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I recently picked up a second Motorola mono amplifier chassis of the quad 6V6 variety. I am looking for the specs on the power transformer, part number is Magnavox 300067-04 394322. It could possibly be 300067-G4. I have two such chassis and this one has a larger transformer, I am hopeing to build a stereo out of the two mono amps.
I can't give you specs from a Magnetbox part number. Tell me a bit more about the amplifier, and I will tell you want it requires. Now many 6V6? Are they Push-Pull, or Single Ended Other tubes? and number of each? Any other details that look important? cheers, Dogulas
Here is a schematic. http://www.triodeel.com/mag278.gif
hmmmm...push-pull-parallel 6V6's. Plus the pre-amp tubes. Say 160 mA at between 275 and 325 volts. Pick your filter type, and rectifier and PSUDii will spit out the rest. You were not quite clear in the original post. You wish to make one more of these? Or you're going to rebuild one with a bad power TX? Instead of parallel 6V6, I'd suggest single pairs of 6L6GC. cheers, Douglas
Using the g2 supply from the PPP amplifier for the anode supply of the SE amp. Nice touch. I'd refine the estimate of required current by another 40 mA, and say the main HV is probably ~300 V or so. Text book SE is close to 250v to the anode. cheers, Douglas
That is pretty cool, I don’t like parallel tubes but if 1 6v6 is enough power, try it…John
see the anode chokes between the anodes? Too much temptation for the oscillation bugs to creep in and work. They are sometimes like the proverbial NY cockroach when trying to get rid of them. no offense to the cockroaches...:) cheers, Douglas
I plane to build a stereo amp useing the larger of the 2 power transformers and the output transformers. The larger pt was "made to fit" and not the original and I was hopeing it could drive 2 6L6 pp's but I may be hopeing for too much. Basically I have 2 mono quad 6V6 pp amps and I want to put them together.
Two of those quad 6V6 amps are going to draw more than 320 mA each. That's a big transformer by most standards. I would call Heyboer Transformers in MI, and get a custom wound. Specify all the heater current you'll need and run with it. It depends on how you want to run the filter, as that will dictate the AC voltage. L-C will be ~340vac, and CLC or CRC would want more like 250vac. cheers, Douglas
I am not going to rebuild acording to the Mag schem I am just going to reuse the transformers and I guess I will go with one pair of 6V6's pp for eah channel. I was just looking for a way to squeeze out a little extra power.
I took a look at the schematic you linked and you may be able to run say four 6L6’s. This will depend on a couple things. First are you planing to try to use the existing output transformers? A push pull, pair of 6V6 is usually used with transformer input impedance of about 10K or so. With parallel 6v6’s it is probably 5k or so. Another thing this is actually two amps and this is low end so how this transformer will work full range is an open question. Let’s start with that…John
The output transformers look great to me, large and heavy, if you like I can post a picture. This very fact is why I want to build this amp, I want to put the ot's to good use. I think the pt may be 250ma, remember this was a replacement and it is larger than the pt in the first chassis that I bought. Right now I am can't decide between a pair of 6v6's or tuned down 6L6's and like you mentioned the ot's will probably match up better with the 6L6's. Sooo many possibilities.
I found a free program that will give an estimate of the current handleing capabilities of a transformer based on the output voltages and the resistance of the windings. I included a link if anyone is interested. http://www.angelfire.com/electronic/funwithtubes/Programs.html
Well, OK then. Go with the 6L6. The fact that they felt the need to run 2! 5U4’s , leads me to believe that the PS can supply > 200ma of b+ The only question is how much filament power is available. The filament string shown, will draw a bit less then 3A, but it continues off to power SK2-Sk3. So there is as a guess at least 1A more to be had. I think it’s doable, with a little caution. Before you start , try running the stage mono full range to get a feel for the output transformer. Lift the .022 cap from the 15K resistor and feed your signal there…John