Hi Terry,
Good to see another VTTC'er
I will answer briefly below...at each question...
Nice looking tube coil BTW :^)
Hope this helps...
Chris Reeland
Ladd Illinois USA
Sent from my Samsung Galaxy Tab® S
On Mon, Dec 28, 2020, 2:12 PM Terry Fritz <terrellf@xxxxxxx> wrote:
>
> Hello,
>
> I am rebuilding and older duel 811 tube coil to a dual 572B coil.
> The coil is actually in good working condition but I am changing out the
> weaker parts to best of bread ones. The older 811 Svetlana tubes have
> gotten holes burned through the plates and stuff. ;)
> I am not very knowledgeable about tube coil things so I have run into some
> questions.
> Here are the pictures, schematic and parts list.
>
> https://imgbox.com/2b6HInfN
> https://imgbox.com/3WydJGVU
> https://imgbox.com/t77lsj9u
> https://imgbox.com/PFLbaBgP
> https://imgbox.com/JRwxfEns
>
> Questions:
> 1. The original microwave caps out of the microwave transformer were
> 1.786uF (C1) but I am changing them to two new caps I had to 2.381uF at
> 2500VAC total. I am thinking the exact value of these caps is not critical
> at all?
>
More is better here. For level shifter. As long as you meet voltage
requirement, which you do...
> 2. There is that C2 cap at 10kV 1nF. Does it really do anything useful
> at all or is it just eyewash and can be removed?
>
This is necessary to protect the level shifter diode and protect the HV
plate transformer/MOT
> 3. The plate transformer (T3) has two ~2nF caps across the heater
> winding. Do they really do anything at all either? If such parts really
> are useless I will remove them.
>
This is necessary again to protect the filament transformer.
> 4. The grid leak thing has a 8.1 kOhm 30 watt resistor in parallel with a
> 2.2nF 2kV ceramic cap (C6 R1). This was original to the dual 811's.
> Should it be changed for dual 562Bs?
>
This should work fine to start with. The 572B is pretty similar.
That said, this is a "tougher tube" graphite plate which also can handle a
little bit more current also.
You should actually eventually change/adjust grid leak circuit to further
take advantage of better tubes.
> Any other suggests are welcome and thank you for your consideration!
>
> Terry
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