Decent x_former with isolation working voltage of 3...5 kV primary to secondary in not the easiest by my experience.
What CSS is made of? MOSFET's or pentode/tetrode?
Well... Radiotron Handbook says that pentode loaded triode stage is still a triode stage...
Then the question would be: Where to get floating 200-300V supply for second grid?
Beveridge circuit uses beam tetrodes with floating zeners.
Triode mu follower will make power supply voltage even more dangerous
Alex
Frustration while building tube circlotron's driving stage inclines me towards transformer...
Hi,
*lol* can feel with You regarding cyclotron´s driver stage. My boss still dreams of such an amp as DD for ESLs and I still try to get him off that idea.
My favourite at the moment would be a SIC-JFET or Triode stage, loaded with a CCS (fixed current or maybe even output voltage controlled).
The CCS could be made of a depletion mode SIC-JFET or MOSFET and cascoded decices to allow for the specified voltage range. I´d prefer heaterless devices for the ´high sided-CCS´ to omit with problems of the power supplies of the heater.
jauu
Calvin
*lol* can feel with You regarding cyclotron´s driver stage. My boss still dreams of such an amp as DD for ESLs and I still try to get him off that idea.
My favourite at the moment would be a SIC-JFET or Triode stage, loaded with a CCS (fixed current or maybe even output voltage controlled).
The CCS could be made of a depletion mode SIC-JFET or MOSFET and cascoded decices to allow for the specified voltage range. I´d prefer heaterless devices for the ´high sided-CCS´ to omit with problems of the power supplies of the heater.
jauu
Calvin
Shall not it be considered as tube "infidelity" or cheating with transistorsHi,
*lol* can feel with You regarding cyclotron´s driver stage. My boss still dreams of such an amp as DD for ESLs and I still try to get him off that idea.
My favourite at the moment would be a SIC-JFET or Triode stage, loaded with a CCS (fixed current or maybe even output voltage controlled).
The CCS could be made of a depletion mode SIC-JFET or MOSFET and cascoded decices to allow for the specified voltage range. I´d prefer heaterless devices for the ´high sided-CCS´ to omit with problems of the power supplies of the heater.
jauu
Calvin
In regard to Circlotron - this one is not intended for driving ESL. Even then
+/- 450V of driving voltage required. No appropriate AF tubes were found,
transmitter and sweep only... Floating heater is not that bad in respect to
floating second grid supply for tetrodes - (I hope my english would be adequate)
galette or disk or vertical sectioned transformer will do it just fine.
Alex
Hi,
I´m not very dogmatic about parts. I do prefer certain types like JFETs, but I try to find and use that device that is most suitable for the task. Transistors are easy to use for CCS and achieve better results. So why should I worry about a suitable Pentode and their associated circuitry when a depletionmode MOSFET (or a cascode formed with it) does the same even better and with less harrasment?? The ´real´ amplyfying device could still be a Triode
KR-Audio has already prototyped and tested a new 4kV Triode for us and as soon as time allows I think I´ll be at it, or one of the SIC-JFETs.
jauu
Calvin
I´m not very dogmatic about parts. I do prefer certain types like JFETs, but I try to find and use that device that is most suitable for the task. Transistors are easy to use for CCS and achieve better results. So why should I worry about a suitable Pentode and their associated circuitry when a depletionmode MOSFET (or a cascode formed with it) does the same even better and with less harrasment?? The ´real´ amplyfying device could still be a Triode
KR-Audio has already prototyped and tested a new 4kV Triode for us and as soon as time allows I think I´ll be at it, or one of the SIC-JFETs.
jauu
Calvin
Hi,
I´m not very dogmatic about parts. I do prefer certain types like JFETs, but I try to find and use that device that is most suitable for the task. Transistors are easy to use for CCS and achieve better results. So why should I worry about a suitable Pentode and their associated circuitry when a depletionmode MOSFET (or a cascode formed with it) does the same even better and with less harrasment?? The ´real´ amplyfying device could still be a Triode
KR-Audio has already prototyped and tested a new 4kV Triode for us and as soon as time allows I think I´ll be at it, or one of the SIC-JFETs.
jauu
Calvin
Thanks,
nice link.
