Cornet2 build problems

shedman · « **on:** 11 May 2009, 08:04 am »

Hi all ,I have started to get back into music after a long time and reading posts here decided to build a cornet 2. However i built it but after switching on the first time the following happens .
No red or green ligts
5y3gt lights up
Following volts at test points 150v = all 372v ,155v 371v and 22v, 300/330 v = 372/385 374/386, 365v=385v
I hope sombody can point me in the right direction please thanks jon (uk 240 volts in )

shedman · « **Reply #1 on:** 11 May 2009, 09:41 am »

Some bright spark put a 1.8k 5watt resistor in ,should be 1.8ohm yes ,That should help

galyons · « **Reply #2 on:** 11 May 2009, 07:07 pm »

Quote from: shedman on 11 May 2009, 09:41 am

Some bright spark put a 1.8k 5watt resistor in ,should be 1.8ohm yes ,That should help

Jon,
Your H+ voltage maybe low with the spec'd 1.8ohm resistor. Seems that, perhaps, the windings are different on the newer Hammond trannies. Most folks are targeting 6.15-6.2V and that will take a +/-1.25ohm resistor.
Cheers,
Geary

hagtech · « **Reply #3 on:** 20 May 2009, 05:11 am »

Yes, please check your heater voltage.

jh

shedman · « **Reply #4 on:** 20 May 2009, 01:12 pm »

Hi Thanks ,put 1.8 ohm resistor in volts 5.6,change to 1.2 ohm resistor volts are 6.05 ok.
All voltages on pcb are within target values .switch on get red light but no green light
must be close? where do i look ? cheers jon

galyons · « **Reply #5 on:** 20 May 2009, 03:28 pm »

Quote from: shedman on 20 May 2009, 01:12 pm

...switch on get red light but no green light must be close? where do i look ? cheers jon

Make sure that your LED is wired correctly. There is a tab on side labeled ?LED*?. The "tab leg" goes in the hole where the "LED" text is printed on the board.

The bottom lip of the LED bulb will have a notch or is flat on the tabbed side. Use a magnify glass, unless your eyes are good!

http://rocky.digikey.com/weblib/Lite-on/Web%20Photos/CAT1509FIG10.jpg

Look at the lip at the bottom of the bulb on the left side to see notch. This provides the correct orientation, now just place the other 2 legs in the holes as they align, (center leg to center hole).

Cheers,
Geary

hagtech · « **Reply #6 on:** 25 May 2009, 06:26 pm »

Can you measure the high voltage rails? There are spots marked on the board in various places. Just use DVM.

jh

shedman · « **Reply #7 on:** 27 May 2009, 10:33 am »

Thanks , checked led , if you mean test points as follows
r203L 330(323) 300 (294) r204L 150 (153) r212L 150(148) r219L 155(152)

r203R 330(323) 300 (295) r204R 150 (145) r212R 150(139) r219R 155 (144).

r107 365 (357).

cheers jon

hagtech · « **Reply #8 on:** 31 May 2009, 07:01 pm »

Looks like it is working fine. LED might be backwards. Have you tried listening to it?

jh

shedman · « **Reply #9 on:** 21 Jun 2009, 10:29 am »

Thanks, when i switch on works great after about 30 secs drops to one channel, i changed led around i get green light for first twenty secs no red ?.i built this in the Hammond chassis had it apart a dozen times checked and rechecked ,i have a project tube box which i fit to test rest of system it all works fine cheers jon

shedman · « **Reply #10 on:** 23 Jun 2009, 12:30 pm »

I have just tested tubes by swapping with tubes on my amp (st35 clone) the ecc83 s worked fine however the ecc82( jj) a new one,after 5 mins turned purple and made a loud high pitch noise ! what a shock i jumped out of my seat ,new one on order dare i say thats the problem fixed ? jon

tubesforever · « **Reply #11 on:** 24 Jun 2009, 05:58 am »

Ouch, sounds like you had an air leak. Once the vacume is gone the tube will run away. Purple? I wonder if the flashing wasn't trying to keep up with the gasses getting into the tube.

