Cracked crack...[SOLVED]

[Chiratas]

Hi,

Having a devil of a time figuring how my Crack could go from working perfectly to dead silent with no mods in between! Literally, I went from a listening session to watching the tube heaters fade to black.

- 240v transformer
- tube heaters, LEDs dead
- only unusual resistance reading is at T6/T10, which reads zero ohms.

Voltage readings are all a bit off...
T1, T2, T4, T5, T13, T15, T21. A1/A6 = 225v
All other points = 0v

Any help much appreciated.
Jim

[Paul Birkeland]

If the tube heaters don't glow, inspect the twisted pair of wiring that goes from power transformer T4/5 to B7/8 and A4,5/9.  This twisted pair of wires heats the tubes, if the tubes don't heat, nothing else will work.

Also, if you set your volt meter to AC volts and measure the voltage between power transformer terminals 4 and 5, there should be around 6-6.5V.

-PB

[Chiratas]

Thanks guys.

Voltage at T4/T5 is 6v. Wiring from transformer to both tube sockets look ok and show continuity.

Will start swapping tubes and reworking all of the joints.Very frustrating...it's quite sad to watch and hear the heaters and volume fade while listening not knowing what just happened!

jim

[Chiratas]

Paul,

At T6 and T10, i get  resistance reading of zero ohms. Would there be any other possible reason besides blown resistors at the headphone jack? And would that in itself be enough to shut down power to the tubes?

For what it's worth, the unused terminals on the jack are tied to ground based on this mod: http://www.bottlehead.com/smf/index.php/topic,2946.0.html


Thanks,
Jim

[Paul Birkeland]

At T6 and T10, i get  resistance reading of zero ohms. Would there be any other possible reason besides blown resistors at the headphone jack? And would that in itself be enough to shut down power to the tubes?

You can measure the voltage at the sockets as well.

-PB

[Loquah]

We had a strange and similar sounding issue on a recent SEX build (it was a mate of mine's kit). We seemed to have continuity, but the tubes wouldn't heat. He resorted to literally resoldering every joint and it worked. I can only assume that there was a partial joint which was somehow enough to create continuity, but not carry the full voltage / current required by the circuit.

PS I'm still learning the circuitry side of things so err towards the suggestions of experts like CB and Grainger - just wanted to add this into the mix from our recent experience.

[Paul Birkeland]

Hello Chiratas,

Did you do the modification to add the extra wiring to the headphone jack for shorting when no headphones are plugged in?  If so, the resistance at 6 and 10 will be zero with no headphones plugged in.

I can say with 100% certainty that replacing every capacitor and resistor in the entire kit will not restore glow to your tubes - that has to be done by following the twisted pair from power transformer terminals 4 and 5 to the 8 pin socket, then the 9 pin socket.  Those wires cause the tubes to glow.  They are isolated from the actual audio circuit itself.  Without heat in the tubes, no LED's will glow, and the voltages will all be way off.

-PB

(Feel free to post pics up here if you'd like a 2nd set of eyes to look over things)

[Chiratas]

Hi Paul,

Yes, I did do the mod to short the headphone jack. Thanks for that! I will go back over the entire build again to try to see what's up.

One strange event this morning before leaving to work was that I plugged in, flipped the power switch, then saw both LEDs light up only to fade within 15 seconds.

Cycling the power switch however did not result in the LEDs going on again. Waited 10 minutes, tried again, no joy.

I'll block some time over the next several days to try to approach this more methodically and post back.

Cheers,
Chiratas

[Chiratas]

Solved! Reheated all the joints between T4/5 and the tube sockets and all is good!

Thanks everyone for the advice...you guys are the best!