The amp schematic posted was quite useful I'll probably hook up my transformers in similar fashion, with the 350V powering the input section, and the 700V lighting up some 6HV5As. Pentode input, cathode follower, and 6HV5A SE output. The 6HV5A would also be a natural for some Schade-style feedback - gotta do something with all that gain. Another possibility would be a pentode differential input like the Pete Millett amp,with source followers driving P-P 6HV5A outputs, again with partial feedback. I'll try the SE amp first to test the concept.
Doing some preliminary calculations, even a 10k output transformer does not squeeze all the useful juice out of a 6HV5A biased at 700V, 50mA (at the tube dissipation limit). A pair in parallel would be interesting working into a 5k transformer, though it would take the Edcor special-order 8k transformer to better exploit the capabilities (the tubes actually run out voltage of this impedance level and could be run with a lower quiescent current).
If I used one 6HV5A biased at 50ma, along with my 8k Transcendar transformers (assuming they can handle the voltage), I would get almost 10W/channel and would still be about 300V away from bottoming out the output stage. I would need about 75mA of bias to get within 100V of bottoming out during peaks. This is over 50W static dissipation - looks like a job for George....
Tll these calculations assume an 8 ohm load, a turns ratio 0f 25:1 for the 5k transformer, 31.6:1 for 8k, and 35.3:1 for 10k.
If I used one 6HV5A biased at 50ma, along with my 8k Transcendar transformers (assuming they can handle the voltage), I would get almost 10W/channel and would still be about 300V away from bottoming out the output stage. I would need about 75mA of bias to get within 100V of bottoming out during peaks. This is over 50W static dissipation - looks like a job for George....
Tll these calculations assume an 8 ohm load, a turns ratio 0f 25:1 for the 5k transformer, 31.6:1 for 8k, and 35.3:1 for 10k.
I was thinking that this monstrosity might be more of a match for the cheap Chinese 811As I have floating around - another candidate for Mr. Schade. It would probably work better with the premium graphite plate version, but those are 40 bucks a pop, so I'll stay with the tubes I have. If anyone knows of a fairly common transmitter tube with ~50-60W capability. feel free to chime in. I looked at an 813, but those are a little too underutilized for this app.
If you're thinking 811A or 813 but the latter is too big, may I humbly suggest the 4-65A in tetrode connection at 700V B+ and 70+ mA to get the anode to a nice cherry red
My 4-65A SE amp ("Meteor") used the 8K Transcendars with PS stacking and had 770V B+ stacked on a 240V driver supply so I ran these puppies at 1000V above ground. 70mA is the max DC as I recall for these but I ran them up to 75mA without noticing much difference in LF power bandwidth. I got about 16W to the speaker from >20W Po at the anode. The 8K Transcendars have a rather high DCR and as such are a little lossy, but to be fair they are only 10W rated...
If I redid this I'd go down to 5K on the OPT and a little lower voltage, and get a 25W Edcor
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What tOObage to use? I got a short list of pairs (but no sets of four)
If I had to order a matched quad, I'd probably cheap out and go for
7591xyz unless someone knows reason this would be inferior choice?
I've heard xyz is less similar to 7591 than a rewired 6L6, is this true?
Mix branded pair of NOS 6HV5 (recently promised these away anyhow...)
Cheap pair of Chinese 6L6 that Tubelab claimed near indestructible.
Severely used, but still functional, 7189 pulls from my Fisher x100.
Directly heated (10V supply might be a slight problem) RCA 814's.
6GT5A, but one is in box that someone has previously marked "weak".
My OPT iron is Edcor 100W 5K CXPP. I got Hammond 10H @300mA choke.
5V4GA recifier, maybe not useful for doubler? Plenty o'sand diodes.
Caps, I got are two 15uF 480VAC oil filled. And a handful of 450VDC
electrolytics the sort one might pull from dead PC switchers...
I got plenty of small signal tubes for the up front, especially an
excess of 6dj8. So prefer to abuse that type wherever possible.
If I had to order a matched quad, I'd probably cheap out and go for
7591xyz unless someone knows reason this would be inferior choice?
I've heard xyz is less similar to 7591 than a rewired 6L6, is this true?
Mix branded pair of NOS 6HV5 (recently promised these away anyhow...)
Cheap pair of Chinese 6L6 that Tubelab claimed near indestructible.
Severely used, but still functional, 7189 pulls from my Fisher x100.
Directly heated (10V supply might be a slight problem) RCA 814's.
6GT5A, but one is in box that someone has previously marked "weak".
My OPT iron is Edcor 100W 5K CXPP. I got Hammond 10H @300mA choke.
5V4GA recifier, maybe not useful for doubler? Plenty o'sand diodes.
Caps, I got are two 15uF 480VAC oil filled. And a handful of 450VDC
electrolytics the sort one might pull from dead PC switchers...
