Hey Whitelabrat,
If you look on Pete Millet's site,he might have some info on your transformer,if you're lucky.
http://www.pmillett.com/Tek_xfmrs.htm
If you look on Pete Millet's site,he might have some info on your transformer,if you're lucky.
http://www.pmillett.com/Tek_xfmrs.htm
You guys in the US are in the great position that you can part out these wonderful old scopes.
I am kind of a TEK fan, I own a couple of more modern "transistor-ated" ones. I am looking to get a decent 5 series simply to do up and use. I know its sad but they are the best. Think about it, dual beam, masses of drift (on a few plug ins), room heating- just the ticket.
Anyway it is a shame that some go this way but I do agree that most are BER and why not strip em out. Lovely ceramic strips (use a silver loaded solder) the best sockets etc.etc. The transformers are awesome and would make the best bench supply. Use the 6080s as pass valves and combine secondarys, 600V at half an amp or more, depends how brave you are, would not be out of the question
Cheers Matt.
I am kind of a TEK fan, I own a couple of more modern "transistor-ated" ones. I am looking to get a decent 5 series simply to do up and use. I know its sad but they are the best. Think about it, dual beam, masses of drift (on a few plug ins), room heating- just the ticket.
Anyway it is a shame that some go this way but I do agree that most are BER and why not strip em out. Lovely ceramic strips (use a silver loaded solder) the best sockets etc.etc. The transformers are awesome and would make the best bench supply. Use the 6080s as pass valves and combine secondarys, 600V at half an amp or more, depends how brave you are, would not be out of the question
Cheers Matt.
This makes for higher overall efficiency, and since the idle current is low the idle dissipation is too. The amp only dissipates power when it is driven, so the average dissipation is much lower than a class AB or class A amp. Heat is lower so tubes and everything else lasts longer.
Since these things aren't main stream, expect to do some experimenting to find the optimum operating point for your particular tubes.
The data sheet looks good, but as I explained above, only some real testing can determine if they will work. I found them on their web site, but I have decided that for this year at least all of my experiments will be done with the collection of stuff that I already have. I have tubes that have been awaiting "testing" for years.
There's not much literature on it. I'd look at the Bascomb King review of the Berning EA-2100 in Audio (some output tube curves shown at low currents) and study the schematics for the EA-2100, BA-150, and EA-230 at the Berning website, Berning's Patent #3995226, but beyond that... I really can't think of any analytical papers.
DigitalJunkie said:
He's got some measurements on the site, but he only did load testing on one model. Mine is very similar though.
Matt.B.H. said:
I didn't want to do it, but I was moving house and I had to lighten my load a bit. They guy selling it practically gave it away so I had nothing to lose. I did salvage some nice parts.
Bernings Patent was good reading and there are a couple of topics that discuss screen drive floating here on this forum. Tubelab has published some very insightful information if you dig around.
I don't expect to heat up the soldering iron on this project for a long time. Maybe I'll have time next year. I don't have any useful measurement equipment either for troubleshooting, especially after parting out my oscilloscope. Excuses, excuses right?
He's got some measurements on the site, but he only did load testing on one model. Mine is very similar though
I read on the TekScopes forum that the TEK warranty covered transformers at the time and that they neither stocked or had made many replacements. Read into this what you like but I would say they are very over-enginered.
You could get on the TEK forum and ask but dont say you stripped it, you probably wont be too popular. Another way of finding the ratings would be to get the manual if you dont already have it. Try BAMA:
http://bama.sbc.edu/
Use the mirror, it does work.
You obviously wont be using all the heater windings so the primary will be well over-rated. I would reckon that you could run the HT secondarys at maybe 150% current without too much trouble.
The trouble with the TEK trannys would be that you cant tell any temperature rise until it has soaked and heated up the core, covers etc. I havnt tried taking the covers off one but if you can and then get closer to the actual windings you could feel if its too much. Also if you can see the wire guage used you can estimate current. I am pretty sure the later transformers of this type were fully potted under the covers so if you do try to take the top one off be careful, dont even think about the bottom one.