The tubes I've got are transmitter tetrodes rated @ 10kV, DC.
Pretty linear in triode connection. I do feel inappropriate to go into
details before amp is built and tested.
FETs are known for very non-linear output capacitance which seems to
be very relevant for a capacitive load.
Alex
Wolfcott tube amps with adjustable damping are made specifically for Electrostats. the Presence Tube Amplifiers
Sure,
any ideas on topology used?
All I could find were spare parts (sic.!) tubeE tubeP tubeG
Does not this smell like consumables
http://www.innoxx.com/deutsch/download/sparepart_8.pdf
Fill the amplifier with the fresh tubes before starting...
Most interesting that higher voltage one requires only two tubes,
very reasonably priced...
Alex
Hi,
Face...we are talking high voltage direkt drive here.....which renders the Wolfcotts OT.
I like the optics of the Innoxx and the use of a µC to control functions and biassing, but they are somehow ´items in between´ as they are no universally usable ESL-amps. You should be beware of and stay within the limitations. The output voltage range is a bit low to drive (segmented) fullrange panels and their current capabilties are a bit low to drive non segmented panels of middle or large size. This leaves segmented hybrid panels and small non segmented hybrid panels as best fitting candidates.
Tubes look like EL/PL519... nice tube, easy to source, attractively priced.
If we want to achieve full power bandwidth of just 20kHz sine(!) we need:
Ipeak[mA]: 62.8 x C[nF] x Vpp[kV] .
Lets assume a non segmented panel of 1nF and rather low voltage needs of 3kVpp (1.06kVrms). Power supply voltage will be app 1.8-2kV. The amp must be able to drive a peak current of ~190mA into the load to fulfill the above stated requirement.
Now segmenting reduces the capacitive load, but such panels typically need more drive voltage, say 200pF and 7kVpp (power supply app. 4kV). Ipeak is then 88mA. Large fullrangers are even more demanding.
jauu
Calvin
Face...we are talking high voltage direkt drive here.....which renders the Wolfcotts OT.
I like the optics of the Innoxx and the use of a µC to control functions and biassing, but they are somehow ´items in between´ as they are no universally usable ESL-amps. You should be beware of and stay within the limitations. The output voltage range is a bit low to drive (segmented) fullrange panels and their current capabilties are a bit low to drive non segmented panels of middle or large size. This leaves segmented hybrid panels and small non segmented hybrid panels as best fitting candidates.
Tubes look like EL/PL519... nice tube, easy to source, attractively priced.
If we want to achieve full power bandwidth of just 20kHz sine(!) we need:
Ipeak[mA]: 62.8 x C[nF] x Vpp[kV] .
Lets assume a non segmented panel of 1nF and rather low voltage needs of 3kVpp (1.06kVrms). Power supply voltage will be app 1.8-2kV. The amp must be able to drive a peak current of ~190mA into the load to fulfill the above stated requirement.
Now segmenting reduces the capacitive load, but such panels typically need more drive voltage, say 200pF and 7kVpp (power supply app. 4kV). Ipeak is then 88mA. Large fullrangers are even more demanding.
jauu
Calvin
Last edited:
That's exactly what I thought.Hi,
Face...we are talking high voltage direkt drive here.....which renders the Wolfcotts OT.
I like the optics of the Innoxx and the use of a µC to control functions and biassing, but they are somehow ´items in between´ as they are no universally usable ESL-amps. You should be beware of and stay within the limitations. The output voltage range is a bit low to drive (segmented) fullrange panels and their current capabilties are a bit low to drive non segmented panels of middle or large size. This leaves segmented hybrid panels and small non segmented hybrid panels as best fitting candidates.
Tubes look like EL/PL519... nice tube, easy to source, attractively priced.
