Refer to ARC's modded ST-70. They ground the 4ohm speaker tap, and
let the cathodes ride upon 0 and 16. Sorta almost like what you wanted?
No grid stopper on the grid input.
1K stoppers on the screen.
I don't think it was oscillating though. The blue flash went fast. Maybe 2 seconds from flipping the B+ on. No chance to go red plate, just a flash and the circuit breaker popped.
Cathode Stripping
It looks like the cathode of the tube that had the blue flash had cathode stripping. It is a chicken or egg situation though since it could have been either the cause of the flash or the results of the flash.
The tube on the left is the one that had the flash. The one on the right had increasing blue discharge and increasing current but never had a major flash. The flash seemed to emanate from the top of the tube, which coincides with the most stripping.
It looks like the cathode of the tube that had the blue flash had cathode stripping. It is a chicken or egg situation though since it could have been either the cause of the flash or the results of the flash.
The tube on the left is the one that had the flash. The one on the right had increasing blue discharge and increasing current but never had a major flash. The flash seemed to emanate from the top of the tube, which coincides with the most stripping.
An externally hosted image should be here but it was not working when we last tested it.
Finally getting back to construction and am about to start final wiring with everything (Hopefully) ironed out.
The wood is oak with an ebony stain that didn't quite take. I was trying for a finish similar to my black lacquer walnut speakers.
Front and top:
back and top:
and bottom ready to wire with tagboard in place, but without heater wire tabs:
I've got to set it aside again. Pop went into ICU yesterday and I'm heading back to SC tomorrow morning. According to my brother, his doctor is recommending Hospice care.
The wood is oak with an ebony stain that didn't quite take. I was trying for a finish similar to my black lacquer walnut speakers.
Front and top:
An externally hosted image should be here but it was not working when we last tested it.
back and top:
An externally hosted image should be here but it was not working when we last tested it.
and bottom ready to wire with tagboard in place, but without heater wire tabs:
An externally hosted image should be here but it was not working when we last tested it.
I've got to set it aside again. Pop went into ICU yesterday and I'm heading back to SC tomorrow morning. According to my brother, his doctor is recommending Hospice care.
Thanks Gary, Pop will be transferred to hospice care tomorrow. My brother will be with him or the transfer, and we will go back down this weekend.
At least he will be more comfortable now. According to the doctor that is all that can be done at this point.
I also got to call our son (USAF) in Germany who hasn't seen pop in 5 years and let them talk.
All in all it was a good trip.
At least he will be more comfortable now. According to the doctor that is all that can be done at this point.
I also got to call our son (USAF) in Germany who hasn't seen pop in 5 years and let them talk.
All in all it was a good trip.
I finally got around to working on it again.
All wiring is complete, but I left the transformer wires long till I get phasing correct, and am sure I'm using this set.
The fuse holder should be moved off center, the power switch moved back opposite of the fuse holder. This would allow the power transformer and power supply boards to be moved back about 1" -1-1/2" to make more room. Layout is kind of crowded.
Wiring went pretty well with the tag-strips, although I ended up using a lot more Teflon tubing to protect leads, than I originally expected to.
I goofed up and mounted two sets of RCA input connectors, One for each pair of speaker terminals. Duh!
I already powered it up when I only had the filaments wired, and checked them.
Next will be checking over the wiring, then check power supplies and bias without the tubes, and finally plug them in and go.
I'll wait till tomorrow for the rest. Too tired tonight to play with electricity.
All wiring is complete, but I left the transformer wires long till I get phasing correct, and am sure I'm using this set.
An externally hosted image should be here but it was not working when we last tested it.
The fuse holder should be moved off center, the power switch moved back opposite of the fuse holder. This would allow the power transformer and power supply boards to be moved back about 1" -1-1/2" to make more room. Layout is kind of crowded.
Wiring went pretty well with the tag-strips, although I ended up using a lot more Teflon tubing to protect leads, than I originally expected to.
I goofed up and mounted two sets of RCA input connectors, One for each pair of speaker terminals. Duh!
I already powered it up when I only had the filaments wired, and checked them.
Next will be checking over the wiring, then check power supplies and bias without the tubes, and finally plug them in and go.
