Circlotron questions

[banat]

Hi Tinitus !

Just think that combination of ecc81 / 12bh7 will be better one .

Here is my proposed PSU schematic for your Circlotron Amp :
In this PSU configuration output power autotransformer CT dont have to be grounded at all , since all start/returnig low level DC current now pass trough two equal 1,8K/5w ground reference resistors , not anymore trough autoformer coil , with perfect equal biased output EL34 power tube in Circlotron output power bridge there will be now real 0 mA passing trough output autoformer coil under no signal condition .

Best Regards !

 

[tinitus]

very very nice, thanks

measured spec sheets on the tubes in question

12BH7Ahttp://www.tubeampdoctor.com/images/File/TAD-Datenblatt_12BH7A-STR_030811-Version 1.0.pdf

12AU7Ahttp://www.tubeampdoctor.com/images/File/TAD-Datasheet_RT005_030811-Version 1.0.pdf

12AT7http://www.tubeampdoctor.com/images/File/TAD-Datasheet_RT002_030811-Version 1.0.pdf

hmm, 12AT7/ecc81 is not *A* version
but if its the right match here, then so be it

I thought the ecc82 would be a better match with the higher voltage rating
and I see now that THD is half of the ecc81

well, just a side note
I do not have vinyl records
and thus not 'bothered' with low level signal source
phonos, riias, MC pickups etc

but ofcourse still want lowest possible 'noise'

 

[banat]

Well you can swap ecc81 with ecc82 anytime when you want and to listen the sonic difference ,since the tube pins arrangement is the same for both tubes , final choice will be personal choice of your ears , regardless to the some tube datasheet specs .

BTW in that Circlotron PSU schematic I forgot to scratch the PT electrostatic shield between primary and secondary coil , this shield have to be connected on the same main PSU ground star point .

Best Regards !

 

[tinitus]

even better

 

[SpreadSpectrum]

Open loop you are not going to get much over 12-15KHz out of a 12AX7- it is high impedance and so is affected by capacitance in the layout. To reproduce the audio passband without phase shift, you need bandwidth to 1/10th and 10X the cutoff frequencies. A 12AX7 won't make it to 100KHz or 200KHz but a 12AT7 will do it with with ease.

So you mean high rp problems. To get out to 200k, you would need to keep capacitive load down to less than 13pF. Maybe you could buffer it with a little mosfet follower soldered directly to the socket pins. I think there was a tiny Supertex mosfet with only a few pF crss.

The high gain and linearity of the 12AX7 could be useful, I wouldn't dismiss it totally but it would require great care to do well. 12AT7 curves don't look nearly as nice.

 

[tinitus]

looks like we have a curcuit

banat, this one is for you
and others who helped and supported, ofcourse


I know a lot more now
a bit busy now, but will be back later
I hope you will too

cheers

 

[Miles Prower]

Just curious, what do you mean by "bandwidth problems?"

With 12AX7s, you get hit coming and going. It's a high gain triode (u= 100) and that means a big Cmiller on the input. It's also designed for low current operation (Pd(max)= 1200mW) and it gets that high u-Factor by driving up the plate resistance (rp= 90K) not the gm, which limits the current sourcing capability. It won't like a Lo-Z, Hi-C load.

Of course, all VTs have "bandwidth problems", as compared to transistors (natural Lo-Z devices). A 12AX7 is likely to need help in the form of output and sometimes input buffering, either a cathode follower or a source follower if you're going to get any sort of high frequency performance from it. Doesn't mean they can't be used, but you have to watch out for that capacitance problem.

 

[banat]

Tinitus

Best Regards !

 

[myvintageaudiocom]

Your Beautiful Amplifers

1. They are Circltron amplifiers.
2. Big mistake trying to modify these. These were built by a complete Genius. You will not out due what is the best in the world.
3. How much do you want for them?
4. My Number is (personal info removed)
5. Undo everything you have done to them, bias each tube at 60 MV=Millivolts. There is a 1 ohm resistor you are measuring the MV with. You can not measure current on the bias circuit.
6. I don't care what anyone on this page has told you unless they were the person that built these beautiful amplifiers.
7. I have a pair of these so I do know what I am talking about.

 

[myvintageaudiocom]

quote: Is it a circlotron? 6n45c is basically an EL509, so this amp aint THAT huge!

here you go sir..

The amp is a circlotron..what i mean by slow is transit response seems slow its hard to describe...that's why i was playing around with interstage (eletraprint) transformers etc.......
I do remember that the man said it was kinda build/designed off of the electrovoice 100a etc..

Please help i would like to get these back up and running..

These r monsters/ Dont know why yours would sound like that. Mine are

beautiful. 250watts, 3hz to 100khz. 60MV bias.

 

[myvintageaudiocom]

Here are the speakers I built for them.

 

[myvintageaudiocom]

Another pic to show there size. These sound just as moving at 1/2 watt all the way to 250. Ive thrown every type of speaker at them. All with amazing results. Throw your Audio Research, Cary amps and single ended crap in a garbage can. These amps cause an emotional experience when listening to them. They will bring tears to your eyes.

.

 

[tinitus]

hey, I see its still alive
got tubes on my mind, again

lats time it ended with this schematic(drawn by Banat)

 

[tinitus]

btw, plan to replace input tube(ecc81) with a Pass BA-3 pre/driver(SS single ended to balanced converter)

mr Toroidy will do the power supply trafos
so I can get all voltages just the way I want them

 

[banat]

HI Tinitus !

Nothing against Mr.Pass BA-3 pre/driver ( SS single ended to balanced converter ) but in my attached schematic for SE operation it is enough to tie ecc81 (-) input via suitable switch or jumper to ground , since tube Ecc99 is allredy differencial amp (or phase splitter) .

Best Regards !

 

[tinitus]

Nothing against .........

hi, nice to hear from you

hmm, I will build mono amps
they could ofcourse have their own mono attenuator as well

but a seperate pre with the needed gain might be convenient to have, for driving other 'low gain' amps

 

[tinitus]

hey, Im happy with what we have so far

just wonder if it would make sense to design with a 2x 6c19n driver stage
with two tubes instead of a balanced double tube, I suppose we would need to 'balance' the two 6c19n PP drivers

well, I have 20x 6c19n
should last at least a couple of years

 

[banat]

Hi again !

My personal opinion is that tube 6c19n is not good for driver stage for many legitime reason , one of the reason is very variable tubes mutual characteristic .
BTW
If you have pre with relative high gain than you can discard first input stage tube ecc81 , balanced inputs will be connected than to grids of diff. driver stage tube ecc99 , some minor driver circuit modification is needed than for that amp configuration .

 

[tinitus]

ok, I understand
lets keep the ecc99

I think the BA-3 have around 30db gain, in normal single ended
don't know if it changes in single end to balanced, or pure balanced
I have the hard to get components

btw, would it make sense to use GU-50, instead of EL34 ?

ahh, higher Ra resistance ?

 

[banat]

1) You have doubt of right performance for that BA-3 pre
2)You have problem to get components for that DIY BA-3 pre

1+2 = Maybe you need to just forget that BA-3 for DIY and implementation for this Circlotron project , sweet old tubes sounds much better than SS anyway

GU50 is just one perfect power tube in many ways , for this simple Circlotron power Amp design Ra is not the problem since you want GU50 to be connected pseudo-triode , but is limited G2 voltage/disipation and 12,6V filament supply .
I suggest you to stick with EL34 audio tube .

Anyway I well send you later modified schematic for Circlotron Amp with only one Ecc99 and 2x EL34 for your SS BA-3 high gain PreAmp .