Cheers Matt
Sorry I cant work out how to add a quote properly. Will re-read the FAQ
I read on the TekScopes forum that the TEK warranty covered transformers at the time and that they neither stocked or had made many replacements. Read into this what you like but I would say they are very over-enginered.
You could get on the TEK forum and ask but dont say you stripped it, you probably wont be too popular. Another way of finding the ratings would be to get the manual if you dont already have it. Try BAMA:
http://bama.sbc.edu/
Use the mirror, it does work.
You obviously wont be using all the heater windings so the primary will be well over-rated. I would reckon that you could run the HT secondarys at maybe 150% current without too much trouble.
The trouble with the TEK trannys would be that you cant tell any temperature rise until it has soaked and heated up the core, covers etc. I havnt tried taking the covers off one but if you can and then get closer to the actual windings you could feel if its too much. Also if you can see the wire guage used you can estimate current. I am pretty sure the later transformers of this type were fully potted under the covers so if you do try to take the top one off be careful, dont even think about the bottom one.
Cheers Matt
Sorry I cant work out how to add a quote properly. Will re-read the FAQ
I did a search for "boat anchor" and found the bama site. I had a print manual for a different version of scope so finding the manual online was priceless. I can get an idea how the secondaries were used which helps. While moving, it was funny to see the look on the guy's face who picked up the small box that I packed the transformer in. A bit of swearing followed.
One thing I'm concerned about is voltage sag. If I were dealing with a Class A amp I wouldn't expect any problems. With screen drive turn up the volume and the B+ may be a whole new game. That's where a toroidal transformer would probably do better. Lots of capacitance may cover spikes otherwise. In any case I've got to work with what I've got for now.
One thing I'm concerned about is voltage sag. If I were dealing with a Class A amp I wouldn't expect any problems. With screen drive turn up the volume and the B+ may be a whole new game. That's where a toroidal transformer would probably do better. Lots of capacitance may cover spikes otherwise. In any case I've got to work with what I've got for now.
I think you have that covered. My current KT88 experiments drive my Fluke 407D power supply into oscillation at anything approaching a reasonable power level. The power supply is 100% original including the tubes and bumble bee caps.
When I add one of the 600uF ASC caps across it, the current meter sits quietly on 150 mA unless I really get carried away. Depeche Mode at the clipping level makes the current meter bounce around a little, but it never goes over 200 even though the peak currents are way higher.
The TEK transformers are overkill and I have never heard anybody say that one wasn't big enough. I have one sitting under my bench from a 500 series scope. I don't know what scope exactly but it had lots of 6DJ8's in it. It was being scrapped for the tubes, so I grabbed the transformer.
I've got a pair of the 120-120 trannies from the 535 scopes. The bottom covers do come off,they aren't potted.It's a bit of a chore to pry the cover up after you've removed the screws,because all the stiff lead wires want to hold it down.
These Tek trannies are pretty beefy,and can take a bit of overload without any complaints,especially if you aren't using all of the heater windings,etc. there should be some 'overhead'.
I've run the 120-296 that I have pretty hard,and it barely got warm.
Try stuffing a 35 pound transformer into one of the flat rate boxes from the post office and then take it to the post office. Place it on the scales for the clerk and watch their expression when they try to move it! The girl punched all of the buttons, the scale read 35 pounds, she printed my receipt, gave me the change, but didn't realize what 35 pounds really was until she tried to move it. After a few futile attempts, she had to fetch someone from the back to move the box. The transformer got to its destination in one piece.
I bought an even bigger one from Ebay. It came from California for $12. My delivery person refused to bring it to the door, I had to go out to his truck to get it.
I'm thinking the 6CG7/6FQ7 option may not be optimal? Rated to 300v. They are similar to the 6AS7, but I don't expect them to take the same beating. I'm thinking pair of 6S4 would be ideal. Maybe the 6N6Pi? Perhaps overkill, but I'm looking to build in a comfortable margin for reliability. Otherwise 7N7's are looking good too.
Any suggestions?
Good news on the Maida. I wish I could have been more help there.
Any suggestions?
Good news on the Maida. I wish I could have been more help there.
