The Amp Garage

Maybe a failed R/J switch that is not closing in Rock setting, resulting in PAB? Measure resistance across switch pins.

Is this formula legit? (B+ voltage squared)/(Plate dissipation x number of power tubes) Example: a 50w (6L6GC x 2) build using a known PT and circuit that consistently produces a B+ of ~455vdc- 455x455 = 207,025 35 x 2 = 70 207,025 / 70 = 2,957.5; So the correct primary impedance would be around 3k...

The wire from the 16 ohm tap back to the main board is the negative feedback, so keep that on the 16 ohm OT tap. If all you want is 4 and 16 ohm outputs, you could just use two speaker jacks, one on the 4 ohm and one on the 16 tap, and eliminate the selector. I would use a switching jack for both, a...

...I want the filtercaps to have a reduced differential voltage (that is the sole goal) but, I don't necessarily want the bias voltage scheme to change too widely. So yes, it would make some sense that moving the bias ground with the HT CT to the B+reducer makes sense but, not the filter cap cathod...

A MOSFET reducer, just like a zener in the same position, just places the high voltage CT one zener-voltage below the negative end of the first filter cap. As long as nothing else is connected and referenced to the CT, this all works fine, as the high voltage winding is galvanically isolated, and w...

As you can see, I settled on three sockets, 7, 8, and 9-pin. Anything else can be jury-rigged, and you can see several examples of that pictured in this thread.

I recall one uT3 build with just three sockets, all hard-wired, two as I described above, plus a second noval for EL84's.

I believe Tony D is using uTMax https://ampgarage.com/forum/viewtopic.php?p=450229#p450229 It has been around for quite some time (2015, maybe?), originally intended to increase voltage and current capability of the uT3. The uT3+ with 400V max Va/Vs and high-current mod is more than adequate now. I ...

Raoul Duke wrote: ↑Fri Apr 12, 2024 8:28 pm Are the LM7812CT and L7812CV functionally interchangeable?

Looks that way. One is STMicro and the other is TI. There will be different suffixes for different manufacturers or things like NoPb.

FWB on an isolated winding with CT unused should not have caused a problem unless there was some error. Possibly incorrect grounding?

What I meant was that one could start with any value for R1 and Rs (within reason) and as long as they can get to half of Vdd and ~ 9v, they will achieve the desired effect. I get stuck on the different values from layout to layout thinking R1 and Rs are part of the bigger “recipe” when in fact the...

Regarding the FET: so I could start with the plans values and work from there then because the “mega” isn’t so much dependent on the actual values - but rather the end result (however you get there)? I don't understand what you're saying there. You could use the 8k2 in the divider (with the 150k) b...

Nice, good to hear it worked out, and your monitors have a new lease on life!

OT secondary has one end grounded and has very low resistance, heater winding is also very low resistance and has a grounded center tap, so yes.

Move this to the For Sale/Trade section?

Sounds fine to me. Here is a case where I've tested the unloaded voltage on a current project with the PT and choke tack-soldered to the board, Heater circuit is not connected, of course. https://ampgarage.com/forum/viewtopic.p ... 85#p464385 No fuse, I just brought it up slowly with a Variac.