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Post by Greg on Mar 1, 2015 11:50:37 GMT
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Post by Sovereign on Mar 1, 2015 11:54:49 GMT
Thanks Greg
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Post by Paul Barker on Mar 1, 2015 14:35:47 GMT
Phil, I just did an idle Google of gk71 amps and came to this page our-house.jp/gk71-6/index.htmScroll down to the gk71 schematic. I m not particularly interested in the driver, the point of interest is the operating point of the gk71 something like 1100v 0.1 amps -200v. So it seems that g2 when triode connected has been pushed to excessive voltages by others. |
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Post by pre65 on Mar 1, 2015 22:36:51 GMT
Hi Paul, I looked at the circuit, but I don't understand the connections to G3.
Mine has a 100R resistor between anode and G2.
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Post by pre65 on Mar 2, 2015 12:06:27 GMT
One of the Audio Talk regulars (Andrew L) has been developing a VCCS filament module in his spare time, and had adapted a version of it suitable for GM70 and GK-71.
Mark J has done some valuable work fine tuning the component selection, and I obtained a pair of PCB to try them for myself. 99% of the PCB components came from Farnell, and now the filament modules are in place on the GK-71 monoblock amps.
Have to say they are a noticeable improvement.
They are powered by a low noise 24V 5A power supply, a pair of them were around £20 on Ebay some months ago, an absolute bargain.
Here is the module on the heat sink. The PCB is missing the smoothing caps and diodes cos the supply is clean DC.
Here is one amp with the new supply (on the right) and one with the old supply.
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Post by Paul Barker on Mar 2, 2015 18:32:59 GMT
Hi Paul, I looked at the circuit, but I don't understand the connections to G3.
Mine has a 100R resistor between anode and G2. The beam forming plates (instead of a g3) are cathode potential in his schematic which is the usual thing. The arrow points to CT which means the centre tap of the 20v AC filament winding. |
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Post by pre65 on Mar 10, 2015 13:05:08 GMT
I'm going to try a cascaded CCS for the driver anode instead of the single Ixys 10M45s chip at present.
I've got some DN2540N5 depletion mosfets coming in a day or so.
And, I have a lash up prototype BMU to try now. 
The 1000va isolation transformers were a job lot, and I got 20 to share amongst my buddies on Audio Talk. I kept 3 for myself.
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Post by MartinT on Mar 10, 2015 13:49:17 GMT
Nice and safe!  |
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Post by pre65 on Apr 5, 2015 15:17:36 GMT
I've started on the rebuild of the 833a amp. One trolley is on the bench at the moment. The mounting holes for the new mains transformer and reactor (choke) have been drilled as have the mounting holes for the four smoothing capacitors. The caps are BHC 1000uf @ 450v so will end up as 250uf @ 1800v, should be enough.  I'm now waiting for some stainless hardware to hold things down so not much more progress for a few days.  |
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Post by MartinT on Apr 5, 2015 16:02:19 GMT
How did your home-made BMU testing go, Philip?
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Post by pre65 on Apr 5, 2015 16:38:27 GMT
How did your home-made BMU testing go, Philip? Not conclusive on using it with the two power amps. But being in a rural location my mains might be quite clean. Next test (tomorrow perhaps) is to try it on everything else. Dac PSU (Maplin 14v) Squeezebox PSU (a MCRU item) Record deck (Garrard 401) CD transport (Cambridge Audio DVD57) Preamp (Audionote copy) Phono PSU (World designs Phono3/PSU3) So a multi way extension lead plugged into the breadboard BMU. |
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Post by ChrisB on Apr 5, 2015 16:45:50 GMT
Love the idea of a power amp with a reactor!
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Post by MartinT on Apr 5, 2015 16:50:40 GMT
...should go without stopping for 40 years or so.
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Post by pre65 on Apr 5, 2015 16:51:20 GMT
Love the idea of a power amp with a reactor! It's not nuclear.  I don't know why but a lot of bigger chokes are called reactors, or is it small reactors are called chokes ? Is there an expert in the house who can tell the differences ? |
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Post by Eduardo Wobblechops on Apr 5, 2015 21:16:53 GMT
I've installed a few Shunt Reactors in substations. Their function is to absorb reactive power to increase efficiency.
There are also variable rating versions, for use when load variation is slow - daily when everyone starts cooking dinner, or seasonal - high demand in the winter.
Sometimes switched in and out as required via a circuit breaker.
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Post by pre65 on Apr 6, 2015 13:52:50 GMT
Tried the BMU on the source side this morning (CD replay) and I felt an improvement.
I have trouble explaining differences, but it just sounded "better".
So I'd say to you all, beg, borrow or loan a BMU and see what you think.
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Post by MartinT on Apr 6, 2015 14:02:38 GMT
I still plan to get one to try out sometime, Philip. It'll be very interesting to see how it compares with the regenerator.
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Post by pre65 on May 23, 2015 11:54:04 GMT
Just to show I'm not totally biased (pun  ) towards valves I'm thinking of a solid state class A amp. It was going to be a JLH design, but now I'm thinking of the Colin Wonfor design he is selling PCBs for. Just waiting to see what the PSU PCB looks like.
In the meantime, I'm accumulating a few parts.
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Post by MartinT on May 23, 2015 12:33:23 GMT
Fan cooling? Those heatsinks don't look likely to be sufficient.
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Jun 3, 2015 8:11:40 GMT
Fantastic, open baffles are the way to go in my opinion. I'm about to start a major speaker re build next week. Now James you have a SECA to build no more speakers |
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) towards valves I'm thinking of a solid state class A amp. It was going to be a JLH design, but now I'm thinking of the Colin Wonfor design he is selling PCBs for. Just waiting to see what the PSU PCB looks like.
