Cornet2 pics but doesn't work

leitmo · « **Reply #20 on:** 14 Jul 2008, 02:56 pm »

Hundreds and thousands and millions of thanks Jim!

I payed for insurance shipping and that's the result!!!

so all i wanted was a Cornet2 running and you've achieved Jim

Thanks again!!!

leitmo · « **Reply #21 on:** 14 Jul 2008, 06:06 pm »

hi again!

when i said "I payed for insurance shipping and that's the result!!"

it was referred to this: "Leitmo, got your C2. It was a mess after shipping. The board had broken loose from chassis, one of the tubes (in tube box) was broken, fuse holder broken, etc. But the chassis was still in nice shape." From Jim Hagerman.

The biggest doubt of sending Cornet back to Honolulu was "handling care" so i decided to pay insurance and express mail service but he received my Cornet2 like read above.

Any suggestion for future international shippings??

Thanks!

JoshK · « **Reply #22 on:** 14 Jul 2008, 08:49 pm »

May I humbly and politely suggest you read Building Valve Amplifiers by Morgan Jones? It would greatly improve your chances of successfully building a second project.

hagtech · « **Reply #23 on:** 15 Jul 2008, 07:47 am »

It's a very good book.

jh

leitmo · « **Reply #24 on:** 15 Jul 2008, 12:02 pm »

thanks for suggestion JoshK! very subtle

i'll try to get it here in Spain or maybe in amazon, in English of course, i had bad experiences with technical books translated to Spanish.

leitmo · « **Reply #25 on:** 24 Jul 2008, 09:47 am »

i've just received Cornet2 repaired, thanks a lot Jim!

i can't wait to get tubes, on/off switch and listen to music.

I'll post pics when working

Thanks again Jim!

leitmo · « **Reply #26 on:** 30 Jul 2008, 02:46 pm »

Hi Jim!

i received Cornet2 and changed voltage connection to 220V as you told me. I used 2 new 12ax7/LPS and one of 12au7 you returned me. plug it but doesn't work, 5y3gt and 12au7 start glowing, both 12ax7 glows only a little bit but no sound, no hum, i'll check voltage points and post results. May be 12au7 was damaged during shipping?

Thanks

ScottRT · « **Reply #27 on:** 2 Aug 2008, 08:59 am »

Man, Leitmo... you have some shit luck!'

I would suspect your tubes. couple years ago I bought a batch of NEW Sovtek LPS for a killer price from an ebay seller, and put them away. 2 weeks ago a friend with a B&K 747 tested all my tubes. 2 of the Sovteks were completely DEAD!!! an 4 others tested for shit. 2 were OK. THis guy musta been selling tubes that were rejected at the factory, but not destroyed.

Have you confirmed your Sovteks are good in another device????

2 years ago I built my Cornet 2 from start to finish in one evening. I was caeful with each step, and it worked perfectly the first time I powered it up. That was 2 years ago.

Well, once you get yours going, you will love it, and decide it was worth the hassle. Good luck.

Scott T.

denverartist · « **Reply #28 on:** 5 Aug 2008, 03:02 am »

Cornet 2 owners are certainly sympathetic to your plight. It seems clear that the problem is related to the 220V operation.

Pete

leitmo · « **Reply #29 on:** 6 Aug 2008, 12:11 pm »

hi everyone!

thanks for answering denver and Scott, since i built cornet 2 i tested 2 12ax7/wa and 2 12ax7/lps so i must believe tubes are ok.

Jim tested Cornet and returned to me so:

- 12au7 i sent to Honolulu is damaged and i have to replace it or
- something happened to PCB during shipping. no component is clearly damaged but i should check it

i'll post results as soon as possible

thanks

amandarae · « **Reply #30 on:** 6 Aug 2008, 06:43 pm »

leitmo,

I truly wish that you can sort out your problem right away and enjoy your phono preamp.

This thread is too painful to watch for us in the sidelines!!

