The Amp Garage

1) If I use typical toggle switches for the DPDT´s (not the small blue ones, but the big power ones), those are non shorting ones, so when I switch from one position to the other, momentarily there will be no load to the output transformer, right? Will that be harmful for the amp? Any mod I can mak...

Vibratoking, yeah, made a mistake there, confused myself while typing. What do you think about the power dissipation question?

Hi guys. I´m going to make my first resistive attenuator, for taming my AC30 inspired amp. Since it´s my first, I´m gonna make a simple one, to test the concept, if I like it in use later I might make an Airbrake. So, I came across this one: [IMG:1000:667]http://i68.photobucket.com/albums/i5/Morocot...

Wow, Ampdoc1, that´s a novel idea! Unorthodox for sure. How about the tube life and/or bad consequences? I´ve read numerous times that the heaters V has to stay +-10% of 6V3 or bad things will happen... And to get DC for power tubes, you´ll need some big ass regulator that can handle a few amps of c...

Well, I looked up the YJM Marshall. Wow! It has a microcontroller controlled (ahem...) power section. Seems to be it controls the screen V, Bias V and something else at the same time. Not DIY stuff, I think. But very clever, it seems to be. Of course judging by a Youtube video is difficult, but seem...

Hi guys. I´ve been experimenting with the MOSFET B+ regulator, currently regulating the power section only. Installed it in a AC30-ish amp, EL84´s in cath bias. Had some trouble with crossover distortion on low voltages, lowered the PI coupling caps but it didn´t dissappear completely, in the lowest...

OK guys. i tried the switch with a 1M R as suggested by Tubeswell. a small sliding 2PDT. First turning the amp off and then, with some trepidation, with the amp on. No problem at all, no sparks, shorts, blown parts or elctrocuted people (me). Just a mild pop. Sooo, I guess you can do it "live". Will...

Tubes, thanks for the suggestion. That book talks about the EF86, right? I supposse the value would be different in an EL84? Sounds as something I should try but will it be the same on an EL84? I mean, increased current, voltages...

Well, that. Can you switch it with the amp on? I´ve read people saying no, it has to be off or in standby. My question is, why? Is it because you will get a big POP? Or will you bust something? Assuming the switch is a break-before-make type, I think this: when pentode connected all is fine. When th...

So Pops, that was for changing the tube in use. I assume it was a single ended parallel power tubes amp? How would this switch interact with the active tube? Or it won´t at all? Cause with the grid grounded, there would be a path to ground trough the grid R´s of both tubes in a a pair. Let´s say the...

Printer, exceptional explanation, thanks a bunch for taking the time! More food for thought. I´ll recheck my output transformer for specs. They are made by a local winder (Argentina) that makes high quality work. Some local amp builders have compared them to Heyboers and they came out not worse or b...

A tube is basically a voltage controlled resistor. We can bias it more on or off, allowing more or less current through it. If we want to allow little current through we cause the impedance between the cathode and the plate to be very high. With it not supplying any amplified signal to the load (th...

What I like about this is that the output impedance doesn't change,... You may want to rethink this since you only have one set of tubes driving half the impedance they are used to. Printer, that was more of an assumption/question than a certainty... I´m not that sure how the whole impedance thing ...

Two things i can think of to do: Ground the input of two grids, shouldn't take much of a switch and will not pop. Take two tubes out and unhook one speaker. Nice idea to ground two grids...i´ll try it! The "take two tubes and change the speaker load" idea will of course work, but my idea has the ad...

(I knew I shouldn´t have used the word "bedroom") First of all, thanks all for the answers. My last answer was kind of in a hurry, had to leave to help a student with his guitar buy. What I´m trying to do is, try to get the lowest possible power out of this AC30 type amp to be able to crank it and g...