Tube Amp Archive

I finally had a chance to record something on the amp. First couple clean parts are with the tone stack and preamp triode bypassed, so just the heptode into the PI. The dirty parts are with the triode and TS back in, master full and gain set at just before it hits preamp distortion. So the majority ...

I've built a couple amps with hi-fi OTs, but I push more watts through them than they're rated for. One is a 8W amp with 3W iron and the other is 18W with 8W iron. I think the limited bandwidth of guitar isn't near the chore of amplifying full bandwidth hi-fi, so to get them working at bit and out o...

Compared to the voltages on the liverpool schem you are running between 30-40V low throughout the PI and preamp. With the Rks from the liverpool and the low voltages, you're running the tubes closer to cutoff than intended. But then the PI in the liverpool is 269V, which is higher than your B+ even....

First thing to check with the headroom issue is the plate voltages in the preamp. If you're running a 250V B+ for the 6AQ5s and using the dropping resistors from the liverpool with a 330V B+, your going to be running the plates really low in the preamp.

Sorry, I see what your saying now. A bridge is unsuitable because it raises the voltage and drops the current, so you need to stick to a FW. A virtual center tap like the 100R pair on a heater supply isn't going to work because it'll draw a whole lot of current at HV, unless you use values higher th...

Looking at the datasheet, the 6BQ5 at 250V is similar to the 6V6 with 250V on the plates, but pretty much every amp used the 6V6 with much more juice on the plates. The voltage swing for max power at 250V for 6BQ5 or 6V6 is only ~30V, but a typical 6V6 guitar amp might take a 50V swing. So the pream...

You can do it the same as Phil's pic just replacing the tube with 2 diodes, and no need for the limiting resistors. Lots of old radios that used selenium bridge recs did it that way too, and I've built a couple amps with recycled radio PTs, diode bridge and virtual CT..

I have some experience using tiny output tubes. There are enough unknowns using out of the ordinary tubes that there are plenty of optimizations to do before you get into finicky things like teflon vs PVC wire. If there is little clean headroom there is probably too much voltage swing from the pream...

Thanks guys, it was a fun design exercise for sure, got me digging through old books for info and even setup a rig for measuring the plate characteristics since the datasheet didn't include one. I'm very happy with the PI and power amp design, the remote cutoff tubes give a lot of nice compression a...

I recently bought a pile of old non-working radios, mainly to pluck the few ECC83s, EL84s and the iron. I ended up with a big pile of RF tubes too, and decided to challenge myself to make use of the most obscure of them in a guitar amp. There was a surplus of ECH81s which is a remote cutoff heptode ...