vitopower

BA-6A Input / Output Design
« on: December 05, 2019, 01:17:16 AM »
I've read all the posts I could find here regarding this but have hit a wall and hoping someone might be able to steer me in the right direction.

Are there any input and output transformers that are less expensive than Sowter that are a good fit?

Thanks
« Last Edit: December 06, 2019, 09:51:33 AM by vitopower »


wlinart

Re: BA-6A Input / Output Design
« Reply #1 on: December 07, 2019, 02:50:58 PM »
I don't know the specifics about it, but i looked at the specs sowter provides.
For the input they say it's a 600/150 to 10K. Edcor has a 600 to 10k model, so that's maybe an option? Carnhill has some output transformers of 10k:600, so maybe one of those in reverse? Although that may be no a good idea, don't know exactly.
The interstage from sowter is a 10KCT/10K. Edcor and carnhill both have a 10k:10k model, so that should be easy.
The output is a 8k:600, which is a common value it seems for push pull output amps, so that should be easier to find. Edcor has one as well: https://www.don-audio.com/Edcor-CXPP10-600-8K-Push-Pull-Tube-Output-Transformer

I hope you find something! Good luck!

ruffrecords

Re: BA-6A Input / Output Design
« Reply #2 on: December 07, 2019, 04:12:23 PM »
For a 4:1 output Carnhill have plenty of 9600:600 output transformers (cannot rememeber if this design required dc in the primary)

For input, OEP do a very capable 1:10 mic transformer for tube designs - the A187A15C. I use this in the poor man's tube mixer design. Do not use an unscreened mic input transformer - you will just get too much hum.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: BA-6A Input / Output Design
« Reply #3 on: December 07, 2019, 04:13:07 PM »
Nobody needs the capability of +40 dBu from a BA-6a.
For studio work where unity gain is desirable,
common practice is to place a constant impedance 18 dB pad after the output attenuator.
That gives the user some play in the control instead of one click from full off.

10k to 16 ohm output transformers are cheap and easy to find.
Due to the high ratio step-down, likely more linear than a 8K : 600.

Gain wise, puts a unit with a 10k : 16 within  2 dB of a padded original.  Do the math.

vitopower

Re: BA-6A Input / Output Design
« Reply #4 on: December 08, 2019, 01:10:52 PM »
Thanks for the thoughtful replies.

Edcor has been great in all my builds.

The Ba6a output does have DC and I've read the original was likely a 10 watter.
   
Line input only is OK for my application.  Does anyone know if the original is hi-NI or permalloy?  Would there be an advantage to sticking with this original ratio/pad or looking for similar composition line input?

Skipping the pad to stay closer to unity on output is a great idea...

« Last Edit: December 09, 2019, 08:42:02 AM by vitopower »

Re: BA-6A Input / Output Design
« Reply #5 on: December 10, 2019, 07:17:13 PM »
Choice for valve output step down is limited enough , Edcor /Carnhill depending on which side of the pond your on is the price beater , 20-25 £ $ or Euros gets you in the game ,   

I think Volker and Ians dual symetric  bobbin idea shows clearly demonstrates HF  superiority over single  asymetric , how much you want to pass cleanly at 20hz is relative to core size .
Now that cnc relieves you of the need for a cog room and a 'Leesonaa'   (pun, Im sure , was intended)  winder  ;D
Machinery and materials are to hand my friends ,it boils down to a few simple questions , core W/D /L ,wire diameter/turns per cm' step  'layer  and  insulation data, 





« Last Edit: December 11, 2019, 05:26:43 AM by Tubetec »

vitopower

Re: BA-6A Input / Output Design
« Reply #6 on: December 12, 2019, 01:15:31 PM »
Choice for valve output step down is limited enough , Edcor /Carnhill depending on which side of the pond your on is the price beater , 20-25 £ $ or Euros gets you in the game ,   

I think Volker and Ians dual symetric  bobbin idea shows clearly demonstrates HF  superiority over single  asymetric , how much you want to pass cleanly at 20hz is relative to core size .
Now that cnc relieves you of the need for a cog room and a 'Leesonaa'   (pun, Im sure , was intended)  winder  ;D
Machinery and materials are to hand my friends ,it boils down to a few simple questions , core W/D /L ,wire diameter/turns per cm' step  'layer  and  insulation data, 

Thanks, Tubetec.
What was Volker and Ians dual symetric  bobbin idea?  I couldn't find searching around

Re: BA-6A Input / Output Design
« Reply #7 on: December 12, 2019, 02:54:30 PM »
https://groupdiy.com/index.php?topic=73674.0

Im not sure if it fits with the BA-6A topology which might need a gapped transformer , 

Maybe there is a way to gap UI lams

vitopower

Re: BA-6A Input / Output Design
« Reply #8 on: February 26, 2020, 11:18:42 AM »
Nobody needs the capability of +40 dBu from a BA-6a.
For studio work where unity gain is desirable,
common practice is to place a constant impedance 18 dB pad after the output attenuator.
That gives the user some play in the control instead of one click from full off.

10k to 16 ohm output transformers are cheap and easy to find.
Due to the high ratio step-down, likely more linear than a 8K : 600.

Gain wise, puts a unit with a 10k : 16 within  2 dB of a padded original.  Do the math.

Would the original T output attenuator now need to be reconfigured as a 16 ohm constant impedance device (to compensate for the jump in transformer impedance ratio) to present the correct load back to output stage, or am I looking at this the wrong way?
« Last Edit: February 26, 2020, 11:39:55 AM by vitopower »

Re: BA-6A Input / Output Design
« Reply #9 on: February 26, 2020, 12:11:04 PM »
Would the original T output attenuator now need to be reconfigured as a 16 ohm constant impedance device (to compensate for the jump in transformer impedance ratio) to present the correct load back to output stage,
am proposing a 16 ohm, L type attenuator, commonly found in loudspeaker dividing networks, as the output control.
it would be  prudent to include a resistor load on the attenutor's output.


 

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