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Old 4th March 2012, 06:28 AM   #101
mogliaa is offline mogliaa  United Kingdom
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Hi Alfredo
Looking really good!! And the new scope as well!
I got another XY analogue oscilloscope for 30 as my old one sort of died.

Got the idea perfectly. I'm currently using a 1uF electrolytic cap. Will add the resistor, shouldn't be too difficult to hack the pcb for this.

I'm traveling at the moment so won't be able to do any work till I return in two weeks

Thanks for the help

PS: please post some of the new plots tomorrow!!
Cheers
Ale
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Old 5th March 2012, 02:55 AM   #102
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Default 6336A Triode curves

Finally a real power tube, a 6336a. It is supposed to be hard to drive. I had to put a series grid resistor of 500 ohms as without it some steps showed some oscillation.

The small variac that I am using to control the level of the HV drive (feeding a HV tranny Hammond 278cx) is running out of steam. I did not use any series resistor to limit the current on the HV drive.

The grid drive is the one from the previous post at 10V per step, so up to -150V.



Click the image to open in full size.

I need to get used to the Rigol XY display, not as clean as the analog scope. The capture below shows a more aggressive HV and some non lineal curves can be seen as I am pushing the small variac. Need to get a beefier one. The current sensing resistor is a 10 ohm 10% (1 watt) i had in my bin. Need to get better ones. So 250mv is 25ma.

Click the image to open in full size.

Next step is to stuff the boards and pots into a box for a permanent setup. For now I think I am leaving the HV supply (with variac) as a separate component as it is heavy.

I may use a pair of LME49810 to make a hybrid 6336A SE amp.

Link to short video clip of analog scope curves

This one is also of an aggressive HV drive, stressing the variac.

Last edited by avincenty; 5th March 2012 at 02:57 AM. Reason: added title
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Old 9th March 2012, 05:40 AM   #103
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Today I traced a GE 6L6GC. The variac can handle this tube. I also captured the xy data from the rigol using a USB stick and opened the .csv data in excel.

Click the image to open in full size.

Click the image to open in full size.
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Old 9th March 2012, 06:13 AM   #104
mogliaa is offline mogliaa  United Kingdom
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Hi Alfredo,
These look really good. Are you still working without a chassis? How do you manage the shielding of the A,G and K cables from your board to the valve socket?
Cheers,
Ale
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Old 9th March 2012, 12:56 PM   #105
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The software becomes more time consuming than the hardware.

Before you capture the data it's a good idea to do a little work on establishing a "settling" algorithm for your ADC. That is, determine the number of measurements at each point, establish a tolerance (per cent) at which you will include or exclude a data-point, and figure out whether to RMS the values, average them or use some other methodology to get the best fitting values. This way you eliminate a lot of the noise. When I did my tracer, the microprocessor didn't have anywhere near the speed to do this but it is much more readily realized today.

I think that you'll find one of the most valuable tools you can use your tracer for is comparing two devices, or the two halves of the same device (ecc83 etc.)
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Old 9th March 2012, 02:21 PM   #106
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Quote:
Originally Posted by mogliaa View Post
Hi Alfredo,
These look really good. Are you still working without a chassis? How do you manage the shielding of the A,G and K cables from your board to the valve socket?
Cheers,
Ale
Yes, still working without a chassis using 2 foot cables. Chassis will come this weekend. I am planning to use an old tube tester as the heater and socket platform.

Alfredo
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Old 10th March 2012, 08:29 PM   #107
tbece is offline tbece  Australia
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Default Re: 200Hz/240Hz PLL stability

For a fast and stable PLL - lock in ~3s - I recommend something like this (pic 1). Series resistor from pin13-pin9 = 220K, shunt cap from pin9 replaced by 470nF, parallell with 68K+10u.

Hopefully I will be able to upload the pictures, they also show the measured lock transient (voltage on pin9) for the original and modified circuit.

The HC4046 is actually quite tricky to use, as the design equations in the data sheet are not accurate. A much better (and much less popular) part to use is the HCT9046A.

/tb
Attached Images
File Type: jpg pll_fix.jpg (31.5 KB, 377 views)
File Type: jpg pll_100hz_lock_org.jpg (77.0 KB, 133 views)
File Type: jpg pll_100hz_lock_tb.jpg (79.3 KB, 54 views)
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Old 11th March 2012, 01:52 PM   #108
mogliaa is offline mogliaa  United Kingdom
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Hi TB,
Thanks for the contribution. It seems quite a different setup for the HC4046.
Today I hacked my PCB to add 100K resistor in series with C9 (1uF) as per Alfredo's suggestion. It did improved locking significantly. However, I do have an issue now with the DC offset. It looks like the grid signal drifts a bit.
Do you recommend making the changes as you suggested earlier? May struggle to add all those additional caps and resistors, but can give it a go.

Attached are two new plots with a high gm triode (6N6P-I) and a very high gm (6Z51P) triode-strapped pentode. Both were a bit of a challenge and added a 1K resistor to the grid wire in addition to the ferrite bead I have around the cable.

Cheers,
Ale
Attached Images
File Type: jpg 6n6p-I.jpg (189.3 KB, 73 views)
File Type: jpg 6Z51P.jpg (190.8 KB, 76 views)
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Old 11th March 2012, 03:35 PM   #109
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You have an issue with the DC offset of the Clock? Is it constant? If it is constant the counter should not care. On my setup I do have a DC blocking cap before my grid driver, otherwise it screws up my negative bias control.
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Old 11th March 2012, 07:29 PM   #110
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Default 12BK5 Trioded Curves

Tested a 12BK5 in triode mode from a batch that I purchased for $1 each. The curve tracer is quite stable. Yesterday I did notice that what I thought was a weak variac ended up being a bad bridge rectifier. I went to a full wave rectifier using 1n4007 diodes and using the transformer center tap to ground. I hooked up the 6336A and now I did not have issues with supplying current.

For the 12BK5 i used a 3K series resistor with the plate drive. I added plate and screen dissipation for a 11.5 W PD curve. Rigol .csv export to excel.

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