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
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
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
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:
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
We might be going over old ground here, reading this post. Audio Asylum Thread Printer
Dean
Interesting, because the HPHV regulator's behaviour, on the test-bench, at least, is that they take ages to reach their target voltage.
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).
Hello herrstagl,
Thank you for this information.
First I have a remark on TR2.
In the D version it was specified as a 100VA transformer, however if you look carefully at the label of the trafo on the foto you can read TRV85 and that would imply according to the FG Elektronik pdf I send you that it is a 160VA and not 100 VA transformer!
Next thing I would like to know is does or can Rufa also deliver baked varnish coils for the choke like for example german supplier of crossover inductors Mundorf can supply on request? Baking the coils will suppress mechanical vibrations that's why I ask.
You may have read the remark of M Knight on page 38 where he said:
"This choke buzzed very loudly and I had to abandon one of the windings. I substituted the 6mH, 2,8A winding with a Lundahl LL1694/2A choke (with the windings connected in parallel)."
So might be a point to think about!
Nevertheless I would like to hear the details from Rufa.
Thank you very much.
Best regards, airtangent
Thank you for this information.
First I have a remark on TR2.
In the D version it was specified as a 100VA transformer, however if you look carefully at the label of the trafo on the foto you can read TRV85 and that would imply according to the FG Elektronik pdf I send you that it is a 160VA and not 100 VA transformer!
Next thing I would like to know is does or can Rufa also deliver baked varnish coils for the choke like for example german supplier of crossover inductors Mundorf can supply on request? Baking the coils will suppress mechanical vibrations that's why I ask.
You may have read the remark of M Knight on page 38 where he said:
"This choke buzzed very loudly and I had to abandon one of the windings. I substituted the 6mH, 2,8A winding with a Lundahl LL1694/2A choke (with the windings connected in parallel)."
So might be a point to think about!
Nevertheless I would like to hear the details from Rufa.
Thank you very much.
Best regards, airtangent
May I suggest you use PSU Designer to design your own PSU for your RTP3? You'll be much more happy with the result than trying cloning the original PSU...
I use Lundahl LL1651 for B+, 5Y3GT rectifier tube in a hybrid bridge using HEXFRED diodes for the negative part. Furthermore two Lundahl 15H chokes and 30uF Mundorf Tubecaps... I'll properly replace the chokes with Tentlabs e-chokes as I find them superior to ordinary chokes.
Replacing 10H chokes in my 6ca7 PP amp with e-chokes from Tentlabs removed the last bit of hum and made them 100% dead silent not playing music on my 95dB/1W/1M speakers...
I use Lundahl LL1651 for B+, 5Y3GT rectifier tube in a hybrid bridge using HEXFRED diodes for the negative part. Furthermore two Lundahl 15H chokes and 30uF Mundorf Tubecaps... I'll properly replace the chokes with Tentlabs e-chokes as I find them superior to ordinary chokes.
Replacing 10H chokes in my 6ca7 PP amp with e-chokes from Tentlabs removed the last bit of hum and made them 100% dead silent not playing music on my 95dB/1W/1M speakers...
Hello Kim
Nice tip about the e-choke. From the paper about the E-choke it seems to outperform the ”oldfashoned” choke in a CLC filter.
As the E-choke has a cap in the input have you tried to use the e-choke in a choke input filter (LCLC where CL equals a E-choke)?
In my own RTP-project the e-choke may com in handy as a inline choke as i have a mains transformer delivering 480Vac and need to drop som voltage.
Your own build looks fantastic – I for one would like to see some more pictures
Best regards
Stig
Nice tip about the e-choke. From the paper about the E-choke it seems to outperform the ”oldfashoned” choke in a CLC filter.
As the E-choke has a cap in the input have you tried to use the e-choke in a choke input filter (LCLC where CL equals a E-choke)?
In my own RTP-project the e-choke may com in handy as a inline choke as i have a mains transformer delivering 480Vac and need to drop som voltage.
Your own build looks fantastic – I for one would like to see some more pictures
Best regards
Stig
Hi Stig,Hello Kim
Nice tip about the e-choke. From the paper about the E-choke it seems to outperform the ”oldfashoned” choke in a CLC filter.
As the E-choke has a cap in the input have you tried to use the e-choke in a choke input filter (LCLC where CL equals a E-choke)?
In my own RTP-project the e-choke may com in handy as a inline choke as i have a mains transformer delivering 480Vac and need to drop som voltage.
Your own build looks fantastic – I for one would like to see some more pictures
Best regards
Stig
You really need a cap before the e-choke so it should be: LC<e-choke>C if you want to make a choke input filter string.
At some time I'll post more pictures of my RTP...
Best regards
Kim
No I haven't, but Allen was always insistent that high transconduction tubes sound good cascoded, but lower transconduction tubes such as the 6SN7 do not. You could use lower mu but high transconduction tubes and still stick to his original vision.
