RCA BA6A limiter

[gary o]

Sorry Rob dont no why I thought it was Robin thanks for those values & info.

Cheers Gary O.

 

[SSLtech]

Hooooo... looks like I might be out 'visiting' the BA-6a nest week!

Anything you want me to check?

keith

 

[gary o]

You mean your getting your hands on someones BA, sounds bit rude, well if you can get any voltage readings, hell any info would be good for me I have much to learn thanks.

Cheers Gary O.

 

[Rob Flinn]

Anything you want me to check?

Keith

If you could get a more comprehensive set of voltage readings that would be great.
I`ve been wondering about the PSU transformer. Somehow I`ve got the secondary quoted at 315v, but after the choke its down to 285v which even with loading sounds a bit low.
One other thing I`ve been wondering is the meter spec F.S.D. Any way you could take a look at that please.

I hope this is not asking too much, but it would definately help things on the way.

 

[V9977]

Hey there Gary O.

Brian did mention a guy in the UK putting together a BA6A.
I had serviced two of these units this year and sent him info
regarding I/S transformer ratios and voltage levels.

I've worked with quite a number of different compressors in the
past. The RCA is by far the coolest.

When the unit is not aligned by use of the BAL-A and BAL-B, excessive thumping, sudden poping occurs.
The resistors accross the primary of the Interstage transformer attenuate both the DC current
flowing through it, as well as the signal.

I would be quite happy to pitch-in with info. and support especialy regarding I/S, BAL-A and BAL-B :wink:

 

[gary o]

Thanks V9977 for passing on info to Brian, its allowed me & im sure others to get on with making our versions of the BA6A, ive ordered Brians recreation of the interstage tran this week, ive got the resistors you mentioned in place{they do what you thought they did CJ} & couple of capacitors inplace of the inta tran for now, ive done the bal A & B hopefully correctly which has brought the thumps down quite a bit, im just hoping they all dissapear once I have the inta wired in, yeah love the BA too lots of great things about it, cant wait to record some vocals thru it,yeah thats great any snippits or hints of info or how it works, components or how to set up would be more than welcombe by myself & im sure others too, Im a bit of an electronics beginner but want to learn just makin this has shown me loads & now I got a great piece a kit too thanks once again.

Gary O.

 

[Jeff Perkins]

If this project is still ongoing, I have a fully functional, unmolested (except for a missing VU meter) BA-6A sitting on my bench. I am currently in search of a manual and schematic. If measurements or values of components are needed, I'm willing to help....Would love a good schematic and actual setup procedures.......

 

[guitarmaker]

I also have a scan of the schematic that's easy to read and has no washed out parts if anyone wants it. PM me an email to send it to.

Steve

 

[ToobieSnack]

hi all

thanks guitarmaker for the schemo
it is clearer than the one I have...
at first I thought i didn't even have it ..
but a search of my computer proved otherwise
my shematic is a bit more crowded and confusing...
at the limit section
the amplification is pretty straight forward

ALSO: I'd like to add that the ba6a is VERY similar to the ba-25
the main difference being ....
ba6a uses 2 tubes for some functions and
the ba-25 uses the dual triodes instead...

so... the ba6a is like a ba-25 with a manley t bar mod.... :grin:

PRR did a great synopsis of the ba-25 ...
I will read through it again to find the answer to a question I have....

how are these 2 units using a rectifier tube to control compression?

if you can answer this it would be sincerely appreciated
thanks
ts

 

[Rob Flinn]

They use a rectifier tube because the control signal only needs to swing in one direction, normally negative. Using the rectifier converts the positive peaks in to negative ones so the control signal only moves in one direction.

In other words the control signal needs to be rectified, hence the use of a double diode. This is true in most compressor side chains apart from maybe the LA-2a, which just needs the light panel to be brighter which can be acheived with an ac signal.

