Tube Amp Archive

Did you change out the pots yourself, or did that happen before it got into your hands? I have an early Mig 50 that will need an overhaul soon and it has the old pots that are prone to failure but have the small diameter shafts (ha!) on them. As far as I know the best solution is to drill out larger...

... my account didn't make the migration to the new website format. The truth is that NOBODY'S account made the changeover. I had the same problem -- when they migrated to the new website my wholesale account lost it's wholesale status, and my entire purchase history was lost. That's a bit of a PIT...

Just an update that i heard back from their support this morning and my account didn't make the migration to the new website format.

Things have been fixed and looks like most parts are still discounted as they were before for those with a Wholesale account.

Anyone else out there have a Mojotone Wholesale account who is a bit confused about the new changes? The email i saw said that a few items would now only be offered at full price but their website seems to have been updated and I am not seeing discounts for ANY items. I will reach out to them as wel...

The Blues Junior and Pro Junior run push-pull, pretty hot, and get about 15 watts RMS. There are some data sheets that suggest running 6BQ5A tubes pretty hot, and you can. The king of the type was the 7189A, which was a very stout tube, high ratings, allows 440V on the plates and 400v on the screen...

It really is tough to know for sure you are shipping an amp with reliable power tubes, especially since 2022. I have started burning in new tubes on a device I made for myself where I can monitor screen, plate, cathode, and grid current before installing them in customers' amps (when time permits)....

I'm not sure its going to be very easy to add a screen grid resistor. I just modified a couple of these for a player. Does your PCB look like this?20250227_091027.jpg Yep! That is the same PCB. Definitely would take drilling a hole or two. This is a customer amp who basically just wanted it running...

Thanks for the intro to your YT channel - I'll subscribe! As a late-comer to the internet knowledge transfer of tube guitar amp design techniques that seems to have peaked somewhere around the mid 2000s, when I was too scared to mod a Blues Driver pedal - I'm grateful for anyone still looking to sh...

I just recently stumbled across your DR103 series and thought it was really informative and well done. I’ve only been at this a short time and search for content like yours to connect what I learn from the great folks here and read from Merlin and Aiken to actual visual examples. Count me in as a s...

Thanks for providing the numbers to back up my suspicion! And you are totally correct about putting the decision on the owner of the amp. If this were my amp i would not be opposed to doing the repair and dumping some time into it. The fun part is this is a shop owned amp, so they are going to have ...

You are correct! I misspoke and this is actually the fuse on the center tap of the windings for the B+ supply. it is listed as 120mA in this schematic; however, the combo version of the amp that i have had a 160mA fuse in place which matched the associated screen printing on the PCB. All other volta...

Just got one of these little guys on the bench. It came in with the description of "having issues" and found that the volume would cut out intermittently. It ended up being a failed EL84 which then blew the heater fuse (160mA Slow Blow) as i was testing it. New EL84 tube is in but the thing absolute...

Hey! Feels a bit ridiculous to post this in a place that has so many skilled guitar amp builders, but I am a small town amp repair tech, former electronics teacher, and current electrical engineer that has recently started filming all of my amp repair videos in hopes of helping educate others on the...

THANK YOU!

I can confirm that removing the cathode bypass cap and resistor (25uF / 2700 ohm) and replacing with a red LED has fixed my issue.

The tremolo is tremming quite nicely now with otherwise all original components reinstalled.

Appreciate the heads up on this very much Sluckey!

Oh interesting.

I was just reading about this mod on Merlin's site. So it is a matter of the bias cap not being able to keep up with the demand on the tube for the faster oscillation speeds?