RCA BA-6A from scratch

[JMan]

There is indeed more of the circuit (including power supply) that has been omitted here — I imagine that’s because no modifications have been made there, although I shouldn’t presume. You can see it on the original schematic, which is easy to find and which I know we have housed in the technical docs here. Here’s a small bit from the user manual describing the 6h6:

 

[beatnik]

Thank you very much for the re upload

 

[DaveP]

The BOM will not be much good after 10 years, better to research a new one.

The most important thing I found was that if the tubes are balanced, it will work without the interstage, just like a Gates SA-39.

The way I designed the switches was too difficult to use so better to keep the original design and obtain some wafer switches.

Good luck
DaveP

 

[lassoharp]

The BOM will not be much good after 10 years, better to research a new one.

The most important thing I found was that if the tubes are balanced, it will work without the interstage, just like a Gates SA-39.

The way I designed the switches was too difficult to use so better to keep the original design and obtain some wafer switches.

Good luck
DaveP

Dave, Do you have the page from your original schematics that shows where your meter connections were? I don't seem to have it in my files and the originals are no longer available on the opening page.

 

[DaveP]

There is indeed more of the circuit (including power supply) that has been omitted here — I imagine that’s because no modifications have been made there, although I shouldn’t presume. You can see it on the original schematic, which is easy to find and which I know we have housed in the technical docs here. Here’s a small bit from the user manual describing the 6h6:

View attachment 86047

Hi,
I have been asked to post the timing and meter connections.
I hope this is helpful.

Best wishes
DaveP

 

[lassoharp]

Hi,
I have been asked to post the timing and meter connections.
I hope this is helpful.

Best wishes
DaveP

Thanks Dave. Can you tell me exactly where in the main circuit you have the destination of the + leg of the meter connecting to in your circuit? (as circled in red)

 

[MidnightArrakis]

Thanks Dave. Can you tell me exactly where in the main circuit you have the destination of the + leg of the meter connecting to in your circuit? (as circled in red)

View attachment 91049

Once all of the various pieces of -- missing -- information can be found out and all of the component parts information can be finally determined.....I am planning on creating a single cohesive and integrated schematic of this circuit for everybody to have and cherish!!! So.....if anybody out there has anything additional and/or useful that they would wish to contribute to this thread, by all means do so and then I will go ahead and create a "compiled" schematic of the "whole enchilada"!!! Keep me posted, OK???

/

 

[DaveP]

Hi Alan,
It goes to the diode bridge on the output pad marked D5

Best
DaveP

 

[lassoharp]

Hi Alan,
It goes to the diode bridge on the output pad marked D5

Best
DaveP

Thanks Dave. So were you only using the meter for output level and not GR? I may be missing something here but am not seeing how GR could be monitored with the meter running from the output pad to ground. Does it not need to be running from the 6SK7 cathodes to ground for seeing GR?

 

[DaveP]

Hi Alan,

The meter was used for measuring the gain reduction via SW6. The connection to R14 was the GR point. To be honest I can't remember any more about it after all this time. There is no way I can check on it now unfortunately. It was in my workshop for modification and my ex-wife took a hammer to it! Fortunately, I had stored the tubes somewhere else. She also destroyed my Auratones at the same time.

Best
DaveP

 

[lassoharp]

Hi Alan,

The meter was used for measuring the gain reduction via SW6. The connection to R14 was the GR point. To be honest I can't remember any more about it after all this time. There is no way I can check on it now unfortunately. It was in my workshop for modification and my ex-wife took a hammer to it! Fortunately, I had stored the tubes somewhere else. She also destroyed my Auratones at the same time.

Best
DaveP

R14 sounds right.

Don't feel bad. I had a version of this circuit built up on a proto board some years ago for testing IS iron with Emrr and have also forgotten exactly how I had the meter connected !

Sorry to hear about the casualties with the ex . . . and glad the tubes made it out alive!

