Speedball: OA, OB over the 10% of tolerance [resolved]

[Fernando]

I have used the vanilla Crack for a few weeks now, and all measurements were within range. Not long ago, I replaced the potentiometer for the Alps Blue Velve 100K, as suggested in a few post in the forum; my goal was to get rid of some imbalance in the left and right channel. This solved the problem, giving me a cleaner sound and measurements within the expected range. To ensure everything was working, I used the crack with the Alps Blue potentiometer for 2 weeks with no issues.

Today, I installed the full speedball upgrade. The small board was within ranges, but I got a few voltage discrepancies on the Large Board. See below:

Terminals -- Voltage (Percentual Discrepancy)
OA ------------- 118v (18%)
OB ------------- 117v (17%)
G --------------- 0 (OK)
B+ ------------- 182v (OK)

Just to reiterate, the values on the Small Board are all within range. All led lights are OK too.

Take in mind that I'm based on Australia, which means a 240V AC configuration on the transformer.

Do you think it is safe for me to use with this measurements? Or should I be looking for a problem here?

Thanks

 

[Paul Birkeland]

Can you post the small board voltages as well, just so we can get an idea of where they are in the range?  I suspect you may be just fine, but it would be good to double check the whole picture.

 

[Fernando]

The readings in the Small Board were:

OA---------------- 90v
IA----------------- 172v
B-A/B----------- 0v
IB----------------- 172v
OB---------------- 90v

===============

Unfortunately, I was checking everything and running the tester reading again when the tester probe slipped and shortcut one of the Tip50 (the one closer to the TOP letters). I don't have electrician knowledge to know the full extension of the damage or how to check it properly. I will deeply appreciate it if anybody could walk me through how to check for any additional damage.

As additional information, just the 2 LED lights close to that specific transistor are off, the other two of the Large Board are OK, and the ones in the Smal Board are also ok. The tubes kept glowing too.

Please see the image here:

Could I just purchase a replacement for the Tip50 locally (I'm in Australia)? If that's the case, is there anything I'd need to be aware of when procuring the replacement?

 

[Tom-s]

I'd suggest trying another (stronger) ECC82. That may draw all voltages down where you'd want them to be.
The readings look good I'd say. It's a strong 6080 but maybe less strong ECC82 in there.

If those reading are from after the "short" your TIP50 is still good to go.
If not, post new readings from after.

 

[Fernando]

I'd suggest trying another (stronger) ECC82. That may draw all voltages down where you'd want them to be.
The readings look good I'd say. It's a strong 6080 but maybe less strong ECC82 in there.

If those reading are from after the "short" your TIP50 is still good to go.
If not, post new readings from after.

To clarify the readings where from before the "short". Afterwards I don't remember exactly if the OA or the OB was closer to 200v (like 197v). Seeing that and the two LED off, I decide to turn it off not to damage something else for the high voltage. If you can confirm that it's safe to get new readings (even with that voltage), then I can get them.

 

[Paul Birkeland]

You will have to set your meter to beep for continuity, then check for continuity between each pair of transistor leads on each transistor until you find the shorts.  Realistically, a new TIP50 and a new 2N2222 will likely get you back up and running.  If you had 200V at OA or OB on the large C4S board, then there would have been an issue that needed to be tracked down.

 

[Fernando]

The readings in the Small Board have changed to:

OA---------------- 90v
IA-----------------  from 172v ---------- to 204v (they still ok, but have a plus 30v)
B-A/B----------- 0v
IB----------------- from 172v ---------- to 203v (they still ok, but have a plus 30v)
OB---------------- 90v

The readings in the Large Board have changed to:
OA ------------- from 118v ---------------- to126v
OB ------------- from 117v ---------------- to 197v
G --------------- 0
B+ ------------- 182v ------------------------- to 204v
Also the Large Board has two LEDs off.

=====================================================

You will have to set your meter to beep for continuity, then check for continuity between each pair of transistor leads on each transistor until you find the shorts.  Realistically, a new TIP50 and a new 2N2222 will likely get you back up and running.  If you had 200V at OA or OB on the large C4S board, then there would have been an issue that needed to be tracked down.

1 - I'm not quite sure how to do it with my tester. It is an AstroAI AM33D - It has the Continuity selector, but you have to manually select ohms to know the values. I have tried but if I pick the value usually I get readings.

