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Thread: 5C3 output power

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    Supporting Member mozz's Avatar
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    5C3 output power

    Has anyone measured the output power on a 5e3 or similar amp? I built a 5c3, part 5b3 and part 5e3. Parts were scrounged, i think the output trans was from a 1962 Lowery organ which i know had push pull 6v6's. Original speaker was gone and a 8 ohm Oakland or Oakford was in there, which had foam surround so i know it was newer than the amp. Here is whats happening, on a scope i can get about 5 watts clean, little more if badly clipping. That is into a 8 ohm dummy load. If i up the ohms to 16, i can get over 10 watts clean. So the output section is happier with the 16 ohms. Makes me wonder if the output trans i am using was originally using a 16 ohm speaker. Plate voltage is a bit low at 325 and screen at 280, but if i use a 5v4 and 5e3 power supply resistors (365 plate 340 screen) i can get more wattage (14.5w dirty) but still it's happier at 16 ohm load. Any thoughts? I do have 680 ohm screen resistors in there, should i lower them or remove them?

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    Last edited by mozz; 10-26-2015 at 12:06 AM.

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    Supporting Member mozz's Avatar
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    Removed the 680 screen resistors, wattage into 16 ohms is 11.3w. Plate voltage doesn't sag with signal, stays at 365. screens drop from 340 to 300. One other thing i noticed is 120v line wattage, it draws about 72 watts idle, only goes up to 73-74 wide open. 22v on cathode doesn't really change unless i go to 8 ohms. Swapped in 6l6's, switched to 8 ohms, smoked the load resistors a little, plate drops 10 volts just plugging them in, drops another 10 under signal. Line draw with 6l6's is 80 watts, goes up to 100w under signal. Cathode is 25v, plate 355v.

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    Quote Originally Posted by mozz View Post
    Has anyone measured the output power on a 5e3 or similar amp?
    From a man who knows (Bruce / Mission Amps)

    "A proper running 5E3, clone or not, with close to "classic corrected voltages" through out the B+ rail, will make around 10-12 watts max."

    I think you need to run it with a 16 ohm load.

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    Supporting Member mozz's Avatar
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    Just found a web page that tells you how to figure impedance approx from turns ratio. So, according to my latest experiment, i come up with a 3,7k load primary into 8 ohms secondary. That is much lower than the usual 6.6k or 8k transformer recommended for 6v6 types. Now, if i use a 16 ohm speaker, that will double my primary and make it see 7.4k, which is right on the money. So, this transformer has to come out or i have to buy another speaker. I have a 6bq5 push pull transformer here, will do my experiment again and see what this impedance is going to be. I have some 12" speakers, a old utah with no labels which measures about 5 ohms, so i think it's a 4 ohm speaker, and another 60's speaker which i measure at 7.3 ohms, i think that one is 8 ohms. I was using the utah in this deluxe cabinet. The 6bq5 transformer was from a hammond organ so i should be able to see if my impedance measurements coincide with any info i can find on the hammond. I'll be happy with 10 or 11 watts.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by mozz View Post
    So, this transformer has to come out or i have to buy another speaker.
    Or...

    You could build something like a 2x10" or 2X12" cab with really efficient speakers to plug it into for gigs and enjoy the lower output from the built in speaker for home practice

    I wouldn't be surprised if an efficient 2X12 at 16R cabinet was twice as loud as the 'comparable to Utah' speaker of the incorrect impedance you have in there. The extra surface area and efficiency work the same way. It'll be MUCH louder. And may even have better tone to boot. I know you may not need that much more volume, but it is a way to make the amp more versatile and improve clean tone loudness. Albiet expensive. Cabinets build cheap enough, but good sounding efficient speakers will be between $85 and $140 each. Ouch! But if you stick with $85 units (Like a pair of Emi Cannabis Rex's) and build your own cab (natural finish, salvage grill cloth, cheap corners) you could do it for about $210. That could be a lot of fun for the money.