Goodluck! I really mean it!

regards,

Abe

hagtech · « **Reply #31 on:** 7 Aug 2008, 03:59 am »

Just make sure you have tubes in right place. From inputs, it is 12ax7, 12ax7, then 12au7, and finally the rectifier. There were two 12au7 in the package when I got it. Somehow, after I sent fixed machine back (both channels working for sure), I realized I neglected to put one 7025 and the power cord back in the box. They're still sitting right here.

jh

leitmo · « **Reply #32 on:** 2 Sep 2008, 09:08 am »

Hi,

Cornet still doesn't work, so i'm thinking it could be a tube, can i change 12au7 with 12dw7 (7247) only for testing??

thanks

Theo · « **Reply #33 on:** 2 Sep 2008, 06:27 pm »

I feel really bad your Cornet built isn't yet working. My suggestion would be not to try other types of tubes, but get a complete set of new and inexpensive tubes for starter. The least expensive good quality tubes are JJ for 12AX7 and 12AU7, and Sovtek 5Y3GT. I'm still on this JJ set and they sound not bad. I have a set of Sovtek 12AX7 and 12AU7 on hand; they also work. I'm in no hurry to swap them in, as the JJ's are doing so well. Stick with it and you'll be rewarded.

hagtech · « **Reply #34 on:** 3 Sep 2008, 08:52 am »

12DW7? No. It is two different tubes in one glass. Both channels need to be same.

jh

leitmo · « **Reply #35 on:** 15 Sep 2008, 02:37 pm »

hi Theo!

i bought a complete set of tubes when i finished Cornet2, it didn't work; i sent it back to Jim, some tubes broke during the travel so i bought a new set of tubes and i think i won't buy any tube, i prefer measuring voltage points before spend more money, sorry i'm a little tired of this

leitmo · « **Reply #36 on:** 28 Oct 2008, 12:59 pm »

Hi!

after some weeks of tube relaxing yesterday decided to make my cornet2 work, i still have same errors as you can see below. Jim repaired and tested...and worked!!! So i can't understand why it doesn't work with me!!!

By now i use:
1 x TAD 5Y3GT
1 x Sovtek 12AU7A
2 x Sovtek 12AX7/LPS

Rectifier tube glows, 12AU7A only glows a few and both 12AX7/LPS just a very little glow

Any suggestion will be appreciated,

Thanks in advance!!!!!

amandarae · « **Reply #37 on:** 28 Oct 2008, 01:45 pm »

The Sovtek tubes, 12AX7LPS, does not glow as much than other 12AX7 tubes but it is working fine. This is normal! Here, read the text...

From our review of this 12AX7 tube: "This is an entirely new 12AX7 design from Sovtek and a great step up in sound quality. They have very large ribbed plates and great sound reproduction. I found them very smooth and well balanced in terms of bass, mids and treble response. The large plates make them more prone to microphonics and in combo amps, so they can be a problem if you like to run things wide open. It is still the best thing Sovtek has produced in a 12AX7, with very good gain and low noise.
I would advise against using them in compact high-powered combo amps where they will be subjected to lots of vibration. One other note about the construction of these tubes is they have filaments that are almost completely encased in the plate structure. They often don't "light up" when working properly. This is not a problem, it's normal for the LPS".

May be it is the same as for the 12AU7. For the life of me, I have never seen a Sovtek 12AU7 though, ever!

regards,

Abe

leitmo · « **Reply #38 on:** 28 Oct 2008, 02:18 pm »

thanks for answering Abe, reading your Sovtek 12AX7/LPS review i must suppose tubes are OK, so there's something wrong in PCB

tubesforever · « **Reply #39 on:** 29 Oct 2008, 07:20 am »

Your voltage at R219 is all wrong. Everything else seems ok. Things are high but these can be adjusted with changing a few resistors in the circuit. I did this with my Clarinet. The Cornet 2 did not require many changes.

Replace that 12AU7 with a completely different brand and retest.

There are only three resistors between the B+ power supplied by the rectifier tube (285 volts) and R219.

R220 and R221 are likely to be ok because if they were not then every other voltage on your board should be all wrong.

R216 needs to be 220 ohms. If you have blown resistors or 220k ohms that might create the issues you have now.

What is the voltage of R215, R218 and R217 on both sides of the resistors?

Your H+ voltage is a little low, however that has nothing to do with the low value at R 219. Either a pair or resistors is way out of whack or the 12AU7 circuit is not functioning.

Let us know the voltages and the resistance.