Some power tubes will glow orange. Very exciting. Sometimes they take out a ballast resistor.

Make sure to check all the resistors feeding and draining that 12au7 tube before firing it again.

I had one mishap with a vintage tube in my Hagerman Clarinet line stage and I had to replace one of the 220 ohm grid stoppers. Thats what they are there for, they kill the problem before it makes its way down the board.

I like the JJ 12au7 tubes, don't hesitate to try more of these. They have very good top to bottom linearity. You just had a bad apple. It happens in the realm of valves and iron.

Also, why not remove the LED at this time and flip it around? Its a lot more fun when the light goes red to green as designed.

Cheers!

shedman · « **Reply #12 on:** 24 Jun 2009, 12:25 pm »

Thanks,Fitted new 12a7,However still only one channel !, as far as the led goes i have switch it around i get red light first 20 sec s or green light first 20 secs but not both together as designed ! is this linked to only one channel ? , all voltages are good , where do i look to fix ? cheers jon

PatOMalley · « **Reply #13 on:** 24 Jun 2009, 11:48 pm »

damn tubes. just had a brand new 12AX7LPS lose the right channel. It went real weak on the right. Swapped back in the Tung Sols and all good.

tubesforever · « **Reply #14 on:** 26 Jun 2009, 07:07 am »

I had the same thing with a vintage NOS tube. Lost just one channel.

However, I lost one channel when my 220 ohm resistor fried.

Make sure you check the 220 resistors around that 12au7 tube. I think you might have lost one when the tube ran away.

Fireproof resistors can fry without you seeing anything on the outside. You have to test the resistors one at a time and make sure they match the other side.

Cheers!

PatOMalley · « **Reply #15 on:** 26 Jun 2009, 11:46 am »

good idea.
btw, all those PRP 220's are getting replaced /w KOA Kiwami's. I bought the PRP 1watts and they do not sit flat. Maybe one got the end cap damaged when I fit them. Who knows? But they go as if one is maybe bad then all are maybe bad.

tubesforever · « **Reply #16 on:** 26 Jun 2009, 02:42 pm »

Shedman,

If the power at the B+ and H+ is right, and the led is not going red to green with proper led orientation, then maybe the comparator circuit is not right or the resisters feeding that circuit are soldered in the wrong spots.

I would double check the board, the resistors and the actual measured value of the resistors feeding that circuit. This part of the Cornet should not be such a problem.

Finally, make sure to double check every 220 ohm resistor around that 12au7 position. If the tube ran away these are there to self sacrifice so the current doesn't effect the rest of the circuit.

If I replaced the tubes with a good fresh set of tubes and one channel was dead, I would look at the B+ feed and the 220 ohm grid stoppers.

These are easy to replace if one has burned up. Using your dmm you can test all 9 pins of the 12au7 and let us know what they read. This will let us know if there is an issue we still need to resolve.

Hopefully you have a fresh set of tubes to use for testing. The JJ tubes are very affordable. Having extras is the easiest way to do testing down the road when these things happen.

Good Luck.

shedman · « **Reply #17 on:** 27 Jun 2009, 03:25 pm »

Thanks tubesforever,ok checked resistors all ok except 107,206l and 206r unable to get reading as dmm keeps just increasing/decreasing ?
12 ax7 volts as 1 =zero 2=164 3 = 160 4 = 327 5 = 6 6 = 6 7 = 157 8 = 152 9 = 328 .All 220 ohm are ok. also fitted new tubes no change thanks jon

shedman · « **Reply #18 on:** 28 Jun 2009, 06:07 pm »

Well at last i have both channels working a iffy joint at r205r and c202r this has taken weeks to fix, as for green light it is still not working but i am havin a rest and play some music cheers jon

hagtech · « **Reply #19 on:** 28 Jun 2009, 08:03 pm »

LED changes from red to green. It's yellow for only a brief moment as it switches over. Channel independent, only indicates power supply status.

jh