The Amp Garage

Pretty cool! It has gotta feel good to see something you no doubt spent many many hours drawing up become reality.

Are the four fuses for the PT HV secondaries and heaters?

Mike

Why not just build a 50w 1987? It would probably be cheaper and easier to find transformers for a 1987 than the 20 watt thing. The 50 watter would only be a few decibels louder than the 20 watt. And neither one would really be a bedroom amp (even at 5 watts). For sure a hand built 1987 would be a ni...

No one close to me has any idea what they are or their market value (collectively maybe a couple of thou'?) I've also got a couple of 60's Gibson amps, which, in some circles, have almost achieved sub-boutique status. I'm not ready to part with my toys. Not yet. Seriously, I don't want them to end ...

I took the volume pot out of the circuit and it tested 1M but I’ll definitely test the treble pot as well. For what it’s worth, the tone controls affect the sound coming through the speakers. If you tested the pot just end to end for being near 1M *also* test out the center wiper. If this connectio...

... Removing bright switch removes all signal Bypassing tone stack removes signal ... The two bolded items consfuse me, but maybe they help narrow down where things are getting dumped? Yea. These are two new bits of information. Your volume pot may be bad and/or the ground connection to the volume ...

Do you have a smart phone with a headphone jack? If so, you can make a crude signal generator with it, a coupling capacitor and a cable. There are many signal/function generators out there for smart phones. Most are free downloads. Then rig up a cable from the headphone out with one of the positive ...

It is a common thing to miswire the input jack so that the incoming guitar signal does not have a ground reference and is floating. This might cause what you are hearing. With the amp off and an instrument cable pugged into the input, measure the resistance from the tip of the cable to the chassis. ...

This is sorta a scientific wild a$$ guess based on it being quite and muffled. Maybe the tone stack is not wired correctly and or has a bad pot or something. Try lifting the tone stack out of the circuit by disconnecting the mid pot from the ground buss. Does that change anything?

Mike

Nice! For posterity, you should post some sound clips! :) I need to bust out some trimmers and play around in my 4 stage SIR #39 type thing. I like the idea of trimmers on the cathodes balance the clipping. I think this is is how the SLO ended up with a 39k cathode resistor. He was trying to make it...

I strongly recommend putting a FRED in series with each rectifier tube anode. This has essentially zero effect if the tube is operating normally, but if the rectifier shorts, the FRED stops the first filter cap or the PT from dying. A few questions about putting diodes in series with a tube rectifi...

Unless I missed something (which is always possible :), it looks like your power supply has no shorts to ground all the way to V1. But something is drawing excessive current and taking out the mains fuse when you go off the limiter. How bright is the bulb when on the limiter and no power tubes? It s...

Pull the output tubes and plug the AC cord straight into the wall outlet. Recheck the voltages on the power tubes. Those readings are with no power tubes. And if I plug straight to the wall, I blow a fuse. Just to clarify the situation. Does the fuse blow when plugged straight into the wall with *o...

I took some voltage readings around the circuit. Numbers in parentheses are with the standby switched off (to the "operate" position). C21 + side: 0v C21 - side: -35v C22 + side: 0 C22 - side: -28 /// Without knowing which layout/schematic these R and C numbers refer to, it is difficult or impossib...

I redid my entire PS section and I’m still blowing fuses (the indicator bulb blows too when I turn it on, no tubes). When I run it through the voltage limiter, everything fired up fine, but straight into the wall, poof. Carefully measure some voltages while it is on the limiter and post them. That ...

I'm not sure it can have an unused triode and still be a TW circuit with a Cathodyne PI. That would be true if it had a LTPI. Therefore, I believe it's something like the following: That has 3 gain stages with pretty much no attenuation between stages ('cept for the tone stack). This is the same as...