Help checking Tube Amp Supply

[sonolink]

Input ground

 

[sonolink]

HV ground (B-)

 

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One question: The PT is not the original (the original hummed too). This is a fine Danbury handmade TX that I've used in many builds. It has, like the original, 2 secondaries: 0-275, and 6.3 with CT. The CT of the 6.3 secondary is grounded together with the EL84s cathodes to the HV ground rail. Is that ok?
Do I need to ground or CT the other winding?
This hum thing is driving me insane.  I've never had such a problem in any of my amp builds. Grrr.....

Cheers
Sono

 

[ruffrecords]

One question: The PT is not the original (the original hummed too). This is a fine Danbury handmade TX that I've used in many builds. It has, like the original, 2 secondaries: 0-275, and 6.3 with CT. The CT of the 6.3 secondary is grounded together with the EL84s cathodes to the HV ground rail. Is that ok?

Yes, that is OK.  I use Danbury transformers my self. They are very good.

Do I need to ground or CT the other winding?
This hum thing is driving me insane.  I've never had such a problem in any of my amp builds. Grrr.....

Cheers
Sono

No, you don't need to CT the HT winding. As your picture showed, the HT is connected to the chassis. This might be the problem. You really need to connect the HT 0V to the chassis at ONE point only. This point in your case is the input connector which you have connected to the chassis. So your additional wire from the power supply 0V to chassis is not needed. I suggest you try disconnecting it. You also need to ensure the mains safety ground is connected to the chassis where the mains enters.

Cheers

Ian

 

[sonolink]

Ian

My input connector is grounded to chassis only. It's not connected to the ground rail on the board. The ground rail is wired to chassis on one place only. The pots  are grounded to chassis also and only to chassis. Same for output connector.
Since the nature of the sound I was wondering if I had left out any ground connection or created a ground loop somewhere. Right now I don't know anything anymore

To be honest I'm about to give up on this amp. I don't know what's wrong with it but I'm very frustrated, lostband confused, out of ideas and it's probably easier and faster to rebuild from scratch!

Ian,
I'm very grateful to you for taking the time to study the schematic and layout and trying to help me.
Thanks a lot mate

Cheers
Sono

 

[ruffrecords]

Ian

My input connector is grounded to chassis only. It's not connected to the ground rail on the board. The ground rail is wired to chassis on one place only.

Which is wrong. These amps generally connect the chassis to the 0V AT the input connector. So, you should connect the input connector to chassis. You should also have a screened lead from the input connector to the amp input. The screen should be connected at the connector end to the chassis and at the amp input end to HT 0V. Look at the schematic you posted and you should see what I mean. There should be no other connection between HT 0V and chassis. This is what I was trying to get across in the last post. If you wire the chassis/0V as in the schematic then your connection from HT 0V at the power supply to chassis is not needed. It is possible that the way you have chassis/0V connected is causing the hum.

The pots  are grounded to chassis also and only to chassis. Same for output connector.

That sounds right.

Since the nature of the sound I was wondering if I had left out any ground connection or created a ground loop somewhere. Right now I don't know anything anymore

I don't think you have a loop but I think you grounding is not the same as the original schematic.

To be honest I'm about to give up on this amp. I don't know what's wrong with it but I'm very frustrated, lost and confused, out of ideas and it's probably easier and faster to rebuild from scratch!

Ian,
I'm very grateful to you for taking the time to study the schematic and layout and trying to help me.
Thanks a lot mate

Cheers
Sono

No problem.  It is always very difficult trying to diagnose by remote control. I am sorry we did not have better success. If you ever bring it back to the UK and fancy a trip to Norfolk I would be happy to have a look at it for you.

Cheers

Ian

 

[sonolink]

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Which is wrong. These amps generally connect the chassis to the 0V AT the input connector. So, you should connect the input connector to chassis. You should also have a screened lead from the input connector to the amp input. The screen should be connected at the connector end to the chassis and at the amp input end to HT 0V.

Mmmm I think I see what you mean. It's odd because I usually connect the input jack ground, pots ground and cathodes to the board's 0v rail. Then I connect the 0v rail, the output jack ground, and Mains earth to chassis. The input lead is a screened cable but I connect the shield only on the input jack side. Of course this grounding scheme is not mine. I copied it.  But I've never had hum loops problems with it. I'll look into that though

/quote]

I don't think you have a loop but I think you grounding is not the same as the original schematic.

Absolutely. The Pro Junior per se is a hummer and hisses like a snake. The idea behind this build was precisely to clean it up since its tone and portability make it a great amp.

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No problem.  It is always very difficult trying to diagnose by remote control. I am sorry we did not have better success. If you ever bring it back to the UK and fancy a trip to Norfolk I would be happy to have a look at it for you.

I know and that's why I appreciate your effort
And thanks a lot for such a nice invitation! Norfolk is precious especially at this time of year. I'll let you know when I'm back in the UK and near you. The beers are on me!

Cheers
Sono