My understanding so far is that serious voltage swing is needed to effectively drive a screen drive output stage. I've been studying Jone's Crystal Palace, and he chooses a 6J5G (6SN7) where it can handle 450v. Ideally a tube with a low output impedance would be used to drive the output, so I would figure a 12B4 would be a good option with a lower plate resistance than a 6SN7, but a bit more input capacitance. Now with the published Universal Drive schematic we have Mosfets in the game so I would figure that low output resistance is less important?
It would also seem that you can swing twice the voltage if a transformer were used instead of a decoupling capacitor? I haven't found much detail on this yet, but is this real? Can I get away with a driver putting out 300Vpk-pk and get a theoretical 600Vpk-pk from a transformer? I would probably need four of them which may be costly?
My goal here is to get as close to 100w output as possible. One other concept is that more tubes in parallel should make for more output with less voltage. I got a bunch of the proposed output tubes (assuming they'll work) so I'm hoping to go PPP for that stage.
So here's the plan so far:
6J6's --> 6CG7 --> 2SK2700 --> PPP Sweeps tubes --> 2022 ohm OPT.
I dug up a quad of 12B4's from the box o' random tubes so they may be an option instead of the 6CG7. I may possibly go for a 7N7 as well, but I ain't got none of them, but that may change cause I need four more compactron sockets.
The power supply will be interesting. A lot of regulating will be going on.
It would also seem that you can swing twice the voltage if a transformer were used instead of a decoupling capacitor? I haven't found much detail on this yet, but is this real? Can I get away with a driver putting out 300Vpk-pk and get a theoretical 600Vpk-pk from a transformer? I would probably need four of them which may be costly?
My goal here is to get as close to 100w output as possible. One other concept is that more tubes in parallel should make for more output with less voltage. I got a bunch of the proposed output tubes (assuming they'll work) so I'm hoping to go PPP for that stage.
So here's the plan so far:
6J6's --> 6CG7 --> 2SK2700 --> PPP Sweeps tubes --> 2022 ohm OPT.
I dug up a quad of 12B4's from the box o' random tubes so they may be an option instead of the 6CG7. I may possibly go for a 7N7 as well, but I ain't got none of them, but that may change cause I need four more compactron sockets.
The power supply will be interesting. A lot of regulating will be going on.
A triode that has a resistor or Css plate load can swing about 2/3 B+. The same triode inductively loaded can swing about 4/3 B+.
There are advantages to using a center tapped choke rather than 2 chokes, because the current cancels in a center tap choke and gives higher inductance.
I am going to try an Edcor inter-stage transformer as a center tap choke.. Should be expensive.
HTH
Doug
DougL said:
A well designed semiconductor based CCS can work well with as little as a few V across it, so the actual swing into a resistive load of a triode with such CCS on top is bigger than one with a resistor on top. Depending on the tride in question, one can get the usual 2/3 B+ with far less distortion (or more output current) than with a resistor on top - in that cese it's more like 1/3 B+.
Chokes do approximate a CCS as far as load lines are concerned, except that there is bucking action so you can get swing over B+ - typically as much over as it goes under (more under clipping conditions, sometimes dangerously more, keyword flyback converter
).
ilimzn said:
In any case the transformer option caught my attention. I think I need some serious B+ to get a lot of voltage swing to push the sweeps tubes.
I may have caught some foot-in-mouth disease and wrote too soon earlier. If I'm not mistaken the driver stage of the Universal puts out a signal that is already split for Push Pull, right? So perhaps a transformer can be used, but it would have to take that differential input and put out a differential output. That way I could possibly use a single push-pull interstage transformer rather than two SE transformers.
I thought this was interesting. The schematic kinda demonstrates what I'm thinking, but has an SE output instead of push-pull:
http://www.audiodesignguide.com/PF2007/PF2007a.html
This is interesting too: http://www.icl.co.jp/audio/english/RC20/RC20.htm
An Edcor XSM10K/10K for the job???
The Beast might be a good place to start (unfortunately, it got pushed out of the 3rd edition, but I think the schematic has been posted here). A CT transformer is a neat idea, wish I'd had one when I built my screen drive amp. But my goodness, they're expensive!
Another alternative is to use a relatively low voltage tube on the bottom of a cascode and use a 1kV or more MOSFET on the top, although it still would require a pretty high B+.
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