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HiFi (Chifi) tube amp build - but my own design.
#47

I finally had a chance to do a test power up on my twin amp build, which is a twin, but not identical twin. With this being my second crack at this, I revamped some things in the layout to simplify construction, clean up & be easier to service. I separated the FB network and put it on it's own terminal strip (upper RH corner) which cleaned up the terminal strip near the driver tube. I also rerouted some of the wiring around the driver to simplify. I pretty much left the output area as it was, except I am trying different screen resistors to see the effect on the G2. I used a 100r resistor on the original, tried a 4.7k and it only dropped it 10v. Just an experiment. I'll probably go back to 100 on the final, although I see a lot of those connected directly to B+. I personally feel there should be something there. I also moved the bias filter cap to the control. Plenty of room, and makes more sense to filter it there right before it's sent to the tubes, and neats up the bias terminal strip. I used different coupling caps, since I didn't order enough of the bigger ones. I'll see if it really makes a difference. They weren't cheap ones either, so I really don't expect anything super different. Same value.

You'll also note that I revamped the power supply. My initial was just that - an initial. I found that my choke fit the existing holes already in the rear of the chassis, and it fit perfectly in that area, which neats up the top of the chassis. I moved the filter caps between the PT and A/C plug, mounted to a couple stickys and glued in place, Stays put, yet not hard to snap off and replace when that day comes. I also used a 5w power resistor instead of that huge 10w. I let it play for 20 minutes and could lay my finger on it with out withdrawing forcefully. I'm using a plain ole 6GH8A driver, Japan, and a couple Russian made 6V6s.

It powered up beautifully without any setbacks other than the fact I must have put the line control in backwards. Simple fix. I did reverse the plate leads on the output tranny and had no feedback issues, so this DOES make a difference! It makes sense as this would reverse the phasing of the transformer. I found the blue lead (at least with this tranny) goes to the low side of the inverter, and the other (brown?) to the high side. I've made this mistake more than once on other amp builds, so learned something. I also had the SAME hum issues from the PT, so moved the trans nuts around and used washers and poly washers as before and made it totally quiet. Not quite as attractive as tying the transformer directly to the chassis, but I'll sacrifice some cosmos for performance. I'm still planning to play around with some other tube types and try a couple different output trannys but I need to set a standard for comparison. Next up is going to be a power, freq response and distortion test. So far my main tester (those 2 things on each side of my head) say is sounds pretty good!

Edit: Mike, I know you mentioned that large yellow cap by the driver tube. It has some pretty thick leads and feels solid. I ran the lead through the terminal strip to the socket. It's not going anywhere.


   

If I could find the place called "Somewhere", I could find "Anything" Icon_confused

Tim

Jesus cried out and said, "Whoever believes in me , believes not in me but in him who sent me" John 12:44


Messages In This Thread
462ron - by 462ron - 10-15-2024, 09:07 AM
RE: HiFi (Chifi) tube amp build - but my own design. - by TV MAN - 12-19-2024, 12:51 PM



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