Tube Amp Archive

Fantastic. I love it when stuff works. Here are a couple of mods I’m planning on doing and would love feedback. I hooked up the other 2 OT wires to create an 8ohm and 16ohm output. The feedback will always be from the 4ohm. Any problem with this? I am going to internally wire the reverb to the first...

Alright, here is what we did and what got. We moved the yellow wire to the wiper. We had to switch the dropping resistor to 3300 and the tail resistor to 15k to get to the point where the 5 pin was reading roughly between -45 to -55. With a plate to cathode voltage of 426v and using a Bias calculato...

So like this? (See pic) No. Leave the jumper in that connects the wiper to the lug on the pot that goes to the diode. The method in the pic is even worse because the power tubes will have no bias voltage at all if the wiper fails. So just like the pic but jumper the two lugs with the wires on them?...

Do what sluckey said. It will probably take a 3.3k bias range resistor in place of the 470R resistor to get what you want. With the yellow wire connected as shown, the bias voltage will default to its hottest setting should the wiper fail to maintain contact with the track. With the yellow wire con...

Work is a beast. It will probably be this weekend before I get to it. Plus I’m waiting on more resistors to come in.

Which should I try first? I’m not ashamed to say a lot of the electrical stuff is a bit over my head. Also, the main output is a switch output. The secondary is not. I am planning on hooking up the other 2 OT wires to create an output for 8ohms and 16ohms for versatility. Any opinions on that? I’ve ...

Sounds doable. I’ll give that a try and let you know.

The Joyner Boys are back again with another problem. We have a twin build that has some issues. It is half from Mojotone and half from Weber. It started as an all Mojotone but we had issues with it and decided to redo the board with turrets. Anyway, the problem followed throughout. First, the amp is...

So this is embarrassing. We got an oscilloscope and were ready to trace the signal. Before we started I wanted to make sure that the power was running correctly to the rest of the amp. It was but while doing this I noticed something ridiculously obvious. One of the caps on the loop board was actuall...

I’m sure we can do a test tone. What frequency? What would we look for on a multimeter? Also, scopes are not that expensive. I know very little about them other than they send out a wave then measure a wave in do you can see the difference. We live building amps, should we just buy one? If so, is th...

Q: Is your FX board ground attached to chassis?
A: Yes.

Q: do you own a scope and can you trace it out?
A: No

We thought of that and switch the in and the out on the loop. Same results, worked in bypass but not when on. Also, we used a patch cable when testing to make sure we were not doing something stupid like leaving a pedal unplugged.

We are having problems adding Mojotone's effects loop to a Weber 6O100. When the loop is off it bypasses fine but when it is on it kills the sound almost entirely (if you turn everything up you can barely hear it). Contacted Mojotone but they just sent a new one that had the same problem so I am ass...

We are using Tung-Sol 6550 which according to the calculator and data sheet are 42 watt. I’ve been calling them KT88s mainly because I forgot we went with the 6550 at the beginning and only realized it when I went to bias it. Also, I kinda thought 6550 was another name for KT88.

I based the number off of the bias calculator. I went with the average.