F6 Amplifier

[Antoinel]

I am not sure what the relevance is for "AC ground". What is important are the bias voltages relative to the bottom of the FET source resistors. We are trying to maintain these voltages at constant levels under varying signal conditions.

The AC drive signal to the upper JFET will be relatively larger in magnitude than for the lower JFET. In your opinion is it or not?

 

[buzzforb]

ZM, Why will it go bottatboom? Dont understand.It is used as Vref for so many bias circuts for transistors.

 

[Rush]

The AC drive signal to the upper JFET will be relatively larger in magnitude than for the lower JFET. In your opinion is it or not?

The AC drive signal is the same for both secondaries of the transformer (they don't know how they are being used). If you have a different resistance across one of the secondaries you may change the amplitude.
Please explain how could the AC drive signal be different in the secondaries?

Rush

 

[Zen Mod]

ZM, Why will it go bottatboom? Dont understand.It is used as Vref for so many bias circuts for transistors.

.....

you need to change places of leds and CCS

read what I wrote about 6k8 res on bobbo's sch

 

[buzzforb]

Choice of Rs on output stage has affect on values of bias network. Is it in parallel with bias network?

 

[Zen Mod]

no
, it isn't in parallel

it is important for for needed bias voltage span which you're having on trimpot

without Rs - say that you need 1V5 max

with Rs=0R47 and Iq=2A , you need 1V more

 

[buzzforb]

Damn, i amignorant. If i use 2sk246, I can run at Idss, correct. Should i use1K resistor above to help with dissipation?

 

[Zen Mod]

you can waste at least 50% of PSU voltage on additional resistor

 

[bobodioulasso]

now choose Rs value & Iq , and calculate that in.

ZM will allow at least 1mA through trimpot , and 3mA through zenner

 

[Zen Mod]

go and build

say tnx! to Pa

if you can't find 3k trimpot - use 2K one , and 1K resistor below

and yes , you can use more than 10uF in series with secondary

 

[buzzforb]

No it isn't ripple or noise.

The objective is to present nearly identical bias conditions to the 2 output FETs. The ideal scenario is when both bias voltages are referenced to the bottom of the FET source resistors. But, to maintain a low and stable DC output offset, the upper bias generator is referenced to ground.

The solution is to integrate the upper bias voltage relative to the output signal (the bottom of the upper source resistor), hence the RC filter.
The AC currents through the transformer windings also modulate the voltages across the integrating capacitors, will cancel if the AC impedances of the bias circuits are the same, thus minimizing 2nd order harmonic distortion. This is accomplished by having identical filters in each bias circuit.

I found in both simulation and actual breadboard testing that single stage RC filters with large values of RC could create low frequency (<< 1Hz) oscillation problems. LTSpice Bode plots show phase margin problems under these conditions.

The 2-pole RC filter eliminates the phase margin problem and makes it possible to make RC as large as desired.

So the 2 pole filter allows bootstrapping of bias section to output node , as Nelson suggested.

 

[Antoinel]

The AC drive signal is the same for both secondaries of the transformer (they don't know how they are being used). If you have a different resistance across one of the secondaries you may change the amplitude.
Please explain how could the AC drive signal be different in the secondaries?

Rush

Rush and lhquam: Please see the attached simplified schematic depicting AC drive. The circuit of the upper JFET is different from that of the lower JFET. Will this mean that the AC drive to the upper JFET is identical [or not] to that of the lower JFET? I do not have the skill or knowledge to answer it.

 

[Zen Mod]

wrong assumption , A.

each coil is fed with bias voltage via , say , 10K resistor ;

what's happening on feeding side of 10K resistor is what makes difference between halves , considering that on upper side 10K resistor will slide up and down , along with it's coil , while on lower side everything is stayin' lazy , leaned on neg rail

 

[bobodioulasso]

go and build

say tnx! to Pa

if you can't find 3k trimpot - use 2K one , and 1K resistor below

and yes , you can use more than 10uF in series with secondary

Thanks, ZM

If only i had a transformer and R100s.
Where to find Jensens in Europe?

