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Old 4th January 2013, 05:56 PM   #381
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Originally Posted by M Knight View Post
based on the Manfred Huber design.
Correction: Based on the Emile Sprenger design.
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Old 4th January 2013, 06:16 PM   #382
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Originally Posted by M Knight View Post
Your RTP3 is simply stunning. Well done!

I wish you well with the AD797s, but feel I should warn you that it is quite likely that you will convert your shunt regulators into RF transmitters.

Allen was very sanguine in his advice about plugging in these sensitive and fast devices but I would advise extreme caution. Do only one board at a time and keep your oscilloscope warm.

The AD797 datasheet gives explicit instructions for power supply bypassing including making provision for a Kelvin return and ensuring the shortest possible lead lengths. The use of an IC socket is quite out of the question.

You may well be lucky but you could also find yourself, as I did, in the invidious position of having to yank out your expensive AD797s because you cannot get the regulators to stop oscillating.
Hi M Knight.

Thanks for the advice. I am using a socket. Fortunately I bought the 797's at a good price a few years ago so nothing lost if they don't behave. They can be used elsewhere. I take it you placed the 100nf cap across pins 4 & 7 as recommended?

Ravi.

I managed to buy a roll of Alpha-Core 25mm x 0.076mm 4n foil back in the mists of time and I keep it in a secret place!! Joking apart, I was just lucky to find this for sale. I had approached Johnson Matthey around 8 years ago and they said they could supply any configuration of foil you want provided you purchased a kilogram. At the time that worked out around £480.00 and I couldn't afford it. If I'd have gone for it, it would be worth a fortune now the way silver's gone up! Don't know if they would still do it....Group Buy maybe?

FYI I just use a craft knife and steel rule to cut the Alpha-Core foil into strips as and when required.

Airtangent.

Off the top of my head; There are four 10 volt secondaries on my large toroid. The three rectified/regulated heater supplies, before they get to the current sources, also activate the coils of 3 NO relays. The 4th regulated/rectified supply for the timer circuit, has it's negative running through the three relays in series before it gets to the coil of a fourth NO relay which allows mains power to the HT TX. The positive for this fourth relay coil is the output from the timer. The theory is that if there is a problem with any of the three heater supplies, it's relay will open and, as a consequence, the HT TX relay will open cutting of the HT power. I'll post a schematic when I get chance.
I agree that a better solution would be for each filament supply to be monitored. I did think that this could be done reasonably simply with a micro-controller which could be programmed to switch a relay if any of the twelve filament voltages/currents fell below a certain value. You could also use the micro-controller to drive a small lcd display to let you know what's happening. A bit too clever for me to work out though hence the simpler approach!

Regards,

Dean
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Old 4th January 2013, 06:41 PM   #383
jpak is offline jpak  United States
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Originally Posted by valve5425 View Post
Thanks Zen Mod. It keeps the room warm as well!!
Very nice build, congratulations!
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Old 5th January 2013, 11:24 AM   #384
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I take it you placed the 100nf cap across pins 4 & 7 as recommended?
Hi Dean,

I did place the 100nF cap. Axial ceramic. Not that easy to get these days. Also, as per the datasheet, I placed, in addition to the 100nF cap, a 1.1R and 4.7uF cap, in series like a Zobel network, in parallel with the 100nF cap. Sparing no expense, the 4.7uF cap is a ROEDERSTEIN axial tantalum cap.

No luck.

Hope you are more successful.

Martin Knight
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Old 5th January 2013, 01:16 PM   #385
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Originally Posted by M Knight View Post
Hi Dean,

I did place the 100nF cap. Axial ceramic. Not that easy to get these days. Also, as per the datasheet, I placed, in addition to the 100nF cap, a 1.1R and 4.7uF cap, in series like a Zobel network, in parallel with the 100nF cap. Sparing no expense, the 4.7uF cap is a ROEDERSTEIN axial tantalum cap.

No luck.

Hope you are more successful.

Martin Knight
Hi Martin.

Sounds like it's a no-goer then so I'll not rush to try it. If I get around to it at a later stage, I'll just pop the 797's in without any further mods (the 100nf caps are in there already) and report back, although I wouldn't think it would be any different to the result you got.

