Cornet2 pics but doesn't work

leitmo · « **on:** 16 Jun 2008, 06:37 pm »

Here i am again, i think is better to finish my last post "transformer is guilty" because it's not right and open a new one with pics of my not finished and not working Cornet2.

For those who don't know the story here it is:
All voltages are around 10% higher than marked on PCB except R219L and R219R voltages, i have between 0 and 3VDC.
Components were checked and replaced but the 2SC3942's i will order to digikey but i'm not convinced they are wrong, it's very uncommon if i buy two damaged components.

Any suggestion??

And now the pics, i'll paint top and bottom covers green, red or orange (i'm not sure), front and rear panel will leave it chrome or paint it black

Thanks!

ecir38 · « **Reply #1 on:** 16 Jun 2008, 10:23 pm »

I'm not the person to be talking to for troubleshooting but I would suggest replacing those pics with some larger ones.

Bill Epstein · « **Reply #2 on:** 17 Jun 2008, 02:29 am »

You checked R217 that the 220 ohms is correct? If so, has to be Q200. Both bad would be rare, but did you have trouble soldering them? Too much heat? Or perhaps the heat sinks toasted them when they were soldered?

hagtech · « **Reply #3 on:** 17 Jun 2008, 06:12 am »

That's a good point. Did you use 220k for any of those resistors?

jh

leitmo · « **Reply #4 on:** 17 Jun 2008, 03:47 pm »

sorry for these little pics i'll post bigger ones tomorrow

all resistors were checked and have correct value, RED RED BROWN GOLD = 220ohm

thanks everyone

hagtech · « **Reply #5 on:** 18 Jun 2008, 04:25 am »

What is plate voltage on 12au7? Base on the NPN transistor? Heater voltage?

jh

leitmo · « **Reply #6 on:** 19 Jun 2008, 06:47 pm »

hello!
i'm very busy this week so i can only post large pictures i'll test the cornet next week...on Holidays!!!!

ohenry · « **Reply #7 on:** 19 Jun 2008, 09:31 pm »

Hope this helps...

leitmo · « **Reply #8 on:** 20 Jun 2008, 02:53 am »

thanks ohenry, i just don't know what i'm doing wrong and getting small pics.

rotcoddam · « **Reply #9 on:** 20 Jun 2008, 03:42 am »

Did you try another meter?
Marty

leitmo · « **Reply #10 on:** 21 Jun 2008, 05:48 pm »

Hello

First of all i don't understand Marty's question:

Did you try another meter?

If you refer DVM (digital voltage meter) always worked fine

Second reply and it's from a tube newbie's

What is plate voltage on 12au7? Base on the NPN transistor? Heater voltage?

How do i measure this values?? DVM negative pin on ground and positive one on... ??

Thanks everyone and enjoy tubes lucky you!!!

hagtech · « **Reply #11 on:** 23 Jun 2008, 06:53 am »

It looks built ok, but when it does finally run, it's gonna hum like hell. You've got an ac wire wrapped all around the chassis right past the input section. You have the RCA jacks all wired up within the bundle of ac wires. You have to keep ac wires far far away from inputs. Or at least have shielding between them.

I can't see why you are getting the voltages you do, unless a tube is bad. Many test points are labeled on the board, each with respect to ground.

jh

leitmo · « **Reply #12 on:** 26 Jun 2008, 09:02 am »

Hello Jim!

I replaced both 12AX7 (i think they are 12AX7/WA) and 12AU7 with same results.

I have not replaced 5Y3GT because i think it's not the problem, if rectifier tube were damaged all voltages were wrong and they're not.

May big caps cause 12AU7 not to receive voltage?? i have no way to test them

Thanks, Joan

hagtech · « **Reply #13 on:** 27 Jun 2008, 06:10 am »

All I can suggest is that you send it in. Should take me all of 10 minutes to figure this out.

jh

leitmo · « **Reply #14 on:** 27 Jun 2008, 01:58 pm »

Hello Jim!!!

Thanks for your patient, i'll send it back to you, so i'llsend it to this address:

http://www.hagtech.com/contacts.html

if everything's correct i'll send it monday.

Thanks again!!!

hagtech · « **Reply #15 on:** 29 Jun 2008, 05:18 am »

Actually, send it here. That is a new PO box and I'm not sure how well they handle large packages, as it is a part-time station (cash only!).

1964 Nehoa Place
Honolulu, HI 96822

jh

leitmo · « **Reply #16 on:** 29 Jun 2008, 05:18 pm »

thanks jim!

i'll send it tomorrow monday, Spanish post office says you'll receive it in 5-6 days

amandarae · « **Reply #17 on:** 29 Jun 2008, 11:19 pm »

Quote from: hagtech on 27 Jun 2008, 06:10 am

All I can suggest is that you send it in. Should take me all of 10 minutes to figure this out.

jh

This is one of the reasons why I choose to build the Cornet 2. Jim will always be there for you!

Leitmo, you will enjoy your preamp sooner than you think...

regards,

Abe

leitmo · « **Reply #18 on:** 29 Jun 2008, 11:59 pm »

hello Amandarae!!!

i'm totally convinced that a new Cornet2 will be born soon, i'll post pics when finished, painted, running...and GLOWING!!!

hagtech · « **Reply #19 on:** 14 Jul 2008, 07:41 am »

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.

I figured out what the problem was. You built the board fine, all resistors and caps ok, transistors fine. The problem was hum. You must have had hundreds of volts of hum. So much the second stage was saturated and clipped into the funny dc levels. Probably 100Vac of hum after just the first stage. The high ac content may have fooled your dc voltmenter.

The lesson is that you cannot do dc first, then chase down hum. Not sure there was even a board ground on this unit. Input wires (without returns) wrapped around the tranny wires is not a good idea. So I re-built the unit. I stripped it down and re-made it entirely. The power switch is gone, the side with the RCAs got flipped so that they are towards the input side of the board. Made things easier to wire. I re-used your interconnects for I/O. Work nice since they have a shield I could use.

Oh, I forgot to change back to 240V. Tranny is plugged in at 120V, so open box and change it first! Oh yeah, heater voltage was a bit low. I forgot to change that too before I bozed it up. You might want to put a 10 ohm resistor in parallel with the 1.8. This makes me think the design of the 370BX changed since I did the original design, as this is now a common issue.

jh