DG-SE1 Tube Amp Build, Part 1: An Awesome Single-Ended Circuit
ฝัง
- เผยแพร่เมื่อ 1 ต.ค. 2024
- Part 1 describes the DG-SE1 circuit and modifications for the AMP 196-00. The DG-SE1 was designed by Dave Gillespie and shared on Audiokarma.org. The starting point for the design was the Magnavox 8600-series console amplifier. I've built three DG-SE1's, two on the 8600-series chassis (with a third underway) and one on the AMP 196-00 chassis. This video series focuses on the AMP 196-00 build, which I completed for a friend in July and August 2022, but includes footage from other builds as well.
Part 2 will describe the planning of the build on paper. Part 3 will describe the modifications to the chassis and the installation of the major hardware components. Part 4 will describe the wiring of the amplifier, and Part 5 will describe the bench and listening tests.
![[Full Episode] The Restaurant War Thailand ศึกพ่อค้าซ่าแม่ค้าแซ่บ Episode 2 | 29 ก.ย. 67](http://i.ytimg.com/vi/r3lfLNH6Ke4/mqdefault.jpg)
Interesting walkthrough, but why would you want to connect a high DC voltage across the speaker terminals?
I didn't mean to imply that you would. Nor would you want to put a high AC voltage across speaker terminals. Without a transformer, you'd block the DC with a capacitor.
I re-watched the video because I was puzzled by your comment, but now I'm even more puzzled. Where did you get the idea that I was connecting a high DC voltage across the speaker terminals?
@@Lancaster_Hi-Fi Do a freeze frame at 9:55. At the output transformer's speaker winding, note that one terminal (green wire) is connected to ground. Now trace the other speaker winding (black wire) backwards and note that there's a 10k resistor and a 150k resistor in series, which in turn is connected to a 255 volt DC source. That's 255 volts DC being fed to the speaker terminals.
@@1834RestorationHouse The 150K resistor is the upper leg of a voltage divider, where the lower leg is 820 ohms. That divider sets the cathode bias voltage to 1.46 V. Ok, that 820 ohms is actually in parallel with the 10K resistor and the speaker coil in series, so the effective resistance is a little less than 820 ohms. In any case, the 10K resistor and speaker coil form another voltage divider. The coil has a very low DC resistance (i.e., much less than the 8 ohms impedance seen by AC signal voltages), so the DC voltage drops to nearly zero across the 10K resistor, and the DC voltage applied to the speaker terminal is negligible. The 10K resistor in parallel with the 300 pF capacitor is the feedback network.
hi ,you put 120 ohm on bias cathode to measure cathode voltage ,if i got single end kt88 can i put a 120 ohm to measure voltage bias like your shematic or other resistance value .thanks
I don't know. If the tubes are grid, or fixed, bias, then you can put a 10 ohm resistor between the cathode and ground. The resistor will allow you to measure the bias current without significantly affecting the bias and also give you a sort of fuse to prevent runaway current and redplating. If the tubes are cathode biased, as in the circuit in the video, the bias current is determined by the value of the cathode resistor. If you want to be able to fine tune the bias current, then you can use a variable resistor in combination with a fixed- value resistor. You need the fixed value to determine the bias current and the variable resistor to change that current. Often, though, cathode- biased circuits eliminate the variable resistor. Sometimes these are called auto- biased, but it really just means cathode bias that you can't adjust.
I got single ended kt 66 cathode bias @@Lancaster_Hi-Fi
Really enjoy the videos thanks. I have a Yaqin MC-13S, really like the amp but have found a mod to bring the preamp plate voltage on the 12AX7 down from about 280 V to around 130 V using a zener diode. Supposedly makes the preamp more stable since there's no need to have the plate run that hot. Any ideas? If you're in St Louis, stop in for a beer sometime.
This looks like an exciting series. Thanks for the solid content-
Thanks!
the rectifier will not fry ....
Have you built one with the 6V6? If you did, what subjective differences do you hear betwren the 6BQ5 Vs 6V6 versions? Thanks! And thanks for sharing all of this in detail..
I have not. I have built similar push-pull amps with 6BQ5 and 6V6. The 6V6 can maybe deliver a bit more power, but it has lower gain and therefore requires greater amplitude at the grid for full power at the plate. To achieve similar sensitivity from similar input and phase-splitter stages requires decreasing the negative feedback, and so the resulting amp has greater distortion, and the difference is visible in the scope at lower frequencies. That is, for the same amp, decreasing the feedback to change the sensitivity from 3 Vrms to 1.5 Vrms significantly degrades the signal below 100 Hz.
In my personal opinion two stages amplification is not enough to apply loudness or any tone correction and Hi Fi (up to my experience) cannot be obtained. But will it be used as stereo HI FI home audio?
I build my amplifier with two triode stages before SE, precisely tuned tone controls and loudness correction . But surely it depends on Your speakers construction and sounding
The role of R14 is for me not clear. In case of burning cathode resistance it may allow plate voltage to cathode and damage the tube But as not damaged do not make any problem
That resistor forms a voltage divide with the cathode resistor and sinks much more current than the tube draws by itself, so that the cathode voltage is stable. It's a simple constant current source.
This is a power amp only. No preamp, so no tone control.
@@Lancaster_Hi-Fi Right - it could be - such configuration allows to decrease output resistance keeping plate current at very low. Good driver for end stage
Of course, it does use potentially precious milliamps, and sometimes every milliamp matters!
why such small value filter caps in the power supply ?
If the capacitor adjacent to the rectifier is too big, the rectifier will fry. Tube rectifiers are less tolerant of big current spikes than solid state. That doesn't explain small values after the choke.
@@Lancaster_Hi-Fi no it would Not fry the tube rectifier. i routinely run a pair of 100uF/500V caps off the EZ-81 , for many years now,,,,, with no issues. You don't know the real reason , do you ?
Whether the rectifier actually fails or not, according to my reading, the reason for limiting the value of the first capacitor is the rectifier. The value can also help set the HT value. For the other caps, I suspect the reason they've traditionally been small values is simply the cost of large values at high voltages.
@@Lancaster_Hi-Fi the real reason goes back farther than that.
So, share already!
Cool! I wish I had popcorn...
That was really interesting! I might have to look at making a switch between ultralinear and triode operation in my A3600 but have it inside the chassis so I don't get tempted to switch it while it is on!
It's so hard! When you flip a switch with music playing, the difference is obvious, but not so much after powering down and waiting a respectable time for high-voltage capacitors to bleed down.
@@Lancaster_Hi-Fi Yeah - my interest in such a switch is not only to hear how different it might sound, but also how the amplifier and circuit adapts to triode mode (how class A and lower output changes heat dissipation). The Luxman A3600 is designed to be able to handle 50W but my 4x KT120s might be putting out much more than that in ultralinear configuration. The casing of the power transformer heats up over time and gets quite hot after a couple of hours of listening.
I've used the little DG-SE1 in my office as a hand warmer. Tube amps don't make good space heaters, but they do function as bad ones!