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Old 14th September 2009, 02:56 AM   #81
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Quote:
Prayers sent for Sherri's mother.
Thanks.

At this time I have two boards built and operational. The parts for the build photos will all be here by wednesday.

This weekend I did some experiments with a hybrid configuration using the board to drive mosfets. I have succesfully done this in the past, but this time I made some smoke. I didn't have the time to figure out why it fried.
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Old 14th September 2009, 06:51 PM   #82
adwsail is offline adwsail  United States
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Count me in on a parts kit. This beautiful PC board is ready for parts! Any word on the appropriate iron?
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Old 15th September 2009, 02:11 AM   #83
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I am posting a picture of my second board. It is seen here being used in a failed hybrid amp experiment. It is built pretty much like the first board except that there is no rectifier tube. There are two 1N5408 diodes where the tube should be. This looks like the best path to chose with 6CW5's due to their high current demands, more than a 5AR4 can make and a 5U4 drops too much voltage.
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Old 15th September 2009, 02:50 AM   #84
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Any word on the appropriate iron?
For 6BQ5's, EL84's, 7189A's and the Russian equivalents:

Funny you should ask that. There was a box containing a Hammond 372HX delivered today while I was at work. Of course I hooked it up when I got home. I put in some Russian 6P14P tubes (cheap on Ebay) and cranked it up. At idle the B+ is 358 volts and at a fully cliped 18 WPC the B+ is 347 volts. At a more reasonable 15 WPC the B+ is 350 volts and the distortion is 2.2% in one channel and 2.4% in the other. At 10 WPC the distortion is 0.5%. Some 7189A's may be able to handle more B+ than this, but the Russian tubes, some EI 7189A's and several NOS or used 6BQ5's are on the verge of screen or plate glow at continued full power operation, so 350V looks like a good place to go.

I made a deal on the Hammond 372HX, so I used it. A 272HX would probably work OK for less money (in 120 volt countries).

For OPT's I am using some surplus guitar amp OPT's that I bought a bunch of 10 years ago. They work excellent for this amp, so I doubt that I will try anything else. They are "80 watt" (really about 25 watt) 6600 ohm to 4,8, 16 ohm without UL taps. I have taken one apart and found low cost construction with zero interleaving, wound on power transformer cores, but they measure good, and sound better. I have tried the lowest cost Edcor XPP10-8-8K OPT's with mixed results. They sound great at low volume but distort at a few watts or so. After all they are only 10 watt transformers.

I would look for something with a 6K to 8K ohm primary, at least a real 20 watt rating more would be better but too big (over 50 watts) will cost some power and sonic detail.

For 6CW5's:

I am still looking for the optimum power transformer. I will report further as I get to look at more transformers, but I am currently using an Antek 1T200.

For an OPT look for a 3K to 4K ohm primary, and similar ratings to the EL84 transformers. I am using the same guitat amp OPT wirh a 8 ohm load on the 16 ohm tap to give a 3300 ohm primary.
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Old 15th September 2009, 01:05 PM   #85
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I emailed Edcor USA regarding their CXPP OT's that we touched on a week or so ago. I haven't heard back from them yet, may have to give them a call and see what they recommend.
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Old 15th September 2009, 10:08 PM   #86
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George-

What are the physical dimensions of the board? I am just trying to get a rough idea of how big a chassis to build.
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Old 15th September 2009, 10:22 PM   #87
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I don't know if anyone noticed this, but Antek now sells heavy gauge steel covers for their toroid transformers. The are as expensive as the toroid itself ($20+) but will cover up the toroid nicely. Just need to figure out which model the amp needs.
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Old 16th September 2009, 12:56 AM   #88
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What are the physical dimensions of the board? I am just trying to get a rough idea of how big a chassis to build.
The board is 5.5 by 8.0 inches.

For $20 each, I'll look at the ugly toroids!

I am in the process of building two amplifiers based on the Simple P-P. One will be a double decker design. The toroids are on the lower deck and will not be visible. The other will simply mount all of the components shown in the last photo on a wood and Lexan chassis. I haven't worked out all of the details yet, but I will post them when I figure it all out.
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Old 16th September 2009, 06:52 PM   #89
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I spoke with Edcor today and it turns out their 25 Watt 3.4K Ohm output transformer is an 8 ohm output, not a 4 ohm. The information on the website was wrong and they are going to fix it.

So that seems to be a good choice for the 6CW5's!
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Old 18th September 2009, 01:03 AM   #90
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Is there any problem with mounting the output transformers on either side of the toroid? I know that with conventional transformers you have to be careful of magnetic coupling, but not sure with toroids.
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