again?

[oguinn]

I mean… if it happens with one tube and none of the others it sounds like you’ve solved it? If it’s intermittent, reflow the solder joints. They’re giving you the advice they’d give anybody with the information you provided in your first post. You tacked the other tubes on as an aside. These things are typical of a bad solder joint since it sounds more intermittent than regular. You’ve spent more time typing replies than it would’ve taken you to reflow the amp.

[Deke609]

Aren't you going to ask me which tube I have installed since I've mentioned that I have a total of 4 different 12AU7's, including two vintage Telefunken tubes? 

I think it's assumed that one uses a known working tube to do testing and only after passing the tests moves on to tube rolling. I would do all voltage checks with the stock supplied tubes (which I believe BH checks before shipping). That way one takes one potential problem source (bad/weak tube) out of the equation and can just focus on whether the amp is working.

cheers, Derek

[Paul Birkeland]

Doesn't this suggest that one of the Telefunken tubes that I recovered from my grandfather's 1960's Scott FM receiver might be wearing out?  I may still have a bad solder connection as well, but also could the one time the OB voltage jumped to 150 V be because I had not installed one of the tubes fully, since it has not happened again?

This is rather unlikely.  Installing and removing tubes also moves the solder joints in the amp around.

[cavedriver]

Well, I wasn't really worrying about which tube I had installed since all the tubes work in my only other working tube amp, which is a Bravo V2 amp that admittedly is known for it's high distortion levels and perhaps not being a reliable test.  So how *does* one determine when they have a bad tube without owning a tube checker?  Say you have an amp and eventually a tube wears out?  Will you hear it?  Short of owning a tube checker, is re-doing this voltage checking from the amp construction an effective way to determine when a tube is burned out?

Fwiw, i probably still have a bad connection and will still be reflowing most of the joints.  Rotating back through the tubes, the GE (came from Bottlehead) and one of the Telefunkens show voltages within range, while the Gold Lion (which I have maybe 200-400 hours on with the Bravo amp) and the other Telefunken have high voltages.  Or does tube performance vary so much from manufacturer to manufacturer that all these tubes could still be ok and I'm just seeing the tube to tube variation?

[Paul Birkeland]

I wouldn't suggest checking 12AU7s with your amp until you're 100% confident about its operation.  With the amp working properly, the plate voltages on the 12AU7 will rise as the tube wears out, and one would expect a Crack with a Speedball to show ~95+V on on terminals 1 and 5 for a worn out 12AU7.

The 12AU7 we sent you with the kit was tested for Gm, so I would use that for the build and debugging if at all possible.