 

[Zen Mod]

dunno for Jensens , somebody will chime in , for sure

for R's - Tea is sending them even to Moon , as greet for Neil

 

[Antoinel]

wrong assumption , A.

each coil is fed with bias voltage via , say , 10K resistor ;

what's happening on feeding side of 10K resistor is what makes difference between halves , considering that on upper side 10K resistor will slide up and down , along with it's coil , while on lower side everything is stayin' lazy , leaned on neg rail

Thank you Zen Mod for your explanation. Since the AC drive to the upper JFET is identical to that of the lower JFET, it follows that lhquam has created a successful clone of F6. Undoubtedly there were additional successful clones in the hands of kasey197, triode_al, bobodioulasso, and others.

Congratulations on your achievement.

Zen Mod: Is the mission to unravel Conceptual F6 accomplished? Where to next? What are the upcoming hurdles? Your thoughts.

 

[generg]

Thanks, ZM

If only i had a transformer and R100s.
Where to find Jensens in Europe?

I can help you with the answer I got on my request some time ago:

"Thank you for your interest in Jensen Transformers. I apology for the delay in sending you an answer to your email below.

At the present time we do not have a distributor in your area, so you can place an order directly with us. Your cost for two each of our model JT-11-FLPCH output transformer would be $135.67 each in US Dollars, plus shipping. They are in stock now.

We recommend shipping by US Air Mail 1st Class Priority Flat Rate for a cost of $16.95. We can fit the two transformers inside the small Flat Rate box that the US post office uses. It should take about 1-2 weeks to arrive to you.

Therefore, the complete total for your order would be $35.67 x 2 = $71.34 + $16.95 = $88.29 in US Dollars.

You can place an order for the transformers by fax or email. Be sure to include your complete address and credit card information. We accept Visa, MasterCard, and American Express. If you are using a Visa card or MasterCard, please include the additional 3-digit code that is on the back of the card, located on the strip where you sign your name. If using American Express, please include the additional 4-digit code that is printed on the front of the card.

We also accept payment by PayPal at: *paypal@jensen-transformers.com"

I did not quite understand the first price mentioned, but the last information, more clear to me, says that we can get in Europe two xformers for around 90 $ normal shipping, fair price....

 

[Rush]

I can help you with the answer I got on my request some time ago:

"Thank you for your interest in Jensen Transformers. I apology for the delay in sending you an answer to your email below.

At the present time we do not have a distributor in your area, so you can place an order directly with us. Your cost for two each of our model JT-11-FLPCH output transformer would be $135.67 each in US Dollars, plus shipping. They are in stock now.

We recommend shipping by US Air Mail 1st Class Priority Flat Rate for a cost of $16.95. We can fit the two transformers inside the small Flat Rate box that the US post office uses. It should take about 1-2 weeks to arrive to you.

Therefore, the complete total for your order would be $35.67 x 2 = $71.34 + $16.95 = $88.29 in US Dollars.

You can place an order for the transformers by fax or email. Be sure to include your complete address and credit card information. We accept Visa, MasterCard, and American Express. If you are using a Visa card or MasterCard, please include the additional 3-digit code that is on the back of the card, located on the strip where you sign your name. If using American Express, please include the additional 4-digit code that is printed on the front of the card.

We also accept payment by PayPal at: *paypal@jensen-transformers.com"

I did not quite understand the first price mentioned, but the last information, more clear to me, says that we can get in Europe two xformers for around 90 $ normal shipping, fair price....

I'm pretty sure that transformer above doesn't have dual secondaries.
Try this one instead, $2 more:http://jensen-transformers.com/datashts/123flpch.pdf
This is the Jensen page you want: JENSEN TRANSFORMERS, INC. - LINE OUTPUT TRANSFORMERS and pick your poison.

Rush

 

[Tea-Bag]

You could put quite a few of those transformers in one of the small International priority mail boxes. They weigh 3.5oz each box (max 4 lbs a box at 16oz per pound). Could still add some bubble wrap padding on them.
I added the R100A and transformer size for perspective, with a little help from my therapist, Dr. Freud. So four of them don't need two of the boxes Generg if that's what they said.

 

[generg]

I'm pretty sure that transformer above doesn't have dual secondaries.
Try this one instead, $2 more:http://jensen-transformers.com/datashts/123flpch.pdf
This is the Jensen page you want: JENSEN TRANSFORMERS, INC. - LINE OUTPUT TRANSFORMERS and pick your poison.

Rush

Yes Rush you are right! The 123flpch is the right one and it costs some US dollars more...... The postal fee to Europe could be the same and the mode of ordering will be the same mentioned!