Tube Amp Archive

Thanks guys, I finally found my issue: I had switched two of the wires that go to the filter caps. After replacing the filter caps and wiring correctly the amp is now working great! The Mojotone layout that I was following showed one red wire and three yellow wires going to the filter caps board but...

Lynxtrap wrote: ↑Mon Aug 21, 2023 2:29 pm Are you sure the solid state diodes are soldered to the right lugs on the rectifier socket? It's hard to tell from the pics, but it looks to me like one of them is going to pin 7 instead of pin 6.

Thanks, there on 3 to 4 and 5 to 6 with the silver markings facing 4 and 6

I took a look under the doghouse and found what looks like a blown/leaking filter capacitor. I assume it needs to be replaced, but what about the other three? (which look alright). Could this be the cause of my problems? Or just a symptom?

I built a lightbulb limiter yesterday and and powered up the amp with the limiter this morning. When i put it in standby it briefly lights the bulb and slowly dims, and when I take it out of standby the bulb lights up and stays bright. This means that I have some kind of short, right?

It’s kinda hard to tell from your photo, but it looks to me like you have the orange 600 volt ground / death cap connected to your standby switch and not the AC power switch. Thanks, the orange death cap is wired from the ground lug to the upper left lug of the standby switch like this (from Mojoto...

So I added in the missing jumper under the board and put everything back together, and now things are even weirder unfortunately. In standby I get proper voltage readings on the rectifier tube, but only AC heater voltages on the power and preamp sections. When I switch out of standby to "on" the rec...

Are all three of these leads soldered to the eyelet where the 4700 ohm resistor is soldered? Thanks! It appears that I missed that jumper connection; my jumper went straight from from the top of the board to the through hole. I had to undo some wiring to get at it and I haven't gotten to reassemble...

Ok so those "1.0?s" were an operator error, wrong voltage range. Looks like the majority of the voltages are good, with exception of V4 and V5 pins 4 and 6, which read very low.

Updated voltage readings:

sluckey wrote: ↑Wed Aug 16, 2023 8:44 pm

ragamuffin wrote: ↑Wed Aug 16, 2023 7:34 pm found a whopping 990+ ac volts on pins 2 and 8 of the rectifier

Set your meter to measure DC VOLTS for pins 2 and 8 for the rectifier. No telling about the other weird readings. Most likely operator error or wiring error.

Pins 2 and 8 read 448 dc volts

https://imgur.com/a/bycXgQ6 gut shot album

Power transformer is this one from Mojotone https://www.mojotone.com/Bassman-Pro-Su ... mer-125P5D

Last night I finished assembling my second amp build, a 5f6a head with a few mods from Rob Robinette's 5f6a mod page. The pilot light turns on, all of the tubes glow, and I get SOME sound, but it's garbled/distorted and almost seems like there's a gating effect... I took voltage readings on all the ...