| Electronics > Projects, Designs, and Technical Stuff |
| Calling all vacuum tube pros: A power supply question |
| << < (3/4) > >> |
| T3sl4co1l:
--- Quote from: vk6zgo on December 12, 2018, 12:45:05 pm ---It's basically a lot of "woo" crap designed to bamboozle gullible "guitar amp" nutters. Back in the day, when there were thousands, nay, millions of pieces of tube equipment in service, such stuff was not used. Heater supplies were just plain ac --- no DC bridges or hinky connections back to the HT line to be seen! --- End quote --- Well, for what market sector? The cheap consumer crap is what's abundant, what everyone remembers; rarely if ever seen, are the pro audio systems of the day. (I haven't seen any myself, but I don't know if you have.) Even that's inconclusive, because they would've opted for PQ types: industrial, long-life, low noise (by design and testing). Making do with junk is probably somewhere between contemporary pro-sumer sector, and modern anything. Not to say there isn't "woo" here. Oh boy is there ever "woo" here! --- Quote ---The only things that had HT on their heaters were directly heated rectifiers, & that's because the heater & cathode were the same part. --- End quote --- Well, various other special cases -- low Vhk cascodes and followers (6DJ8?), high voltage parts (indirectly heated rects were on separate circuits, as often as not, I want to say..??; damper diodes are rated for high peak voltage in one direction only; etc.). But by and large yep, 6.3V was usually grounded, and maybe you had a "HUM BAL" trimmer (either end to heater power; wiper to GND) that did SFA anyway. ;D Tim |
| In Vacuo Veritas:
--- Quote from: vk6zgo on December 12, 2018, 12:45:05 pm ---It's basically a lot of "woo" crap designed to bamboozle gullible "guitar amp" nutters. Back in the day, when there were thousands, nay, millions of pieces of tube equipment in service, such stuff was not used. Heater supplies were just plain ac --- no DC bridges or hinky connections back to the HT line to be seen! The only things that had HT on their heaters were directly heated rectifiers, & that's because the heater & cathode were the same part. --- End quote --- Bullshit. There was a cathode to heater max voltage rating and Tektronix certainly *did* connect some tube's heater's to a higher voltage. Unless you consider physics "woo". |
| cvanc:
Here's a little update. Please see attached image. The voltage doubler *does* have a DC path to ground, at the junction of C30B/C/D as some of you have mentioned earlier. The drawing is confusing but it actually SHOWS this ground down at the filter caps for the filament supply. The final cap in the filament circuit is C30A, which is, of course, the 4th cap of the C30 quad cap, and of course all 4 caps are in one of those old style twistlock metal cans. So one mystery solved. I still wonder why the B+ doubler connects down to the filament voltage and basically 'sits on top of it'. :-// Thanks for all the thoughts and suggestions, it's always great to kick stuff around with you folks here. |
| T3sl4co1l:
I noticed that earlier, that C30 has its odd section out there, but didn't put it together that they've drawn it wrong but it's connected correctly anyway -- good old fashioned multi-part metal can caps! Tim |
| SeanB:
They wanted a little more HT supply out of the standard HT transformer, so simply biased the HT rail with the filament supply to get this. Probably a transformer that was both in stock, common to many models and thus low cost to them, but just not enough voltage to give the rated power. Without the added voltage most will have a B+ of around 275V unloaded, and I would guess the filament supply is a 24VAC winding, so they got around 35V of boost, giving the 310V HT rail they wanted after the RC smoothing, with only the use of a standard to them transformer, that gave 115VAC and 24VAC as secondary voltages. Cheaper to have the extra capacitors and diodes than to pay for the extra copper to wind a 250VAC winding onto a custom transformer as well. Using a RC filter also saved a very expensive LC filter on the HT rail, despite the resistor dissipating a lot of power, and the associated voltage loss, more than made up by the extra 35V supply to otherwise waste. LC filter would have under 5v loss with decent hum reduction, but the size and extra cost, over the 1N4007 diode and the extra 40uf 400V capacitor. |
| Navigation |
| Message Index |
| Next page |
| Previous page |