PPP 6CB5A schematic? Look OK?

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Re: PPP 6CB5A schematic? Look OK?

Postby Blair » Mon Jun 17, 2013 7:20 am

Yeah, I've looked just about everywhere for a PP schematic using these, but got nothing. I spent a few hours yesterday during the kids nap time making brackets and mounting the parts I have.

Now, I need to order Output iron and figure out the front end to make sure I can drive these tubes.

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Re: PPP 6CB5A schematic? Look OK?

Postby kheper » Mon Jun 17, 2013 7:45 am

Vinyl Savor, in his "low cost" SE 6CB5a, uses a single 6N7 section to drive the output tube. Maybe an old Williamson style input and drive circuity? 6N7, 6SN7 or similar.

1/2 6SN7 (volt amp) -> 1/2 6SN7 (concertina) -> 1 6SN7 (long tail pair)

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Re: PPP 6CB5A schematic? Look OK?

Postby Blair » Mon Jun 17, 2013 2:52 pm

How bout something like this?

Image

That gives me a similar circuit to the Williamson. I could go with anode output and use the gain in the second section I suppose also, but I'm not sure what that 5.4 gain section will do in increasing my voltage swing.
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Re: PPP 6CB5A schematic? Look OK?

Postby DeathRex » Mon Jun 17, 2013 3:48 pm

Usually you'd want the feedback on the tube just before the LTP, but since the second section is non inverting it might not really matter, except the feedback is 'farther' away.
Don't need a AC balance with a CCS.
6CG7's anode resistors should be about 47K.
The second section of the 6GF7 is using alot of current for not doing anything.
Might be better to replace the 6GF7 with a 6DT8, 6AB4 or 12AT7.
Or maybe better yet a 6EJ7. Check out Greggs Dynamull driver board http://www.classicvalve.ca/docs/DynaMull_docs.pdf
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Re: PPP 6CB5A schematic? Look OK?

Postby Blair » Tue Jun 18, 2013 8:16 am

I have a few 12AT7s. How about this? Is the network from the signal to ground between the two sections of the 12AT7 necessary? I believe it's there to control ringing and oscillations.

Image

This is two gain stages which should give me plenty of voltage swing I would think.

Image

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Re: PPP 6CB5A schematic? Look OK?

Postby DeathRex » Tue Jun 18, 2013 9:18 am

You gotta raise up the second 12AT7s cathode resistor to something like 33K, and about the same value for the anode resistor. You gotta make the cathode voltage about 3-4 volts above the grid voltage, which is determined by the first 12AT7s anode voltage.
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Re: PPP 6CB5A schematic? Look OK?

Postby Blair » Tue Jun 18, 2013 9:33 am

Something like this?

Image
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Re: PPP 6CB5A schematic? Look OK?

Postby DeathRex » Tue Jun 18, 2013 5:06 pm

You have to bypass that bottom 33K, or your gain will be close to zero.
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Re: PPP 6CB5A schematic? Look OK?

Postby Blair » Tue Jun 18, 2013 5:51 pm

Other than a bypass across the lower 33K, does it look like a good starting point?

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Re: PPP 6CB5A schematic? Look OK?

Postby DeathRex » Tue Jun 18, 2013 6:39 pm

Well yea, it's real close to Shannon's Eiclone driver board. Look at page 24 with the 6SN7 and the LM334Z.
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Re: PPP 6CB5A schematic? Look OK?

Postby Blair » Wed Jun 19, 2013 7:10 am

:) I love spinning my own wheels to get back to point A.
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Re: PPP 6CB5A schematic? Look OK?

Postby sorenj07 » Wed May 03, 2017 5:50 pm

did you ever get around to building this?
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Re: PPP 6CB5A schematic? Look OK?

Postby Gingertube » Mon May 08, 2017 1:02 am

There are a few tricks to using TV Horizontal Output Tubes, Sweep Tubes or whatever you want to call them.

First - Data Sheet Power ratings are for TV Horizontal Output use. When using in a Class AB Audio Amp the rating is much higher.

For guidance:
The horizontal output tube used commonly here in OZ was a 6DQ6A - rated at 15Watts, the tube manufacturer published recommended operating conditions when using for a Class AB Audio Amp and recommended biasing for 20 Watts dissipation. That is: the "normal" 70% of max. dissipation bias point for Class AB Audio use was 20W per tube.

Second - Triode Mode and Ultralinear Mode means that you can run screens at higher voltage than the data sheet max G2 voltage rating, because as the anode voltage pulls down then the screen voltage is reduced too.
Problem is in pentode mode when the anode voltage pulls below the screen voltage and screen current sky-rockets. In that case stick to max G2 Voltage ratings (220V for 6CB5).

As you push up the screen voltage then the required grid bias voltage increases significantly.

THis may be of interest:
http://www.ozvalveamps.org/goldentone/g ... 964rdw.gif
Using 6DQ6A for 40W Git Amp, thre was also a 60W version of this amp and 2 x 6DQ6A pushed to teh max. were capable of 85 Watts out.
Also interesting power supply configuration to generate B= and 1/2 B+ for the screen supply.

You should have no problems getting 50W per pair (100W for a quad) of 6CB5


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Re: PPP 6CB5A schematic? Look OK?

Postby Blair » Mon May 15, 2017 8:11 pm

In short. No.

I'm still hanging onto the iron I intended to use for this project including 500mA 10H Chokes and 1.5K Sister 200W outputs. Life has just gotten in the way.

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