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Posted

Nice work!

Question: have you considered mounting the bias LEDs such that they can be seen through the top panel? It looks like it would be a bit of a pain to do, but it would give a visual indication that input tubes are up & running with the bias current flowing through them. Something similar could also be done for the B+ supply, when all the LEDs light up you know the amp is good to go, and if something doesn't light up you know where to start looking for the problem.

Posted
Nice work!
Thanks!

Question: have you considered mounting the bias LEDs such that they can be seen through the top panel? It looks like it would be a bit of a pain to do, but it would give a visual indication that input tubes are up & running with the bias current flowing through them. Something similar could also be done for the B+ supply, when all the LEDs light up you know the amp is good to go, and if something doesn't light up you know where to start looking for the problem.

Actually yes, I had given that some thought and it wouldn't be hard to do with the two existing LEDs. What I had considered doing was drilling an LED sized hole in the terminal board and just poking the LED through that way. Since I have a ring of holes around the base of each tube for ventilation I'm pretty sure you'd be able to see the LEDs light. In the end in the interest of time and actually not wanting any sort of "tube illumination" I abandoned that concept.

Question though, how would you propose to tap an LED off of B+?

Posted
Question though, how would you propose to tap an LED off of B+?

In my case I stuck a 150k resistor in series with the LED and wired the whole thing between B+ and ground. Adjust the value of the LED to get the current and LED brightness you want, and also keep in mind that you might need multiple resistors depending on the B+ voltage in your amp so that you don't exceed the voltage spec on the resistors.

Posted

Or if you decide to use a resistor string off B+ to bias your heaters, you can just put an LED in series with that.

Damn, now that's a thought.

I will see about asking them to send one to Florida. Assuming, you know, I havnt bought one before then.

Posted
...Adjust the value of the LED to get the current and LED brightness you want...

Had a brainfart, that should say adjust the value of the resistor.

cetoole's solution is the neater one, it whacks all the problems at once. If you're doing the heater bias, you already have the resistors in place for the LED.

Posted (edited)

But does Nate sing the "Have it your way" song? :)

BTW Mike, Have you considered a pit crew for audio gear? A complete system change in under 13 seconds would be perfect for you. :P

Edited by swt61
Posted

Thanks guys. Ari and I will be working on her a bit this weekend to see if we can tweak some of the buzz out of the output. It's pretty ok with even low impedance open headphones but not with closed cans. We've got a pretty good idea where to start so I'm hopeful she can be made to have an acceptably black background. These types of things are to be expected with PTP builds so I'm not surprised.

Posted

The 307A based MenaceTC is slated to start construction some time in December and god-willing be fully burned-in in time for CanJam. I've acquired the lion's share of parts for that beast but the layout is about 10x as complex as the "Lite" version so it's going to take a lot of planning.

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