 

[MidnightArrakis]

Hi Alan,

The meter was used for measuring the gain reduction via SW6. The connection to R14 was the GR point. To be honest I can't remember any more about it after all this time. There is no way I can check on it now unfortunately. It was in my workshop for modification and my ex-wife took a hammer to it! Fortunately, I had stored the tubes somewhere else. She also destroyed my Auratones at the same time.

Best
DaveP

I'm just wondering.....will the transformer detailed within the attached datasheet be adequate enough for the high-voltage power-supply? What is the total plate current requirement for a single channel? Also, what is the total heater current requirement for a single channel? I appreciate all of your assistance!!!

/

 

[MidnightArrakis]

Hi Alan,

The meter was used for measuring the gain reduction via SW6. The connection to R14 was the GR point. To be honest I can't remember any more about it after all this time. There is no way I can check on it now unfortunately. It was in my workshop for modification and my ex-wife took a hammer to it! Fortunately, I had stored the tubes somewhere else. She also destroyed my Auratones at the same time.

Best
DaveP

Or.....would one of these transformer specifications be much better?



THANKS!!!

/

 

[beatnik]

With full wave diode rectification you need 480V C.T. as shown on DaveP schematic

I believe the HT current consumption is around 150mA

240V should be ok if you used bridge rectifier - just leave the CT isolated. With bridge I think you need more current

 

[JMan]

I'm finishing up a BA6A (not nearly as impressive as yours, but built from the Dr*p pcb instead), and I'm thinking I want to use this circuit for the 6sk7 heaters.

I have two really ignorant questions about it -- first, what is the function of the amber neon? I can sort of intuit what it is doing there, but I've just not encountered this in my limited experience and would like to learn something new!

Second, the diodes marked D3 and D4 (which appear to actually be two pairs of parallel diodes, but not quite in the diode bridge configuration that I'm most familiar with -- again, just noting for myself where I am seeing something new), are there any special considerations when selecting these? I've got baggies upon baggies of 1n400x types, and I'm assuming these would work?

EDIT: Also, 47000uF caps at C21 & C22! Wow, those are going to be some big caps! Mouser literally isn't offering me the option to filter for caps above 33000uF (but I'm probably just doing it wrong).

 

[Piedwagtail]

Centre tapped transformer hence two diodes, doubled up for heat dissipation. Quadruple for fun.
Parallel as many 10000uf or 22000uf as you want. Try a rig and listen to hear what makes any difference.
Worry more how you twist in those heater wires at socket and displace away from ac wires. That's not shown on a schematic.
Try building by ear not numbers.
Map is not the territory

 

[Ricardus]

Try building by ear not numbers.

Our ears are the weakest link in the chain, so no.

This post just reeks of home stereo audiophile dogma.

 

[DaveP]

We all had to start somewhere.

The amber neon was when I used to turn on the tubes before the HT (red neon)
The resistor R75 will have to be more than 0.47 ohms if you only want to light up two 6SK7's. Maybe 4.7 ohms?
The configuration using a centre tap transformer allows more current through than a bridge. Back in the day, I used two pairs of schottky diodes to get a lower forward voltage drop Now I use SR1503 solar panel diodes for even lower Vf, 1N4000 not a good choice.

I use DC heaters for all my tubes, so I don't worry about wire dress apart for minimising length and keeping them flat to the chassis. AC heaters have to be well twisted to cancel the ac field.
best
DaveP

 

[scott2000]

This post just reeks of home stereo audiophile dogma.

When Mr Piedwagtail speaks, I always try to listen ..
Groovy...kinda like UBK...

Still trying to decipher the parable of the se 6sk7/q7 limiter drawing..lol

 

[Piedwagtail]

Only a parable for those that haven't aged.
One of my current glimmers, Scott, is a simple four ear SE tube output mixer with the Valley VCAs gutted from a Gatex and a Lundahl 1671.
Someone else can make it perhaps.

Thankfully, DaveP appeared.