Thursday, January 14, 2010

Biased and ready for a home!

So I got my 1ohm 1W 1% tolerance resistors from Digikey a week or so ago and got the amp biased. The calculations I did showed I should have been running ~37mA through the output tubes. Turns out it was running quite hot at 56mA. So things have been tweaked down to the numbers when you calculate using 70% of max for the tubes (25W max the tubes can do, 70% of which is 17.5W; 17.5W / 475V plate voltage gives the magic number 37mA). Now the tubes should last a bit longer than if I'd left it unbiased :).

More pictures to come soon. I'm starting to accrue the tools required to do the head cabinet, and hope to get started by the end of the month.

Saturday, January 2, 2010

Audio Samples!

Don't forget, this amp has yet to be biased, but it still sounds pretty good I think. Here are four samples...

*Update: Samples no longer online. My Linux servers hard disk ate shit.

Amp Sound Samples

Now I need to start tweaking those knobs to start finding those magical sounding places that this amp is sure to be hiding from me. Check out my capacitor discharge device! Resistors and alligator clips for the win!

Still fighting with getting video with good audio, so hopefully the clips tide you over for now. I'm hoping my resistors get here Monday so I can bias this baby. Enjoy!

Windows Movie Maker Sucks

It really does. I was recording some video with a decent cardioid mic on the cabinet running into line in and it sounded really good. Too bad it was so out of sync it was like watching a dubbed Kung Fu movie. So I'm going to try to get that ironed out in the not too distant future, but in the meantime, check out these tubes glowing! Yes, my camera is a piece of shit.

Oh, I also tried recording some video with my iPhone but Steve Jobs didn't equip the thing with a microphone capable of handling how awesome this amp is. I'll try again later this evening with the laptop, and even if the audio/video is out of sync, I'll post it so you can get an earful.

Friday, January 1, 2010

And it sounded like...

So I put in a few solid hours over the past couple days. First I re-did the power section and heaters. Then I put the board back in and got down to business. After a few more hours punched today, I ended up with this...

Yessirree. That power light is ON! After this picture was taken I went ahead and checked all the necessary voltages to ensure that things were functioning as they should, and sure enough, all was well. Next, I unplugged it and discharged the filter caps. I then went ahead and installed the three preamp tubes (JJ Tesla 12AX7) and fired it back up, and they started glowing a nice warm orange. My heart melted. I flicked it off, popped in the two output tubes (JJ Tesla KT77), plugged it in to a 4x12 full of celestions and turned it back on again. The output tubes lit up in unison with the preamp tubes; a beautiful sight indeed. No hum, no squeals, just the smooth sound of a 4x12 cabinet on the receiving end of a 50 watt head. I plugged in my guitar, turned up the preamp and master volumes, and a smile a mile wide hit my face.

I have yet to bias the amp as I am waiting on a couple 1 ohm resistors from Digikey. I hope to have them on Monday so I can adjust the flow through the output tubes, and then I'm going to record some video/audio of the amp in action. Make sure you check back here on Monday!