Hello everybody,
I love triode sound, but my SE amp similar to Tubelab's Simple SE (that space was for you, George) just doesn't have the power, even to drive my Fostex FE127 Bi-Poles, and one of my buddies has a whole box of 6v6s. as well, I notice that there are about 50 old Magnavox 6v6 PP amps on ebay at any given time, and I was wondering what kind of power I could expect out of it if I shorted it to Triode mode, I know the 6v6 doesn't work well as a Triode (something about grid current, its over my head...) but I wanted to know how well it would work.
Even if I had to buy two cheap 6v6 amps, I'd be happy to, if it would give some sweet Triode tunes. As well, the amp will (for the time being) be actively crossed (DSP, sorry guys) at 100hz to a sub so a top of line OPT is not really that important.
6v6s seem alot cheaper than 2a3s, that the way I see it....
-Moose
I love triode sound, but my SE amp similar to Tubelab's Simple SE (that space was for you, George) just doesn't have the power, even to drive my Fostex FE127 Bi-Poles, and one of my buddies has a whole box of 6v6s. as well, I notice that there are about 50 old Magnavox 6v6 PP amps on ebay at any given time, and I was wondering what kind of power I could expect out of it if I shorted it to Triode mode, I know the 6v6 doesn't work well as a Triode (something about grid current, its over my head...) but I wanted to know how well it would work.
Even if I had to buy two cheap 6v6 amps, I'd be happy to, if it would give some sweet Triode tunes. As well, the amp will (for the time being) be actively crossed (DSP, sorry guys) at 100hz to a sub so a top of line OPT is not really that important.
6v6s seem alot cheaper than 2a3s, that the way I see it....
-Moose
alexmoose said:
6V6's are incredibly linear in triode mode and, as far as I know, have a great reputation. Using 2.5K 10W SE transformers, you can expect about 6W from 6V6's in paralleled SET, maybe a little more if you can drive them into A2 using a cathode follower or something. THEN you'd have some grid current, but for normal pure class A, you don't have to worry about grid current at all.
Tom Schlangen has traced triode and UL curves for 6V6 and may other popular tubes:
http://www.tubes.mynetcologne.de/roehren/daten/as_triode_e.html
SveinB.
http://www.tubes.mynetcologne.de/roehren/daten/as_triode_e.html
SveinB.
Moose,
You may spend less buying all new parts. The Edcor XPP15-8-8K O/P trafo is inexpensive. That "iron" would allow you to try both multi-amped and "full range" operation with triode wired 6V6 family tubes.
To get full HF extension, some linearizing loop NFB around the Edcor O/P trafo is (IMO) appropriate. May I immodestly suggest you build an "El Cheapo". EC owes much to the "Musical Machine" design Poinz posted. However, EC is a bang for the buck project, rather than an all out assault on SotA.
You may spend less buying all new parts. The Edcor XPP15-8-8K O/P trafo is inexpensive. That "iron" would allow you to try both multi-amped and "full range" operation with triode wired 6V6 family tubes.
To get full HF extension, some linearizing loop NFB around the Edcor O/P trafo is (IMO) appropriate. May I immodestly suggest you build an "El Cheapo". EC owes much to the "Musical Machine" design Poinz posted. However, EC is a bang for the buck project, rather than an all out assault on SotA.
The original reason I though of this was looking at Tom's curves (thank you, Tom!)
Is there any difference at all between Parallel single-ended operation, and Push Pull class A? I don't remember there being a difference, other than the OPT is a lot cheaper for Push pull.
Buying new may indeed be cheaper, but the cheapEST would be using crap I have lying around (i thought of this immediately after posting last night). I have a 300-0-300v transformer from an Air-Chief, that I will never get around to fixing, and a perfectly good (looking) RCA 5Y3 with it. I still need some OPTS, and the 6v6s themselves, but that isn't too much.
Thank you all so much for your responses
-Moose
Is there any difference at all between Parallel single-ended operation, and Push Pull class A? I don't remember there being a difference, other than the OPT is a lot cheaper for Push pull.
Buying new may indeed be cheaper, but the cheapEST would be using crap I have lying around (i thought of this immediately after posting last night). I have a 300-0-300v transformer from an Air-Chief, that I will never get around to fixing, and a perfectly good (looking) RCA 5Y3 with it. I still need some OPTS, and the 6v6s themselves, but that isn't too much.
Thank you all so much for your responses
-Moose
alexmoose said:
Power O/P from PSE and Class "A" PP is the same. However, with PP, the option to cut 1 of the pair off during peak power demand and enter Class "B" is available. Both the "Musical Machine" and "El Cheapo" exercise the option to obtain approx. 6 WPC from a PP pair of trioded 6V6 family tubes.
Another difference between PP and PSE is the cancellation of internally generated even order harmonic distortion products. The 12AT7 combines well with that cancellation to yield a highly satisfactory net HD spectrum.
