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Old 7th January 2002, 09:34 PM   #1
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Default opt transformer question

i found this beat up tube amp at the fea market it was only 10 dollars so i bought it. the opt trans formers a potted and have no markings on them other than "GG02" on the bottom of them. the id i can find on the amp is "made in japan" where the logo was on the front was cut out and a large vu meter was installed sideways in its place but since i only bought it for parts thats not an issue anyway. it used 4- 6BM8's 3-12AX7's and 1-5AR4.
question is.....when i check the primary side of either opt xformer(green and blue wires) i get readings of 220 ohms on both of them. ther is only one other wire (red) on the primaryside.
is this a good reading or are these things fried? all of the schem's i have looked at call for 2000 to10,000 ohms.

thanks..mike
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Old 7th January 2002, 09:44 PM   #2
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You're measuring the DC resistance of the primary. The resistance that is specified in the schematics is the impedance. If you are getting 220 ohms in the primary, chances are that the transformer isn't fried.
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Old 7th January 2002, 09:47 PM   #3
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Could the schematics be refering to AC impedance whereas you are measuring DC resistance?
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Old 8th January 2002, 04:00 AM   #4
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Sounds like you got a good amp. Antique Electronics have some very nice 6BM8s made in Yugo and packaged by Westinghouse for less than $5 ea. Or did last time I bought any. I have some surprisingly nice little 6BM8 mono blocks made in Japan for Calrad. Big bang for the bucks! Get that thing on a variac, check your tubes and play the thing before you tear it up. You might be surprised.
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Old 17th April 2002, 08:21 PM   #5
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i tore it up!! and then i started building this. i just got it back from a friend who is a cabinet maker and did the wood work for me. the chassis is thick alum plate that was part of a old equip cabinet that i cut out the back and part of one side so i have somewhere to mount the switch/fuse/power cord to. the inputs and outputs will go below that and when i get done with everything my wife wants done around here i am going to wire it for either 6bm8's or 6bq5's......havent decided on that yet.

cheers, mike
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Old 17th April 2002, 08:23 PM   #6
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the back
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Old 18th April 2002, 02:14 AM   #7
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Nice job! What is on each side of the power tranny is that covers for the two output trannys for "dress up" or are they made like that?
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Old 18th April 2002, 09:23 AM   #8
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those are potted transformers that are made that way. should look good after i repaint them


mike
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Old 22nd April 2002, 12:05 AM   #9
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after the stain and metal polish
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Old 22nd April 2002, 04:50 PM   #10
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Mike,
Those potted opts look just like the Calrads that were potted(not all of them were) The stereo model of what I have in mono blocks is Calrad SA30 and there is a Sam,s Photofact on it ,number 565-7. If the Electrolitic cans were Elna chances are that is what you had. The amp design without the bass, treble and switching is very simple. You could put a volume pot between your input jack and the 12AX7 on each side and use the Calrad circuit as a guide and build a very nice amp indeed. If you can't get your hands on the Sam's let me know and I can give you a copy of the AF15 mono block schematic which is the same circuit. Since the 6BM8 is a triode-pentode vs the beam amplifier of the 6BQ5 you will end up with a lot more options for modification down the road with the 6BM8s. They also cost less. Nice looking amp by the way!
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