Hi everyone!
It's been a minute since I've worked on my pmillet Wheatfield HA-2 clone! It had a nasty 60 hz buzz that rendered it unusable, so I sold off the power transformer and stuck it on a shelf to be forgotten about for about 13 or more years. Since then I've moved houses, my kids are grown, and I've wrapped up a masters degree. Having some free time and a pile of non-functioning projects, I turned my attention back to the old creation. It was an easy decision since I had all the parts, and just needed a power transformer and some free time.
So the redux. I've learned a lot more about tube amps and circuits in the last decade and when looking at my build, I decided it needed a completely new layout. I used rather large aluminum plate I had laying around and pulled all the good parts off of the previous attempt. I paid more attention to the filament wiring and moved the rectifier as far from the in/out tubes as possible. Three substantial component changes were made: big Edcor power transformer, a huge 600uf film cap replaced the B+ filter section, and the stepped attenuator was replaced with an Alps RK27. I only needed to buy the Edcor.
Last night I got to do a smoke test, and no hum or buzz! OK. Put on some music, and there were good sounds. OK. So I put on a pair of HD650 headphones and wow, this baby slaps.
Some questionable decisions might be the distance of the high voltage filter sections from the tubes, but nothing seems to be oscillating so that is good. Voltage is still a bit low with the 5U4GB rectifier, right around 250v. I'm not sure this is a problem though so I'm not likely going to sweat it. I'll try it with a 5AR4 at some point. Also I could probably benefit from a lower resistance choke.
I have some oak panels I've salvaged from an old piece of furniture that I'm going to use to make the chassis, so stay tuned for that. I also need to clean up some of the wiring that was done for the smoke test. Hooray!!!
It's been a minute since I've worked on my pmillet Wheatfield HA-2 clone! It had a nasty 60 hz buzz that rendered it unusable, so I sold off the power transformer and stuck it on a shelf to be forgotten about for about 13 or more years. Since then I've moved houses, my kids are grown, and I've wrapped up a masters degree. Having some free time and a pile of non-functioning projects, I turned my attention back to the old creation. It was an easy decision since I had all the parts, and just needed a power transformer and some free time.
So the redux. I've learned a lot more about tube amps and circuits in the last decade and when looking at my build, I decided it needed a completely new layout. I used rather large aluminum plate I had laying around and pulled all the good parts off of the previous attempt. I paid more attention to the filament wiring and moved the rectifier as far from the in/out tubes as possible. Three substantial component changes were made: big Edcor power transformer, a huge 600uf film cap replaced the B+ filter section, and the stepped attenuator was replaced with an Alps RK27. I only needed to buy the Edcor.
Last night I got to do a smoke test, and no hum or buzz! OK. Put on some music, and there were good sounds. OK. So I put on a pair of HD650 headphones and wow, this baby slaps.
Some questionable decisions might be the distance of the high voltage filter sections from the tubes, but nothing seems to be oscillating so that is good. Voltage is still a bit low with the 5U4GB rectifier, right around 250v. I'm not sure this is a problem though so I'm not likely going to sweat it. I'll try it with a 5AR4 at some point. Also I could probably benefit from a lower resistance choke.
I have some oak panels I've salvaged from an old piece of furniture that I'm going to use to make the chassis, so stay tuned for that. I also need to clean up some of the wiring that was done for the smoke test. Hooray!!!