Anyone finish their monster amp yet? Mine is on hold while I research cathode follower output stages, and a few other "out there" concepts.
I have discovered that the surplus Plitron transformer mentioned earlier in this thread really does not like DC imbalance. Even 10 mA of imbalance causes visible distortion at 20 Hz and only 50 watts of power. It is likely that some type of bias servo is needed.
I got an email claiming that this transformer is simply an unpotted Plitron PAT4141-00. I have not found anything to disprove this. The pat4141 is made for bass guitar.
The data sheet for the pat4141 says "The power bandwidth starts at 14 Hz. The transformer can handle 400 watts. This will enable eight 6550 or KT88 or equivalent tubes to be used with an anode voltage of 560 volts. The frequency range extends to 117 KHz without feedback. This full range transformer provides clear bass guitar sounds like attacks, slaps and other modern sounds."
It can be found here.
http://www.plitron.com/pdf/pat4141-00.pdf
Mine is currently connected in parafeed connection in a SE cathode follower amp. A big P-P cathode follower amp is planned. Experimentation has just started, but is on hold for 2 weeks. I won't be here.
I have discovered that the surplus Plitron transformer mentioned earlier in this thread really does not like DC imbalance. Even 10 mA of imbalance causes visible distortion at 20 Hz and only 50 watts of power. It is likely that some type of bias servo is needed.
I got an email claiming that this transformer is simply an unpotted Plitron PAT4141-00. I have not found anything to disprove this. The pat4141 is made for bass guitar.
The data sheet for the pat4141 says "The power bandwidth starts at 14 Hz. The transformer can handle 400 watts. This will enable eight 6550 or KT88 or equivalent tubes to be used with an anode voltage of 560 volts. The frequency range extends to 117 KHz without feedback. This full range transformer provides clear bass guitar sounds like attacks, slaps and other modern sounds."
It can be found here.
http://www.plitron.com/pdf/pat4141-00.pdf
Mine is currently connected in parafeed connection in a SE cathode follower amp. A big P-P cathode follower amp is planned. Experimentation has just started, but is on hold for 2 weeks. I won't be here.
Still have not played with the Plitron surplus transformers. My procrastination department is firmly controlling this project.
Have you considered the circlotron circuit.
"No output tube DC in transformer... DC output current is removed from the output transformer through the use of a bridge circuit."
http://circlotron.tripod.com/
Schematic here
http://circlotron.tripod.com/a100e.pdf
Have you considered the circlotron circuit.
"No output tube DC in transformer... DC output current is removed from the output transformer through the use of a bridge circuit."
http://circlotron.tripod.com/
Schematic here
http://circlotron.tripod.com/a100e.pdf
I briefly played with Circlotrons about 5 years ago. I built one with 6AS7's using industrial control transformers for power supplies. The requirements for 2 identical independently floating HV power supplies (per channel) make the Circlotron a little more difficult at the 400 watt level. It still could be done with a few Antek power toroids though.
I often get these wild circuit ideas. Most of them die before they are ever born, but some get simulated, and a few (despite objections from the procrastination department) get built. I have dreamed up something that is extreme even by my standards. It requires vacuum tube, solid state, multiple microprocessors and even DSP technology, but may open up new possibilities in high power tube amps, both SE and P-P. The simulations are done, and some sub - circuits have been built, and are working. For this to work, certain constraints are placed on the output tube topology. A circlotron will not work here, so for now I will play with cathode followers, BIG cathode followers.
Some of the experiments are here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=105859
I often get these wild circuit ideas. Most of them die before they are ever born, but some get simulated, and a few (despite objections from the procrastination department) get built. I have dreamed up something that is extreme even by my standards. It requires vacuum tube, solid state, multiple microprocessors and even DSP technology, but may open up new possibilities in high power tube amps, both SE and P-P. The simulations are done, and some sub - circuits have been built, and are working. For this to work, certain constraints are placed on the output tube topology. A circlotron will not work here, so for now I will play with cathode followers, BIG cathode followers.
Some of the experiments are here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=105859
I bought a 12 pack of these ACME surplus control transformers from this guy.
$12 + 12 shipping for two transformers (or $12 each shipped).
http://cgi.ebay.com/350-VA-ACME-TRA...ryZ97184QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
He has a lot of them. I figure 3 transformers for each mono block for a circlotron. Adding LCLC chokes and oil caps, the amp is gonna be heavy.
Will be looking at your other thread also.
$12 + 12 shipping for two transformers (or $12 each shipped).
http://cgi.ebay.com/350-VA-ACME-TRA...ryZ97184QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
He has a lot of them. I figure 3 transformers for each mono block for a circlotron. Adding LCLC chokes and oil caps, the amp is gonna be heavy.
Will be looking at your other thread also.
tubelab.com said:
All Diy Audio is on hold for me right now. I have moved into an industrial loft type warehouse building. The ceiling is almost 16 feet high! The HiFi sounds very good in an open space. I have to knock down the bathroom ASAP and rebuild it. Once I get that task out of the way it will be full speed DIY amplifiers.
BTW, I did purchase two of the 400-0-400 transformers in post # 62. Antek has a good product offering there and the shipping cost and packaging methods were excellent! Thank you very much for the recommendation Tubelab.
I very badly want to finish my Krell KSA50 and get on to this 807 tube business.
