Hi all, here is something based on the 6216 pentode. It's an odd tube that nobody really seemed to notice. Datasheet for the curious. https://frank.pocnet.net/sheets/127/6/6216.pdf The advertised use was an active filter to replace an iron core choke. Pretty high heater current for only 10 watts dissipation. I used a 5670 because the chassis was from a previous project and the sockets were wired for the WE 407A, same tube but a 20v heater. Output iron is vintage Tamura and the power transformer is from a hifi chassis.
No pictures yet as I'm still tweaking the design. My chassis used octal output tubes so I'm sketching up some adapter plates so 9 pins can be mounted in their place. Going to get them laser cut from somewhere.
No pictures yet as I'm still tweaking the design. My chassis used octal output tubes so I'm sketching up some adapter plates so 9 pins can be mounted in their place. Going to get them laser cut from somewhere.
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> odd tube that nobody really seemed to notice
It is generally in the 6Y6 club via the TV V-Sweep craze. I can't remember just which tube was 6.3V 1.2A and 10W. But I'm sure it is that tube re-specified for a specific pass-tube application. It is easy to see on the graph that a bigger choke would filter better (and no heater power). The kicker is "jet aircraft". This tube plus heater supply may have been an ounce lighter than a lump of iron. And ounces matter in aircraft.
> Pretty high heater current for only 10 watts dissipation.
Heater is current ability. You have "for audio" tubes which work at medium current, audio output limited by dissipation. OTOH you have "switching" tubes which work to HIGH current and need BIG cathodes (and heaters). Outright switching like the extremes of a TV sweep tube. Full-ON switch like a filter pass-tube. And audio amplifiers for very limited B+ such as transformerless home radios. Given free choice, you jack the plate up to 300V, need far less current to touch 10W Pdiss, can use much smaller/cheaper cathode.
It is generally in the 6Y6 club via the TV V-Sweep craze. I can't remember just which tube was 6.3V 1.2A and 10W. But I'm sure it is that tube re-specified for a specific pass-tube application. It is easy to see on the graph that a bigger choke would filter better (and no heater power). The kicker is "jet aircraft". This tube plus heater supply may have been an ounce lighter than a lump of iron. And ounces matter in aircraft.
> Pretty high heater current for only 10 watts dissipation.
Heater is current ability. You have "for audio" tubes which work at medium current, audio output limited by dissipation. OTOH you have "switching" tubes which work to HIGH current and need BIG cathodes (and heaters). Outright switching like the extremes of a TV sweep tube. Full-ON switch like a filter pass-tube. And audio amplifiers for very limited B+ such as transformerless home radios. Given free choice, you jack the plate up to 300V, need far less current to touch 10W Pdiss, can use much smaller/cheaper cathode.
Very nice circuit!
A couple of gotchas though:
1. Put a safety resistor from the bias wiper to the negative bias supply.
Otherwise, if the wiper opens, you get Zero bias and max quiescent smoke.
2. Connect R6 and R16 directly to the pin 5 socket tabs. And move R3 and R17 directly to the coupling caps, C3 and C4.
That makes the resistor a true grid stopper.
As it now is, it does not perform R6's and R16's intended reason for being there.
All else looks good to me (or else just escaped my attention at this late hour).
A couple of gotchas though:
1. Put a safety resistor from the bias wiper to the negative bias supply.
Otherwise, if the wiper opens, you get Zero bias and max quiescent smoke.
2. Connect R6 and R16 directly to the pin 5 socket tabs. And move R3 and R17 directly to the coupling caps, C3 and C4.
That makes the resistor a true grid stopper.
As it now is, it does not perform R6's and R16's intended reason for being there.
All else looks good to me (or else just escaped my attention at this late hour).
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The 6216 looks vaguely similar to 6W6 (and clones 12/25/50L6, 6GC5, 6DG6, 6DB5 ) but the 6216 has lower screen current. (flatter plate curves) So may sound different.
6LG6 has similar low (even lower) screen current with flat plate curves, but is a much bigger tube. The Compactron tube socket could fit the Octal chassis holes.
6LG6 has similar low (even lower) screen current with flat plate curves, but is a much bigger tube. The Compactron tube socket could fit the Octal chassis holes.
As the circuit is drawn, feedback will be shunted to ground by C5.
