Got through 20 pages until my 4 month old started calling me.
Anyway got a question regarding the floating power supplies.
How many amps do they need to deliver (B-/B+)?
I can buy a lot of 5 trannies for just 35 USD.
220/28V @ 3 amps.
Thinking I can either use voltage doublers to increase 112 @ 750ma no?
Or put 2 in parallel and voltage double twice to 112 v but keeping the current higher at 1.5amps.
Is this maths correct?
I can also use one of the to power 4 x 6080 heaters in series.
Got a 350-0-350 on the market also with a further 6.3V and 5V secondaries at 6 amps for very little (25 USD). Might just grab these
I need to go back to the other 12 pages I skipped.
Anyway got a question regarding the floating power supplies.
How many amps do they need to deliver (B-/B+)?
I can buy a lot of 5 trannies for just 35 USD.
220/28V @ 3 amps.
Thinking I can either use voltage doublers to increase 112 @ 750ma no?
Or put 2 in parallel and voltage double twice to 112 v but keeping the current higher at 1.5amps.
Is this maths correct?
I can also use one of the to power 4 x 6080 heaters in series.
Got a 350-0-350 on the market also with a further 6.3V and 5V secondaries at 6 amps for very little (25 USD). Might just grab these
I need to go back to the other 12 pages I skipped.
You can put the filaments in series and get away with that- I built an amp that had the filaments in series with the AC line (and a big dropping resistor). It worked fine, but not the sort of thing I would recommend :/
I don't see where you are getting the 112V from, but if you can do 112VAC @1.5 amps that will be a bit of overkill for 4 6AS7s, but it will work fine.
I don't see where you are getting the 112V from, but if you can do 112VAC @1.5 amps that will be a bit of overkill for 4 6AS7s, but it will work fine.
It all depends on how many power tubes you plan to use (and of course how much bias you put to them...).
The current through the voltage doubler cap could be hard on the cap. At any rate if you are only planning four 6AS7Gs in one channel, 750mA should be enough.
The current through the voltage doubler cap could be hard on the cap. At any rate if you are only planning four 6AS7Gs in one channel, 750mA should be enough.
Planning to start with one channel with 6080 tubes.
What can I use instead of the 6SN7?
I have some 6SL7 tubes but are quite different.
I do have some 6SN7's but back in UK. Maybe I can get them sent over if there is not a similar substitute..
Just got a power tranny 350-0-350 (450watt), 6.3 @6amps and a 5V tap for just 28 USD!!!
What can I use instead of the 6SN7?
I have some 6SL7 tubes but are quite different.
I do have some 6SN7's but back in UK. Maybe I can get them sent over if there is not a similar substitute..
Just got a power tranny 350-0-350 (450watt), 6.3 @6amps and a 5V tap for just 28 USD!!!
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6SL7 has a high plate resistance so you have to be careful. Perhaps buying a couple of 6SN7s is worth considering, if you want to use this tube, as they're readily available.
Great, have a few of these. Also 6N2Ps.
Now tranny question:
These 220/28v trannies I could buy. @ 3 amps.
If I use 2, and connect the secondaries of both in series I will have 56 volts @ 6amps no? Can I connect the secondaries of both in series?
So then I could use a voltage doubler for 112 V @ 3 amps.
4 a 6080s at 85mA for example.
85mA x 8 (8 cathodes)= 680 mA in total. Plenty of headroom.
This looks great to me.
I have a set in UK at my fathers house. I'll get him to send them over.
No. Double the voltage, halve the current (or overstress your transformers), you can't have both.
Why 112V anyway ? Hook two transformers back to back with their secondaries together and you get isolated 230V AC which will rectify and filter into nice 300V DC, perfect for tube projects. Hang the heater chain between the two transformers.
Greetings - I have been trolling this thread for some time now, and cleaning some other projects off my "bench" before I start this particular insanity. I would like to thank all of you for a pretty impressive indepth study of building an OTL, especially all of mullardel34's hard work and Ralph's insight! A few questions, however.
1) What is the thought about DC vs. AC heaters? It's been mentioned a few times, but not directly answered (or I missed it).
2) What do people think about isolating the power supply in another chassis? Would the noise reduction be outweighed by increased capacitance between the PS and stages or not? Good idea, bad idea, or no-op?
3) How about valve (or Hg Vapor) rectification?
Thx
Chris
1) What is the thought about DC vs. AC heaters? It's been mentioned a few times, but not directly answered (or I missed it).
