Voltage check questions on Crack w/ Speedball [solved]

[DenverDude]

Hello Paul (and everyone) -

I just finished installing the Speedball upgrade and was performing my voltage check, and I came up with some numbers that seem low, so I wanted to run this by you before I plugged my cans into the unit. The following measurements were more than 15% off your recommended voltages on the low side:
T2 = 121
T4 = 121
T7 = 79
T9 = 83
T13 = 118
T15 = 154

Just wanted to make sure these aren't too low ... thanks

 

[Paul Birkeland]

Yes, that is no bueno.

I'm guessing the voltages were more in line previously?

Crunching the numbers, you are drawing twice as much current as you should be. 

How are your voltages at T1/T5?

Also, if you disconnect the red wire at terminal 13, do your voltages pop back up a little above 200V? (Be careful, with no tubes sucking down current, the power supply will stay charged for several minutes)

 

[DenverDude]

Thanks for the quick reply, Paul. My measurements for those Terminals are:
T1 = 76
T5 = 73

As for disconnecting the red wire on T13, once I disconnect it, should I test the voltage with or without the tubes in?

Thanks again for your help...

 

[Paul Birkeland]

Either way, they wont be that different in either case.

 

[DenverDude]

Ok ... so I removed the red wire from T13 and here are my readings:
T1 = 0
T2 = 0
T3 = 0
T4 = 0
T5 = 0
T7 = 0
T9 = 4
T13 = 221
T15 = 221
T21 = 222

 

[Paul Birkeland]

OK, this is good news, essentially your power supply is OK.

Now, connect the red wire back to T13 and run the amp with just the 12AU7.

The voltages at T1, T2, T4, and T5 will essentially tell the whole story.

If you have something like 220v at T2/T4 and ~80V at T1/T5, then you know your small green C4S boards are functioning.

In either case, let us know what you find.

-PB

 

[DenverDude]

Ok, so here you go:

T1 = 74
T2 = 204
T4 = 204
T5 = 71

So it appears that my small boards are working ... so we're cooking with grease now ... what's next to check?

And I will admit, I had an issue with the larger board in soldering in one of the 2N2222A transistors. One had bad solder bridges, and I ended up breaking the lead on that one, so I picked a spare 2N2222A transistor up at a local computer store and used that. The other I fixed more solder bridges and I'm sure it got very hot ... not sure what it takes to burn those up, but my iron gets to 750 degrees F.

Just thought I'd give you the whole story on the big board...

 

[Paul Birkeland]

Yeah,

I got a Crack repair in the other day with basically the same symptoms you describe.  You are indeed correct, your front two Speedball boards are working as one would expect. 

At this point, how about we just get you a fresh start on that back PC board? 

-PB

(Note - to do this, you can just PM me your name)

 

[DenverDude]

Hi Paul - Sent you a PM yesterday ... thanks again for the help.

 

[DenverDude]

Hi Paul -

I received the large circuit board kit from Eileen today, and I assembled it and all the voltages were well within range. I think the issue was either a transistor I may have fried or some solder bridges I didn't catch, but it works great.

I am now listening to R.E.M., Radiohead, Johnny Cash and Miles Davis. When there's no music, it is so quiet, and I can already tell there's even more clarity with the Speedball upgrade. Will be listening to it all week.

Thanks so much again ... I now owe you more than a drink (maybe a bottle ... you like whiskey?) ... take care.

 

[Doc B]

If you send whiskey Josh will end up with it. The rest of us are dry these days. PB is a total sucker for candy though.