Suggest you put C5 in parallel with R14 (or remove it entirely.)
Suggest you put C5 in parallel with R14 (or remove it entirely.)
Yes it was always a real circuit. A few things have changed form the original schematic. The 10k resistors on the phase splitter were too low and weren't able to swing enough voltage so they were increased to 30k. The screen voltage was raised to 150 and regulated with an 0A2. The feedback resistor is also different.
THD is measured at 0.2% at normal listening levels and output power is 10 watts or so. I'm going to get roasted for saying this but my friend says (and I agree) it sounds better than the Sony VFET kit I was lucky enough to win.
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astouffer,
Looks real good!
Good job continuing the design changes until it worked satisfactorily.
Have fun listening!
P.S. I will not build any vacuum tube amplifier unless I put on at least one Handle.
Looks real good!
Good job continuing the design changes until it worked satisfactorily.
Have fun listening!
P.S. I will not build any vacuum tube amplifier unless I put on at least one Handle.
A 6W6 (Vertical Amp tube) looks quite similar to the 6216 except for plate current rating. A 10/6JA5 (another Vertical Amp tube, cheap too) does have similar specs to the 6216, including current, but higher Pdiss at 19 Watt. The 10/6JA5 has plate curves that are almost a photocopy of the near extinct, acclaimed EL506 tube, except for lower screen V. And so matching the lower screen V of the 6216 and 6W6.
I loves me a real circuit 🙂 and it is nice to see the 5670 usefully employed - I use it too and think it one of the more linear triodes with mu in the 30s. So kudos
and two questions:- Did you have to elevate heater voltage much?
- Could you post a schematic for the power supply and maybe some measurements of idle voltages?
I loves me a real circuit 🙂 and it is nice to see the 5670 usefully employed - I use it too and think it one of the more linear triodes with mu in the 30s. So kudos
- Did you have to elevate heater voltage much?
- Could you post a schematic for the power supply and maybe some measurements of idle voltages?
Nope didn't have to elevate the heater, just a resistor across each side to ground. Schematics and voltages are going to take a week or so. My new job is sending me to Toronto.
As promised here are some updated schematics with voltages. I didn't feel like drawing out all the transformer windings. The power supply is all reclaimed parts from other devices. Filter caps from a motor drive, bias transformer is from an old clock radio. No idea where the filter choke came from or it's limits. It only gets warm.
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To me the 6W6 is a 25L6 / 50L6 repurposed as a vertical amp! 🙂
Makes a good series passer in a low power regulated PS too.
Thanks for sharing the schematics. I have one question though - shouldn't the lower output of phase splitter be taken from the point between 1k and 10k resistors? In the configuration you're using one side gets slightly higher signal. Cathodyne resistors from signal outputs to supply rails should be equal for balanced operation.
Less of an issue with the resistors increased to 30k as in the final schematic - but the reality is to use whichever connection results in equal (or the most equal) amplitudes. Cathodynes are pretty good right out of the box, but not always perfect. And neither are the resistors.
That 6216 looks like Yet-Still-Another 50C5-oid to me - it’s like they copy the same “Class A Audio Amplifier” table and paste it into all kinds of 7, 9 pin and octal that have the 7.5 watt heater. Many can be had for cheap (or free) so you can’t knock that. Actual ratings were more based on what bottle it was in and how much abuse factor was expected given the target application ( ie, aircraft vs. table radio). There were differences in materials and construction which didn’t really change the electronic properties too. Since there were so many of those types in use (up to and including the 50L6) it’s not hard to find suitable output iron to recycle either. The 6216 probably cost a pretty penny in it’s day, but I doubt the military is buying them anymore.
That 6216 looks like Yet-Still-Another 50C5-oid to me - it’s like they copy the same “Class A Audio Amplifier” table and paste it into all kinds of 7, 9 pin and octal that have the 7.5 watt heater. Many can be had for cheap (or free) so you can’t knock that. Actual ratings were more based on what bottle it was in and how much abuse factor was expected given the target application ( ie, aircraft vs. table radio). There were differences in materials and construction which didn’t really change the electronic properties too. Since there were so many of those types in use (up to and including the 50L6) it’s not hard to find suitable output iron to recycle either. The 6216 probably cost a pretty penny in it’s day, but I doubt the military is buying them anymore.