Regards.............Dean
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Old 5th January 2013, 01:27 PM   #386
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Originally Posted by valve5425 View Post
Hi Martin.

Sounds like it's a no-goer then so I'll not rush to try it. If I get around to it at a later stage, I'll just pop the 797's in without any further mods (the 100nf caps are in there already) and report back, although I wouldn't think it would be any different to the result you got.

Regards.............Dean
Gosh, no, Dean.

What I want is for you to report back that the addition of the 1.1R resistor and the 4.7uF cap CAUSED the chip to oscillate!

Martin
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Old 5th January 2013, 03:13 PM   #387
Alex M is offline Alex M  United Kingdom
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Originally Posted by M Knight View Post
I don't know. I don't use Allen's SuperReg boards any more. I built instead the HPHV shunt regulators based on the Manfred Huber design. These boards use a Burr-Brown OPA655 FET-input opamp. It is a very good chip and is stable in this circuit.
I also use the HPHV regulators in my RTP3. This was partly because the PCB foils and user manuals were in the public domain, and partly because I felt it was a more sophisticated design. I suspect that they are only marginally stable, though, as I would get interference with FM radio for a minute or so after I applied power. I haven't had a chance to check them with an oscilloscope, since I don't have access to one. I have also built a pair of HPHV boards with AD9631 op-amps instead of OPA655 (which, as you may know, are now almost unobtainable). I used Emile's PCB layout in all cases, but my personal feeling is that the HPHV PCB has some of its tracks much too close together for hobbyist use.

A longer-term problem with the HPHV as I have built it is a tendency for the output voltage to hit the target voltage almost immediately (in fact with a worrying overshoot) instead of ramping up over a minute or so, which all of my boards did originally.

My plan is to replace the HPHV regulators over the next few months with the Salas SSHV2 shunt regulator, which is a much simpler design and promises to less twitchy.

Alex

Last edited by Alex M; 5th January 2013 at 03:15 PM.
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Old 5th January 2013, 03:31 PM   #388
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My misunderstanding Martin. Don't know when I'll get them swapped but I'll keep you posted.

We might be going over old ground here, reading this post. Audio Asylum Thread Printer

Dean
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Old 5th January 2013, 05:04 PM   #389
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Originally Posted by Alex M View Post
A longer-term problem with the HPHV as I have built it is a tendency for the output voltage to hit the target voltage almost immediately (in fact with a worrying overshoot) instead of ramping up over a minute or so, which all of my boards did originally.
Interesting, because the HPHV regulator's behaviour, on the test-bench, at least, is that they take ages to reach their target voltage.

Quote:
Originally Posted by Alex M View Post
My plan is to replace the HPHV regulators over the next few months with the Salas shunt regulator, which is a much simpler design and promises to less twitchy.
Wow, the Salas regulator doesn't use a chip, wide bandwidth or otherwise, as an error amp (and doesn't require a power supply, crude or sophisticated, to support one).
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Old 5th January 2013, 08:09 PM   #390
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Originally Posted by airtangent View Post
Hi valve 5424,

Regarding your remark „To be on the safe side I've used relays to switch off the HT should any of the heater supplies fail“ I would like to ask you some questions.

Having read this I would be highly interested to see how you accomplished that.

My first question is do you mean by any of the heater supplies the two rectified DC voltages for low and high heater in the PS or do you really refer to each of the 12 CCS supplies?

There is already a relay in the power supply which switches the HT on with a certain delay after the filament voltages in the PS have come up.
However there is no provision for monitoring condition of the individual filaments during operation.

So could you tell us more in detail ( schematic and actual build up? ) how you made this?

If you really monitor each filament individually I would assume that since the filaments are fed by CCS’s you need to detect the actual voltages as measured at the filaments of each tube separately in order to check health of filaments or not?

It would definitely be a nice additional feature to have for all 12 tubes in the RTP3C/D and I can imagine that there are other users here who would be very interested as well.

Please let us know.

Thank you very much.


Best regards, airtangent
As promised. Dean
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