I got plenty of small signal tubes for the up front, especially an
excess of 6dj8. So prefer to abuse that type wherever possible.
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Lets see. You have a power transformer that makes big voltage and enough power for a 120+ watt amp. You have some 35LR6's. You have some "rusty transformers". That sounds like a good place to start. The red board has proven this to be a good combination with nothing more than a 7 pin pentode (or a 6GU5 hexode) for a driver and a dose of Schade.
My next version (far from finished) will use a tube that is pinout compatible with the 6EJ7 (several $1 tubes to choose from) and a dual triode (probably a 6FQ7) following the driver for a little more gain and the ability to "cross wire" the Schade feedback. Mosfet followers for AB2. This works great on my 6SL7 - 6SN7 driver board. More gain and drive capability is needed for screen drive and dual drive experiments.
The 35LR6's have a center tap on the heater, so you can wire them for 17.5 volts (undocumented but it's pin 7). The power transformer has 3 X 6.3 volt windings, wire them in series and hook them up.
700 volts and a 6600 ohm load should make enough power to crank those OPT's good. I have had them to 650 volts and well over 150 watts using a 3300 ohm connection.
I should have specified "for single ended duty". P-P is more complicated than I want to get into now at 700V B+, especially as I already have 2 other P-P designs I'm trying to complete. These will test out two concepts - an all solid state diff front end (jfets + bipolar cascode) driving a 6JB5/6JC5 output stage (SMPS and Baldwin output iron), and a pentode front end driving a source follower and autotransformer splitter with 6P3S-E outputs (Fisher 400 power and output iron). I already know a jfet differential front end cascoded with triodes works quite well - I'm using one in my "Kingfisher" P-P 7591A amp. The next logical step was ditching the triodes and using bipolar or mosfet cascode.
Several of these will be showing at Burning Amp this year.They will give me some ammunition for handling some more ambitious P-P designs. One of these would be a largish 35LR6 p-p that I've had in mind for some time. I need to choose a front end, and I'm stubborn and refuse to use anyone else's design (this is My learning experience, dammit!). Designing and building an SMPS for a big P-P amp is somewhat daunting as well. I'm cutting my teeth on the smaller "Lil' Devil" amp that will also benefit from the compactness of an SMPS. I plan to be bringing up that amp (it has the sand-state cascode diff front end) using bench supplies maybe as early as this weekend.
The 4-65A suggestion was interesting - not too pricey, either.
Several of these will be showing at Burning Amp this year.They will give me some ammunition for handling some more ambitious P-P designs. One of these would be a largish 35LR6 p-p that I've had in mind for some time. I need to choose a front end, and I'm stubborn and refuse to use anyone else's design (this is My learning experience, dammit!). Designing and building an SMPS for a big P-P amp is somewhat daunting as well. I'm cutting my teeth on the smaller "Lil' Devil" amp that will also benefit from the compactness of an SMPS. I plan to be bringing up that amp (it has the sand-state cascode diff front end) using bench supplies maybe as early as this weekend.
The 4-65A suggestion was interesting - not too pricey, either.
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I know that feeling. The more times someone tells me that I can't do something, the more effort I put into doing it.
Given a 50 to 60 watt tube I would guess that you are looking at roughly 20 watt SE amp. From a 700 volt supply I'm guessing thats a 6.5 to 10 K ohm OPT. Do you have such a critter. These aren't cheap.
Tubes in that realm aren't cheap either, and I wouldn't rule out the 813 either since they can still be found at hamfests for under $10. A pair of paralleled 35LR6's is another option, as is the 828 transmitting tube.
I just did some calculations assuming each of my two boat anchor power transformers would power a monoblock amp with 700V B+ and 350V intermediate supply. Dust off the 813 operating as a pentode, with Schade style feedback. Assuming that you can drive the 813 to within 100V of ground (just possible) and using a 5k transformer, it looks like one could get 35W of class A power into 8 ohms with sufficiently capable output iron. The 813 is cruising at 120 ma bias current (84W dissipation).
A dollar triode/pentode tube, the 6AG9, would be a nice candidate for driver and cathode follower duty. It's a compactron, so it won't look so terribly shrimpy next to the 813. It would run very nicely off the 350V supply.
I was all hot to trot (sooner or later, that is) to build a monster SE amp using the GM-70 triode, but this one might get done before it. Super-Schade, anyone?
A dollar triode/pentode tube, the 6AG9, would be a nice candidate for driver and cathode follower duty. It's a compactron, so it won't look so terribly shrimpy next to the 813. It would run very nicely off the 350V supply.
I was all hot to trot (sooner or later, that is) to build a monster SE amp using the GM-70 triode, but this one might get done before it. Super-Schade, anyone?
