Very Impressive! I have never made a high powered tube amp. I have built 25 watt monoblocks with EL34's and it can get to very loud listening levels with my speakers. The few time I have cranked them was with friends over listening to rock, most of the time they loaf around @ a couple of watts.....which is why I was thinking my next build be SE. I have a little Chinese 5wpc single ended tetrode which is cool, it's a Shanling STP-10 and has a nice little IPOD dock. I find that that stereo is all I need for daily listening levels. I have a Slewmonster SS amp I built that OStripper designed on here that cranks out the tunes for loud listening.
BUTTTTTTTTTTTTTTT...................100wpc tube amp would be pretty boss.😱
As far as dampening goes I do think my speakers are tube friendly. My only use for feedback was to squeak a little bit more power out and keep THD under 5%. I was thinking of going cascode with the 12AX7 for huge gain and use more feedback but I am trying to keep the tube count down. I don't disagree in that a Mosfet is the way to go but I would like to keep it all tube. If I were using a transmitting tube that was meant to be operating in positive grid territory then I would choose a Mosfet. I didn't think sweep tubes liked grid current so I figured a 6SN7 CF was a good compromise.
I agree!! SO many projects, and so little time
I was reading through an old Klipschorn brochure and it recommended the Brook 12A, which is a push pull 2A3 amp. Some of these sweep tubes in triode mode would be a cool project to make a "cheap" Brook 12A.
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Tubelab are you home? How was your road trip? Do any of the Walmarts you passed by still have any LED lighting left? 😉
Currently on Captiva Island in Florida, after visiting the Motorola plant in Ft. Lauderdale where I worked for 41 years. We also stopped in the Orlando area to visit friends. We are leaving here on Friday with two planned stops before getting back to West Virginia late Sunday night.
We stopped a Walmart right off of I-95 in central Georgia....no LED lights. Also visited Planet Surplus near I-95 in New Smyrna Florida for a rack cabinet, several blank rack panels, and an unknown electronic device that will be cannibalized for its cabinet. We stopped at 4 Walmarts on the rural route to the Orlando area and found ONE light. I may look for more on the return trip, but I now have 4.
The big red board gets REAL LOUD when running at full tilt into a pair of 96db efficient speakers with 15 inch woofers. You can't be in the room with it. I used to open the house windows, crank the amp, and go outside to mow the lawn without hearing the mower! Next door neighbors were never home. They are firefighters that worked 3 days on, 3 days off, live at the fire house when on duty.
I recently purchased a second set of Plitron OPT's in the Swap Meet section of this forum. They are rated for "400 watts at 20 Hz" and I have seen 525 watts at 1KHz flow through one of them with 4 X 35LR6, again in Pete's big red board with both channels paralleled through a single OPT. I believe that there was more power left in the amp, but my old HP power supply was tapped out making 650 volts at about 1.2 Amps.
I have no need for a stupidly powerful amp, but I will probably build one now that I have all the parts and no excuse not to. I have been using the OPT's that I have for big amp experiments. I don't know how much power it will make yet, but 1 KW would be nice (500 WPC). That's about the limit of a US spec wall outlet (15 Amp) assuming a 65% plate efficiency with heater power and power supply losses.
We stopped a Walmart right off of I-95 in central Georgia....no LED lights. Also visited Planet Surplus near I-95 in New Smyrna Florida for a rack cabinet, several blank rack panels, and an unknown electronic device that will be cannibalized for its cabinet. We stopped at 4 Walmarts on the rural route to the Orlando area and found ONE light. I may look for more on the return trip, but I now have 4.
The big red board gets REAL LOUD when running at full tilt into a pair of 96db efficient speakers with 15 inch woofers. You can't be in the room with it. I used to open the house windows, crank the amp, and go outside to mow the lawn without hearing the mower! Next door neighbors were never home. They are firefighters that worked 3 days on, 3 days off, live at the fire house when on duty.
I recently purchased a second set of Plitron OPT's in the Swap Meet section of this forum. They are rated for "400 watts at 20 Hz" and I have seen 525 watts at 1KHz flow through one of them with 4 X 35LR6, again in Pete's big red board with both channels paralleled through a single OPT. I believe that there was more power left in the amp, but my old HP power supply was tapped out making 650 volts at about 1.2 Amps.
I have no need for a stupidly powerful amp, but I will probably build one now that I have all the parts and no excuse not to. I have been using the OPT's that I have for big amp experiments. I don't know how much power it will make yet, but 1 KW would be nice (500 WPC). That's about the limit of a US spec wall outlet (15 Amp) assuming a 65% plate efficiency with heater power and power supply losses.