If we want to achieve full power bandwidth of just 20kHz sine(!) we need:
Ipeak[mA]: 62.8 x C[nF] x Vpp[kV] .
Lets assume a non segmented panel of 1nF and rather low voltage needs of 3kVpp (1.06kVrms). Power supply voltage will be app 1.8-2kV. The amp must be able to drive a peak current of ~190mA into the load to fulfill the above stated requirement.
Now segmenting reduces the capacitive load, but such panels typically need more drive voltage, say 200pF and 7kVpp (power supply app. 4kV). Ipeak is then 88mA. Large fullrangers are even more demanding.
jauu
Calvin
Even Beveridge was using 6LQ6 which is sweep tube.
Max DC voltage on pl519 has to be no more than 700V(cold).
Every other specs are pulse ones, no static curves provided above 450.
Search yielded multiple refences of unreliable operation at
the conditions you have mentioned.
Cathode stripping and arcing are the most cited problems.
It is nice to know that you are trying to develop custom
tube for the particular applications.
In regard to CCS load - breadbording showed substantial
rise of harmonic distortion(two to three fold), probably due to lower supply
voltage - which seems to be the goal of CCS use.
In regard to HF full power - what will be sound pressure level,
let's say at 15kHz and full swing voltage at the transducser?
My moving coil speaker, rated at 35W 100% duty has 6W rated tweeter...
Alex
Hi,
as a rule of thumb You calculate the breakdown voltage limit for a given stator-stator-distance. If You have a panel with 1mm d/s the s/s value is twice of it, 2mm. Breakdown voltage of air is around 2kV/mm. So the limiting signal voltage is 4kVpp. In any case should the peak signal voltage (2kV in this example) be lower than the membrane bias voltage. If You think of Audiostatics 8mm of s/s distance You get an idea that drive voltages can quickly become very high indeed.
An amplifiers power supply voltage must be at minimum the desired peak signal voltage plus losses in the stator insulation plus losses within the amps-circuit. So for 4kVpp the power supply voltage will be app 2.2-2.5kV.
For 3kVpp (see Innoxx) You need probabely 1.6-1.8kV of supply voltage, which suggests a DC plate voltage of 800-900V. That is not too far above the datasheet value of 700V(cold) of a PL519. With screening You´ll find tubes that will withstand these conditions quite well. If You look at the Acoustat amp that uses 5kV supply voltage, hence 2.5kV DC plate voltage and the 6HB5 (770V) and even this worked somehow.
jauu
Calvin
as a rule of thumb You calculate the breakdown voltage limit for a given stator-stator-distance. If You have a panel with 1mm d/s the s/s value is twice of it, 2mm. Breakdown voltage of air is around 2kV/mm. So the limiting signal voltage is 4kVpp. In any case should the peak signal voltage (2kV in this example) be lower than the membrane bias voltage. If You think of Audiostatics 8mm of s/s distance You get an idea that drive voltages can quickly become very high indeed.
An amplifiers power supply voltage must be at minimum the desired peak signal voltage plus losses in the stator insulation plus losses within the amps-circuit. So for 4kVpp the power supply voltage will be app 2.2-2.5kV.
For 3kVpp (see Innoxx) You need probabely 1.6-1.8kV of supply voltage, which suggests a DC plate voltage of 800-900V. That is not too far above the datasheet value of 700V(cold) of a PL519. With screening You´ll find tubes that will withstand these conditions quite well. If You look at the Acoustat amp that uses 5kV supply voltage, hence 2.5kV DC plate voltage and the 6HB5 (770V) and even this worked somehow.
jauu
Calvin
Thanks,
for me the idea/topology would serve the best
knowing that devil is in the details... like take a boxfull of tubes to get few with required ratings.
Alex
Further thoughts, progress
Alot to chew on from this thread, any developments this winter? I went to Innoxx (OTL) site again, also alittle google. They presented at a show (nice Pics) but I couldn't find any review there or from other threads, a quickie would be nice.
