Ceriatone clone Bassman 5F6A hum problem?

[HotBluePlates]

... the diodes have the safety function. ...

The solid-state diodes do not have a safety function. They keep the amp working if the tube rectifier short-circuits from plate to cathode.

If the tube rectifier short-circuited, there would be a large a.c. voltage applied to the filter caps, which would blow them up. The solid-state diodes "pre-rectify" the voltage before it is applied to the tube rectifier. Now if the tube rectifier short-circuits (and looks like a straight piece of wire), the amp still functions without damage.

You might not know the tube rectifier even failed unless you notice a slightly different sound to the amp due to the slightly higher supply voltage.

NOTE: Maybe I've been lucky, but I've never had a rectifier tube fail. So this addition is normally not worth it to me to install in my amps. But if you were building an amp for a professional, touring musician, you might install these in an amp intended for stage use so the amp keeps working during a performance no matter what.

[vincenzo]

The voltage at pins 4 and 6 is no longer AC. Only the positive half cycles of the AC waveform pass thru the diodes, so what you have is pulses of DC. Your meter does not know how to measure those pulses. This is OK. Nothing to be concerned about.

I'm very happy to read this

[vincenzo]

The solid-state diodes do not have a safety function. They keep the amp working if the tube rectifier short-circuits from plate to cathode.

If the tube rectifier short-circuited, there would be a large a.c. voltage applied to the filter caps, which would blow them up. The solid-state diodes "pre-rectify" the voltage before it is applied to the tube rectifier. Now if the tube rectifier short-circuits (and looks like a straight piece of wire), the amp still functions without damage.

You might not know the tube rectifier even failed unless you notice a slightly different sound to the amp due to the slightly higher supply voltage.

NOTE: Maybe I've been lucky, but I've never had a rectifier tube fail. So this addition is normally not worth it to me to install in my amps. But if you were building an amp for a professional, touring musician, you might install these in an amp intended for stage use so the amp keeps working during a performance no matter what.

Thank you for explication!!
So, we can say that the diodes have a security function to the filter cap?
If the rectifer tube short-circuits can damage the PT?
What precaution I can take for increase the safety of the amp (tubes, cap, PT, OT ecc..)?

[HotBluePlates]

... So, we can say that the diodes have a security function to the filter cap?
If the rectifer tube short-circuits can damage the PT? ...

Yes, the diodes prevent damage to the filter cap or power transformer if a rectifier tube short-circuits.

A short-circuited rectifier is a rare failure though. I only mean to say those extra diodes may never be needed (but they do no harm and are cheap to include).

[vincenzo]

I do not want to upload photos, too tired. However, if you like, you can see the photos here.

https://www.facebook.com/photo.php?fbid=10200130160095055&set=pcb.10200130170255309&type=1&theater

What do you think?

I hope to do a movie on Yuotube soon!

[vincenzo]

This is a video where you can hear the hum of my amp, so you can assess whether it is normal or not.
As you can hear, when I plug the guitar or only the cable the breath becomes a hum.
Also you can note that when I touch the cable the hum change and sometimes becomes a breath.
Please kindly wish to consider whether this is acceptable or not.
Consider that does not bother when I play.

5F6A Hum

[kagliostro]

Have you fluoreshent lamp in that room ?

Did you tried with other cables ?

The only thing you do as to vary the Humm we can hear (when vol pot is at max)

is to touch the rubber part on the jack ?

During the video registration the other plug of the cable was connected to the guitar ?

K

[vincenzo]

Have you fluoreshent lamp in that room ? No, I haven't. Only a led lamp.

Did you tried with other cables ? No, I'll try.

The only thing you do as to vary the Humm we can hear (when vol pot is at max)

is to touch the rubber part on the jack ? Yes, but not always. Sometimes the hum not vary. But it seems that tapping the rubber part has some effect on the humm

During the video registration the other plug of the cable was connected to the guitar ?Ye, but I've tried also with the other plug not connect to the guitar. The humm not vary.

K

[tubenit]

That hum would be very unacceptable to me.  I think you have a short or grounding problem or perhaps a bad guitar cord.

with respect, Tubenit

[vincenzo]

That hum would be very unacceptable to me.  I think you have a short or grounding problem or perhaps a bad guitar cord.

with respect, Tubenit

Thank's for your opinion. Are you referring at the noise before or after I plug the guitar cord?

[tubenit]

The initial noise is somewhat more than I'd want but perhaps within normal limits.

The noise after you plugged in would be unacceptable to me. Try a different guitar cord and even a different guitar to see if there is a change?

with respect, Tubenit

[vincenzo]

The initial noise is somewhat more than I'd want but perhaps within normal limits.

The noise after you plugged in would be unacceptable to me. Try a different guitar cord and even a different guitar to see if there is a change?

with respect, Tubenit

Ok, let's focus on the noise after I plug the cord. I've noticed that on the Bright Low Input it isn't. On the Bright High Input it is loud. On the Normal Low Input is low and in the Normal High Input is lower.

[tubenit]

On the Bright High Input it is loud   

in the Normal High Input is lower.

May NOT be the issue ............ having said that, I have had on several occasions, the silver mica cap (used as a bright cap) be bad and create hum.

Just a thought.

With respect, Tubenit

[vincenzo]

Ok, the problem of the buzz after plug the guitar cord seems to be resolved.
I think the jack nut make a ground loop. In fact, moving the noise ceased. I only thight the nut while holding the jack. But I non understand... the jack are isolated.

Anyway, now I want to focus on the first noise. I have to add some information before I left. The noise is louder with the Normal vol. With the bright vol it is weaker. Also, the noise is perceptible after vol 7. I soldered two 100R resistor betwen heater wire and ground, though my PT have a heater center tap but nothing has changed.

[vincenzo]

Hi guy,
the hiss or breathe problem seems disappeared. I replaced the V1 and the amply was silent.
When I turned on the amp with the new V1 raising the volume of the hiss was imperceptible. But recently, after playing a bit at low volume, I increased the vol pot to maximum and the breath was more accentuated. It 's normal that the heating tube is more noisy? In addition, with the old V1 tube the hiss was stronger with the Normal volume, now the hiss is louder with Bright Volume. Why is this?

Anyway, some pictures of the amp