Solved: Speedball Voltage Problems

[Justin Scharber]

All,
This is my first post.  I have been following the forums for several months as a "guest" trying to learn as much as I can and finally joined the forums.

I completed my Crack build a couple months ago with no issues.  I took everyone's advice and waited before installing the Speedball upgrade to learn and enjoy the Crack in it's original state.  I'm really enjoying the amp with my HD 650s.

This weekend I completed my Speedball upgrade and seem to be having some voltage problems.  My readings are listed below.  I'm concerned about the negative voltages I'm getting at terminals 6 and 10.  I also measured the voltage rise to the headphone jack during power up; it was 0v to 22v to 0v.  All of my LEDs light up.  I have noticed that the LEDs on the smaller two boards aren't lit as bright as the rest (larger board and A terminals).  I also had someone conduct a visual to make sure they didn't notice any cold solders (although I'm still not ruling that out).

Finally, at a slight risk I plugged in a pair of headphones to see if I was at least getting some sound and I am.  Actually it still sounds great.  However, there is a very noticeable noise floor; like a constant hiss.  I isolated the hiss to the amp by removing the inputs.  Even with the volume knob at 0, I still have the same level of noise floor.

Voltages (Required  Measured)
1- 75  101
2- 170  179
3-   0    0
4- 170   179
5-  75   79
6-  0    Fluctuates between -(NEG)20 to 0
7- 100   120
8-  0    0
9- 100   118
10- 0    Fluctuates between -(NEG)20 to 0
11- 0    0
12- 0    0
13- 170  179
14- 0    0
15- 185  185
19- 0    0
20- 0    0
21- 206  219

a1- 75  95
a2- 0    0
a3- 1.56  1.54
a4- 0    0
a5- 0    0
a6- 75  97
a7- 0    0
a8- 1.56  1.54
a9- 0    0

b1- 75  98
b2- 170  179
b3- 100  120
b4- 75  95
b5- 170  179
b6- 100  117
b7- 0    0
b8- 0    0


The high voltages coupled with a couple fluctuating negative voltages make me think I have a tube that might be failing or failed.  Any advice would be greatly appreciated.
Thanks in advance for everyone's help!!

[Paul Joppa]

I'm on vacation and don't have my files handy, but the 12AU7 plate voltages are a bit high, suggesting a weak tube. Nothing so far out of line as to cause worry. The different LED brightness is normal. The noise should not be there, since the tubes are already run in and it was not noisy before the upgrade. Is it in both channels?

[Grainger49]

Justin,

Welcome!  

And congratulations on your patience!  Speedball is reported to be the largest improvement you can make so you will be excited when this is sorted out.  Below I have grouped the tube pins and terminals that are connected.

Let's see what is out of spec (in red):

Voltages (Required  Measured)
1- 75  101
a1- 75  95
b4- 75  95

5-  75   179
a6- 75  97
b1- 75  98

7- 100   120
b3- 100  120

9- 100   118
b6- 100  117

6-  0    Fluctuates between -(NEG)20 to 0
10- 0    Fluctuates between -(NEG)20 to 0

The HLMP diodes for the 12AU7 are spot on, within reason.  So the two sides of that tube are working well.  

I'm looking, T1 is tied to tube pin A1 and tube pin B4 (~6V difference).  T5 is tied to tube pin A6 and tube pin B1 (~82V difference).  So those have to be the same voltage.   You may have misread them.  Maybe it didn't settle down before you read T1 and T5.  T1 and T5 will be different because of the small C⁴S boards that feed these terminals.  

T7 and T9 are just a little out of spec.  Maybe your incoming AC voltage is above 120V?  

I am really with you on the fluctuation on T6 and T10.  Once you start it up there should be zero volts DC there.  AC volts indicate signal.  But you should have no signal with the volume at zero.

Try reseating the tubes several times to clean the pins and tube socket.  If you have a different pair of tubes roll them and see if the voltages even out.  

As for noise, I'm with Paul, you have broken in the tubes.  Try retouching the solder joints.  Speedball should have made your Crack more quiet!

[Justin Scharber]

Thanks for the quick replies!

Terminal 5 was a mis-type.  It's actually 79VDC.  I will correct the original post to reflect that; good catch.

My incoming VAC usually measures 121-122; just a little above 120.

I don't have any other tubes to try right now.  I have been planning to get a couple, but haven't pulled the trigger yet.  I guess it's time.  :-)  In the meantime, I will try reseating the current ones a few times to see if I can clean the connections a little.

