Tweet
I've been waiting for about 7 weeks for tube sockets I ordered from China. They were lost for about 3 weeks by China Post and have now been in U.S. customs for almost a month (the seller was awesome. They're shipping me a new order on Monday even though it's anyone's guess which will arrive first. Either way I'll have 54 new sockets instead of 27)...
Anyway, last weekend I bought a PT and OT for a Valve Jr and decided I'd use some sockets I already had (not usable on the PCB I've got for the breadboard) and stick them in a computer power supply (which has just enough space to build a Valve Jr). So right now, half of the power supply chassis is on my breadboard (see photos) with 2 sockets in it. I built the circuit last weekend, but couldn't get it working. Part of the problem was my wires were way too long. I re-laid it out this morning and trimmed about 5' of wire in the process and it worked right off the bat. The sound file was the very first time I played with it. I was just checking the range of the gain and master volume.
The circuit itself is actually a variation of the first Valve Jr. I didn't have any 2.2K resistors for biasing the preamp stages, so I ended up going with red LEDs (Vf=1.6V) and that seems t work fine, though I"m going to do a little experimenting.
I used a 1M grid leak on the first preamp instead of the 68K the schematics call for. And I used 56K grid stopper because I didn't have any 68K resistors either (got some on order). And obviously, I added the master volume.
I'm really, really pleased with the way it's worked out. It's not completely quiet, but for not being inside a chassis and the wires running through the air, it's pretty darn quiet.
When I first decided to do the breadboard idea, I was afraid it was going to be like those toys you buy when you're a kid that look so awesome on TV but aren't nearly as cool in real life. I didn't know if it was going to be as easy a platform to work with as I imagined. The good news is, it totally is. I can't imagine an easier way to breadboard amps. I highly recommend building one of these. It took me about 45 mins to an hour to breadboard the Valve Jr. from scratch (having already cut the hookup wires and having the components selected) using just a little flathead screwdriver.
Oh, and there are 3 transformers there. The two silver ones on the far side are the PT and OT for the Valve Jr. The black one is a Thordarson that I use for the filaments. The Thordarson plugs into the wall and the Valve Jr PT plugs into the variac, so I can maintain stable filaments. Because the Thordarson isn't loaded on the HT, each heater line runs through three 1 ohm 1W resistors in parallel (for 1/3 ohm) to drop the voltage down to 6.29V (otherwise it's up around 7.15V). You may also notice I ran the filament line under the board. It was just to kind of have it away from the other stuff.
Anyway, last weekend I bought a PT and OT for a Valve Jr and decided I'd use some sockets I already had (not usable on the PCB I've got for the breadboard) and stick them in a computer power supply (which has just enough space to build a Valve Jr). So right now, half of the power supply chassis is on my breadboard (see photos) with 2 sockets in it. I built the circuit last weekend, but couldn't get it working. Part of the problem was my wires were way too long. I re-laid it out this morning and trimmed about 5' of wire in the process and it worked right off the bat. The sound file was the very first time I played with it. I was just checking the range of the gain and master volume.
The circuit itself is actually a variation of the first Valve Jr. I didn't have any 2.2K resistors for biasing the preamp stages, so I ended up going with red LEDs (Vf=1.6V) and that seems t work fine, though I"m going to do a little experimenting.
I used a 1M grid leak on the first preamp instead of the 68K the schematics call for. And I used 56K grid stopper because I didn't have any 68K resistors either (got some on order). And obviously, I added the master volume.
I'm really, really pleased with the way it's worked out. It's not completely quiet, but for not being inside a chassis and the wires running through the air, it's pretty darn quiet.
When I first decided to do the breadboard idea, I was afraid it was going to be like those toys you buy when you're a kid that look so awesome on TV but aren't nearly as cool in real life. I didn't know if it was going to be as easy a platform to work with as I imagined. The good news is, it totally is. I can't imagine an easier way to breadboard amps. I highly recommend building one of these. It took me about 45 mins to an hour to breadboard the Valve Jr. from scratch (having already cut the hookup wires and having the components selected) using just a little flathead screwdriver.
Oh, and there are 3 transformers there. The two silver ones on the far side are the PT and OT for the Valve Jr. The black one is a Thordarson that I use for the filaments. The Thordarson plugs into the wall and the Valve Jr PT plugs into the variac, so I can maintain stable filaments. Because the Thordarson isn't loaded on the HT, each heater line runs through three 1 ohm 1W resistors in parallel (for 1/3 ohm) to drop the voltage down to 6.29V (otherwise it's up around 7.15V). You may also notice I ran the filament line under the board. It was just to kind of have it away from the other stuff.
Attached Files
Comment