I would skip the tube rectifier, there is no need for it in a single ended amplifier. Saves you some watts through the power transformer that can be better used by the tubes. With SS rectification you can increase the size of the filter capacitors and have less hum. Other than that build it like two amps in one chassis but with a dual pots.
This is true if you always play in the clean zone away from compression. Drive that amp a bit into compression and the average tube current goes up, especially the screen grid current in the output stage. A tube rectifier will exhibit a nonlinear response in output drop in this situation which does contribute to the overall "tone" when compared to a stiff solid state rectifier.
In this case it may not make that much difference since a "cranked" tone is not desired.
In the late 1990's I built about a dozen "turbo champ" amplifiers. No two were alike, and the output tubes ranged from a 6V6GT to a KT88. Some got a pair of car stereo speakers obtained cheap when a local K-mart failed, others got real guitar speakers, or something scavenged, usually from a console organ. Most used a 125CSE or the organ transformer, for the OPT, but the power transformers were scavenged from all sorts of stuff, with some of the KT88 versions getting a 6K7VG for 430 volts of B+. All of them had a "tube/SS" rectifier switch and even with a resistor in series with the diodes there was an obvious difference in the sound, especially when blasted with my trusty Zoom 505.....hey, it WAS the 1990's.
This schematic was drawn up from memory after the fact. No two amps were the same, and none probably matched this schematic exactly.
Attachments
And if some voltage drop is wanted with SS diodes a series resistance can be put in the circuit simulating the vacuum tube rectifier. But as said this would be mostly clean. A pair of uf4007 diodes should do.
Thanks for reminding me of that, jjasniew -- turns out, all of my guitar-direct tests happened long enough ago that 🙂eek🙂 no valve amplifiers were involved!
Maybe I should keep my opinions to myself 'til I've had more relevant, modern experience!
Cheers
If you like the sound of a champ you should follow your original plan. To really enjoy the stereo effects you need to build one clone of the champs speaker-compartment for one of the channels. If you put both speakers in the same cabinet, it will no longer sound like a Champ and you will far from fully hear the stereo effects, since the speakers are too close to each other
Yes, it´s far better building 2 separate, independent Champs, the main point being that you can separate them as much as you wish to keep stereo illusion.
Sise by side in a bedroom? 2 meters away in rehearsal or a small Club? 6 meters away in a Stadium?
All possible.
Sise by side in a bedroom? 2 meters away in rehearsal or a small Club? 6 meters away in a Stadium?
All possible.
Two amps would be fine but if you already have a power transformer that is suitable then one combo amp with both channels in it and another cab with just the speaker can work. Put the speaker a pleasing distance from the combo. After all, stereo amplifiers in one chassis have been around for a while.
Apart from the general tube vs. SS rectification sound discussion, a pair of 1N4007's won't do less. There's no need for fast recovery diodes in the 50/60 Hz world.
Best regards!
May be yes I would get the best of the stereo effect building two champs, but what a I heard from a stereo Magnatone is just crazy... in a combo box. That's why I am seduced by the twin stereo champ. By the way a Magnatone gives volume/frequency tremolo and reverb, but i will do it with numeric pedal board as:
-I play alone thru the effect chain to a stereo looper then to the stereo amp
-I play with a friend, him through is effect chain to a mono channel, me the same through my effect chain to my independant channel
At the begining I was about to go for 5U4GB, but the internal resistor is quite high and I am loosing something arround 20 DC volts on the power stage compared to the single channel with 5Y3S.
I think I will get with the GZ34, instead of the 5Y3S because I could divide the power resistor by 2 and double the caps to 40uF, but the DC Voltage is now to high.
Question 1: Do I have to increase resistors and decrease caps to have good average for current and DC Voltage?
I wonder now If I should add somewhere a choke like on some other circuit. I know what a choke do in serie (filtering, and limiting current variation) but I don't know any strategy about that in a PSU.
Question 2: What do you think about adding a choke?
Thank you very much for help.
Even a non stereo amp with two speakers in the same cabinet sounds more open. Depending on how far you play from the amp having the speakers in the same cabinet would be fine. I have my amp three feet away from myself, I may have to do a 2x8 one day.
The larger the capacitor the less the ripple voltage (hum), the larger the resistors do the same thing but at a cost of a voltage drop across them. So if you have too much voltage dropping across your power supply resistors is a worthwhile thing. But it also does add heat to your circuitry.
Adding a choke does the same to AC as a resistor with its impedance but it has a lower resistance and your dc voltage is higher. Putting the choke right behind the rectifiers and before the capacitors causes the voltage to be higher. The proper power transformer with a lower output voltage needs to be used for this. In this position the choke needs to handle the amp's total current and are physically large, heavy and expensive. As a compromise some amps have a choke in between the first filter capacitor and the second. So the screen current and the preamp current is filtered more.
A good thing to play around with is the Duncan Power Supply Calculator. you can while away a few hours with it.
PSUD2
I only skimmed the paper so I can not attest for all of it but it seems like it may be helpful.
https://www.dhtrob.com/overige/pdf/dhtrob_psu.pdf
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Estimating load for Duncan Amps PSU tool HOWTO?