2) What do people think about isolating the power supply in another chassis? Would the noise reduction be outweighed by increased capacitance between the PS and stages or not? Good idea, bad idea, or no-op?
3) How about valve (or Hg Vapor) rectification?
Thx
Chris
If you build it right, AC heaters will work fine. You can wire the filaments in anti-phase in the output section easy enough.
You don't need to isolate the power supply, but I would keep input and high impedance wiring away from AC lines and rectifiers (basic layout rules, IOW). There is an argument for *not* having an external supply, as the currents in the output section might be more than you want to run long-distance.
Valve rectification is hard to do to say the least. Voltage drops in some tube rectifiers are in some cases as high as the B+ in the output is! You are far better off using high-current HEXFREDs or the like, and even the lowly silicon rectifier can do quite well if you are careful.
I started work on this OTL. It is not easy. Its a lot of work to wire point to point. And there a lot connections to solder. I choose to use DC on the drivers and the output tubes. It can't hurt. And it always worked well in single ended amps. Off course they are completely different topologies. Its simple enough to do. And to me DIY is about going the extreme. Which for a manufacturer is not easy with the cost of doing business these days. I have to say many audio firms charge a lot for their products and they are not even point to point wired. And to me at the prices some of them ask they should be. You have to like that Atmasphere goes the extra mile with point to point.
Thank's to you both for responding. As far as valve rectification, I was thinking either Hg vapor, or Halogen gas rectifiers (should be pretty low drop, and, yes, I know the risks with Hg). As far as split supplies, I was thinking keeping them pretty close, probably less than 0.5M away. Anyway, thank's again.
I am not sure if you need to work with Halogen gas rectifiers. You can use 4 conventional tube rectifiers instead. I know of one inexpensive new old stock TV tube damper diode that can push a lot of current. I will have to dig it up in my audio files. I have used this in a 300B. This rectifier is built like a tank. Also there is a still in production Russian tube rectifier that can pass a lot of current. And I will dig that up as well in my tube files. If you do work out a rectifier solution I would like you to post the details. Because my speaker are Spendors and are fairly easy to drive I am building this OTL with 4 power tubes per channel. Which I am pretty certain would be much easier to use with tube rectifiers. If I like like the amp and I find the power to be a little to low. I will simply build another one and bi amp my speakers. I will post pictures soon of one channel under construction.
You can't put all of the power supply .5M away. There is inductance and resistance in the cable. Some of the filter caps needs to be physically close to the load.
One resonable compromise is to place the transformers, chokes and first filter caps remote and then distributing ithe rest of the supply in the amp chassis. The load runs off the last filter cap, place that cap near the load.
The other thing is safety. You can not just run 300V wires along a shelf for 0.5M. You need to either place both chassis inside the same cabinet (But few home HiFi builders bother with cabinets.) or have some sort of fool proof conduit. It is hard to engineer a high voltage interconnect that could pass any kind of certification. Think about 20 years from now if the insulation cracks. In the old days they would us screw terminals or an octal plug. But they also built cars with no seat belts and un-padded steel dashboards.
One idea I had was to use the kind of coax cable and connectors used for high power radio antenna leads. But it seems there are many good inexpensive and safe HV connectors on the market High Voltage Connectors
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ha! - nice to hear I'm not the only one who feels this way. I've only built one tube amp so far, but the simplicity of the schematic didn't translate into less work for the construction. Lots of chasis work followed by lots of point-to-point soldering. In the end I had to rewire the whole thing to be satisfied with it.
On the rectifiers - I've never built an OTL so I'm kind of guessing here, by my gut feeling on this item is to stick with SS. Your power supplies are not choke loaded, and the current has to be sufficient to drive the load so you have big capacitors to charge up - with high current charging spikes demanded from the rectifiers. In fact I'd be looking to make the power supply a CRCRC to alleviate this somewhat.
Mate....u must twist those wires!!!! At least the ones close to the preamp section.
Use a cordless drill and it's done in a jiffy.
I am aware of the wire routing. I have a lot of room in this chassis layout. I am using distance and the perfect dielectric air to address this. The power tube heater wiring is routed to the outside and away from critical areas. Like wise the heater wiring for the driver tubes is away from critical areas. In the end the heater wiring does have to enter the tube and that is the closest point to all the other wiring on the pins any way. More critical will be the transformer and rectifiers. These can generate a lot more fields and trouble. They will be place all in the front of the chassis far away from the back of the chassis where all the sound enter and exits.