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opt transformer question

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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.

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.
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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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!
It seems to be a bit low in capasatance and calls for a pretty heavy duty choke. The 6C4 is an interesting choice for a driver. I would go with it as is but have some extra caps to go into the power supply just for grins later to see if it helps your bass responce a bit that being your only source of capasatance. Other than that I like 5V4s as they are soft start and can extend the life of the rest of the tubes. Another tube that looks like it could easily go in where the 6C4 is could be a 6267/EF86.Probably a different pinout but there is the possability of some fairly easy tube rolling there. You have all kinds of room under that chassis so you can modify and play with that thing for years. Have fun and be carefull of getting zapped.
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