The Amp Garage

Alexo wrote:Tap the hot lead, or one of 'em.... if it squeals, swap the primary wires and you'll be fine. I think the scientific approach is to wire your primaries in such a way that it won't be a royal pain in the butt to swap them if things go awry.

Thanks ya'll. I like your idea of "science", Alexo!!

How do I tell which side of the output tranny should be used as the tap for the negative feedback loop? The tranny I'm using is a Hammond 1750N. It has a common wire and three other wires, one for 4/8/16 ohm operation respectively. Do I use the common wire or "8 ohm" wire (as I am using an 8 ohm cab...

Hired Hand, Keep in mind I started this thread, so I'm certainly no expert, but I think the impact of changing the values of either the resistor or the capacitor will be a shift in the rolloff frequency. I think the presence circuit forms a low pass filter. As I have learned from this thread, no NFB...

Hey Phil and Martin, Thanks a zillion for your replies. It totally makes sense to me now. I'll be using just what you suggested Martin, a 100K resistor across the pot. After I sat down, digested what you said and then broke out a pencil and paper and ran through a whole mess of combinations using th...

Hey Gang, In TUT, KO'C suggests the inclusion of a safety resistor strapped across the bias pot. How would I go about calculating the proper value for that resistor? Here's the bias circuit I'm using. I added the second pot to give me discrete control over the bias for each tube. I know many of you ...

Always contrive it so that if the pot failed your bias voltage would go up to full negative. Hey Ronsonic, Could you expand on how exactly you would do this? In TUT, KO'C talks of a safety resistor strapped between the bias supply and the wiper of the pot going to the grid. How do you calculate the...

I have replaced a 4.7K feedback resistor with a 1M pot. When I run the pot all the way up (i.e. little to no feedback), my presence control doesn't seem to do a darn thing, which seems to make sense as it appears that the presence circuit is dependant on the feedback voltage. Right?

ted

What? you didn't like my answer Bob-I, Actually, I just about blew beer out the nose!! While not the technical answer I was looking for, I suspect there is much to be said for heaven and the Magic Smoke. I promise I will stop messing around with the the settings of my amp. I sure don't want to mess...

Hand vibrato and control over the strings

As I said, I am not a guitar player. I am simply plucking a single open string while muting the others with my hand. There is no hand vibrato or control over the strings, period. I simply don't have those skills.

Hey CaseyJones, With all due respect (and I mean that, I've learned a ton from you), on this, you're just wrong. I can't play guitar. All I am doing is plucking a single open string to get what I'm talking about. I have the preamplification stages all dimed, and the feed to the final stage of amplif...

OK, so I was messing around last night with my amp (a Dumble clone) and I cranked up all the preamp gain stages all the way but I set the level to the power amp section as low as it would go. The resulting sound was very distorted (in a good way) but the overall volume was quite low (you could easil...

Hey CaseyJones, As usual, I have learned a ton from you. I have also learned that a 1/2 watt 10K pot can't take the power, apparently. It worked for a while, but when I cranked it up, it appears to have fried. Well, for the moment, I replaced it with a 50K pot, it'll probably fry too, but maybe it'l...

Yo Ears,

I can't count past ten without pulling off my shoes and using my toes! I guess I'll have to opt for the trial and error method...

Ted

I mounted the pot on the back of the chassis as I kinda guessed that it wouldn't be a front panel type of control. I also noticed what you mentioned...the presence control actually does something now. Originally, I had the output tranny wires reversed, leading to horrific motorboating. I didn't know...

I've got a pot in place of a fixed value resistor in my negative feedback circuit. What am I doing to the amp when I adjust the resistance from 0 ohms to 10 Kohms? Am I doing something that will cause harm? The original circuit called for a 4.7Kohm resistor. I notice an increase in volume when adust...