The Amp Garage

Thanks, guys. Feedback and questions will inspire improvements! Tom, the beauty of the numbers is that you can see where your operating points are, how they move, and what will happen to the frequency response as you change the values of the R's and C's. Phil, yea, I don't think you or your clients ...

Here's something I've been working on for a while that others may find useful. This gathers up knowledge I've gained from a variety of sources including this forum and, notably, help and encouragement from the Valve Wizard. Constructive feedback of any kind is welcomed, as I'm sure it is not perfect...

Ron, Really great stuff here! I'll definitely have to take some time to read through this material. My $0.02: Skimming through I noticed that on page 46 of the build guide you have: 4. Using a DMM, Place the black negative lead onto a good chassis ground. With the red positive lead, check and adjust...

Great thread here; lots of useful stuff! ...To me it is one of two things, the OT has the wrong impedance for the voltages, or the power supply lacks the headroom needed. Both of which as pretty easily to check and if I have another one here I will check both. Can you elaborate a bit on this? Re the...

Martin, great job!! If you're doing a dead on 124 clone this looks good. However, I'd probably consider going a little more generic on the back panel, lose the square switches, adding an impedence switch. losing the auxillary outlet and doing a cutout for a din jack instead of the XLR. Thanks! I do...

Not being happy with any of the currently available D-type chassis, I decided to try to make a drawing from the #124 info. I think the attached file is pretty close now after a couple of days of nudging things around to agree with pictures and known part dimensions. Any comments?

MPM

My God, all the jack and switch mounting nuts are oriented the same!! :shock: I think someone previously observed that the nuts on the front panel toggle switches have been positioned "in phase." Another fine example of this type of obsessive behavior can be seen on a certain record-setting airplan...

Not to 'jack this thread (and you know that means I'm going to try...) What other examples of Dumble tones are out there? Steely Dan is one of my favorites, as is Joni Mitchell's Miles of Aisles (a desert island disc for sure) and I'm aware of the David Lindley and Jackson Browne associations with D...

It seems like balancing the idle currents to zero out the net current through the OT primary (the static part) would always be a good thing, and then balancing the "effective" Gm on each side with the PI trimmer (the dynamic part) would be a way to get a symmetrical output (or un-symmetrical in a co...

Not to hijack the thread, but BB is like George Burns. Those stogies should have killed Burns in his 70's, but nope. BB's been fat for decades and as big as Shamu for about a decade. Obviously, he's relatively healthy as far as his cardiovascular system goes. At 83, he's way past the biblical three...

Interesting discussion on the sonic effects of PI balance.

Given this unusual feature, I wonder why HAD did not also include separate bias adjustments for the two sides of the power stage?

MPM

Let's say the relay contacts are open and there is no resistor across them. There will almost certainly be a voltage difference across the contacts, and when they are closed a pulse will be fed into the signal path, causing a pop in the speaker. The resistor is there to reduce the voltage differenti...

There are a lot of you's here but it looks right to me. I just redrew that part of icracer's schematic myself in order to get a better look at the topology of the tone stack and the effect of the R/J switch. The 22M resistors are wired across the relay contacts so there is no "pop" when the relay is...

Structo, thanks for the comment. The internal baffle is the heavy line with the ~45 degree bend in it. I also thought about letting air in from the front, and this is really the same idea, i.e. forcing the convection flow to move from front to rear across the entire chassis (dashed line) instead of ...

I've been sketching up plans for a tubes-down head cab a la #124, and recalled some earlier discussion about the internal temperatures getting quite high.

Adding a fan is one option, but has anybody tried using an internal baffle as shown in the attached drawing to improve the airflow?

MPM