Lab RAT - an unorthadox take on a classic

[PRR]

I don't coddle power supplies either. Rectifier current rating should be much more than the transformer (not the load). If I am bored I might look at main cap ripple rating; but in audio gear we usually throw so much uFd per Amp in there that sheer bulk ensures tolerable ripple.

Ask your power company. After a summer power failure, they will just throw the breaker ON for thousands of houses. The start-up surge of the thousands of air-conditioners greatly exceeds the nominal rating of all the transformers. The system goes "HHHRng" for a second, and power is up again.

[vigilante397]

Got my 9AQ8 today and I have to admit feeling a little underwhelmed. The convenience of 9V heaters is brilliant, but it is quite a low gain tube. From my quick breadboard testing I think it would make a fine clean boost, and I may try it with 9V on the plates like a valvecaster, but with 180V on the plates it's just too clean to be useful to me.

[vigilante397]

I'm allowed to necro-bump a topic if it was my topic to begin with, right?

I never updated this because I was working on this before I actually knew what I was doing, so I put together a PCB and had it fabbed, then when it came back it didn't work so I just gave up on the project. Fast-forward to a couple weeks ago, I was getting ready to put in a PCB order and one of my good friends asked "what ever happened to the Lab Rat?" So I dug up the schematic (the file was long gone, I referenced the one in this thread), made a couple changes, and sent it out for fab. It came a little bit ago and I got it put together and fired it up, and was very pleased with the results.

The changes I made over the previous version:

• used SMD instead of through-hole, except for the LM308 and clipping diodes
• ditched the baxandall EQ and put the filter control back in, but wired it backwards with a C taper so it behaves like a typical tone control
• used a 6N21B tube instead of a 12AX7 so I could fit it in a 1590B
• changed the boost section a little, getting rid of the input cap in favor of a more typical grid stopper resistor
• ditched the diode on the ground pin of the regulator so the heaters run at 6V instead of 6.3V

Here's an updated schematic:


Here's a semi-organized gutshot:


And a quick phone pic of the outside: