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Been hearing about the RH84 and its bigger brother the RH807 for a while now so figured I would give one a try. Got a EL84 SE transformer set out of some sort of recording equipment off eBay and fired up the soldering iron. Its a unique cathode biased pentode schematic with a short local feedback. You can read more about the design on RH's website. Most the the technical information is in the RH807 section:
http://www.tubeaudio.8m.com/
I had most of the parts in my collection except the 10uf caps and 1M grid resistors so it was a pretty quick build. Initial listening though my test speakers is favorable. I can hear a tiny bit of hum as I did not have a 20H choke around so just used a resistor. I will buy one next time I put in a parts order to cure that. Click the picture for more information and undercarriage shots.
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Posted by Shaneon Monday, March 08 @ 04:54:06 EST (32 reads)
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Dynaco FM-3 Modification
Got this FM3 as part of a deal with an SCA35 and some other Dynaco stuff. Figured I may as well redo it and see what the hype is about. Now I have never owned a tube tuner so I do not have much to compare it to. It does not look as its ever been run much as the 10K resistors that are know to fry up had not even browned the board yet. Click the picture to see the mods.
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Posted by shaneon Thursday, March 04 @ 08:34:44 EST (67 reads)
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GM-70 Beast
I have always wanted to build a big broadcast tube amp. At first I wanted to build an 805 amp but after researching quite and finding out how difficult they are to drive I switched to an 845 design. I tried to get tubes for a while and not wanting to break the bank I settled on the GM-70 as it’s almost the same and way cheaper. Good thing as the first day I got the tubes in the mail I dropped one on the cement floor. If that was an 845 I probably would have cried. I was going to use a Tubelab SE as a driver board with some 45’s through some 10M45’s to the GM-70s but went with a simpler design from Nicholas Chua that uses a choke loaded triode strapped 12GN7A and a fixed bias on the GM-70. I am glad that I did as his DC heater supply for the GM-70 is very good. Since I wanted to do this on a reasonable budget it took me over a year to get the parts together. The output transformers came from Taiwan, the tubes from the Ukraine, plate chokes from Thailand and the main power supply cap from Russia.
Click the picture for the full story.
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Posted by Shaneon Friday, August 07 @ 09:39:04 EDT (117 reads)
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Tube Database
I finally got around to entering most of my tubes into my database. It was quite a bit of work to get things set up but now once its set up I can enter in tubes as I order and buy them.
The database can be seen here
Check out the "List All" and the Search function.
The structure is based on OpenDB and I wrote all off the categories, item structures and types. Since the program was originally written for collecting movies it was quite a bit of changes.
Since I wanted to have pictures of every tube that I entered. I had to come up with a simple way to take and upload pictures to my web server. I solved this with a wi-fi SD card from Eye-fi. The SD card goes in the camera and when ever you are near your wi-fi network it automatically uploads the pictures to you computer. Unfortunately this only works with windows and Mac. I made a folder on my windows box for the pictures to upload to and got a script to ftp any file dropped into that folder to my webserver. Now when I want to enter a tube I take the picture of the tube and just enter the link to the picture in the form I made. It works pretty smooth and you can enter ina tube in under 30 seconds.
If you would like to try this for yourself let me know and I will help you.
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Posted by Shaneon Wednesday, March 25 @ 10:48:48 EDT (101 reads)
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833A making mad light
Shot of my 833A lit up. Want to make a serious SE amp with a set of them. Got this one for a deal so I was just testing the filament. Oh and in case you are ever wondering if you can fire up an 833A with a ATX power supply even if its rated for 20A. No, no you can not. It causes lots of smoke, smell and very little else. Anyone have a spare ATX?
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Posted by Shaneon Tuesday, October 28 @ 15:25:44 EDT (167 reads)
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