Dragonfly tweeking

[craigmillard]

Hi Guys,

One for the tubey types

Im looking to build a version of dougs amp the dragonfly:

http://www.aronnelson.com/gallery/main.php/v/DougH/amp/Dragonfly+Amp/Dragonfly.GIF.html?g2_imageViewsIndex=1

But am going to use 6n6p's instead of EC99's, can anyone see a problem with this? will the bias need altering or the transformer primary adjusting?

6n6p datasheet:
http://www.lampizator.eu/UPGRADE/RU-6N6P.pdf

From what i can tell you can straight drop them in as long as you alter the heater wiring..

Cheers all!

[craigmillard]

Anyone?

[danielzink]

If you don't get an answer here.....you might try posting over at AX84 in the Firefly forum (http://www.ax84.com/bbs/index.php?area=17)

HTH, Dan

[iccaros]

I believe the Heaters are wired different, meaning you have to wire 6.3 + and - on pin 4 and 5 and pin 9 goes to ground. and ECC99 is pin 4 and 5 tied together and pin 9 the other side of the 6.3 volts.

They are similar in other specifications, you should measure your cathode current when in operation to see if you need to change your bias point, I have found that I needed to adjust between ECC99's.  I change the cathode resister with a resistor half its rating, and added a 1ohm with measuring points, and a pot (1K) 2 watt. to allow me to adjust the bias as needed. this amp has more interactions with bias as  you are setting both the cathode bias and the grid bias at the same time.

[craigmillard]

cheers for the response iccaros!

Yer the heaters are all good, i have used the Russian tubes before and know about the heaters..

Sounds like a good idea with the biasing.. Have you built this amp then?

[iccaros]

I have build a few variations on this amp, I have not built it 100% like in the diagram, I used a Brownface two knob EQ with out the FET, but I think the FET would improve some Issue I had getting rid of it..

nice build and the ECC 99's sound a lot like EL84's wired as a triode, so good luck

I do not rewire my sockets for those tubes, I built some adapters, but given how cheep those and other EU tubes (6n2P) are, I am thinking of adding a switch now for the heaters.. Merlin has  a good ideal, I just have not tried it.. It adds some parts but would let you swap tubes with no issues..
http://www.valvewizard.co.uk/heater.html