[leitmo]

Hi everyone!

last week i finished my first Cornet2 and found some voltage errors (i post it and found some excellent recommendations from Jim

so i started checking all components, one by one.

i checked a half of the components when i tested the transformer secondary (i thought it could be the source of the voltage errors)

I measured voltage on secondary wires to Ground Chassis, RED, GREEN and YELLOW wires are doubled so they are supposed to be the same voltage but these are the results:

GREEN/YELLOW - GROUND: 124V
GREEN1 - GROUND: 128V
GREEN2 - GROUND: 130V
RED/YELLOW - GROUND: 75V
VIOLET - GROUND: 55V
YELLOW/BLACK - GROUND: 109V
YELLOW1 - GROUND: 107V
YELLOW2 - GROUND: 108V
RED1 - GROUND: 188V
RED2 - GROUND: 38V

strange, isn't it?

i'm not an expert on electronics but i'm convinced that the transformer doesn't work properly,
so if i change it everything should work??

Thanks for the patient!!!

[hagtech]

Are you measuring AC or DC?  In-circuit, the transformer will act completely different than if unloaded.

jh

[leitmo]

Hello Jim!

I plug primary wires (220V) to PCB but secondary wires were unplugged so i measured between Ground and secondary wires one-by-one. All values are AC, transformer output is always AC, isn't it?

I asked AES, i'll better copy-paste their answer:

Hello Joan,
Could try measuring between the following wires:
Red to Red = 550 VAC
Green to Green = 6.3 VAC
Yellow to Yellow = 5 VAC

It looks like the measurements from your e-mail were measured from the center tap which comes out to about half of the Ideal:

RED-RED/YELLOW: IDEAL 550V REAL 300V
GREEN-GREEN/YELLOW: IDEAL 6'3V REAL 3'47V
YELLOW-YELLOW/BLACK: IDEAL 5V REAL 2'78V

According to your measurements the transformer is working properly.

The voltages marked as REAL are my measurements.

AES is right, transformer works ok? How can i get the ideal voltages?


A last thing only to be sure: my mains is 222VAC so i connect 370BX to 220VAC

Secondary has 4 single wires (GREEN/YELLOW, RED/YELLOW, VIOLET, YELLOW/BLACK) and they are connected to quick release terminal marked on PCB.
Secondary also has 3 pair wires (RED, GREEN, YELLOW) and i have to connect the two wires of same colour, isn't it?

Thanks for the patient Jim!

[leitmo]

more info about secondary voltages:

AES asked me to check follwing voltages:

RED-RED: 550VAC
GREEN-GREEN: 6'92VAC
YELLOW-YELLOW: 5VAC

with secondary wires unloaded i measured:

RED-RED: 605VAC
GREEN-GREEN: 6'92VAC
YELLOW-YELLOW: 5VAC

are this values correct for unloaded transformer?

i've checked all components and are where they are supposed, so the most probably error source is:
a- cold solder
b- a short, but there should be smoke or blown fuse, isn't it?
c- malfunction component

any idea?

More thanks for the patient

[Theo]

When you measured voltages on the board, is your board mounted to the chassis?  If your board is mounted to the chassis with metal standoffs, you could be shorting something.  My board didn't measure right when I used metal standoffs, and measured normal once I replaced with nylon standoffs.

[leitmo]

hi Theo!

i measured both ways. mounted to the chassis with metal standoffs and not mounted but...it makes me think because PCB was touching chassis because if not it falls to the floor, so i have to hang it with a rope 

i'm not an expert on electronics so all recommendations will be welcome

Thanks Theo!

[hagtech]

The tranny is probably ok.  Unloaded, the voltages read high.  The is because of winding resistance.  The specs are written fro full loads.  I don't use any of the windings at full load.  Hence, the application matters a lot.  What are you getting for dc voltage on heaters and plates (working circuit)?  What are you using for a meter?

jh

[leitmo]

Hello Jim!

Excuse me jim i don't understand first question: What are you getting for dc voltage on heaters and plates (working circuit)?
Answering second question use a Velleman DVM (max AC/DC voltage 1000V)

i looked for shorts with metal standoffs but i'm quite sure are isolated from chassis.

If 365V voltage check point isn't ok (and it's the nearest to voltage input point) it means that malfunction component must be before this point, isn't it? if possible i would like not to unsolder and check all components, but if i have to i'll do it anyway

Could be diodes? i checked 1.8R 5W resistor and it's ok, C100 C101 and C102 are ok too.

Thanks all of you!

[leitmo]

Hello everyone!
Hope you're getting a pleasant weekend!

i've replaced metal standoffs and used nylon standoffs and things went better, not perfect but...take a look (Thanks THEO!!!):



all voltages are about 10-12% higher than marked values on PCB except heater voltage (5'77VDC and has to be 6'3, isn't it?) and R219L and R219R, these two resistors worries me. Any suggestion?

Thanks everyone!

