[hagtech]

I think the problem is the 12au7.  For some reason they seem to be breaking down.

jh

[leitmo]

Hello Jim!

after last failed test i went for a walk and thought about this, it's almost impossible that both transistors don't work so the problem is before.

Before there's c209, c210, c211, r223 and then Q100, Diodes etc... but if diodes were wrong i wouldn't have more voltage in all points except these two, isn't it? So i think i must check or change c209,c210 and c211. How can i check these caps if my DVM only supports 2uF caps, i can only check c211 (100nF 50V).

i tried two brand new Electro Harmonix 12AU7A with same results on both cases.

[amandarae]

voltages from 5Y3GT:

pins 4 and 6: 293VAC (between pin and ground chassis)
pins 2 and 8: 380VDC (between pin and ground chassis)

so rectifier tube works properly?

Assuming you are using a hammond 370BX, the secondary voltage spec is 550 VCT.  The way I understand it, you should have close to 275 V from pin 4 or 6 with respect to ground.  From 550VCT, the rectified(full wave) voltage should be close to 389 volts rms.  Taking into account the 60 V drop of the rectifier, you should get a B+ of close to 328 volts.

With yours at 293 - 0 - 293, the rectifiied voltage should be close to 414-60 volts, or close to 354volts.  It seems that the 294 is a bit high.  Also, are you sure you are using a 5Y3 tube?  From your data, it looks like the voltage drop is only close to 40V which is for a 5U4 tube.

Sorry if that is all I can provide you. 

regards

[leitmo]

Hello amandarae!

Last week i was totally convinced i bought a 5Y3GT but i'm getting doubts (just joking), yes it's a 5Y3GT from TAD.

All voltages are a little bit higher than marked values on PCB i.e: 150V marked --- 171V measured, 300V marked --- 315V measured...

My main is 222VAC and i connected transformer as 220V, should i try it at 240V or it won't work?

Thanks everyone!

[hagtech]

Hmm, the problem is just not obvious to me.  But something is wrong.

jh

[leitmo]

Hi everyone!

hope you've enjoyed a nice weekend,

i must confess i feel lost with these voltage error on R219L and R.

Should i replace all power supply components (caps,resistors and diodes)?

May be replacing only R219's??

perhaps Q100 and Q200?

somebody has a clue??

PS: tube sockets are ok, and connectivity from tube socket to resistors is checked

Thanks!

[Bill Epstein]

Don't give up, I for one am still looking forward to a happy conclusion.

The Cornet is so worth it.

You should be able to test all the resistors while attached to the board. The caps have to have 1 leg detached. Maybe replace the semi-conductors.

You can always send it to Jim and just be out the postage.

Regards,
Bill

[leitmo]

thanks for the support Bill!

i've checked all resistors (1 leg detached) and caps less than 2uF (my DVM doesn't support capacitance higher than 2uF), big caps has been replaced or moved to different position of PCB to notice any voltage change. I also replaced 2N3906 and tubes without any solution.

The only component i can not replace is 2SC3942 transistors, i didn't find it where i live. The local electronic store says  they have equivalent transistors but i'm not sure about them. Any suggestion about 2SC3942 equivalent??

Thanks!

[Bill Epstein]

Digikey has them. You can't get them from Spain? Here's Digikey Spain page for the part priced in Euros.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=2SC3942-ND

I wonder, tho, have you really carefully examined the board traces with 6X magnification? 

[leitmo]

hi Bill!

i can get 2SC3942 from digikey page but i don't want to pay shipping from USA for only two transistors that's why i'm looking for equivalent.

I didn't examined board traces with magnification (like Sherlock Holmes) but i'm checking continuity following schematics, sometimes i find strange results:

some caps  have continuity between legs and after few seconds it disappears, i suppose tester pins discharge caps (i know i should discharge with resistor).

[hagtech]

A TIP50 should work fine.

jh

[leitmo]

Hello Jim

i'll try TIP50

Thanks for the patient!