Concerning Screen Diss of the 6GE5...
All the 12GE5 that I have, you cant actually See the screen-grid in the tube. No holes in anode and the slots in the mica at the top dont go deep enough towards cathode to see either-- I guess with that one, its a case of checking the screen-current/volts to see how hot--or not--its getting....
Looks from the pics Ive seen that the 6HJ7 has nice big holes in anode to see whats going on...
All the 12GE5 that I have, you cant actually See the screen-grid in the tube. No holes in anode and the slots in the mica at the top dont go deep enough towards cathode to see either-- I guess with that one, its a case of checking the screen-current/volts to see how hot--or not--its getting....
Looks from the pics Ive seen that the 6HJ7 has nice big holes in anode to see whats going on...
True. Most of the 12GE5 I have here, you cannot see the insides. I do have a few Raytheon 12GE5s though, that have the big square holes in the plate edge, just like the 6HJ5. They also have cooler fins up top on the g1 and g2. And a black plate like the 6HJ5.
I hadn't thought of this before, but maybe the big plate holes on the edge also serve as g2 cooling windows. What you see immediately through them is the g2 support rods. The 6HJ5 has a robust 6 Watt spec for g2. I suspect the 6HJ5 was designed for reliable RADAR display scopes, then got written up as a TV sweep tube for additional sales.
I have a few GE 12GT5 tubes here which do have the big square holes in the edge of the plate. 12GT5 was designed by RCA, so maybe that is spec'd in. It is a very similar tube to the 12GE5 otherwise.
Pic below, top right is the Raytheon 6HJ5, bottom left is Raytheon 12GE5, bottom right is GE 12GE5:
2nd pic has 12GT5 at top.
I hadn't thought of this before, but maybe the big plate holes on the edge also serve as g2 cooling windows. What you see immediately through them is the g2 support rods. The 6HJ5 has a robust 6 Watt spec for g2. I suspect the 6HJ5 was designed for reliable RADAR display scopes, then got written up as a TV sweep tube for additional sales.
I have a few GE 12GT5 tubes here which do have the big square holes in the edge of the plate. 12GT5 was designed by RCA, so maybe that is spec'd in. It is a very similar tube to the 12GE5 otherwise.
Pic below, top right is the Raytheon 6HJ5, bottom left is Raytheon 12GE5, bottom right is GE 12GE5:
2nd pic has 12GT5 at top.
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Here's a question for ya....
Say I run a 6GE5 at 350 plate and triode-wire using a resistor to screens to drop volts to below 220--its alleged highest G2 voltage....
What would be the effect of doing this....?
Say I run a 6GE5 at 350 plate and triode-wire using a resistor to screens to drop volts to below 220--its alleged highest G2 voltage....
What would be the effect of doing this....?
tube-lab has done experiments afaik, g2 voltage when triode wired can be exceeded....
i have 21hb5's that i plan on running SE triode at 250 volts plate, similar to a 2A3, but at higher cathode currents of say 80mA...
i have 21hb5's that i plan on running SE triode at 250 volts plate, similar to a 2A3, but at higher cathode currents of say 80mA...
I think a resistor from plate to g2, to get down to 220 V, would make the output plate impedance go higher and seriously lower the power output of the "triode", not to mention distortion problems.
I haven't had any problems running the g2 up to 350V on the curve tracer in "triode" mode. You just have to try it, no problem with $1 tubes anyway. But put a fusible resistor in the cathode circuit to protect the OT. Some SE OTs have a UL tap you could try. Some have tried a LV Zener in series with g2. That will limit power output.
I haven't had any problems running the g2 up to 350V on the curve tracer in "triode" mode. You just have to try it, no problem with $1 tubes anyway. But put a fusible resistor in the cathode circuit to protect the OT. Some SE OTs have a UL tap you could try. Some have tried a LV Zener in series with g2. That will limit power output.
smoking-amp, i encountered bias runaway in my parallel EL34 triode wired,
cathode resistor biased amp, running 320 volts plate at about 60mA cathode current,
what do you think happened and how? there were no obvious signs on the tube itself....
cathode resistor biased amp, running 320 volts plate at about 60mA cathode current,
what do you think happened and how? there were no obvious signs on the tube itself....
