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Re: [TCML] Rebuilding VTTC

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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