Tubes 101 - Intro to Tube Preamp Design
- Thread starter vigilante398
- Start date
great primer on how tube circuits work. With this info you can pretty much analyse how all tube amps work since they’re all just variations on this theme. Just add more or less stages, more or less interstage filtering, different component values, etc.
Now we can look at the JCM800 preamp and see why it’s so bright, look at all the treble peaking on every divider, and the small bypass cap on the first stage. Wouldn’t take much to make it way higher gain too, could change the second stage to a more traditional gain stage (or just copy the first one) and bypass cap on the final stage.
Also I clearly don’t browse enough here I didn’t know you made kits for the space heater, it’s such an exploitable circuit also, easily could be modded to whatever type of gain stage you want for a ‘V1’ in front of an amp to make it high gain. And I see you’re sending PCB’s to musicding, that’s good for me!
Now we can look at the JCM800 preamp and see why it’s so bright, look at all the treble peaking on every divider, and the small bypass cap on the first stage. Wouldn’t take much to make it way higher gain too, could change the second stage to a more traditional gain stage (or just copy the first one) and bypass cap on the final stage.
Also I clearly don’t browse enough here I didn’t know you made kits for the space heater, it’s such an exploitable circuit also, easily could be modded to whatever type of gain stage you want for a ‘V1’ in front of an amp to make it high gain. And I see you’re sending PCB’s to musicding, that’s good for me!
vigilante398
Authorized Vendor
There's nothing wrong with breadboarding a preamp circuit; they're low enough current that a breadboard will be able to handle it, you just need to be extra careful about the distance between things. I used to do it that way, I designed a breakout board PCB with a tube socket and 9 header pins so I could plug it into a breadboard, and even now the high-voltage SMPS module I sell PCBs for has the pins spaced so that it can be plugged into a breadboard. That's how I used to prototype tube circuits.
These days though my prototypes are a little more unconventional because I generally go straight for a PCB layout. I've built enough preamps that I tend to know what the topology should look like without breadboarding it, then when the PCB comes I can tweak component values as needed before finalizing the design, and when it's verified I have something a little more tangible and repeatable than a breadboard.
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