Paul, I will not take anymore of your valuable time. I will end by giving you the current transformer wiring. upper xformer , Red is from high voltage of power supply. blue lead comes from pin 2 orange connects to pin 3, . green from upper, goes thru a 220 uf, electrolytic bypassed with a 270K resistor to gnd. the small output has a connection from pin 3 thru a 3.3 solen to the orange lead. bl.,brn,red,yel are not connected. Out put to binding posts is via blk. and 16 ohm yel. to speakers. I am going to have to wait several weeks for the x formers the tfa 204s to arrive. Thanks you so much for your help,I have really learned alot,and as you have noticed I have alot to learn. You are so kind to share your knowlege with me. J.
C/4s original SEX ,voltage questions.
- Thread starter najo49
- Start date
grainger, Thanks for your input. I see the ohms law, and I appreciate the heads up. I have now got that sorted out.The amp does not produce sound ,and I assume thats because I have converted to parallel feed,from the original mu follower. and the original output cannot work. I am waiting on a pair of tfa 204s,but I wanted to listen to it until the new xformer arrives.
Grainger49
New member
Hey! I put the 10 year old C4S boards into my FP 2 a few months back. I got the incoming and outgoing voltage leads swapped. It drove me nuts! (short trip!)
I spent a couple of hours reversing the LEDs. To no avail. Then PJ got my head straightened out and it sounds awesome!
I had to turn down my sub by a couple of clicks. Maybe I should turn it down another. The bass is much firmer and extended.
I spent a couple of hours reversing the LEDs. To no avail. Then PJ got my head straightened out and it sounds awesome!
I had to turn down my sub by a couple of clicks. Maybe I should turn it down another. The bass is much firmer and extended.
Paul Joppa
Moderator
It's no problem, I am genuinely interested in seeing you get this thing working. Sometimes I make short answers when I'm in a hurry, so apologies if I seemed curt.najo49 said:
The reason I asked for tube voltages is to be sure all four tube sections (two per tube) are operating correctly. The high voltage (453 vs. 410 expected) might be caused by one section failing to draw enough current. Check the voltages at the actual tube socket pins, don't rely on wires that connect one socket to the other - there could be a bad connection or a broken wire.
The old output transformer (now the plate choke with feedback coil) appears to be connected correctly. I assume the "270K" resistor is actually 270 ohms? I would encourage you to raise it to 390 ohms, 5 watts. The higher wattage will give a longer life, and the higher resistance will reduce the total current through the plate choke, reducing its distortion.
From your description, there is only one lead of the small output transformer connected, so it's no wonder there is no sound. The 3.3uF Solen should go from pin 2 of the tube socket (NOT pin 3) to the orange lead of the transformer (I assume that it the lead marked "1.25 watts" on the transformer). The black lead of that bundle is shown in ref 3 going to ground.
Your numbers show 155 volts across the 6K resistor (453-298), which by Ohm's Law would be about 26mA current. This would be 4 watts dissipation, exceeding the rating - no wonder it is hot! Best to check the resistance in case the heat has damaged the resistor. I would encourage you to replace it with a 6K 5watt resistor - but not until we get the high voltage down to where we expect it to be. But the circuit says you should have only 18mA (total of 16mA to tube pin 5, and 2mA through the three 50K resistors on the PC board). The plate voltage is close enough (225v vs. 250v expected) so I expect the 16mA is correct - leading me to suspect the 50K resistors may not be wired in series. The old boards were very confusing in that area, so it's worth inspecting them. There should be three resistors in series, with 100v across each one (adding up to 300 volts across the string).
Incidentally, I do recognize how much of a pain it is to be entirely clear and complete in posts like these, where we can't see what the other is doing. But we are usually successful eventually!
Paul, Thanks,I just thought you must become tired of dealing with a beginner. I am now retired,a musician ( string bass) playing with various Orchestras . I am tryi ng to learn enough to partially at least design a few things. And I have quite a collection of tube amps. I have a Heathkit wm 6, 70w push pull, ever seen one? They are very rare only 2 k were built.But I have many others all rebuilt by me.
I am waiting on the 204 x formers. But I did something fun with the sex amp that is working and still wired in the first version. I have a transformer,it is 117v primary and a pair of 19v secondaries and a pair of 7.5 v secondaries. I hooked it up in the place of the original transformer. primary to the 3.3 up cap output and the other lead grounded to sex gnd. I used the 19v secondaries on gnd. and the other as the positive out put. And to my surprise GREAT things came out. It had more power, I do not know how much but it was a big improvement on the original trans. And no feed back except what the chock adds. Why does this work?It has a oval magnet structure and the windings on each side of the oval. And I tried the 7.5 outputs and they sounded pretty much the same. I have no idea what the output resistance is but I thinkk the 19v outputs sound best. What do you think. J.
I am waiting on the 204 x formers. But I did something fun with the sex amp that is working and still wired in the first version. I have a transformer,it is 117v primary and a pair of 19v secondaries and a pair of 7.5 v secondaries. I hooked it up in the place of the original transformer. primary to the 3.3 up cap output and the other lead grounded to sex gnd. I used the 19v secondaries on gnd. and the other as the positive out put. And to my surprise GREAT things came out. It had more power, I do not know how much but it was a big improvement on the original trans. And no feed back except what the chock adds. Why does this work?It has a oval magnet structure and the windings on each side of the oval. And I tried the 7.5 outputs and they sounded pretty much the same. I have no idea what the output resistance is but I thinkk the 19v outputs sound best. What do you think. J.
Hank Murrow
New member
najo49 said:
Dear J; Indeed, I remember that Heathkit 70watter, because I built one back in the days of mono when I was 15 or so and drove a Stephens 15" coax loudspeaker in a Voice of the Theater system I built myself. Hey, it could be heard on the ridge a half mile distant from my parents' house! Think "Night on Bald Mountain" in the balmy California evening air..... Went on to Dynakits until they went solid state, but now Bottlehead Customs has built my Final Music System, and with Orcas & BUF Subs I am a very happy camper. Just hoping I get a couple more decades to enjoy it.
Cheers, Hank
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Hank, I use a pair of altec speakers for my low power system, the 15 ohm vintage 15 inch woofer, horn and driver. I can not imagine what a 70 watt speaker would do with them, loud !. I love my wm 6s and I have completely restored them,paint,teflon wiring ,all the resistors and caps . They look like new and and hands down the best push pull I have ever heard,they are paired with the proAc 2.5s or the pro ac tab 50 sigs in my high power system. Thanks for you reply, j.