If there's a good OPT for this, for myself, I'd pop the $100 each for Eimac 100TH triodes with Schade feedback
But it would be just for show; I can't afford to run an amp like this on a daily basis due to the power consumption and my limited off-grid power resources
The Hammond 1628SEA looks just capable of the job, as it's rated for 30W and 120 ma current. Proletarian iron, but available. If I want something a bit better or more capable, I'll have to keep looking (and probably be prepared to shell out some bux).
Michael - the glowing anode-type RF tubes are kinda neat and photogenic, but they also creep me out a bit, especially when you add the big heat radiator anode caps charged to lethal B+. I'd want to use a cage or a chimney on those bad boys
Michael - the glowing anode-type RF tubes are kinda neat and photogenic, but they also creep me out a bit, especially when you add the big heat radiator anode caps charged to lethal B+. I'd want to use a cage or a chimney on those bad boys
The 1628SEA is a 5K ohm OPT. I have two of them. They don't sound near as good as the Edcor CSXE 25-8-5K which I also have. The comparison isn't bad on low efficiency speakers where you run the amp hard, but on Lowther based horns the Hammonds absorb all the low level details. They are also less efficient than the Edcors costing about 1 watt on a 10 watt amp.
Assuming I copy the CBS/ADA power supply, is the rest of this optimal?
My load would most likely be an Eminence Wizard 16ohm. Input handled
by stomp box, so's hopefully no need for actual "knobs".
I am concerned mainly that somewhere I've been too conservative?
Most peeps squeeze more than 50W from a pair of 6L6 with a 5k opt,
or am I mistaken? Or is that sort of power only unlocked with AB2?
Or they are counting the full area under a square wave, not sine?
Why did CBS/ADA seem to think 130W was the magic number?
I don't have that OPT, so its maybe not apples to apples...
My load would most likely be an Eminence Wizard 16ohm. Input handled
by stomp box, so's hopefully no need for actual "knobs".
I am concerned mainly that somewhere I've been too conservative?
Most peeps squeeze more than 50W from a pair of 6L6 with a 5k opt,
or am I mistaken? Or is that sort of power only unlocked with AB2?
Or they are counting the full area under a square wave, not sine?
Why did CBS/ADA seem to think 130W was the magic number?
I don't have that OPT, so its maybe not apples to apples...
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Hello All,
Now that I have these ten pounders what do I do with them?
I also have a completed Simple SE PCB that has never seen an input signal. The task is to fire up this Simple SE with the 235 volt ten pounder. The power and driver tubes will draw near 2.5 amps of 6.3 volts. I expect to need a resistor to run in series with the “main” 6.3 volt secondary winding (the one with the center tap). The rectifier tube needs 1.9 amps of 5 volts. I expect that one of the other 6.3 volt secondary windings with a series resistor will take care of the rectifier. I also expect that the series heater resistors soften the startup inrush. BTW this is a breadboard project just to play with the toys on hand including the FFT computer.
Any thoughts or recommendations? Does anyone smell smoke?
DT
All just for fun!
Now that I have these ten pounders what do I do with them?
I also have a completed Simple SE PCB that has never seen an input signal. The task is to fire up this Simple SE with the 235 volt ten pounder. The power and driver tubes will draw near 2.5 amps of 6.3 volts. I expect to need a resistor to run in series with the “main” 6.3 volt secondary winding (the one with the center tap). The rectifier tube needs 1.9 amps of 5 volts. I expect that one of the other 6.3 volt secondary windings with a series resistor will take care of the rectifier. I also expect that the series heater resistors soften the startup inrush. BTW this is a breadboard project just to play with the toys on hand including the FFT computer.
Any thoughts or recommendations? Does anyone smell smoke?
DT
All just for fun!
Unfortunately was too busy with car repairs for any amp build.
At least I did finally made it across town to pick up my 30lbs.
Maybe the finest iron I've ever seen? Especially impressed the
original cloth covered wires in perfect condition. And the copper
strap, an extra rarely seen today... The end bells also stamped
of thicker stronger stuff than I'm used to.
OK the varnish is maybe a little messy looking, but its a beauty
none the less.
At least I did finally made it across town to pick up my 30lbs.
Maybe the finest iron I've ever seen? Especially impressed the
original cloth covered wires in perfect condition. And the copper
strap, an extra rarely seen today... The end bells also stamped
of thicker stronger stuff than I'm used to.
OK the varnish is maybe a little messy looking, but its a beauty
none the less.
The varnish is lumpy, and a little soft. Sanding it smooth for painting could be a pain.
Probably just strong solvent on a rag then (with gloves, outdoors) ? I don't think we
want to get carried away and risk loosening any varnish inside... How does one best
protect those cloth wires during the process?
I'm fine with the lumps, mine are stayin' ugly.
Probably just strong solvent on a rag then (with gloves, outdoors) ? I don't think we
want to get carried away and risk loosening any varnish inside... How does one best
protect those cloth wires during the process?
I'm fine with the lumps, mine are stayin' ugly.
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