6D22s damper diodes.

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pre65
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#16

Post by pre65 »

The mains transformer is 0-360 + 0-360 with centre taps connected together, so 0-720. There are also two 6.3v secs, one is used for both 6D22s diodes, and the other is for the 6SN7 and EL34.

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#17

Post by Paul Barker »

Can't fault it.
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#18

Post by andrew Ivimey »

who could but ... (and I may be wrong)) Phil raises the heaters to HT - errrrmmmm why? Is there no reason why the otherwise delightful 6D22s shouldn't have a nervous breakdown?

ooops I am just about to be sprayed with strange and exotic sprays!!!!!


aaaaaaaaaaaaaaaaaaaarrrrrrrrrrrrrrrrrrrrrrggggggggggggghhhhhhhhh
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#19

Post by Paul Barker »

It's a short thread Andrew, if you go to the beginning you will see why.
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#20

Post by andrew Ivimey »

Just been there -yes I see what you mean - I think our Philip misstreats these excellent rectifiers!
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#21

Post by Paul Barker »

Did a very swift google on the subject and straight away found there are production quality problems. Triode dick described on his 211 amp how he ran out of them. He bought another 8 and pfft they went. His fisrt cap was only 15uF. He ended up using EY500's.

Our Phil I think it's time to use a different rectifier. The pundits who first suggested the 6d22s were either people with a vested interest in sales (Eric Barbour) and people with low voltage amplifiers (relative to what you are doing)

The English rectifier made for the job is the U19. But there would be series resistance and first cap criteria to observe. If you want to try them I can send you two, or is it dual mono? Do you need 4? Your power transformer probably has virtually no resistance this data sheet shows R source minimum 500ohm tdsl says 600 ohm. first cap 4uF. But it is designed for RMS of transformer 2.5 kv. It may be that at your voltages the full 500ohm isn't necessary. But you would need a lot more dc resistance than is healthy for your final voltage. You would also best heat the filament before turning on the ht if you can't provide the full 500ohm or it may short.

Maybe try full solid state?


Microwave diodes would be reliable and cheap if not boutique!
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#22

Post by pre65 »

What about solid state damper diodes, to use with 6D22s in a hybrid bridge ?
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#23

Post by colin.hepburn »

Why the hybrid bridge what is the reason behind this my 6D22s in my J E Labs EL34 are just connected to the 6.3 tap as in this link my 360-0-360 CT TX
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#24

Post by Paul Barker »

Because Phil needs twice the voltage.
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#25

Post by pre65 »

Yes Colin, you should know the difference between full wave and bridge rectification by now. :wink:

As Paul says, it's all about what voltage you need from a given transformer.

My transformer is 0-720v and I'm looking for HT of up to 1000v.

Depending on how you rectify, and if choke, or cap input the range of output from any given transformer is huge. Ideally, one selects from all these variables and buys all the necessary bits to start a project, but sometimes we can't (or don't want to :wink:).
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#26

Post by Andrew »

I recall Andrew I built a version the "Doddington Special", Andrew had used 6D22S for the rectifier, when we came to try this amp at a meet, we all wanted to hear it, we ended up subbing one damper diode with a solid state job from a box of parts I had with me. In my mind, at least, 6D22S were already moving into the suspect category.

Some Russian valves are great but others vary in quality a great deal, Nick, myself and others have found that not all 6N6P, for example, are created equal.

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#27

Post by pre65 »

Yes Andrew, I remember that occurrence.

Do you remember the details of those SS damper diodes ?

The ones I've seen seem to be 1500v max.
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#28

Post by Paul Barker »

I am just wandering why are you chasing solid state damper diodes? If you are going solid state then you are better off multiplying FRED's and paralleling them with 1 meg 2 watt resistors to equalise the voltage across them, and if you like follow Morgan Jones with the 10nf cap across each one, though I have yet to hear a difference on FRED's.

Back in the day you could only get FRED's from Michael Percy (who was the most unreliable component supplier, people put in an order and git it a year later. The excuse eventually came that he was moving home at that time.) but now the world is your oyster.

The reason you were led into using tv damper diodes in the valve arena was because of the slow start and the mythical popularity of them spurned by Eric Barbour's need to create an impression in his new job selling Svetlana Valves primarily to America. He was supported in this by other "great" or influential American valve audio pundits and the job was complete, to create an Aura of perfection. But all it really is or ever was, was a means of dealing with the voltages and currents with a built in slow start. It all fell down with reliability issues.

Now pick yourself up and start again. But to start in the solid state arena with damper diodes is not the right move.
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#29

Post by Andrew »

pre65 wrote:Yes Andrew, I remember that occurrence.

Do you remember the details of those SS damper diodes ?

The ones I've seen seem to be 1500v max.
Much less than 1500v Phil, the "Dodd Spesh" was quite low HT voltage, as I recall. Personally, I'd go with Paul and use quality series diodes and balancing resistors, make sure the resistors are rated appropriately.

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#30

Post by pre65 »

When looking for alternative diodes they seem either to be high voltage/low current or low voltage/high current.

I looked at FRED diodes before, but could not find the ideal parameters.

Any one know of a diode that does 2KV and 2 amp ?
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