5y3 rectifier, no B+

[pietro_moog]

hi guys.
i rewired my 5f2a, and everything looks like the schematics.
my 5y3 doesn't work, so i thought my rectifier finally blew. i tried my sovtek 5y3 (just to try, and i know that is ok. i only used e few days before receiving a real 5y3) and that doesn't work too.
both tubes light on, and seem to behave like working ones.

voltages are fine, pinout too.

do you have any suggestion, before buying a 20€ new rectifier?
is there a way to test a 5y3?

[big_teee]

Is the HT AC present at the Rectifier from the Power Transformer?
Looks like a pretty simple layout. I did not see a HT fuse on the Schematic.
Terry

[pietro_moog]

i don't understand.
you asking me if i wire the 5v heaters to the rectifier? yes.

so you're saying that my rectifier is busted? damn..

[Danelectron]

Can I ask why you rewired it? Did it work OK before? Do you have a voltage tester?

[pietro_moog]

i added a reverb circuit. yeah, it was fine before.
i have a voltage tester. do i have to check anything in particular?

[big_teee]

i don't understand.
you asking me if i wire the 5v heaters to the rectifier? yes.

so you're saying that my rectifier is busted? damn..

No that was not what I was saying.
You have 5v AC to the Rectifier heaters.
You said the tube was glowing, so that is probably ok.
You have high Voltage AC from the Power Supply to the Rectifier tube.
The Rectifier Converts the HV AC (or B+ AC), to B+ DC.
If the HV AC is not there you would not get any B+.
Or any kind of internal blown fuse on the HV AC.
I am not that familiar with that amp so Maybe others have better things to check for.
Good Luck,
Terry

[Danelectron]

Sorry, I reviewed your original post and you say the voltages are fine. That would indicate the 5Y3 is fine. Can you post a schematic of the exact modifications you performed?

[pietro_moog]

cool. so HV means high voltage. yes, they are there.
what do you mean with internal blown fuse on the HV AC? something inside the transformer?
whatever, i think maybe the best solution is ordering a new tube and see what happen next.
the circuit is so simple that it has to be the tube.
it was fine a pair of weeks ago, and looks fine now,there are no moving parts on the inside now.
i just don't get how..

[Danelectron]

cool. so HV means high voltage. yes, they are there.

So you have high voltage there. I'm gonna take a shot and assume you mean at the output of the rectifier tube. In most amps that would indicate you have a working rectifier tube. The other tube you swapped in you stated was working fine in another amp. Do you think that is your problem?

The "internal fuse" that big_teee was referring to is in some amps. It is for the B+ circuit, but a lot of the older amp designs didn't utilize that protection. Not the issue here.

It would be a help if you could post a schematic of YOUR modification. Did you add the reverb circuit yourself? Are you sure you got it right? If it worked fine before the modification would it make sense to recheck the modification? Just a suggestion. Good luck.

[pietro_moog]

the schematics, and the circuit itself in my amp are fine.
my point is i don't have a B+ voltage at the output of the rectifier (pin 8 in the case of the 5y3).
all the voltage coming from the transformer are here,and not having a DC voltage out makes deduce that the tube is broken. fine. NOS 5y3 are very frail.
but the other tube, the sovtek one -which is more rugged- that i used for a bunk of hours and stored in the original box inside a closet, should work.
this thing makes me think that something is wrong somewhere, and it's not the amp because it's not receiving anything.
what i don't understand is what is wrong. it's very simple circuit, and the rectifier it's just a tube. point.

do you guys know any test i could make to find out if the tube is working on its own?

[dwhutchens]

First check that the center tap of the power transformer hasn't been disconnected from ground. Disconnect the wire from pin 8 to the first filter cap. Set the meter to 1000 vac and check between pins 4 and 6, should be 600 ~ 700 vac. Check pin 4 to ground, should be 300 ~ 350 vac, same for pin 6 to ground. Set the meter to the dc range. Pin 8 to ground should be 300 ~ 400 vdc. No dc = bad tube. A shorted tube will blow the main fuse or smoke the transformer if the fuse is too big. A NOS 5y3 is not fragile, they can last 40 years in the proper circuit. A shorted b+ rail will take them out. Also using more than 10 to 20 uf for the first filter cap can kill them.

[pietro_moog]

really? i have 47uF as the first cap, i thought it would be fine..

[dwhutchens]

I've heard that the sovtek 5y3s are closer to a gz34 so it might be ok for them but not for a real nos 5y3. Look at page 2 of the data sheet:
http://boozhoundlabs.com/howto/pdf/5Y3GT.pdf