[hagtech]

Something wrong with the 12AU7.  Are the CCS transistors installed right?  Maybe a photo of the actual board?  I think some of the resistors are wrong.  Most voltages are high, meaning load is too light.  Except for heaters, which is low.  I'd say the CCS are not even connected to the tube.  Or something like that.

jh

[leitmo]

Hello Jim!

I'll check the resistors and probably change transistors, CCS transistors are Q200 isn't it? it's strange both of them are wrong but i'll try it, if it doesn't work i'll post a pic

When everything will work i suppose voltages get down or should replace more components?

Thanks Jim!

[hagtech]

I'm not saying both of them are wrong.  I am saying this is a clue to look at.  The fact that they are both reading the same is another clue.  Could just be a bad tube.

jh

[leitmo]

you're right Jim, it's very strange to buy two wrong transistors at the same time, i have cheked all resistors and are OK, so i'll buy a new 12AU7 and test it.

[leitmo]

this morning i installed new 12AU7 and ALL voltages were ok, then i switched off and turned on again and voltages on R219L and R219L went wrong again (about 2VDC) and the rest of voltages increased a 10-15%.

i tried old 12AU7 but i had same results.

So reading the schematic i think i must check shared components between L and R channel:

R223, C209, C210, C211

and components surrounding 12AU7:

R215, C205, R218, Q200, R217, R219, C208, R222

I'm quite sure about Q200 transistors installation but i want to be 100% sure:

they must be soldered with printed side "looking" tubes, not heatsinks, isn't it?

Thanks! all suggestions will be welcome, i don't know what else to check

[hagtech]

Do you have a real 5Y3 installed?  Try a 5AR4 instead, to make sure you get a turn on delay.  Wondering if the heater-cathode insulation is breaking down on the 12au7.

jh

[leitmo]

yes, it's a 5Y3GT by TAD (tube audio doctor). Does exist only one type of 5Y3GT (also known as 6087)?

i bought this 5Y3GT:

http://www.amptek.es/index.php?lang=0&aptd=1&id_prod=166&id_cat=2&id_subcat=3&id_man=2

amptek called "direct heat double diode rectifier", is the suitable tube, isn't it?

i'm sure it will be an stupid error and it's my fault but i can't find it, i was thinking of replacing LED's transistors but i don't think it will help

Thanks a lot for the patient Jim!

[leitmo]

one more question Jim:

how can i check heater-cathode insulation?

[leitmo]

sorry for dividing replies, i'm just discovering causes of my doubts:

this page:

http://www.amptek.es/index.php?lang=0&aptd=1&id_prod=166&id_cat=2&id_subcat=3&id_man=2

sells 5Y3GT as a "direct heated double diode rectifier"

this one:

http://thetubestore.com/5y3types.html

sells 5Y3GT as a "indirectly heated full-wave rectifier tube"

and this page:

http://www.tubedepot.com/so-5y3gt.html

as a indirectly heated diode.


After reading this specs i must suppose that my 5Y3GT is not suitable for Cornet2??

i should buy Sovtek's 5Y3GT and not TAD's one??

Thanks everyone at audiocircle and Hagerman's forum!!!

[amandarae]

sorry for dividing replies, i'm just discovering causes of my doubts:

this page:

http://www.amptek.es/index.php?lang=0&aptd=1&id_prod=166&id_cat=2&id_subcat=3&id_man=2

sells 5Y3GT as a "direct heated double diode rectifier"

this one:

http://thetubestore.com/5y3types.html

sells 5Y3GT as a "indirectly heated full-wave rectifier tube"

and this page:

http://www.tubedepot.com/so-5y3gt.html

as a indirectly heated diode.


After reading this specs i must suppose that my 5Y3GT is not suitable for Cornet2??

i should buy Sovtek's 5Y3GT and not TAD's one??

Thanks everyone at audiocircle and Hagerman's forum!!!

Boss,

It should not matter.  AFAIK, directly heated means the filament or heater is the cathode.  For example, the DHT (Directly Heated triode) like the 2A3, 45, 300B, etc uses the filament as the cathode.  For the rectifier that we use, IDH will have a few seconds of delay for the rectified B+ to reach its value while DH gives you B+ faster or almost at turn "on".

If you look at the schematic of say, 5AR4 and compared it to 5Y3G, you can see that the 5AR4 has a filament, and the cathode tied together whereas the 5Y3G have the filament acting as a cathode also.

As for the 5Y3's(G, GT, GA), the electrical characteristics are as follows:
1.) All have a voltage drop of 60 Vdc at 125 mA.
2.) All have a Max Dc output current of 125 mA, and max peak inv. voltage is1400 v.
3.) GT and GA can supply 350 volts rms at 440 ma peak per plate.  while G have the same except it can only supply 375 mA per plate.

In my Cornet II used or use 6106 5Y3GT, G, GA, GB, and any 5AR4 without any problems.  If I were you, I will double check the transformer wiring, then the resistor values and the capacitor orientations.

goodluck!

[leitmo]

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?