As limited a design and component compromised as the Acoustat was (is) they can sing to me and I'm convinced a sorted out OTL would find many a happy home. I own the Acoustat Otl's and read Broskie's comments on PRPP's wanting (need) to see a constant load. He showed several possible alt. configurations, one I remember is moving the P-P output down from the upper tube to between the lower tube's plate and the load resister into the upper tube. Also if one were to bi-amp and use trans couple for bass and a OTL for mids/highs how much would that improve the load for the PRPP. Sort of like the problem Strickland was looking at but instead of spreading the impedance by the way he wired his two trans together, this would separate the huge swings into two paths, lessor of two evils? I'm hoping to recieve a loadline on the KR 845 to well past the 1250v plate 
Acoustat OTL owners if you did the AA mods or have Dan Fanny boards I would suggest you install a power switch that needs to be energized for operation. This would prevent a power on situation right after losing power unexpectedly - bad to terrible.
Alot to chew on from this thread, any developments this winter? I went to Innoxx (OTL) site again, also alittle google. They presented at a show (nice Pics) but I couldn't find any review there or from other threads, a quickie would be nice.
As limited a design and component compromised as the Acoustat was (is) they can sing to me and I'm convinced a sorted out OTL would find many a happy home. I own the Acoustat Otl's and read Broskie's comments on PRPP's wanting (need) to see a constant load. He showed several possible alt. configurations, one I remember is moving the P-P output down from the upper tube to between the lower tube's plate and the load resister into the upper tube. Also if one were to bi-amp and use trans couple for bass and a OTL for mids/highs how much would that improve the load for the PRPP. Sort of like the problem Strickland was looking at but instead of spreading the impedance by the way he wired his two trans together, this would separate the huge swings into two paths, lessor of two evils? I'm hoping to recieve a loadline on the KR 845 to well past the 1250v plate Acoustat OTL owners if you did the AA mods or have Dan Fanny boards I would suggest you install a power switch that needs to be energized for operation. This would prevent a power on situation right after losing power unexpectedly - bad to terrible.
Hi,
yes, everything that reduces the impedance variation for the Acoustat-like SRPP stage should improve things.
We have driven the KR845 up to 2kV without probs. But afaik, KR hasn´t produced 845s for a while and doesn´t want to do so in future. Simply too much effort to be economic.
jauu
Calvin
yes, everything that reduces the impedance variation for the Acoustat-like SRPP stage should improve things.
We have driven the KR845 up to 2kV without probs. But afaik, KR hasn´t produced 845s for a while and doesn´t want to do so in future. Simply too much effort to be economic.
jauu
Calvin
DIY innoxx/acoustat/twinstatic clone amp
I've been seaching the web and reading here for a while. I'm now gathering up parts to start work on a DIY amplifier. I have the schematic of the Acoustat x and pictures of them all. Lookes to me like they all use 4 sweep tubes per side. Does anyone know if the output cicuits are similar? I mean a "bottom" tube with cathode at or near ground and a "top" tube withe the plate connected to B+ and the output taken from a point were they connect?
I've allready decided on a tube driver circuit and screen supply circuits that are different than the Acoustat x. Also no automatic on and no equalization. Input will be PC sound card, MP3 player, stereo headphone level.
That should keep it in the DIY world.
Jim
I've been seaching the web and reading here for a while. I'm now gathering up parts to start work on a DIY amplifier. I have the schematic of the Acoustat x and pictures of them all. Lookes to me like they all use 4 sweep tubes per side. Does anyone know if the output cicuits are similar? I mean a "bottom" tube with cathode at or near ground and a "top" tube withe the plate connected to B+ and the output taken from a point were they connect?
I've allready decided on a tube driver circuit and screen supply circuits that are different than the Acoustat x. Also no automatic on and no equalization. Input will be PC sound card, MP3 player, stereo headphone level.
That should keep it in the DIY world.
Jim