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Old 4th September 2009, 01:17 AM   #51
Salas is online now Salas  Greece
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But you can parallel two rectifiers, can't you?
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Old 4th September 2009, 01:20 AM   #52
agent.5 is offline agent.5  United States
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I am pretty sure mercury rectifiers can handle pretty much anything that you throw at them. 866A is good for 1A peak, 872A is good for 5A peak.

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Old 4th September 2009, 01:24 AM   #53
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The current drawn by this board with 6CW5's is more than my old Fluke power supply likes to put out (current meter is pegged). I got this brilliant idea to wire two power supplies in parallel. Dumb idea. They fight each other and the current meters look like windshield wipers!
What about paralleling them through a couple diodes,to isolate the outputs from each other? I've used this trick before on various supplies,and it usually works out okay.
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Old 4th September 2009, 01:35 AM   #54
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Originally Posted by tubelab.com View Post
The current drawn by this board with 6CW5's is more than my old Fluke power supply likes to put out (current meter is pegged). I got this brilliant idea to wire two power supplies in parallel. Dumb idea. They fight each other and the current meters look like windshield wipers!
Are these adjustable voltage supplies? Can you set one at say 10 volts higher than the other, and let it peg on max output? Then the other should pick up the slack when the load gets hard, and you should see the current on it pick up. Maybe what you need is an adjustable current supply and an adjustable voltage supply. Fix the current on the one at 300 mA or whatever it can do, and let the other regulate the voltage.

Or maybe they just don't work like that.
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Old 4th September 2009, 01:53 AM   #55
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Yes, it is possible to parallel two rectifier tubes, and mercury vapor tubes can be found that will put out an amp, but neither of these options will plug into the Simple P-P board.

Back in high school electronics class I use to parallel identical Eico tube regulated supplies without a problem. I don't have two identical supplies, so I tried to connect my Fluke 407D in parallel with a Knight kit supply. Both are tube regulated without current limiting. I got them both real cheap, very used, and have never done any repairs or upgrades on either. I have never had the cover off of the Knight, and it works OK but it needs to be smacked every once in a while. I opened the Fluke when I got it, took one look at all of the really old leaky caps and decided that I would just plug it in and see what exploded. It worked and I have been using it ever since. I routinely overload it, some times it gets mad and starts oscillating, but it has been hanging in there with its meter pegged without complaining today. I have a really big HP power supply (650 volts, 1.7 amps.) but it likes to blow things up, so I am not going there yet.

I wired a good size (maybe 300VA) power toroid in place of one of the OPT's and did some testing. The max power dropped by a watt or two. The distortion is low, and the frequency response is 6 Hz to 69 KHz. I am in the process of connecting up the second one, and I will do some listening.
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Old 4th September 2009, 02:39 AM   #56
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Originally Posted by tubelab.com View Post
I wired a good size (maybe 300VA) power toroid in place of one of the OPT's and did some testing. The max power dropped by a watt or two. The distortion is low, and the frequency response is 6 Hz to 69 KHz. I am in the process of connecting up the second one, and I will do some listening.
It's rather convenient that a well balanced push/pull amp is virtually immune from problems arising from core saturation. Let's you do all sorts of things that flat out don't work in SE.
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Old 4th September 2009, 03:25 AM   #57
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OK I got an amp running with no conventional transformers. The choke is a $7 EI choke, but the power and OPT's are toroids and this thing sounds good. I tried using a 5U4 for a rextifier, but it didn't work well at all. I wired in a couple of FRED's and they work fine. More experiments later.

All of the conventional transfornmers in the photo are not connected.
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File Type: jpg Toroids_1.jpg (381.9 KB, 905 views)
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Old 4th September 2009, 03:38 AM   #58
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That looks like a very versatile amp you are checking out there George. Lots of ways and tubes and OPTs. Its gonna draw interest. What kind of camera you use and your pics are so vivid and true? No flash?
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Old 4th September 2009, 05:29 AM   #59
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Originally Posted by tubelab.com View Post
I found that many 8BQ5's work just fine since Hammond transformers supply nearly 7 volts on their filaments. These can often be found cheap.
I have 17JB6's in place of the 12JB6's in my Drake TR-3.

I have a ton of the '17's and not so many of the 12's and was a bit surprised that they worked fine, and have done so for years.

I'm sure at some point the emission will drop enough that they will have to be operated at their rated filament voltage.

Or just thrown away, and start over with some more 17JB6's.

Win W5JAG

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Old 4th September 2009, 05:39 AM   #60
w5jag is offline w5jag  United States
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The 6CW5 likes current, and lots of it, at a low B+ voltage like 250 volts. I am seing average current in the 380 mA range for the complete amp. Peaks go to almost 500 mA when you crank some Metallica! This is too much current for any common rectifier tube, and the board was not set up for solid state diodes. Power transformers with ratings to support this aren't common either.
A couple of diode rectifiers can be placed in an 8 pin tube base to drop in the tube socket for 6CW5 users, or tack soldered to the board in place of the socket.

I still see the commercial versions (e.g. SS-5U4) of this arrangement pretty often at hamfests.

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