Hello Kim,
I don't know if an own power supply design based on PSU designer would make me much more happy than cloning Alan's original power supply. One of the hallmarks of Alan's design is the use of a LC configuration in the HV PSU as he pointed out it's advantages in his Tube Preamp Cookbook. Actually it is a LCRCRC design and since the Lundahl LL1685 is a double choke he applied an additional choke in the ground path of the HV. Again I cannot judge if a PSU designer made HV supply would be sonically superior however the E-choke cannot be used in such a configuration since it requires an input and output cap as Guido Tent confirmed on my inquiry. So what one could do then is replace the first R with an E-choke which would probably make as well a clear improvement. However what I personally dislike about the E-choke is the use of electrolytic capacitors which is one of the things Alan abandoned when he switched over from C to D version and I would agree that electrolytic capacitors are not the last word in a HV PSU as I have found out on my own with my WOT ( with output transformer ) line stage which uses an RGN1064 mesh tube rectifier in combination with a CLCLC configuration. Replacing all the electrolytic capacitors there with MKP Polypropylene in oil capacitors of the same capacity in uF made sonically a huge difference clearly for the better with the MKP caps in my opinion!
Best regards
airtangent
I don't know if an own power supply design based on PSU designer would make me much more happy than cloning Alan's original power supply. One of the hallmarks of Alan's design is the use of a LC configuration in the HV PSU as he pointed out it's advantages in his Tube Preamp Cookbook. Actually it is a LCRCRC design and since the Lundahl LL1685 is a double choke he applied an additional choke in the ground path of the HV. Again I cannot judge if a PSU designer made HV supply would be sonically superior however the E-choke cannot be used in such a configuration since it requires an input and output cap as Guido Tent confirmed on my inquiry. So what one could do then is replace the first R with an E-choke which would probably make as well a clear improvement. However what I personally dislike about the E-choke is the use of electrolytic capacitors which is one of the things Alan abandoned when he switched over from C to D version and I would agree that electrolytic capacitors are not the last word in a HV PSU as I have found out on my own with my WOT ( with output transformer ) line stage which uses an RGN1064 mesh tube rectifier in combination with a CLCLC configuration. Replacing all the electrolytic capacitors there with MKP Polypropylene in oil capacitors of the same capacity in uF made sonically a huge difference clearly for the better with the MKP caps in my opinion!
Best regards
airtangent
I'm a little confused as to what people are trying to achieve regarding PSU's. I understand that you may just wish to clone the original VSE PSU in which case you would try to get the same parts but, if that is not what you require, then there are numerous ways to achieve a quiet amp.
Personally I have always tried to steer clear of bridge rectifiers as I always understood that diodes introduced switching noise into the B+. When I have had to use them, they have been Scottky's, individually bypassed with caps. I generally use rectifier valves which have the benefit of a slow power on. Additional benefits are that you can vary the type of valve in order to drop more or less voltage, dependant on your TX secondary voltage and what rectified voltage you require. Allen gave the impression that you could never have too much iron, hence large TX's and chokes. This is just my own view, but I would be reluctant to introduce more silicon in the form of an E Choke, there's enough for my liking with the Mosfets in the SuperRegs!
If you're using a shunt regulator, HPHV, SuperReg etc, then surely that will filter the majority of noise and ripple, so ripple upstream of the regulator will be less of a concern! I'm measuring 0.06mv ripple on my 300v output! (To be fair that's with my DMM, I haven't checked with an oscilloscope but I'll do that at some stage.)
I find that Duncan Amps PSUD2 is an invaluable tool for designing the PSU. I use it to ensure that ringing is negligible and, by adjusting rectifier valve, chokes & caps, get the voltage I require. I'm usually surprised at how little capacitance I need to get a decent supply. I agree that the caps would preferably be paper in oil, which in itself would restrict the amount of capacitance you could squeeze into your chassis but I'm still getting acceptable performance with a mix of PIO's and electrolytics. I concede that this is not ideal but, all the same, it sounds OK and there is NO hum.
Another source for TX's and chokes in UK is VVT transformers. They may be OK for European builders. (I haven't used them myself so make your own mind up about them!)
Like I say, I'm just trying to understand what PSU's people are building. I'm certainly no expert and in no way am I trying to tell people how to do things. Thanks.
Personally I have always tried to steer clear of bridge rectifiers as I always understood that diodes introduced switching noise into the B+. When I have had to use them, they have been Scottky's, individually bypassed with caps. I generally use rectifier valves which have the benefit of a slow power on. Additional benefits are that you can vary the type of valve in order to drop more or less voltage, dependant on your TX secondary voltage and what rectified voltage you require. Allen gave the impression that you could never have too much iron, hence large TX's and chokes. This is just my own view, but I would be reluctant to introduce more silicon in the form of an E Choke, there's enough for my liking with the Mosfets in the SuperRegs!
If you're using a shunt regulator, HPHV, SuperReg etc, then surely that will filter the majority of noise and ripple, so ripple upstream of the regulator will be less of a concern! I'm measuring 0.06mv ripple on my 300v output! (To be fair that's with my DMM, I haven't checked with an oscilloscope but I'll do that at some stage.)
I find that Duncan Amps PSUD2 is an invaluable tool for designing the PSU. I use it to ensure that ringing is negligible and, by adjusting rectifier valve, chokes & caps, get the voltage I require. I'm usually surprised at how little capacitance I need to get a decent supply. I agree that the caps would preferably be paper in oil, which in itself would restrict the amount of capacitance you could squeeze into your chassis but I'm still getting acceptable performance with a mix of PIO's and electrolytics. I concede that this is not ideal but, all the same, it sounds OK and there is NO hum.
Another source for TX's and chokes in UK is VVT transformers. They may be OK for European builders. (I haven't used them myself so make your own mind up about them!)
Like I say, I'm just trying to understand what PSU's people are building. I'm certainly no expert and in no way am I trying to tell people how to do things. Thanks.