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 Post subject: Re: 845 amp project
PostPosted: 14 Nov 2019, 00:07 
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Joined: 15 Nov 2013, 10:16
Posts: 244
Location: MB, Canada
Kev56 wrote:
Hello Gents,
Superb build and so exciting to see it can be done DIY.
I'm brand-new here, and am about to dive into my own DIY journey. I'm looking to start with Speakers that I will drive with a system very similar, if not identical to what you've built here, "thehoj". Your painstaking efforts have yielded what appears to be a system sonically rivaling a "Cary Audio" build.
I have hopes of building a system that sounds as close to this as I can get, but for a fraction of the $50K plus price tag. I was an Electronics Technician in the Coast Guard for 30 years and am quite comfortable with solder, a solder gun, flux and alcohol LOL. The voltage issue does not frighten me,, as I worked on many systems, including a 1,000,000 Watt Loran Transmitter during my career. I hope not to offend, is it possible to build a system similar to yours for under $5,000-$10,000?
My desire is to fill my 20'X 15' vaulted ceiling living room with ample, gorgeous sound from many genre's.

Reading your posts was a delight. You clearly put a tremendous amount of time and effort into creating a masterpiece.
Look forward to your input.
Kev56


Thank you for the kind words. Paintstaking is an understatement though. I can only imagine how many hours I've invested in this between research, simulations, prototyping, sourcing parts, trial and error, custom parts, etc.
You most definitely could put something like this together for under $5K. For one I spent a lot on the output transformers, like way more than any other part of the amps. They're Monolith Magnetics S-5 output transformers http://monolithmagnetics.com/products
They were cheaper when I bought them, but they retail now for $525USD per transformer. You could probably get something cheaper that would be suitable. I had also considered Electra-Print https://www.electra-print.com/singleended.php which would have been cheaper, but went with Monolith in the end.

The power transformers that I used are a combination of run of the mill Hammond transformers, and some I got custom wound from Heyboer https://www.heyboertransformers.com/
I can't really say enough good things about them, super super helpful, and able to do pretty much anything you could want. The custom power transformer for the power amp section was I think $180 USD. The PT for the driver section was more like $120 USD.
I would have an in depth conversation with them if you were to order something from them though, there are a ton of variables with their construction, grades of iron, stuff like that.
I used Transcendar chokes https://www.transcendar.com/ and they were great to work with as well, they used 10KV lead wire on everything for me at a minimal extra cost. Also very reasonably priced stuff.


The chassis' were all done from Landfall Systems https://www.landfallsystems.com/?content=products/main They'll do custom sizes, and they'll also do CNC work, they send you CAD files that you can draw in all the cuts and holes you want. It's a bit of work but totally worth it. They'll also anodize everything for you for an additional cost which I would highly recommend.
They use thick good quality aluminum as well.

The design is based of off the Tubelab research and design http://tubelab.com/designs/845-se/
Basically you could come up with whatever driver you like to swing enough voltage for you, and the mosfet source follower design of the "Power drive" circuit handles the needs of the A2 operation of the power stage. http://tubelab.com/articles/circuits/power-drive/

As for high voltage caps, I used Polypropylene HV caps (1500V) made by cornell dubilier which I got from Mouser or Digikey rather than electrolytics, just simpler and safer I think. Though more expensive. I also used some Solens. If I were doing it again I would have used all Solen caps, like these 1500V ones https://solen.ca/products/capacitors/fast-capacitors-630v-1500v-ppe-ppm-pesg-polypropylene/pesg5100alv/

I used Rod coleman regulators for the 845 tubes filaments http://lyrima.co.uk/dhtreg/dhtRegIntro.html
There seem to be 2 camps on this type of regulator, but all I can say is that they work awesome and are dead quiet. I would use them again in a heartbeat.

There a million little odds and ends too, but that's part of the fun figuring that all out.
One thing to take note of is using proper wire, that's rated for the voltages you're using. Also I would recommend taking beyond extra care in being careful of the high voltages, though I think that goes without saying.
I'm sure I'm forgetting all kinds of things, but I would recommend putting a lot of time and effort into research, look at what other people have done, try to learn how to use LTSpice to draw up your circuits and run some simulations to make sure that what you're doing should work in theory https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html#
It's free, and there's a learning curve, but there are some good guides out there.

If I were to do it again I think I would do them as monoblocks just to reduce the weight of the chassis'. The main power amp chassis weighs over 100 lbs, so it really sucks to move around.
One other thought I've had a few times is thinking about potentially doing this based on the GM70 power triode rather than the 845. The 845 tubes are expensive, and GM70's can be had for a lot less. They have similar specs and are supposed to sound really good as well.. I can't really comment on them too much though.

One thought on the 845 tubes though is don't mess around with buying cheaper B-stock tubes from ebay, don't buy used ones, don't seek out NOS tubes, just get the Shuguang 845B tubes from here https://www.thetubestore.com/shuguang-845b Don't go for the fancy versions, don't get the cheapest ones you can find. Just trust me, get these Shuguang 845B tubes from thetubestore. I've had problems with tubes that crackle, tubes with QC issues, tubes that are too expensive, etc. These Shuguang 845B tubes are awesome (from a reputable source).


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 Post subject: Re: 845 amp project
PostPosted: 14 Nov 2019, 09:46 
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Joined: 05 Nov 2019, 19:16
Posts: 3
Location: New Orleans, LA
Wow, thanks so much for the info.

Agreed with your warning on voltages. As a young technician in the 80's I worked on a Collins HF-8022 10KW Transmitter. While troubleshooting a Power Supply problem that was blowing the main Cbkr, my boss and I had to remove the front cover and observe what was going on.
At 6500Vdc, we had a highly insulated wire (Litz I believe) that had become nicked by blowing up against a rub point from the cooling fan. So, it didn't trip while we had the cover off, only with it on. Scratched our heads a great deal. When we finally had it set up to operate with the cover off, it shorted to ground on energizing.

The Blue Arc Flash along with the smell of Ozone is one I will never forget, LOL. So the continued warnings about voltage measurements and danger is highly regarded and will be adhered to I assure you.

I will keep you posted on my progress, it's going to take a bit of time I'm sure.

Thanks much,
Kevin


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 Post subject: Re: 845 amp project
PostPosted: 14 Nov 2019, 10:24 
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Joined: 15 Nov 2013, 10:16
Posts: 244
Location: MB, Canada
Kev56 wrote:
Wow, thanks so much for the info.

Agreed with your warning on voltages. As a young technician in the 80's I worked on a Collins HF-8022 10KW Transmitter. While troubleshooting a Power Supply problem that was blowing the main Cbkr, my boss and I had to remove the front cover and observe what was going on.
At 6500Vdc, we had a highly insulated wire (Litz I believe) that had become nicked by blowing up against a rub point from the cooling fan. So, it didn't trip while we had the cover off, only with it on. Scratched our heads a great deal. When we finally had it set up to operate with the cover off, it shorted to ground on energizing.

The Blue Arc Flash along with the smell of Ozone is one I will never forget, LOL. So the continued warnings about voltage measurements and danger is highly regarded and will be adhered to I assure you.

I will keep you posted on my progress, it's going to take a bit of time I'm sure.

Thanks much,
Kevin


Wow that sounds pretty intense. I look forward to following a build log if you choose to do one. It'd be cool if you started a thread documenting your research and progress with the project!


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 Post subject: Re: 845 amp project
PostPosted: 14 Nov 2019, 10:55 
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Joined: 05 Nov 2019, 19:16
Posts: 3
Location: New Orleans, LA
Definitely! Will start sometime after the first of the year. Will start the build log. Thanks much


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