The 5Y3 is good for 125 mA. of B+. That's not enough for 4X 6V6s and their drivers. The heater current draw in a 5AR4 is the same 2 A. as in a 5Y3, but the current handling capability and forward drop characteristics of the 5AR4 are much more favorable for this project. Holding the value of the 1st cap. in a CLC filter down (say 10 μF.) allows a critical few extra mA. of B+ to be safely squeezed out of the Air-Chief power trafo, while still yielding the 360 V. B+ rail an "El Cheapo" works best with. FWIW, I suggest you start with a value less than 10 μF. in the 1st filter position and tweak the value upwards until the rail voltage (under load) is where it should be.
The Air-chief Transformer is what the polish would call "kaputski", the potting is leaking out, the outside is rusty, and the insulation frays when I bend it (because the potting wax leaked on it) , and it kinda smells like Beef Jerky.... so it looks like there will be a 50 dollar investment in an Allied, or Hammond Transformer. I like the look of Elcheapo (once I found the schematic), however, does anybody know what the voltages are? B+ both B+2s, and B-? and I might use a SS rectifier if I need the extra boost in voltage (not likely).
-Moose
-Moose
alexmoose said:
Moose,
The 'T7 based splitter driver works "best" with IB = 3 mA. and 200-220 V. on the anodes. The drop in the 50 KOhm load resistors is 150 V. Losses in the "check valve" decoupling circuitry are less than 2 V. So, a 360 V. B+ rail is "perfect". When the B+ rail is that "tall", use 390 Ohm cathode bias resistors.
40 V. is enough on the B- side. Examine the schematic closely and you will see that 90 V. are dropped in resistors. The Allied 6K27VF B- trafo was selected for cost reasons.
A $29 AnTek AN-1T300 toroidal power trafo will take care of a tube rectified B+ supply and signal tube heater needs. The data sheet is here. Use the 6.3 V. winding to power the heater of a 6BY5 rectifier. Use the 12.6 V. winding to power the signal tube heaters. A suitable low cost O/P tube type is the 12AB5, but ALL 6V6 family tubes work. Series wire the heaters of "6" V. variant pairs.
I will judge you to be sensible.
You lose slow warm up though.
I do not see any discrete MOSFETs in your schematic? The 10M45 can be replaced by a cascode or other CCS.
Edit: oops, not Alexmoose schematic, but Poindexter's. FETs can be subbed, reverse transfer capacitance can be big whoop in tube circuits, though.
You lose slow warm up though.I do not see any discrete MOSFETs in your schematic? The 10M45 can be replaced by a cascode or other CCS.
Edit: oops, not Alexmoose schematic, but Poindexter's. FETs can be subbed, reverse transfer capacitance can be big whoop in tube circuits, though.
Sharper tools than I have opined that the 10M45 is just a pair of beefoid cascoded mosfets. Actually, a single DN2540 has plenty of dynamic resistance; several megohms. Couple hundred Kohms would be plenty for good circuit balance in the LTP.
If you use the AnTek 1T250 for the mains trans, you can still get plenty of B+ (over 320v) with sand diodes, and you can switch that winding with a second switch, that's what I'm gonna do. I actually like the sound of sand rectification better; faster, more transparent. Put a fullwave doubler on the 12.6v winding, there's yer bias supply. I use an Amveco 62035 for the tail, I get -66v with the secondaries seriesed, but I'll be talking to John about the smaller AnTek stuff too; they now make 5VA and 10VA cores. Transformer sourcing is always a problem - these guys look like a godsend to me.
Poinz
If you use the AnTek 1T250 for the mains trans, you can still get plenty of B+ (over 320v) with sand diodes, and you can switch that winding with a second switch, that's what I'm gonna do. I actually like the sound of sand rectification better; faster, more transparent. Put a fullwave doubler on the 12.6v winding, there's yer bias supply. I use an Amveco 62035 for the tail, I get -66v with the secondaries seriesed, but I'll be talking to John about the smaller AnTek stuff too; they now make 5VA and 10VA cores. Transformer sourcing is always a problem - these guys look like a godsend to me.
Poinz
Poindexter said:
hey-Hey!!!,
I have built LTP cathode loads from high voltage and large resistors. I have also built with single and cascode MOSFET's. The single has more impedance than any of the R's I tried but the sonics just suck compared to the cascode and low( by comparison ) R. I suspect the wacky gate capacitance that comes out of the single application. The cascode does away with most of that capacitance. It is quite worth the extra trouble.
cheers,
Douglas
That makes sense, Douglas. Some people have used the 10M45 like a mosfet and cascoded them. I can tell you that the 6GK5 LTP with the single IXYS chip sounds noticeably more transparent than the 5965s with a 24K tail, and burns rather less power in the tail, too. I'm really glad I found this part. I put a 250Ω resistor in the control circuit with a 100Ω 12-turn pot, and it's fun to adjust the OP of the front end up and down with a screwdriver and hear what I can hear.
Poinz
Poinz
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