 

[ToobieSnack]

rob
thanks ... ever so much ... for your reply and great info... :grin:

can I ask:

how is this rectified signal acting on the other tubes to control compression?
is this a case of starving or saturating plates with electrons?

thanks
ts

 

[ToobieSnack]

hey all

found this quote from PRR on the ba25 which is extremely similar to this beast,,,

PLEASE NOTE.. this is the description for the ba25 so specific R and C values do not apply to this schematic..

just the basic concept

PRR quote

the rectifier compares the negative peaks of the output voltage to the positive voltage on R47 wiper. When output voltage exceeds the set level, the excess ends up on V2's grids, in a direction to reduce its gain. That's how it limits.

the grid acts like a flow control valve on the tube.....actuated by the voltage from the rectifer...

just thought it would be something someone might want to know

the PRR synopsis of the RCA ba25 unit is nice ref for understanding this design.. thanks again PRR :grin:

later
ts

 

[rafafredd]

I would love to see this BA25 schem. For some reason, I can´t get my hands on it. Is there a link?

 

[ToobieSnack]

rafa
cool to see you here...
i always enjoy your comments and you seem like....
A VERY COOL GUY... :grin: :thumb:
I welcome your input always
thanks

as for the ba25 :
not only is the schemo available...
PRR wrote a simply beautiful synopsis on it's theory of operation at my thread here:

http://www.groupdiy.com/index.php?topic=7499&highlight=rca+ba25

I have the schemo hosted and plan on keeping it up ... but you might also benifit from downloading it .... just in case..
It literally took me years to track down ...and funny enough... it was right here in my backyard practically...it also let me to this forum....

if you go back and forth between the 2 designs you will find amazing similarities.... they are almost identical....
in fact....i'd be interested to know the differences :shock: :grin:
anyway thanks for your interest
I love all things RCA....
later
ts

 

[penquista]

hi,

at the moment i'm building a BA-6A clone, i'm using the detailed version of the schematic i found at several places in the net. by the way, i cleaned up the schematic a bit, retyped all the values of the components so its quite readable now. if anybody wants a copy, just give a shout.

at the moment i'm using edcor transformers, but my plan is to replace them as soon i have the money for the sowter transformers.
i got a power transformer with 160-0-160, this should be the 320V rms indicated in the schematic. the problem i have now, is that the voltage after rectification (i`m using a 5r4 as indicated in the schematic) is less than 180V. this is not enough to start the voltage regulator tube.
it would be great to get a recommendation what to do.

My first idea was to replace the tube rectifier with solid state. that should give me ~225 V
Would that be enough?

the other thing i would like to say, is that i have been reading a lot in this forum in the last few month and it has been a lot of fun learning. A lot of thanks to all the persons who make this forum such an interesting place.
I can't contribute with any electronic knowledge yet, there is still to much to learn, but i hope someday to be able to give back at least some part of all i got in this forum.

Christian

 

[jensenmann]

Sharing would be really nice. Maybe you can host it?
:thumb:

 

[Rob Flinn]

i got a power transformer with 160-0-160, this should be the 320V rms indicated in the schematic. the problem i have now, is that the voltage after rectification (i`m using a 5r4 as indicated in the schematic) is less than 180V. this is not enough to start the voltage regulator tube.

That is because you need a 320-0- 320 transformer if you use a valve rectiifer. The only way you will get 320 rms with the transformer you have is to use a solid state bridge rectifier across the 160 - 160 on your transformer

 

[HarryH]

Since the BA6A is on my to build list,I am wondering if I can use a 425-0-425 300ma 5v3a 6.3v 2a transformer for the mains in a BA6a? I was given two of these and was trying to find a good use for them.
Harry

 

[Rob Flinn]

Harry

This transformer should be OK, you will need to use a resistor to drop the HT voltage to the appropriate level. You can find this out by added the current drop through the various stages of the compressor. You then work out how much voltage you need to drop. Put the values into ohms law & that should give you a resistor value. when you have the resistor value use the P=IV power equation to calculate the power rating the resistor needs to be. WHen you have this value, I usually overate it by at least 50%.

 

[HarryH]

Thanks rob,
I thought that would be the way it should be done,but I am not well enough versed in this stuff to trust myself going at it alone.Its not so hard building off one of the numerous well documented projects here,but It is more difficult trying to learn how everything works.I generaly feel like Homer Simpson with a soldering iron.
Harry