[Laudanum]

The higher DC voltage at startup is apparently normal (with film caps, or,  possibly speedball).  I measured 22 volts after speedball and Film caps.  9 volts with the stock Crack.   It's supposed to be due to the film caps and not speedball and I cant say personally if that was true in my case.  I installed film caps before speedball but never measured the startup voltage until after speedball was installed.   Anyway, if it's falling back down to 0 volts, I wouldnt worry about the 22Vdc after initial turn on.   But just out of curiosity, are you still using the stock 100uf electrolytic output caps or have you upgraded those with films?

[Justin Scharber]

From what I've read in posts by other members, I agree that the voltage rise to 22 seems fairly normal after the speedball upgrade.

I'm still using the stock caps.  Before the Speedball upgrade, my amp was completely stock.  My next step after ensuring Speedball was working properly, was to roll a few tubes and them possibly look into changing caps.

I'm still at a loss as to what could be causing my voltage issues.  I will try reseating my tubes tonight a few times to see if that makes a difference and start looking into new tubes (probably a new 12AU7 and switching to a 6AS7G).

I hope it's just an issue with the tube pins and sockets being "dirty" but I'm still open to any and all suggestions.

[Grainger49]

Justin,

Good information.  That indicates that Speedball allows more voltage through.  We will bank that information.

You have higher voltages coming out of the power supply than is expected.  If new tubes doesn't fix it you can add some resistance to the second 270 ohm resistor in the power supply to shed the unwanted voltage.

A key question is does the voltage on T6 and T10 end up at zero and stay there? 

[Laudanum]

Measuring at 6 and 10 would be the same as measuring at the jack, if Im not mistaken anyway.  If so, there would be DC leakage there, in the mv range.  Im wondering if it's just a meter thing with the  neg. 20 - 0 Vac fluctuations there.  Im assuming it's jumping around pretty quick.

[Justin Scharber]

T6 and T10 do fluctuate at a fairly high rate; telling me that there might be some type of noise being introduced; I'm just not sure what the frequency content is.  It never seemed to settle out and I tried taking the measurements several times with the amp on for a little while (5 mins or so); ample time for the voltages to settle.  Maybe after a tube swap they will.  I will start looking for new tubes tonight.

Thanks again for all of the help!

[Grainger49]

To Desmond, right, those are attached to the output jacks. 

Justin, be certain that you have the meter on DC.  If you get a reading of DC longer than about 30s without it going to zero and staying there something is wrong with the output capacitors.  Their job is to block the DC out of the output.  All caps would leak at startup but if it stays there something is wrong!

It sounds like yo have done this, just be sure you are on DC not AC.  The noise you are hearing will read on AC.

[Justin Scharber]

Update.

I went over all of my solders last night and didn't find any glaring issues but I put the iron to all of them just to reseat everything.  I also reseated each tube several times to see if I could clean up those connects.  Afterwards, I grabbed the DMM (verified it was reading DC) and got a few different readings.  Also, T6 and T10 were mV; not V.  See below:


Voltages (Required  Measured)
6-  0    Fluctuates between -(NEG)20mVDC to 0
10- 0    Fluctuates between -(NEG)20mVDC to 0

a1- 75  101
a6- 75  101

b1- 75  103
b4- 75  103

The noise floor is still there.  I'm at a loss except for rolling some tubes.  I have some on order now.  I will let everyone know how that goes, but in the meantime if anyone has suggestions, let me know.

Thanks again for everyone's help.

[Laudanum]

Not sure about the higher AC voltages but I dont think there is anything to be concerned about with the fluctuating DC in the milli-volt range at 6 and 10.   I asked about this same thing after my build and there wasnt any concern.  Electrolytic caps leak a little bit of DC ... aside from the initial spike a few seconds after Crack is first turned on.   I know there is a bit of semantic differences in this thread but Paul Joppa referred to that fluctuating DC in the MV range as leakage.   See this short thread, Paul J's response is last ... http://www.bottlehead.com/smf/index.php/topic,1847.0.html

[Grainger49]

I am betting the new tubes will bring the voltages back in line with "expected."

In the mean time listen!

[Justin Scharber]

Update:

I ordered new tubes and they arrived very quickly.  I started by replacing the input tube (12AU7) and BINGO!  I was eager to hear the difference and it's absolutely dead quiet.  I can definately tell a difference.  I'm going to measure the voltages this weekend but I expect that everything will read nominal with the new tube.  I also ordered a 6AS7G and will install it to see if I can hear any changes. 
Thanks again for everyone's advice and help!
Have a good weekend.

[Laudanum]

Congrats.  Glad to hear you got here up and running right again.