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Old 23rd March 2013, 09:01 PM   #2891
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Quote:
Originally Posted by andyjevans View Post
The Reg needs to supply 11.5v (10v + 1.5v). Add 5 to 7 volts as Rod says and you have 16.5v to 18.5v. By going down to 15.4v you risk going too low now. Did you specify to Rod that you were using filament bias to provide 11.5v to a 26? The resistors in the Regs vary with the supply voltage. The small potentiometer on the Reg should be working in its range, and if it isn't doing anything send Rod an email - I'm sure he'll help. Note also with Rod's regs that they don't give you a fixed voltage/current out. This varies a small amount with the supply voltage, which is why the adjustment is there. Not like a LM1084, for instance, which gives you a steady output irrespective of the supply voltage. Do you have a 1,000v cap on the input of the Reg, as suggested for outboard supplies with umbilicals?

I'd be surprised if it's the regulators. I've never had a problem like that, and if they are correctly specified and built they are very reliable - it's a high quality part. Did you check the grid stopper (up to 1K on the pin) and the grid leak (100K or whatever) on the input? If that's all correct I'd be looking at the B+.
Hello Andy,

I have, from the input RCA, a 100k volume pot, then 390 ohms to the grid of the 26. Not enough?

I checked the parts that Rod sent me, R8 is 3.3k.

Abe
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Old 23rd March 2013, 09:03 PM   #2892
CV6045 is offline CV6045  United Kingdom
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Just a thought, have you checked for instability coming from your B+ supply.... if you are using a Choke/Capacitor...then instability could result if the combination selected is at or near the Ripple Frequency....
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Old 23rd March 2013, 09:04 PM   #2893
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Originally Posted by Rod Coleman View Post
Yes, Andy makes a good point. The value of R8 is tailored to the incoming supply voltage. And for filament-bias the voltage is higher, so the 3.3K resistors for R8 are the ones to use.

And as Andy reminds us, 1000uF/35v is needed at the PCB input, where an umbilical is in use.

Both these parts are required to guarantee stability.
Please see my response to Andy. Thanks!
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Old 23rd March 2013, 09:10 PM   #2894
CV6045 is offline CV6045  United Kingdom
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Okay I see your response to Andy...you have already suggested to him that the B+ supply should be checked
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Old 23rd March 2013, 09:36 PM   #2895
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Originally Posted by amandarae View Post
Hello Andy, I have, from the input RCA, a 100k volume pot, then 390 ohms to the grid of the 26. Not enough? I checked the parts that Rod sent me, R8 is 3.3k. Abe
That should work as long as the volume pot is all hooked up correctly. It's what I have myself, anyway!

It's looking like something isn't right in one filament supply if the trimmer isn't adjusting properly. You could measure all the voltages in each Reg and compare one with the other. That's a bit laborious, but may reveal a part not working or a dry joint or something. You can easily spend hours looking for faults - just being very methodical and measuring voltages and resistances at each point. It's useful if you have one fully working part.

At times like these I love my bench supplies.....
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Old 23rd March 2013, 09:39 PM   #2896
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Can be also the trimmer, please check.
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Old 23rd March 2013, 09:47 PM   #2897
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Hello guys,

Here's the latest of what I got. These measurements were with: B+=207Vdc input to shunt reg, then reg voltage at ~150vdc. Plate voltage on the tube is ~145V, with 1.45V on the filament. Supply voltage to the Rod Coleman reg is 17.2Vdc, through umbilical, 1000uF, input of regulator. Output of regulator is 1.45V + 9.5V(Vrk).

Click the image to open in full size.
Click the image to open in full size.

The two pics above are measured from Plate of the 26(1st pic), and Cathode of the 26.


The bottom pics are measured from the regulated B+(AC content of the output of the HV Shunt Regulator), and the regulated DC output.

Click the image to open in full size.
Click the image to open in full size.

I do not see anything significant on the B+(regulated output) above.

regards,

Abe

Last edited by amandarae; 23rd March 2013 at 09:52 PM. Reason: add
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Old 23rd March 2013, 09:54 PM   #2898
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Quote:
Originally Posted by CV6045 View Post
Just a thought, have you checked for instability coming from your B+ supply.... if you are using a Choke/Capacitor...then instability could result if the combination selected is at or near the Ripple Frequency....
Hello, I have 20H, 47uF, 10H, 47uF, 0.36H, 47uF filters for the raw DC of B+.

Abe
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Old 23rd March 2013, 09:55 PM   #2899
CV6045 is offline CV6045  United Kingdom
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All looks as you would expect....if it was me I would be tempted to try the 26 on 1.5 volts AC and do away with the Rod Coleman regulator....see what happens !!!



Quote:
Originally Posted by amandarae View Post
Hello guys,

Here's the latest of what I got. These measurements were with: B+=207Vdc input to shunt reg, then reg voltage at 150vdc. Plate voltage on the tube is 145V, with 1.45V on the filament. Supply voltage to the Rod Coleman reg is 17.2Vdc, through umbilical, 1000uF, input of regulator. Output of regulator is 1.45V + 9.5V(Vrk).

Click the image to open in full size.
Click the image to open in full size.

The two pics above are measured from Plate of the 26(1st pic), and Cathode of the 26.


The bottom pics are measured from the regulated B+(AC content of the output of the HV Shunt Regulator), and the regulated DC output.

Click the image to open in full size.
Click the image to open in full size.

I do not see anything significant on the B+(regulated output) above.

regards,

Abe
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Old 23rd March 2013, 10:04 PM   #2900
CV6045 is offline CV6045  United Kingdom
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Do you have a copy of the RCA TT3 Tube Data Book....if not I can email you a copy....page 75 to 77 is worth a read, and it may point you in different direction



Quote:
Originally Posted by amandarae View Post
Hello, I have 20H, 47uF, 10H, 47uF, 0.36H, 47uF filters for the raw DC of B+.

Abe
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