5F6A low volume

[tboy]

I realized I forgot to solder feedback resistor to out... ...Now the amp has right volume but sometimes it disappears. It also seems to produce some sort of oscillation when I increase the volume control and it has background noise.

Are you sure you have the correct polarity for the feedback? Having positive feedback where it should be negative could cause those symptoms.

[vinceg]

Update

I checked the heaters voltage at the output of the transformer with socket heaters wires disconnect and it is 6.25V. Right. Then, I extract all tubes and I measured the heater voltage on each socket and it is 6.10V. Then, I measured heater voltage with all tubes in and it is 5.7 -5.9 V. Doing tests, extracting preamp tubes I understood that with only the power tubes in the heater voltage is about 5.7 V. Is it right or there is a problem?

About the low volume, I built a Audio probe and I injected a 1KHz signal at amp input. Then I checked with probe at V1 preamp out and there was a signal. Then I checked at V2 pin 8 and I heard a very strong pop and I was scared and I left. So I bet the probe at pin 3 of the power tubes and I heard an amplified noise but not the signal. I need your help to use the probe in the correct way and find the cause of the low volume.

Update
I think I think I found the point where the signal is interrupted. At V2 pin 1 there is signal but at pin 6 and pin 8 there is not signal. Why? I try swapped the tubes V2 and V3 but there is no change. I also checked with smartphone camera for unwanted contacts and also with tester but it solder seems right.

[Chuck H]

Are you using a light bulb current limiter or Variac type adjustable transformer during this testing?

[vinceg]

Are you using a light bulb current limiter or Variac type adjustable transformer during this testing?

No. Did I make any trouble?

[Chuck H]

No. Did I make any trouble?

No. I'm trying to figure out why your filament voltage is low. It is already below 6.3V with that transformer winding unloaded. This is a problem. It would be typical to see that unloaded voltage be higher than 6.3V to compensate for loading with tubes installed. Do you know your power transformer brand and model number?

[vinceg]

No. I'm trying to figure out why your filament voltage is low. It is already below 6.3V with that transformer winding unloaded. This is a problem. It would be typical to see that unloaded voltage be higher than 6.3V to compensate for loading with tubes installed. Do you know your power transformer brand and model number?

Ok, low volume problem solved. V2 pin 5was broken and half of the filament getting no power.

About heater voltage, mi trasf is a Hammond 290DEX. It has about 6.3 V at out without tubes. What could be the problem?

[eschertron]

Are the Hammond 290DEX primaries specified for 120VAC/240VAC? Is you local wall voltage much less that 240VAC?

[Helmholtz]

And please check your actual mains voltage at the PT primary.
The Ceriatone layout shows a 240V/120V PT.
If your mains voltage is only around 216V, this would be an explanation for the low heater voltage.

[vinceg]

Are the Hammond 290DEX primaries specified for 120VAC/240VAC? Is you local wall voltage much less that 240VAC?

And please check your actual mains voltage at the PT primary.
The Ceriatone layout shows a 240V/120V PT.
If your mains voltage is only around 216V, this would be an explanation for the low heater voltage.

In Italy we have 220VAC on wall. It, of course, is subject to oscillations, generally between 210 and 230VAC. In my house it is quite stable around 220VAC
Could this is a problem? My amp has worked from 2013 before this re wiring.

[eschertron]

All your secondary voltages are low by over 8%. This does explain heater voltage sitting below 5.7vac. If the amp has worked sufficiently well for you in the past, we can ignore the low voltage for now.

[vinceg]

Are the Hammond 290DEX primaries specified for 120VAC/240VAC? Is you local wall voltage much less that 240VAC?

And please check your actual mains voltage at the PT primary.
The Ceriatone layout shows a 240V/120V PT.
If your mains voltage is only around 216V, this would be an explanation for the low heater voltage.

All your secondary voltages are low by over 8%. This does explain heater voltage sitting below 5.7vac. If the amp has worked sufficiently well for you in the past, we can ignore the low voltage for now.

If the network voltage is this, could I do something to raise the values?

[Chuck H]

What eschertron said. 5.7V is low, but according to the math it's just what you should have using a 240V PT at 220V. So we ignore it for now...

In fact, from what I've read here, a tonal detriment due to low filament voltage isn't really apparent until you get down under 5V and that lower voltages also tend to reduce noise and increase tube life. I'm not saying it's good to run low. The tube is designed for 6.3V so something is going to suffer at least a little. Maybe a tiny decrease in gain? Since tube life is reported to increase I don't suspect cathode poisoning damage. Anyway, From what I've read here it's not a problem until you get a lot lower than where you're at now.

[g1]

So you fixed the volume problem by connecting (1/2) V2 heater.
Is there still some other problem or does it now sound like before?

[Helmholtz]

Since tube life is reported to increase I don't suspect cathode poisoning damage.

Sorry to distract, but what is the source of this info?

[Helmholtz]

In Italy we have 220VAC on wall.

Nominal mains voltage in the whole EU (including Italy and GB) is 230V (+/-23V) since 1987 (IEC standard 60038).