The Amp Garage

I see the 5k1s on the power tubes at grid 1 are soldered directly to the leads heading back to the main board (like an old Marshall or Vox). This looks simple enough, but just wanted to check as to the correct mechanical connection before soldering. Is this a “J” hook situation or is there another ...

Stephen1966 wrote: ↑Wed Apr 17, 2024 12:48 pmI'm also thinking that the voltages in this amp are not going to be as high as in the first Tweedle Dee, stock transformers and only three filter stages with a stock (value) 250 Ohm bias resistor on the power tubes.

5Y3 rectifier will make a big difference too.

To be strictly correct in eliminating position 1 you would do this:

I'm having trouble following you. Maybe refer to the TP (test point) number where you are measuring? What is "PT"?

Good to hear you are happy with the result! Yes I have made some small adjustments re the schematic at the top of this thread. What you posted just above is the latest. There are a couple of ways you could do six positions, one would be to recalculate all of the resistor values to keep the "taper," ...

One example of a Tweedle Dee has been documented already thanks to CW, but I suppose there might be some interesting evolutionary changes in this later example.

Take a look at the free .pdf download Phil S posted to see if you really want a hard copy. You can get virtually any tube data sheet from https://frank.pocnet.net, and that is what most of the 750 pages of RC-30 contain, and in an abbreviated format. The remaining 200 pages cover circuit theory and ...

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.