Help checking Tube Amp Supply

Btw this is the original Fender schematic

And this is my layout

> where should I look for the solution?

Did you read my post?

I did indeed and thanked you for your input. I calculated the current draw following your line of thought and came to the conclusion that it was too low and asked if my conclusion was right, not sure if that was what you meant since English is not my native language and to discard any language barrier (for which I apologise).
If the problem is that the tubes are not pulling current, since I already said to Ian that they were glowing, I suppose the reason is, as you say

PRR said:

No path from Cathode back to B- (missing connections in cathode networks or ground path).

Click to expand...

So I apologise if it seemed like I didn't read your comment but I did.

I understand that "cathode networks" is anything wired between the tubes cathodes and ground and that's what I have to check right? (That's what I meant by where should I look for the solution?")

Cheers
Sono

Pins 3 on v3&4 had a bad solder joint 

Thanks PRR for your help on that.

Now I have massive hum with vol down but I have sound!

I guess I need to rework my grounding scheme

Thanks again

Cheers
Sono

I got rid of most of the hum with the heaters' CT and two 47 Ohms resistors.
Still have some though, and when raising the volume pot there's also hiss.

I chopsticked it and I get pops from some cables. Notably pins1&2 on v1 and the EL84s cathodes. I wired this connecting both pins 3 together and then I wired v4's pin 3 to the ground rail. Maybe the joint on the ground rail is bad. I'll resolder all that tomorrow.

I still haven't heard it since it was late here when I fixed the cathode connections so I'll play it tomorrow. I hope the sound is good

Any other ideas to clean the hum and hiss are most welcome,  although I suspect most has to do with proper grounding...

Good night and thanks again
Cheers
Sono

It is not unusual for a guitar ham to hiss at high volume settings. There is a lot of gain in the first stage before the volume control and that is what you are hearing.

Hum can be caused by several factors. Make sure the heater wires are twisted, laid close to the chassis and kept away from sensitive signal wires. You could replace the two CT 47 ohm resistors with a wirewound 100 ohm pot and adjust that for minimum him.

If the hum is at mains frequency then it it likely to come from the heater wiring. If it is mostly twice mains frequency or higher then it it likley to be insufficient smoothing/decoupling of the HT supplies.

Cheers

Ian

Ian

Thanks for the tips
I've done some of them, like twisting all AC leads, etc.

Would you mind taking a look at this link please? At the bottom of the page a DC offset is described to reduce hum. The guy says to ground it to the virtual ground resistors. Would that be the 47R resistors on the heaters central tap? If so, the connection would be to one of the 2 resistors right? Do you reckon this dc offset is worth a shot?

This is the link:
http://home.comcast.net/~machrone/bjr/pjmods.htm

Cheers
Sono

Ok so the amp sounds fine now. It's steady and doesn't oscillate.  Tone is great BUT it hums like hell.

I suspect it's mains hum since the pitch is the same as the ceiling fluorescent light and it happens independently of the amp's volume being on or off.

My guess is this either happens after the vol pot or is picked up after it.

So I've rewired several times every AC line I could think of but no go. I even tried a different TX with a CT on the heaters winding and same thing.

When I chopstick it the hum doesn't change.

I've attached some pics of the build in case something is obviously wrong.

Any ideas?
Thanks a lot for your help

Cheers
Sono

V3&4

V1&2

Pots

PT

Looking at the last pic I wonder if your bridge is wired correctly. If the bottom most tag is the HT 0V then there should not be a diode's cathode (with the band on it) wired to it from the bridge. However, if it is HT+ then it is probably OK.

Cheers

Ian

Here's a close up pic. Would that be the source of that loud hum?
It's driving me crazy 

Cheers
Sono

That wiring looks OK to me. First we need to find out if it is mains hum or hum in the HT circuit. You can determine this with a simple test. Turn the amp on and let it warm up. Then turn it off at the mains whilst listening to the speakers. If the hum continues for a short while then it is main hum coupled into the circuit comehow. If the hum immediately disappears it is hum on the HT line.

Cheers

Ian

Ian,

Thanks for your help 
I just did the test
The hum disappears immediately.

Cheers
Sono

OK, this looks like HT hum. A common cause of HT hum is if the output tube(s) draw too much quiescent current.  A smple way to test fro this is to remove the phase splitter tube V2, turn on the amp and see if the hum is still there.

Cheers

ian

Ian
Thanks for your help

I tried without v2 and there's no hum
What's the next step?

Cheers
Sono

Some voltages in case it helps:

Mains: 234vac

HV: 271 vac
TP22: 382vac/174vdc
TP23: -11
TP24: 347
TP25: 323
TP 26: 252

V1
pin 1: 160
pin 2: 0
pin 3: 1.3
pin 6: 157
pin 7: 0
pin 8: 1.3

V2
pin 1: 178
pin 2: 17
pin 3: 44.8
pin 6: 175
pin 7: 15.5
pin 8: 45

V3
pin 2: -9.2
pin 3: 0
pin 7: 344
pin 8: 322

V3
pin 2: -9.2
pin 3: 0
pin 7: 344
pin 8: 322

All heaters have lowish but correct voltage (5.8vac)

I tried replacing all tubes with known working ones and plugged a different amp in the same outlet to discard that too.

Cheers
Sono