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Old 6th February 2012, 05:47 AM   #1551
vgeorge is online now vgeorge  Greece
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18v raw dc for the regulator I suppose.
170v anode seems too much. With a 10ohm filament resistor you are going to have around 9-10v bias. Open the #26 datasheet see the loadlines and then set your operation point. 140-150v seems better, and you are going to have around 5mA then, depending on bias.
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Old 6th February 2012, 08:07 AM   #1552
euro21 is offline euro21  Hungary
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#26 preamp, filament bias (Rod Coleman regulator), 220V B+ supply (SSHV2).
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Old 6th February 2012, 11:16 AM   #1553
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I'm not sure use two CCS's this way, they will fight one another with tempeature dift and oscillate unless the first one is much bigger than the sond?

Question

If there is a Cascoded CCS before the VR tube regulation would two CCS's still oscillate? People are using a SSHV2 ahead of their Cascode CCS plate load.
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Old 6th February 2012, 12:58 PM   #1554
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Quote:
Originally Posted by Original Burnedfingers View Post
Question

If there is a Cascoded CCS before the VR tube regulation would two CCS's still oscillate?
No. It takes 5 minutes to convince yourself of it if you already have the dn2540. You will learn a lot more from soldering four components than 4 pages of discussion here.
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Old 6th February 2012, 02:41 PM   #1555
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Quote:
Originally Posted by vgeorge View Post
18v raw dc for the regulator I suppose.
170v anode seems too much. With a 10ohm filament resistor you are going to have around 9-10v bias. Open the #26 datasheet see the loadlines and then set your operation point. 140-150v seems better, and you are going to have around 5mA then, depending on bias.
Thanks and I'll follow all the numbers.
The reason I asked that I could control more closely if I know the formula for calculation.
Regards
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Old 6th February 2012, 03:32 PM   #1556
iko is offline iko  Canada
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Originally Posted by albertli View Post
What I worry is I don't know how to calculate the current/mA with filament bias. My plan is to run about 170v at anode and 18v dc to feed the filament. Would this be on the range??
Let's assume you have 1.05A running through the filament and that your bias resistor is 10R. The voltage differential between grid and cathode will be Vgk = I * R = 1.05 * 10 = 10.5V

Look at the data sheet for #26 and draw a vertical line at Vp = 170 volts. Assess roughly where the -10.5V curve crosses the vertical line and from that point draw a horizontal line that will cross the Y-axis. That will tell you roughly the plate current. Don't worry about decimals, there is enough variation between individual #26 tubes to invalidate any precision in your design.
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Old 6th February 2012, 07:04 PM   #1557
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Hey guys....I decided to join the fray....

I stuck to Kevin's schematic as a starting point, and built up some boards over the weekend. I'll be using two chassis (PSU and Signal) as most are here. Some key points:

Silk TVC volume control
Tentlabs ultra-low noise filament supplies
Electraprint iron

I hope tonight to finish up the woodwork on the chassis, and start to make real progress ! Here's some photos of the boards:

Click the image to open in full size.
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It seems a given that there will be noise issues.....My first approach will be to shield the boards in hammond enclosures (may or maynot help ?) under the chassis.
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Old 6th February 2012, 07:43 PM   #1558
vgeorge is online now vgeorge  Greece
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Noise will come only from filament supply or proximity with transformers. My chassis is not fully shielded and I have no noise even with sensitive speakers.
You also might consider put the tvc at the output, as per Thomas Mayer.
Very nice build by the way so far!
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Old 6th February 2012, 11:05 PM   #1559
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Just purchased 2) SSHV2 boards with parts
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Old 7th February 2012, 04:08 AM   #1560
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Originally Posted by ikoflexer View Post
Let's assume you have 1.05A running through the filament and that your bias resistor is 10R. The voltage differential between grid and cathode will be Vgk = I * R = 1.05 * 10 = 10.5V

Look at the data sheet for #26 and draw a vertical line at Vp = 170 volts. Assess roughly where the -10.5V curve crosses the vertical line and from that point draw a horizontal line that will cross the Y-axis. That will tell you roughly the plate current. Don't worry about decimals, there is enough variation between individual #26 tubes to invalidate any precision in your design.
ikoflexer,

Thanks N I benefit from this.

Albert
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