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GU-46 push-pull & single-ended amplifiers
GU-46 push-pull & single-ended amplifiers
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Old 10th December 2017, 08:40 AM   #11
jazbo8 is offline jazbo8
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GU-46 push-pull & single-ended amplifiers
Quote:
Originally Posted by thomasweissbach View Post
from other sources I have the Info that the GUs should be loaded with low impedance.
Where can you find that information? It seems the HV capability of the tube is wasted by running it at just 1kV.
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Old 10th December 2017, 12:20 PM   #12
Bandersnatch is offline Bandersnatch  United States
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It is BIG... I like it...

Let me suggest something in terms of topology. You'll need EL34 for signal tubes, and a single B+ supply for the plates and front end. Your OPT will need U-L taps( which you can use or not for the GU46's ).

The 500W plate will allow ~200 mA idle current, which working through a 10k a-a load in Class A gives you ability to swing nearly 1kV( a 200 mA idle plus 200 mA more on an increasing g1 swing will take the plate near zero V)

should be able to get 200+ W in Class A. Tasty.
Check out the pdf in post No. 4. Substitute EL34 for the 6AU6...
Looking to build a 25-30 WPC Push Pull amp - Need Help

Also, given the curves, you should set g2 V to deliver 450 mA at g1=0V if you're going to run pentode mode.

Or you could avoid the nutty B+, and run U-L on a significantly lower B+ with less a-a loading. Some calculation is required, and you'll need to get some current measurement at lower than 500V g2 voltage to pick U-L tap location, and a-a loading. And still get some nutty big power.

On the nutty power, you will discover the limits to OPT construction at this size if you manage to continue. going over 200W for the first build is a reasonable target, and sails well into the part of the map labeled, "Here Be Monsters".
cheers,
Douglas
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Last edited by Bandersnatch; 10th December 2017 at 12:28 PM.
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Old 10th December 2017, 03:00 PM   #13
banat is offline banat  Serbia
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Here`s updated PSU schematic , each GU46 tube can have separate filament winding , separate balancing hum pot and separate analog instrument to monitor IQ for each power tube, I think that each analog instrument need to be calibrated to show around 0,7A at full scale .
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File Type: jpg GU46 psu updated.JPG (503.3 KB, 190 views)
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Old 10th December 2017, 03:19 PM   #14
Bandersnatch is offline Bandersnatch  United States
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Each GU46 should have its own filament trans. I like to keep the filament supply separate. Also, a small variac to dial in exactly the right voltage on TT DH tubes is useful. If you grab a filament TX that requires a 10% reduction in primary voltage so that the output is right on, cuts flux density in the filament Iron and leaves it less likely that it will vibrate due to the load.
cheers,
Douglas
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Old 10th December 2017, 04:31 PM   #15
banat is offline banat  Serbia
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Hi Douglas

I understand your arguments but personally I like compact one single power transformer solution , IMO what is important is to have several taps on the primary side ,it is not bad to have from 230VAC up to 250VAC in 5VAC steps , by connecting main voltage on the right tap will allow to get close as possible that critical 8,3VAC for filament supply .

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Old 10th December 2017, 04:43 PM   #16
Bandersnatch is offline Bandersnatch  United States
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Quote:
Originally Posted by jazbo8 View Post
Where can you find that information? It seems the HV capability of the tube is wasted by running it at just 1kV.
How much power is the OPT going to be able to handle gracefully? There are a large number of tubes that can make big power from HV, and that HV insulation makes things more difficult. In the scheme of things, IMO of course, even getting north of 100W full bandwidth gets difficult...let alone doing that at HV.

Those anodes will support a substantial Class A amp...likely bigger than good OPT's can be had. The tube has gm in large numbers. Low ratio OPT will help too. Going after a 1 kW, AB design could be done, but I would solve the smaller problems first.

The anodes, judging by its envelope shape are Tantalum, and function as getter and so must be run at adequate dissipation to get them hot enough for that duty.
cheers,
Douglas
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Old 11th December 2017, 06:57 AM   #17
jazbo8 is offline jazbo8
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So is 200W (1k x 0.2) bias, which is just 40% of Pa_max, hot enough for the anode dissipation?
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Old 11th December 2017, 08:57 AM   #18
Bandersnatch is offline Bandersnatch  United States
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Quote:
Originally Posted by jazbo8 View Post
So is 200W (1k x 0.2) bias, which is just 40% of Pa_max, hot enough for the anode dissipation?
That was based on an estimate, from a data sheet that I believe listed 'output power' instead of anode dissipation.

For this pup, the maximum continuous anode current may put a lower limit on B+ required to achieve adequate dissipation.
cheers,
Douglas
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Old 11th December 2017, 10:50 AM   #19
thomasweissbach is offline thomasweissbach  Switzerland
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Dear all

There has already been a GU-46 project on diyaudio, as a SE relatively low power amp.

High power GU46 SE amplifier - help with certain issues

ClassZ seems to have achieved functionality with 12hg7 tubes as direct driver tubes.

This seems to be a working cirquit, at least in SE, with low output power.

This cirquit used after an LTP in pp could be a starting point, this was my assumption.

I do not need 200+ Watt as output power, especially not, when they come to the price of poor sound quality. Therefore the potential costs of this project would be too high.

I like this big tube, and I would like to build an amp that delivers good sound quality. This has higher priority than max output power.

I tend to go with a 200W OPT since this should be enough for pp based on ClassZs Project, run under the same conditions - hopefully.
And Bandersnatch pointed it out - OPTs with ≥200W are getting poorer results than smaller ones, this would support my idea.

Building the real beast could probably be done with this tube, it has hughe potential for high output wattage, at horrifying voltages - this I will leave to the professionals. I have to little girls that need a dad for some more years .


I read a lot about driver tubes now, but I do not have the detailed knowledge to decide what would be the best solution.

Did anybody build something compareable, using maybe EIMACs or other large and powerfull transmitter tubes, run at lets say, relatively low voltages compared to their max specs?

I thought that there have been some PA or stage amplifiers in the 70ties with EIMAC tubes or so... Could be another starting point.

Greetings, Thomas

Last edited by thomasweissbach; 11th December 2017 at 10:53 AM.
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Old 11th December 2017, 11:52 AM   #20
Bandersnatch is offline Bandersnatch  United States
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The biggest so far has been 4E27 run at 600V for ~50W output. 10k a-a OPT( a modified clone of the S-265-Q ). Am next going PP HY51A around the same voltage, with cathode drive to zero bias on the HY51A. This requires some power to drive the IT that will feed the cathodes...

The 4E27 runs a circuit like the 6AU6 St.70; two stages, volt amp/phase split and the finals. The HY51A will be three; two for the driver amp and then the finals.

I like ability to deliver power, but in ~50W increments I use active cross over and efficient speakers...SPL is adequate under most conditions...

Low power with Tantalum anode tubes is problematic; the plates have to come up to operating temperature...and the cathodes have max continuous current limits. At the dissipations required some serious power is available. With the big ones, this power output easily outstrips the OPT's capability to deliver the goods compared to one of say 60-70W( full bandwidth, yes? ).
cheers,
Douglas
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