Tube Amp Archive

Ha ha!!! I cleaned it for the photo. It was a disaster.

And it's done.

Use the tone control on your Les Paul... It is much more effective with this circuit than with others. Doing that as well. The pickups in my Standard are MCP Detroiters, so they are not only kind of hot, but they don't clean up the greatest. My Replica is out at the moment, but it has Wizz in it an...

Good to hear. I was wondering about the hum you mentioned earlier and if there was some other issue to resolve, but apparently not. Where'd you end up with the resistors in the bias circuit? I think the hum was due to having the chassis open on my bench, which is in a room completely lit by flourec...

Just reporting back. Got the 1 ohm's in and biased up properly and finally got to jam on this thing. Sounds friggin awesome! What a fun amp to play. I really like the way it feels, especially with the highest bright cap engaged with my LP. A little too bright, but so much fun. I think going to a 250...

Oh, totally agree. I just tagged the 1 ohm in to make sure I wasn't going crazy. I'm going to grab my Fluke and a couple more 1 ohms on Tuesday. Until then, im hoping tomorrow to finally hear this thing, with my Power Station as it's really really loud and I have children... and I like the paint how...

On, I only had one 1ohm resistor on hand so only one tube has it. I'll have to get another one from work on Tuesday to really check. The tubes are matched of course though.

Okay, I put some JJ EL34s in it. 395V at the plates. Pin 5 reads -24V. Voltage across the 1 ohm is 41mV. This is just over half the bias pot sweep. So with the JJs it looks like it's working just fine. Maybe I did have a marginal power tube?

Yeah, I understand. I'm just surprised that the two values that seem to be the most common (150k and 220k) both aren't getting me to the correct bias range. Oh well though. We'll see what happens with both different tubes and a value in the middle. Thanks.

I can't seem to get both the bias current and the pin 5 voltage in line with what should be expected. The exact voltage on pin 5 doesn't matter. The voltages on pins 3, 4, and 5, and the current you measure will all be varying as you change the bias pot, but all that matters is that you hit the dis...

Here is a picture of my board. It shows I've got the correct values at least. Ha ha.

If your B+ is around 400V then the rest of the secondary voltages should be pretty much as expected. If you want more idle current, increase the 220k, or decrease the 47k in front of the bias pot. Either way, you need to make the pin 5 voltage higher, meaning a bit less negative. This doesn't make ...

Would a lower wall voltage cause this? My wall voltage is about 112-115V.

My bias supply is the same as the schematic/layout. No variation other than the bias feed, which is 220k right now.

I could try different tubes, but I don't think it'll make a difference.

The 1 ohm measures correctly.

Put the 220k back in and try the measure the bias across the 1R resistors... With the 220k in there, I get 412V at the plates, -28 on pin 5, and 42mV on the 1 ohm resistor. This is at the lowest setting on the bias pot. So, if I'm understanding this correctly, it looks like I need a bias feed resis...

Okay, so I think my meter was causing an issue, so I went to the resistor method. I set the bias to 35mA and the plate voltage dropped to 400V. This is still a pretty cold bias. The max the bias will put out is about 38mA, so my bias range isn't even high enough to set 70% dissipation, which takes ...