Crack worked, but Speedball doesn't.....HELP

[milosz]

I built the Crack amp, it worked fine.

I put in the Speedball, it doesn't work. Some sound coming through, extremely low level- barely audible - on my 300 ohm cheapo Sony test 'phones, which sounded fine and loud on the basic Crack before I added the Speedball.  Checked all parts and wiring ten times, no mistakes. Checked all transistors and diodes they all check OK, no opens no shorts.  Ohmed the resistors, all OK.

SYMPTOMS: B+ on terminal 2 starts out at ~170 vdc or so, then as the 6080 warms up the B+ drops to 60 volts.  This ain't right, of course.  But since I checked the wiring, the parts etc etc and there are no errors... what could be wrong?

NOTES:
1. On all Speedball boards, one one diode of each pair lights up. (There are 4 pairs of LEDs.  One LED of each of these 4 pairs lights up, so there are four diodes lit and next to each lit diode is a dark diode.) [The cathode diodes for the 12AU7 both light.]
2. Terminal 1 (12AU7 plate / 6080 grid) is 58 volts. Terminal 5 (other 12AU7 plate / 6080 grid) is 60 volts.  But don't forget, B+ is getting loaded down to 60 volts.
3. Remove the 6080 tube and the B+ (terminal 2) stays at about 180 volts. With the 6080 out of the circuit, terminals 1 and 5 are also at 180 volts.

Any suggestions?

[ironbut]

Have you tried some other tubes? Also, be sure you have the locater in the right spot. I managed to jam a 6080 into the socket wrong once. The locater was worn and so was I (that night at least!)

[milosz]

Since it worked before putting in the Speedball upgrade  I am reluctant to blame the tube. I guess it's possible that the 6080 is bad in some weird way that makes it somehow incompatible with the Speedball,  but I am struggling to picture how, electrically, this could be possible.

In any event I have no spare 6080 on hand, nor any 6AS7 either.

I have to think it's something I did wrong somehow. But this thing is so simple....I don't understand why I just can't find the problem.

But, if all else fails I will buy a new 6080 and try it.  It is worth considering.  Thanks.

Any other ideas out there....?

[Doc B.]

Double check to see that there are 2N2907 transistors in the little boards by the 12AU7 socket and 2N2222A transistors in the bigger board over the 6080 socket. These the the metal cased transistors.

[Jim R.]

Well. Doc beat me to it, but the first thing I would have suggested is to check all the transistors and make sure they're oriented correctly and that the heat sink mounts are done correctly as well.

-- Jim

[milosz]

They are 2N2907A's.  Orientation is correct I believe, see the photos:

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Flf.org%2Fmilosz%2Fphotos%2F1.jpg&hash=96bd3a2cbbfa031b5fbd4060078c356c61ad2cda)
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Flf.org%2Fmilosz%2Fphotos%2F2.jpg&hash=ebc3c573657b0debebb620580cb6f1bbfaeb4169)

[milosz]

WAIT!   THAT'S IT!!!!   I GOT MY 2n2097'S AND 2n2222'S SWITCHED  AROUND!  And when I was going over and over this board looking for a wiring mistake or an open/shorted device I was thinking, "these four small-signal transistors are the same...." when in fact there are two different kinds.  

Doh!

I was so sure I had a wrong wire someplace that I forgot to read the numbers on the parts.

THANKS  GUYS!!!!!

[milosz]

Ahhh!  All working now.

This is now my favorite amp for my Sennheiser HD800s.  I have a bunch of other amps - including OTL tube jobs: Little Dot MK III, Cavalli BIJOU- and solid state: CK

[milosz]

Ha ha, yeah I could part with the CK

[Paul Birkeland]

Just out of curiosity, did you swap the transistors that came with the kit, or substitute new ones?

[milosz]

Just swapped the Bottlehead-provided 2N2222A and 2N2907's, which I had put in exactly wrong.

I  somehow made the assumption that "all these TO18 transistors are the same." This assumption overrode the processes in my brain as I followed the directions to build the thing.  I just saw "solder transistor to board" and didn't pay attention to the transistor types.  It's just chance that I got all four in the wrong places.

There's a problem when you've been working with electronics for years, you start assuming you know what you're doing......  :-o

[c_hatfield]

Same symptoms...
SYMPTOMS: B+ on terminal 2 starts out at ~170 vdc or so, then as the 6080 warms up the B+ drops to 60 volts.  This ain't right, of course.  But since I checked the wiring, the parts etc etc and there are no errors... what could be wrong?

NOTES:
1. On all Speedball boards, one one diode of each pair lights up. (There are 4 pairs of LEDs.  One LED of each of these 4 pairs lights up, so there are four diodes lit and next to each lit diode is a dark diode.) [The cathode diodes for the 12AU7 both light.]
2. Terminal 1 (12AU7 plate / 6080 grid) is 58 volts. Terminal 5 (other 12AU7 plate / 6080 grid) is 60 volts.  But don't forget, B+ is getting loaded down to 60 volts.
3. Heat sinks get crazy hot!

Here's the switch, the 2N2222A transistors (ones with the mounting flange to attach the the heat sinks) are mounted correctly.  The 2N2907 transistors are the questionable ones.  The ones shipped with my kit do not have the silver (assuming aluminum) back as the ones used in the manual photos.  I installed them with the writing facing opposite the LEDs. 

FWIW, it sounds amazing without the Speedball upgrade - almost dead quiet (only the slightest low level hum - and I used the 5/6 mod of connecting PT 14 to 22L).  The only modification I made was to add a Goldpoint Mini-V attenuator.  Compared to my SEX (also using a Goldpoint attenuator and V-Cap in the output stage), it's much more involving.  Really digs deeper into the music and seems to retrieve more information... spacial cues, ambiance... and MUCH quieter!

Anyway, any help is greatly appreciated!

~Hat

[c_hatfield]

OK, so I'm a dope... I was referencing the TIP-50 and MJE350 transistors.  I'll swap the 2N222A and 2N2907 transistors and give it another whirl.

Now, I may not know the difference between transistors, but do know fantastic sound when I hear it... and this sounds FANTASTIC!!!

Thank you Doc (and PB, PJ and JC) for another stellar design!

[JC]

Now, see, I was wondering about that.  I thought maybe Doc had found some new variants of these small-signal transistors!

Good deal!

[c_hatfield]

Finally corrected the diode mix-up and WOW!  thought it was silent before... it is dead quiet, and insanely resolving.  the only non-stock items are the goldpoint attenuator and cardas rhodium rca's i had lying around from another project.  doc, this thing is SICK at this price point!!!