As long as we're bouncing around in all quadrants of possibility, I recall finding some EICO HV power supply in Goodwill, which I sold on ebay for some good money. I spun it as having enough power for a tube guitar amp - and it would be a fairly easy matter of replacing the HV powersupply with it - and be able to dial in any B+ voltage you want - even on stage. Just like Eddie with his variac - only better.
Someone bought it, but I'll never know what for. If you're going to design/build a power supply from scratch, why not make it fully electronically regulated and adjustable? With a 6L6 tube as the pass element like that EICO had? At intel, we designed powersupplys with programmable droop - the higher the current, the lower the voltage - at any slope you want. It's entirely possible.
You could even make a op-amp envelope follower on the amp's input signal, use that DC control signal to tell the power supply to instantly droop following the input level envelope, or increase with it. Have two of 'em - one for the output tubes, another at a different rate for the driver tubes. I'm sure this has all been thought out before with the patents taken, however in DIY land - do as you like!
I'm sure a tube regulated B+ power supply, realized several times, would be as easy to draw up as Tubelab's schematic from memory. It's just an unusual thing...
Someone bought it, but I'll never know what for. If you're going to design/build a power supply from scratch, why not make it fully electronically regulated and adjustable? With a 6L6 tube as the pass element like that EICO had? At intel, we designed powersupplys with programmable droop - the higher the current, the lower the voltage - at any slope you want. It's entirely possible.
You could even make a op-amp envelope follower on the amp's input signal, use that DC control signal to tell the power supply to instantly droop following the input level envelope, or increase with it. Have two of 'em - one for the output tubes, another at a different rate for the driver tubes. I'm sure this has all been thought out before with the patents taken, however in DIY land - do as you like!
I'm sure a tube regulated B+ power supply, realized several times, would be as easy to draw up as Tubelab's schematic from memory. It's just an unusual thing...
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Maybe best to clone the Magnatone`s speakercompartment. I heard the size of the speaker`s baffle is important for the tone of an amp
Cheers!
Cheers!
I still have several. I got this Knight Kit at a hamfest at least 30 years ago. It worked good when I got it and did so for a long time. It sat idle and was left in an unheated shed for about 2 years during my retirement related relocation where it was subject to two winters with a low of -12F. Upon reawakening it was not happy eventually releasing some magic smoke and the stink of a venting electrolytic. Rebuild time.
I replaced every cap in the thing and every resistor that didn't measure right. I was surprised to find 4 X black plate RCA 6L6GC's inside, so they went to the Dayton hamfest where they fetched more $$$ than I originally paid for the power supply. The supply lives on with Chinese tubes. It stays in regulation well beyond the end of the current meter.
The manual with schematic is included here. There are 4 X 6L6GC's to supply a rated 200 mA, and it will go to well beyond 300 mA without complaint. One or two tubes is all that's needed to VVR a whole Champ or two.
I created a "sagulator" with a simple mosfet follower, a zener diode string, few parts and a couple pots. One pot set the voltage, the other allowed for modulating the regulated voltage up or down based on a sensing signal developed elsewhere in the amp. For the usual push pull class AB amp this was usually an output tube cathode. For an SE amp like the Champ, the output tube screen grid is a good choice. In some cases you can sense one of the preamp tube's plate voltage, or even use a pedal to modulate the B+ for weird effects and long sustains.
I was looking through my stuff and I started rearranging guitar cabinets. I have a 4x10 that I built and have speakers for it. I decided I'll put them in tomorrow and give me some more shelf space. But I could not find them. I found one extra, could not find the four. Finally found them under some reverb tanks. Can't see the forest for the trees some times. In the process I found two speakers that looked the same, transformers may be different. Nope, two identical units out of console radios. Ten inch though, makes for a rather large cabinet for a bedroom amp, not enough volume for jamming with. Angle the baffles a little?
Hello
I made a simulation with the original circuit and 5Y3, and a second circuit with a 5U4GB and a transformer that gives the enough amps but with 330V peak to peak instead of 325V of the transformer on the mono version
The PSU give 10 more DC volts...
Is it a problem, and how could / should reduce it?
Thank U.
MONO: https://lh3.googleusercontent.com/p...nvkw9MSU9xVrhBdGq8mQ=w1281-h691-no?authuser=0
STEREO : https://lh3.googleusercontent.com/p...pdWcj9FvR5tw6i7-oVNA=w1284-h691-no?authuser=0
I made a simulation with the original circuit and 5Y3, and a second circuit with a 5U4GB and a transformer that gives the enough amps but with 330V peak to peak instead of 325V of the transformer on the mono version
The PSU give 10 more DC volts...
Is it a problem, and how could / should reduce it?
Thank U.
MONO: https://lh3.googleusercontent.com/p...nvkw9MSU9xVrhBdGq8mQ=w1281-h691-no?authuser=0
STEREO : https://lh3.googleusercontent.com/p...pdWcj9FvR5tw6i7-oVNA=w1284-h691-no?authuser=0