tube talk

a DIY, modified Mullard 5-20 monoblock design

tube talk

Postby audioray » Fri Oct 29, 2004 10:19 am

how come no talk about tubes for eyclone amp.
and on bias method.. how to do it for diff. tubes
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Different tube/ transformer combo's

Postby TerrySmith » Sat Oct 30, 2004 8:55 am

I have often thought of using a PA-774 / Z565 on an Ike board with 6L6's (coke bottle shaped of course), for a lower power more econmical build. Or maybe try 6V6's or KT66, This amp could be more universal than we think.

With a Z565 opt, it may require cathode bias.
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Re: Different tube/ transformer combo's

Postby Shannon Parks » Sat Oct 30, 2004 9:19 am

TerrySmith wrote:I have often thought of using a PA-774 / Z565 on an Ike board with 6L6's (coke bottle shaped of course), for a lower power more econmical build. Or maybe try 6V6's or KT66, This amp could be more universal than we think.

With a Z565 opt, it may require cathode bias.


That's the idea! My plan is a 270HX/Z565 cathode biased 6B4 PP amp. It is just on the slow 'to do' list. The higher Z of the output makes it a pure Class A operation with great dampening.

Ray, I've used Sovtek KT88s biased at 65mA and EI KT90s biased at 70mA. Both fantastic. Set the idle at ~75% max dissipation.

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Postby TerrySmith » Sat Oct 30, 2004 11:55 am

The phase inverter tube (6SN7) gets 445v. How will it react with lower voltage?
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Postby Shannon Parks » Sat Oct 30, 2004 12:49 pm

TerrySmith wrote:The phase inverter tube (6SN7) gets 445v. How will it react with lower voltage?


Terry,

Nothing slips past you, does it? :wink:

I have an undocumented CCS circuit in the Eiclone (Rev B). Basically, you cut the trace to the 6SN7 where I have a footprint for AC coupling cap. Then you ground the LTP cap, lose the tail resistor, and add a LM334Z with a 10 ohm current set resistor. You can then increase the plate resistors, too. So instead of losing over 120V across the tail resistor, there's only a 7V or 8V drop. I guess it is 'documented' now.

This also permits the 6SN7 to drive a fixed biased 6B4G with the smaller grid resistors. Spec says 50K max, but I see some classics used 100K.

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