2 - I'm not sure how to test the TIP50. Supposedly it is a NPN transistor, and for the information I found on the Internet, the BASE should be the middle one, but I'm getting readings in both when I put the positive probe on the Left leg.

===================================

Editing point 2: I think I understand why I was getting so confused. Most guides on the Internet assume that the transistor always has the Base in the middle, and that's not the case of the Tip-50 (NPN) and the MJE 350 (PNP).

And I think I found where the problem is, or at least part of it. One of the 2N2222A (NPN) close to TOP is not working. I will buy a replacement for that and the LEDs.

Can anybody confirm if this one is a good replacement?

https://www.digikey.com.au/en/products/detail/good-ark-semiconductor/2N2222A/18667994

I don't know if these values are correct:
Current - Collector (Ic) (Max)800 mA  ---------------------------------------------- this one I have seen versions with 600 mA
Voltage - Collector Emitter Breakdown (Max) 40 V --------------------------- this one I have seen versions with 50 V
Vce Saturation (Max) @ Ib, Ic 1V @ 50mA, 500mA
Current - Collector Cutoff (Max)10nA
DC Current Gain (hFE) (Min) @ Ic, Vce 100 @ 150mA, 10V
Power - Max 500 mW

 

[Paul Birkeland]

1 - I'm not quite sure how to do it with my tester. It is an AstroAI AM33D - It has the Continuity selector, but you have to manually select ohms to know the values.

You turn the knob on the meter to the beep setting.  You'll know it's set correctly when you touch the meter probes together and it beeps.

2 - I'm not sure how to test the TIP50. Supposedly it is a NPN transistor, and for the information I found on the Internet, the BASE should be the middle one, but I'm getting readings in both when I put the positive probe on the Left leg.

And I think I found where the problem is, or at least part of it. One of the 2N2222A (NPN) close to TOP is not working. I will buy a replacement for that and the LEDs.

If you're not sure how to test the TIP50 but you are sure that the 2N2222 is bad, I guess I'd want to know how you've come to the conclusion that you need a 2N2222 but at the same time you are unable to test the TIP50. 

In any event, it would be a good idea to fit a new tip50 and a new 2N2222 on the side of the large C4S board where you have the voltage discrepancy. 

 

[Fernando]

You turn the knob on the meter to the beep setting.  You'll know it's set correctly when you touch the meter probes together and it beeps.
If you're not sure how to test the TIP50 but you are sure that the 2N2222 is bad, I guess I'd want to know how you've come to the conclusion that you need a 2N2222 but at the same time you are unable to test the TIP50. 

I arrived to this conclusion (that the 2N2222 is not working correctly) by comparing the values between each other. Reading in continuity, I got the following values:
Transistor 2N2222A (NPN) Continuity only  ----- 839 collector----- 843 emitter
Transistor 2N2222A (NPN)  (Closer to TOP) -----1      ----- 1

I checked all the other transistors and resistors, but they don't seem to have a discrepancy like those two.

In any event, it would be a good idea to fit a new TIP50 and a new 2N2222 on the side of the large C4S board where you have the voltage discrepancy. 

Yes, I was thinking on replacing those exact two pieces (TIP50 and 2N2222), but also the LED lights; the latter seem to be dead now. However, I'm not sure what are the attributes of the 2N2222A in the Speedball. Because of that, I'm unsure whether the replacement parts that found (on a local store) would be a good fit; I found the following:

Current - Collector (Ic) (Max)800 mA  ---------------------------------------------- option 2: I have seen versions with 600 mA
Voltage - Collector Emitter Breakdown (Max) 40 V --------------------------- option 2: I have seen versions with 50 V

Is any of those two suitable? If not, what should I be looking for?

 

[Paul Birkeland]

Any 2N2222 and any old TIP50 will work OK in those positions. 

 

[Fernando]

Any 2N2222 and any old TIP50 will work OK in those positions.

Thank you so much. I didn't want to put something wrong in the Speedball.

 

[Fernando]

Finally, I replaced the broken components. I ended up replacing 2N2222, TIP50 and 2 LED lights.

The new readings in the Large Board have changed to:
OA ------------- 116v
OB ------------- 118v
G --------------- 0
B+ ------------- 182v

=========================

My first impressions of the upgrade are similar to other people. I can perceive that it is a more clean and fast sound. But I think that the mids are not good compared with the vanilla crack. Probably in the future I'll do a little bit of tube rolling to get back those mids and at the same time preserve the upgrade improvements.

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Thank you all for helping me with this issue.