Tube Amp Archive

just to wrap things up: grids-to-ground were fine, output transformer tested fine since grids were fine i started checking cathodes... and that's when i found that the 150k cathode resistor on the phase inverter measured open! works now, only issue is that the reverb won't turn all the way off. but ...

I've got an ampeg j-12-r (https://el34world.com/charts/Schematics/Files/Ampeg/Ampeg_j12r_.pdf) I'm looking at for a friend and I'm scratching my head. with guitar it's making almost a bitcrusher sound and trailing out quietly. if i wait a few seconds and hit the strings hard again the volume will in...

would technically be a violation of the paypal terms of service to have a payment marked "friends and family" rather than "goods and services" you'd have no recourse if the dude mailed you, say, a 60lb bag of sand instead of an amp. if i'm getting a good deal i prefer local purchase with cash vs sha...

here's what i have on the lab series. i also have info on the l3 (killer little combo!) but it's completely different than the rest of the amps in the series

I see a lot of bat eared guys using 12-19k and there are a lot of TW amps with 22k on the first grid. I live about three miles from a military flight path. I have to cut <40kHz. yeah i have a local npr affiliate in my small town. had to add a grid stopper to the low gain input of a master volume su...

pdf64 wrote: ↑Wed Apr 12, 2023 8:41 pm Grid stoppers act as part of a low pas filter, whereas coupling caps act as part of a high pass filter.

yeah i confused some things here and muddied the waters. this is what i get for trying to multitask

Reeltarded wrote: ↑Wed Apr 12, 2023 8:16 am Keep these simple circuits as late as you can with the high cut being great just before the PI input

again not high gain, but fender used a lot of 500-1000pf coupling caps right before the phase inverter which follows this suggestion

i'm never really that scientific about it. generally use 10-39k even on lower gain (like fender) builds for grid stoppers (every preamp stage has one, not trying to save a few pennies like fender usually did). if it's something high gain 100k or 220k like soldano did that being said, it's an interes...

is it just a small tuning coil for an oscillator? if it's a big heavy hunk of iron i'd suspect either a measurement error or a bum/shorted part

which baldwin organ did it come from? i usually keep better notes but the big ole choke i pulled out of a 2x6l6 baldwin organ measured 7H and frankly would've been overkill for a pi filter in a champ. you should be able to get away with the deluxe reverb-style choke (i used the bigger 90ma fender-st...

i mostly buy jj because the philosophy i've adopted from someone smarter than me is that if it sounds good with jj tubes, it'll sound good with any fancy tube one could throw in it

easiest way to figure out what it does is to sketch out the pot at its rotational extremes. all of the way to the treble side it acts like a 'bright cap' on the volume control. all of the way to the bass side it's a capacitor to ground. capacitor acts like a short to ground for higher frequencies bu...

for what it's worth, a sick solid state amp will continue to get sicker the more it's turned on. a current-limiting device (like a lightbulb limiter) is absolutely mandatory for troubleshooting. i also wouldn't plug into a load until it's sorted

xtian wrote: ↑Wed Mar 01, 2023 10:47 pm For small quantities (<100) tubesandmore.com (cedist.com) is great for carbon film: https://www.tubesandmore.com/products/r ... -tolerance

if i remember correctly it's cheaper to buy 100 than it is to buy 20 once the quantity discount is factored in

ahhhhh i get it now. i would look into the trainwreck type 2/lar mar master volume, replacing r37 and r38 with a dual-gang pot