Hopefully sooner than later cause I'm really starting to miss my solder iron.
I decided to bump this topic to see if anyone had made any progress with the big plitrons. I have been planning on using them for some PP 6C33 amps for most of the time I have owned them, but never have been completely convinced that is the way i wanted to go. The 6LW6 sweep tube idea is pretty intruiging.
Anything to report by the Plitron owners?
Anything to report by the Plitron owners?
No. Both my transformers are sitting inside their boxes. I guess we are all waiting for someone to do something.
My thinking has always been that this transformer will make a good Class AB Circlotron, as described here.
http://circlotron.tripod.com/
schematic here
http://circlotron.tripod.com/a100.pdf
Unfortunately, so are mine. Life has been in the way a lot lately. I have been averaging about 4 or 5 hours of tube time per month lately. This months allotment was all used up yesterday when I spent the whole afternoon extracting 75 watts from a pair of KT88's. The knob on the power supply wouldn't go any higher. All I managed to blow up was two IXYS 10M45 chips and two resistors. Didn't even get the KT88's to glow. I really do need a bigger power supply before attempting to build the monster.
The KT88's are Electro Harmonix. They sound good and are the most rugged KT88's that I have seen recently. Getting a box full of used ones cheap didn't hurt either. The power supply is an old Fluke 407D that I got for $25 on Ebay (+$45 shipping!). It is absolutely original with a 1970's calibration sticker. I have had it for a few years. I planned to rebuild it when it finally dies, but it keeps going despite my abuse. It is rated 0 to 555 volts at 300 mA. I have had it go unstable with a 250 mA load, and I have seen it work fine with a 400 mA load.
Yesterdays experiments involved running a SimpleSE board in push pull. I didn't change the bias resistor from the value used in the original class A SE application. The much lower load impedance of the P-P OPT dragged the tubes out of class A at high powers though. I tried B+ voltages from 400 volts to 552(max). The bias current varied as the voltage was changed due to the use of cathode bias. With 552 volts (about 490 across the tube) the tube current about 100 mA. No glow though even with the lights off. Some pictures here: http://www.diyaudio.com/forums/showthread.php?s=&threadid=123320
Tubelab,
Do you have a view on why the 10M45 blew. That is, was it overvoltage or over power (insufficient heatsinking)?
Are you using these as the load in the driver or as current sources in the output tube cathodes?
I've been doing some modelling using DN2540 current sources in the cathodes of 300Bs running at 75mA. With 80V on the cathodes of the 300B the power dissipated by the DN2540 is 6 watts, so for a KT88 where cathode volts is likely to be more like 40V then you can expect 3 to 4 watts dissipation and therefore a heatsink capable of say 6 degrees C per watt would be required.
BTW the IXYS webpages seem to indicate that they consider the 10M45 as obsolete although I see Digi-Key still has heap of stock. The current production (TO220) item is an IXTP 02N50D which appears to have superior specs to the 10M45 plus it is 500V rated vs 450V.
The DN2540 still has the edge in Coss and Crss so will have better high frequency performance. Pity about its 400V rating.
Cheers,
Ian
Do you have a view on why the 10M45 blew. That is, was it overvoltage or over power (insufficient heatsinking)?
Are you using these as the load in the driver or as current sources in the output tube cathodes?
I've been doing some modelling using DN2540 current sources in the cathodes of 300Bs running at 75mA. With 80V on the cathodes of the 300B the power dissipated by the DN2540 is 6 watts, so for a KT88 where cathode volts is likely to be more like 40V then you can expect 3 to 4 watts dissipation and therefore a heatsink capable of say 6 degrees C per watt would be required.
BTW the IXYS webpages seem to indicate that they consider the 10M45 as obsolete although I see Digi-Key still has heap of stock. The current production (TO220) item is an IXTP 02N50D which appears to have superior specs to the 10M45 plus it is 500V rated vs 450V.
The DN2540 still has the edge in Coss and Crss so will have better high frequency performance. Pity about its 400V rating.
Cheers,
Ian
Yeah, it was a blonde moment that resulted in about 400 volts between the source and gate!
I was using them as ordinary mosfets (which some believe they are) in the upper devices of a cascode (12AT7 for bottom). I was using a seperate power supply on the gates so that I could adjust it to find the best voltage. After I got it all dialed in, I shut off the main supply but left the gate supply on. Zap. I replaced them with Toshiba fets.
I now have two toasted chips. I am going to crack them open to see what the die looks like.
Mouser now stocks the 10M90 which is good to 900 volts. I got some but have not had time to play with them yet.
Did someone say 'big amps'?
200 watts RMS, rather more peak, all triodehttp://img102.imageshack.us/img102/6060/bigamps004mz5.jpg
200 watts RMS, rather more peak, all triodehttp://img102.imageshack.us/img102/6060/bigamps004mz5.jpg
back side:
An externally hosted image should be here but it was not working when we last tested it.
Heavily modified Ballantyne Royal SoundMaster MX-24's. Used to power ~800 drive-in theater speakers each. Surprisingly wide bandwidth 25-20000 -1dB @100 watts from an all interstage transformed topolgy from 1949. They run 6SN7 differential IT push-pull 6B4G IT PP 805. They were modded by William Hardy of Vintage Amplifier Restoration. They run my linearrays usually, but right now two are on some Fisher XP1A's from 1964, lol!
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