• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

New Tube Pics!!

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#3
Re: Nice Job Gavin

Positron said:
And this is only your second major project I believe?

Keep up the good work Gavin. You did a nice job.
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Thank you Steve. All of the agonizing over parts selection and color and cussing....etc, were worth it. Now if I can be as successful with my 5687 buffered linestage I will be a really happy tubehead.


🙂 🙂
 
#10
DrDeville said:
Very pretty!

Signal lines crossing at right angles... :checked:

AC lines crossing at right angles... :checked:

Is that "Tea for the Tillerman" I see in the first photo? :checked:

😀

Best,

George "Some Memories Are Forever" Ferguson
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Hi DrDeville. That is indeed "Tea for the Tillerman". Good eyes!! I thought that I had done everything much better than I did with my first amp but you what? This amp has more hum than my first humble project does. Go figure huh? When I say hum I mean from the filament wiring. It is a very low level hum that you can only hear from about a foot away from the loudspeaker, which is 97 dB 1w/1m, so it don't take much. I'm going to run a voltage divider from the B+ to ground and bias the heaters up about 40 volts or so and see if that makes any difference. I'm also going to get a bright flashlight and see if I can spot any cold solder joints. The hum seems to subside somewhat after the amp fully warms up which tells me I have a bad joint (resistor?) somewhere. I may swap some tubes around also. Thank you very much for the compliments. Cheers.
 
#11
Re: Great looking Amp...

mourip said:
Did you make the base yourself?
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No. I'm not that good at finish carpentry. I had a cabinetmaker that lives nearby make the frame and one for my planned linestage also. Any competent cabinetmaker should be able to build you a frame with dovetail joints on the corners. The cost was only $20.
 
#12
That is indeed "Tea for the Tillerman". Good eyes!!
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That album is part of the music that is forever a part of my gestalt.

This amp has more hum than my first humble project does. Go figure huh?
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Indeed. I doubt you're discouraged, and you shouldn't be. As you undoubtedly know, there's plenty of things you can do--resolder joints, adjust the wire paths, use coax for the filament wiring, switch to DC filament power, etc. You'll get rid of it.

Thank you very much for the compliments.
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You deserve them. Thanks for the photos. 😀

Best,

George Ferguson
 
#13
DrDeville said:


use coax for the filament wiring
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What a novel idea. Hadn't thought of that one. I solved the problem. I found that the 5687 I was using was microphonic. I also biased the filaments approximately 40v above ground. No more problem. You have to put your ear about 4 inches from the speakers to hear any hum or hiss. I can live with that.


😉
 
#17
Thanks Gavin,

To save others digging:

From Sir Bas Horneman, I gather that electrons emitted from the heater itself can travel to the cathode, causing hum. Raising the heater bias stops this effect.

But perhaps the major advantage is preventing filament-cathode arcing in designs where the cathode can swing high above ground.

Thanks again, and I hope I got that right!

Best,

George Ferguson
 
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