Hmm, a cathode resistor is supposed to prevent that. Was there an elect. cap across the resistor? Maybe it got too hot? With paralleled tubes, maybe one had a bad socket connection so the other tube overheated with doubled current? Separate cathode resistors for each tube?
the cap across the resistor blew, the resistor a 10w 350 ohm became 375 ohms, i have since changed them all to 400 ohms and changed caps...trimmed B+ a tad lower also...
Ah--Looks as though I'll have to rig one up and torture it to death in Triode--Tubelab style, although I don't think it'll need to be done dynamic, just a variable supply to the tube and variable bias--Being triode wired class A, hardest time for the tube would be with no signal anyway.....
Now I'll need to search through all my 12GE5, see if I have one somewhere--with that tiny hole in the plate to see whats happening.....
Now I'll need to search through all my 12GE5, see if I have one somewhere--with that tiny hole in the plate to see whats happening.....
What g1 circuit resistance are you guys using with sweep tubes, mainly the 6HJ5? I see in the datasheet it says 1Meg. Is it the same for fixed and cathode bias?
That 1 Meg. value would be spec'd for switching service, where some bias drift can be tolerated. I would use the 6L6GC spec as a guideline, 100K for fixed bias, 500K for cathode bias. And lower yet, if pushing the Pdiss specs. Maybe George has some recommendation on this.
I see Pete Millett used 100K grid R for the DCPP amplifier using 6JN6/6GE5 in fixed bias.
http://www.pmillett.com/dcpp.htm
I see Pete Millett used 100K grid R for the DCPP amplifier using 6JN6/6GE5 in fixed bias.
http://www.pmillett.com/dcpp.htm
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Or better still, Drive it with MOSFET Tubelab powerdrive style to avoid blocking-distortion....
Any idea the Rp of 6HJ5 in Triode, G2 connected to plate...?
Any idea the Rp of 6HJ5 in Triode, G2 connected to plate...?
The 6HJ5 datasheet gives gm1 = 10,000 microMhos and Mu = 4.2 at 80 mA.
So for triode config. at 80 mA: Rp = 1/gm2 = Mu/gm1 = 420 Ohms at 80 mA.
(gm2 = gm1/Mu = 2380 microMhos)
For a different current: triode Rp' = 1/gm2' = Mu/gm1',
and gm2' varies near consistently at the 0.3 power of current (for this tube).
(one could also work from gm1, but that varies less consistently as a power law versus current)
Example for 40 mA: gm2' = (40/80)^0.3 x 10,000/4.2 = 1934 microMhos
and Rp' = 1/gm2' = 517 Ohms
So for triode config. at 80 mA: Rp = 1/gm2 = Mu/gm1 = 420 Ohms at 80 mA.
(gm2 = gm1/Mu = 2380 microMhos)
For a different current: triode Rp' = 1/gm2' = Mu/gm1',
and gm2' varies near consistently at the 0.3 power of current (for this tube).
(one could also work from gm1, but that varies less consistently as a power law versus current)
Example for 40 mA: gm2' = (40/80)^0.3 x 10,000/4.2 = 1934 microMhos
and Rp' = 1/gm2' = 517 Ohms
I was just playing around with some wimpy output transformers, nothing too cereal. When I pull the trigger on some real SE iron I plan to direct couple a cathode follower to the 6HJ5. Pretty much the same exact thing as tubelab's powerdrive but with not as much power lol.
420 ohm plate impedance 🙂
eh......with 3k:8 iron that would be like 1 ohm output Z no?
3000/8=375
420/375=1.12
Not too shabby.
80mA, 23.5W P-Diss, 420 ohm Rp, 3k5 p-p, 300v +B, looking at 1.75 ohm O/P impedance before any NFB.
Reading through a load of old posts by Tubelab screwing the 6AV5/6GE5 types hints at the G2 max 220V can be exceeded a fair amount on these sweep tubes, but I think 300V is a reasonable amount, and we know sweep-tubes max plate diss is very conservative anyway, hence running a 24W tube at 23.5W...
Allegedly 19.6W RMS, and 0.182 H3, G1 stays negative by -2v at peaks--all with pinch of salt as this is results of a sim....
Not shabby though, wonder how will play in real life...
Reading through a load of old posts by Tubelab screwing the 6AV5/6GE5 types hints at the G2 max 220V can be exceeded a fair amount on these sweep tubes, but I think 300V is a reasonable amount, and we know sweep-tubes max plate diss is very conservative anyway, hence running a 24W tube at 23.5W...
Allegedly 19.6W RMS, and 0.182 H3, G1 stays negative by -2v at peaks--all with pinch of salt as this is results of a sim....
Not shabby though, wonder how will play in real life...
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