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    Don't forget the joker g1's Avatar
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    Quote Originally Posted by mozz View Post
    a old utah with no labels which measures about 5 ohms, so i think it's a 4 ohm speaker, and another 60's speaker which i measure at 7.3 ohms, i think that one is 8 ohms.
    I don't think I've ever seen a speaker that measures a DC resistance of more than it's rated impedance. So I would be more inclined to think the one that measures 5 ohms is an 8ohm speaker.
    Double check your readings to be sure. Also check the reading with the probes shorted and subtract any probe resistance from your measurements.

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    Supporting Member mozz's Avatar
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    Quote Originally Posted by g1 View Post
    I don't think I've ever seen a speaker that measures a DC resistance of more than it's rated impedance. So I would be more inclined to think the one that measures 5 ohms is an 8ohm speaker.
    Double check your readings to be sure. Also check the reading with the probes shorted and subtract any probe resistance from your measurements.
    Yeah, i don't know what i was thinking, impedance could never be lower than the DC resistance right? On my B&K bench meter it measures 4.89 ohms. I have read Utah and a few other speaker makers were basically making clones of better speakers back in the 70's, this is actually a radio shack speaker made by Utah and is listed as a guitar musical instrument speaker. I have swapped in my other 12" speaker so for now this stays in and if it sounds bad i will put the utah back in. ........................................................ ..................Back to the amp, i am happy now, put the 6bq5 tranny in there and it works like it should. Doing my impedance experiment on this, i came out with 8.1k, which is right where a 6bq5 trans should be. The test is this. Apply a 1khz signal to the trans. In my case, i used a Samsung tablet headphone output with a app called signal generator, a few others didn't work but this simple app did. I put it on the output, cranked up to max and i measured .272 volts, move the meter over to the primary and i get 8.68 volts. Divide 8.68 by .272 and you get 31.9, this is your turns ratio. Square this and you get your impedance ratio 1017, multiply this by 8 ohms secondary and you get 8.1k. Perfect for 6bq5 or 6v6 push pull amps.........................................Back to the amp. Installed 6bq5 output transformer, 5y3 rectifier PLATE 345V SCREEN 312V CATHODE 19.8V DISSIPATION 12.2W (JJ6V6S) OUTPUT 8 OHMS 10.25W/CLEAN 13W/DIRTY...............5V4 rectifier PLATE 381 SCREEN 343 CTAHODE 22V DISSIPATION 13.5W (JJ6V6S) OUTPUT 8 OHMS 12.75W/CLEAN 16.5W/DIRTY.........................Reason i even did all this was because i am using scrounged parts, impedance's unknown and it just didn't seem much louder than the tweed Champ i just built. When i measured and saw 5 watts, i knew something was wrong. Thanks for the help. Will be a regular now. Also member of the Agile guitar forum, if you are familiar with those guitars from Rondo, stop over and become a member.

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  8. #8
    Supporting Member mozz's Avatar
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    Click image for larger version. 

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    Basically the final schematic. Used a Musical Power Supplies output transformer, has 6.6k and 8k pri, 4,8,16 sec.

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    Bent Member Chuck H's Avatar
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    Which primary did you use? And how does it sound? I've never even heard of Musical Power Supplies.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    Supporting Member mozz's Avatar
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    Actually i put a dpdt switch in there so i can switch between the windings. The power transformer is oversized so running 6l6 doesn't overheat it. I have gotten 26-28 watts with the 6l6's. I found Musical power supplies has "very" decent prices on transformers. I was surprised how nice it was made and very heavy sized wires, they will be getting much more business from me. Didn't get to play it much yesterday when it was finished, but today i have a few hours, never got to try anything with humbuckers in this yet but will today to see how it breaks up.

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    Supporting Member mozz's Avatar
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    Humbuckers and grid leak bias don't play well together. I left the 6SC7's in there and put it in cathode bias, sounds much better. WGS speaker and i'm all set now. Building a tele current project, then a 6g15, then a wah pedal.
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