5F6A low volume

[vinceg]

Maybe the tube or a contact of the tube socket is bad? Are the plate resistors correct (82k and 100k)?
What Vdc are the V3 grids pins 2 and 7? They won't measure correctly, but they should measure very close.

Voltage at pins 2 and 7 is 24V. Plate resistors are correct.

[pdf64]

Does the setting of the presence control affect the wacky reading? Or how the meter leads fall in relation to the amp chassis?
I’m thinking that it may be due to oscillation caused by the meter/leads increasing ‘bad’ coupling. Hence it sounding good when it’s not being measured.

[vinceg]

Does the setting of the presence control affect the wacky reading?

I do not konw, I'll check tomorrow

Or how the meter leads fall in relation to the amp chassis?
I’m thinking that it may be due to oscillation caused by the meter/leads increasing ‘bad’ coupling. Hence it sounding good when it’s not being measured.

Sorry, but because of my bad english I do not understand what do you mean.

[Helmholtz]

To me the voltage readings indicate that the lower triode system of V3 is not conducting. Would mean that only one of the power tubes gets a drive signal. Sound should be distorted. Reason could be a bad tube or bad (socket) contact.

Of course also oscillation can produce strange voltage readings. In this case twisting the meter leads and keeping them outside the chassis and away from tubes should change voltage readings. Please use tube shields.

[vinceg]

Update
Finally the socket has been delivered.
I changed V3 socket and now voltages at pins 1and 6 are right, about 230VDC.
The amp seems sound fine.
I noticed some pop when I touch wires around pots controls but they have disappeared as soon as I moved sone wires.
There is only a slight background noise that does not depend from volume controls. I do not know if it is normal.

[vinceg]

About heaters voltage, considering that I have a wall voltage of 220VAC, PT input voltage 240VAC, it is 5,7 VAC with all tubes in. How can I increase hetars voltage?

[Chuck H]

You really can't. Well, I suppose you could add a more suitable and dedicated filament transformer, but I wouldn't. Sometimes you can get a couple of tenths of a V by using heavier gauge filament wire and keeping the runs as short as practical. Your build looks like it has ample gauge wire for the filaments and they're not overly long, so there's not much to be done there either.

[vinceg]

Probably, if I used a PT with 220VAC primary winding, like my house wall voltage, I would have a higher heater voltage, but I would have to spend a lot of money. Or would it be better to use a voltage stabilizer to power the amplifier?

[Chuck H]

Something like an autotransformer might be a good solution for you because you could use it for any amp as well as for repairs. Also expensive. Probably a little more than a power transformer. Less work than changing the power transformer though.

[pdf64]

Using the same principle as a mains bucker, a small transformer, eg with a 20V secondary, could be used to boost a 220 mains supply to create a 240V feed for the amp.
See http://www.geofex.com/Article_Folder...t/vintvolt.htm

[g1]

Why are you worried about 5.7VAC at the heaters? Is it causing a problem?
It should run fine like that. If anything, it's better than running heaters 10% over, which many amps do.

[vinceg]

This is a small video that you hear background noise. Can you help me to find problem?
https://youtu.be/vx6LWXCLwwQ

[Chuck H]

That sounds like instability and/or possibly a bad tube or tubes to me.

Do any of the controls affect the noise? If you turn down the treble does it stop?

If you turn up the volume and treble does it get worse?

If you tap on the tubes, what noises do they make?

[vinceg]

I refer to background hum like not to whistles, even if this is a problem. Anyway, the whistles disappears after few minuts

Hum is not affected by controls.

Only V2 tube is noise on speaker when I tap it. But I changed three tubes in V2 and it is always noise at tap.

[vinceg]

That sounds like instability and/or possibly a bad tube or tubes to me.

Do any of the controls affect the noise? If you turn down the treble does it stop?

If you turn up the volume and treble does it get worse?

If you tap on the tubes, what noises do they make?

I'm amazed! I discoverd that V3 tube was too hot, then I swap it with new tube. Background hum and whistles are disappeared but amp volume is slightly decreased.

Let's say that the volume that was first heard at 1 now we hear at 3