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PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread
http://www.diyaudioprojects.com/Forum/viewtopic.php?f=9&t=1232
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Author:  ILoveHiFi [ 06 Mar 2020, 04:47 ]
Post subject:  Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

So you have to first understand how the circuit is designed to create the best wiering.

Then you identify which parts can and cannot have long wiering.

Then ground wiering is more off exprience and is hard to explain how to do it properly.

Drawing a layout on paper or computer means you have a proper plan before building, most dudes just do it without a plan so the layout is never going to be great.

Friendly advice is to ground the amplifier part together, then you take only one wire from the power supply part then insert it at the mid point of the ground in the amp part.

Author:  mbunjes [ 06 Mar 2020, 05:14 ]
Post subject:  Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

Thank you. I understand that for example grid stoppers have to be close to the tube sockets and that's how I've drawn them. Are there any others ?
Also I've seen several choices for the star ground; close to the input socket or close by the first elco in the PSU or just somewhere in the middle of the amp. What do you think ?

Author:  ILoveHiFi [ 06 Mar 2020, 19:55 ]
Post subject:  Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

Ground close to input is mostly the best choice, but make the local ground close to the ampflication part, not close to the RCA jacks cause your causing extra resistance in the ground which detoriates the perfomance.
Then fly two wires from input directly to the L and R inputs and local ground.

Anything connected or related to the gird should be close to ground and have short ground wiering to prevent noise.

Author:  mbunjes [ 11 Mar 2020, 10:06 ]
Post subject:  Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

Although I get the impression this forum is not actively monitored anymore, I still have to try to get answers to my questions.
The following is my latest layout. I'm pretty happy with it but a few things still aren't clear :
What would the best way be to connect the heaters ? My idea was to to connect the 6 - 0 - 6 wires from the transformer to a tag board and from there run two wires to each tube. Somewhere I read it's not a good idea to daisy chain the heaters although it would be a lot easier.
Also, will the grounding be alright the way I proposed it ?

Author:  gofar99 [ 11 Mar 2020, 15:53 ]
Post subject:  Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

Hi, I'm not sure what gave you that idea, but the thread is checked whenever there is a new posting. There are times when an answer is not provided, but that is usually because the question has already been answered earlier and the individual did not successfully seek it out. As for the immediate question, either way will be fine. I use both. In virtually all the designs with DC powered heaters I series the tube heaters. It works fine, is easier and more efficient to do that. It should be noted that all the commercial kit amps (all the way to KT120s) do that as well. For AC heaters either way is OK and there are no particular advantages to one over the other. If you do series the heaters then the center tap would go the heater reference voltage tap. This would be in the range of 1/3 the B+ voltage. If you ground any part of the heater circuit you will both increase the residual noise level and risk tube failure of the driver tube. They are rated for up to 200 volts between any cathode and any heater and seemingly should be fine. Unfortunately the reality is different and They do fail. Usually with internal arcing and it is rather dramatic. The spike generated is huge.

Your grounding seems OK.

Good listening
Bruce

Author:  mbunjes [ 11 Mar 2020, 17:17 ]
Post subject:  Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

Thanks very much Bruce. I'm not sure I follow though, what do you mean by "the center tap would go to the heater reference voltage tap" ? Do I lead the CT as a very long wire from socket to socket and finally to the B+ circuit ? I have a hard time visualizing the whole heater thing. I understand not to ground any part of the heater circuit.
Sorry for my limited knowledge.

Martin

Author:  mbunjes [ 11 Mar 2020, 17:32 ]
Post subject:  Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

I've drawn in the heaters as I understand it.

Author:  gofar99 [ 11 Mar 2020, 17:53 ]
Post subject:  Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

Hi, I have attached a partial schematic of a poddwatt (only one channel) that shows the heater configuration. It uses AC heaters. The orange lines show how the reference voltage is applied to the heaters. The result is that the entire heater circuit is floating above the signal ground level by a DC voltage (no current is used, just a reference voltage only) of around 1/3 the B+ voltage applied to the anodes.

I hope this helps

Good listening
Bruce



Attachment:
Single channel type E partial.png

Author:  mbunjes [ 12 Mar 2020, 01:04 ]
Post subject:  Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

That looks easiest. The ct is not even connected to the tube sockets anymore. So to be absolutely clear in my mind, the 5751 is fed with 12 V so i would use only pin 4 and 5 ?
I was planning on using the power supply variant that doesn't have the diode and trim pot for each channel, does it make much difference ?

Author:  gofar99 [ 12 Mar 2020, 08:48 ]
Post subject:  Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

Hi, That is correct on the pins 4 and 5 and it doesn't matter which version you choose. The heaters all are configured the same way.

Good listening
Bruce

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