Can anyone give more info on this amp?

[mg16]

Hi,
I am looking for a good el84/6bq5 schematic to build someday soon hopefully.
I have built 300b and 45's se before.
This Dynaco circuit looks easy to build, and similar to an st-35 that gets good word of mouth.
Anyone know the power output of this one, and the input tube it uses which isn't labled. Also whats with the 100 ohm resistor shown in the input tube?
Is this internal to the tube itself?
Any help greatly appreciated.
thanks,
mg16

 

[mg16]

sorry heres the url

http://www.triodeel.com/dyna6bq5.gif

 

[mg16]

ok its 12ax7

i can see the input tube is 12ax7 when i went to the url.
my printed copy i am looking at cut off the 12ax7 in the picture.
wierd way of drawing the 12ax7 threw me.
Anyone build this and know the power output?
thanks,
mg16

 

[Colt45]

around 16 watts for 300v / 130ohm Rk, IIRC.


yeah, just checked data.. 300v, w/ 130ohm shared Rk nets you 17watts @ 10% THD, i guess the NFB will knock the distortion down though.

 

[EC8010]

PP EL84 will deliver almost 17W (straying into Class AB). A more reasonable figure is 10W, which takes Class A and output transformer limitations into account.

 

[mg16]

EXCELLENT! Thanks very much

Thanks a ton.
I think I will make the feedback tank circuit either switch selectable or switchable varying from 0 to the value shown.
To do this, would I hold the fb cap fixed at .001 uf, and make the resistor variable from 0 to 1k, or would the cap have to vary with the 1k fb resistor?
The time constant is 1 us., should that remain constant?

thanks
mg16

 

[stokessd]

You've got a lot of good choices. There's the dual triode input like the link to Ned's site above or like the fisher designs (SA-16 for example), then there are the pentode/triode designs which fall into two general catagories. The single triode like the dyna circuit and the heath circuits which use a single triode section as a split load inverter. Then there's the mullard 5-10 circuit witch uses a pair of triode sections as a long tail pair phase inverter.

I've got a lot of schematics for EL84 amps in my site. They are a personal favorite of mine for driving the original Quads.


Sheldon