I'll wait till tomorrow for the rest. Too tired tonight to play with electricity.
Sure is DIY, good stuff! A couple of questions, are those handles on top of the chassis beside the OPT's? 2nd question, you are using a 100R balance pot on each pair of output tube cathodes, and 2 bypass caps, did you arrive at that by experiment? It is unusual, but that doesn't mean much these days. The whole amp looks pretty compact to me, well done.
I found the handles in the cabinet section of a local hardware store (Lowes). They make it easy to pick up. Not my idea, but a good one none the less. Yes, 100R Wire wound 5W pots, the two additional cathode resistors are 220R, and there is an additional 27R from the pot common to ground, for a total equivalent of 324R. The cathode bypass resistors are from cathode to ground.
Amp in place.
An externally hosted image should be here but it was not working when we last tested it.
Looking good (as is the Klipsch) 
I just finished stuffing a couple of 6P1-EV into my old SE amp. The amp was originally designed to run ECL86 with the OPT meant for 3.5 ohm load. I could never get a great deal of power (>2W) out of the them with 8 ohm speakers, but the 6P1's seem to like the higher transformed impedance better, especially right at their limits on the plate and screen. The 6N1P-EV driving them is also near its dissipation limit. No unwanted red bits yet though
I just finished stuffing a couple of 6P1-EV into my old SE amp. The amp was originally designed to run ECL86 with the OPT meant for 3.5 ohm load. I could never get a great deal of power (>2W) out of the them with 8 ohm speakers, but the 6P1's seem to like the higher transformed impedance better, especially right at their limits on the plate and screen. The 6N1P-EV driving them is also near its dissipation limit. No unwanted red bits yet though
I didn't bother matching cathode resistors, or potentiometers and ended up with about 39.1mA on one set of tubes and 40.8 on the other set.
Next amp I'll match components to see how it effects operation.
The amp has been running for about four hours now, and is sounding pretty good.
I've got a P-T31 (5K SE to 8 Ohm) from AES that I got to see just how good (or bad) it was for $14. I ran a frequency sweep and it looks pretty good for a small SE amp if I use some GNFB. I may make a small SE stereo amp as a replacement for the (now blown) computer speakers for the wife's computer. I figure three tubes will do for the whole amp. Two of the P-T31s and a small power transformer like the Allied #: 227-0067 ($22.32 plus shipping). Chassis for $15 and I'm looking at around $70 for parts I don't have already.
So many amp topologies, so little time....
Next amp I'll match components to see how it effects operation.
The amp has been running for about four hours now, and is sounding pretty good.
I've got a P-T31 (5K SE to 8 Ohm) from AES that I got to see just how good (or bad) it was for $14. I ran a frequency sweep and it looks pretty good for a small SE amp if I use some GNFB. I may make a small SE stereo amp as a replacement for the (now blown) computer speakers for the wife's computer. I figure three tubes will do for the whole amp. Two of the P-T31s and a small power transformer like the Allied #: 227-0067 ($22.32 plus shipping). Chassis for $15 and I'm looking at around $70 for parts I don't have already.
So many amp topologies, so little time....
I know what you mean. I just sold the Meng 6P1, so I have been building a EL84/6BQ5 PP amp out of salvaged console parts to take its place. It's almost there, just really have to make a wooden skirt so it can stand on its own rather than on old wooden blocks. I am driving it with 6N1P-EV's in concertina (may try 6N3P as they seem to sound happier at lower currents).
You can tell I have a bunch of Russian tubes
Then there's a box of 5B/254M's sitting there, some NOS 807's and a couple of NOS 812-A's that I would love to try.......
Wish I could afford some new iron for them but SE OPTs are SOOOO expensive when you want to push a bit of current through them
You can tell I have a bunch of Russian tubes
Then there's a box of 5B/254M's sitting there, some NOS 807's and a couple of NOS 812-A's that I would love to try.......
Wish I could afford some new iron for them but SE OPTs are SOOOO expensive when you want to push a bit of current through them
Steve, you didn't end up favouring LED arrays over cathode resistors then? I remember you did do some experimenting with them.
Gary, hope your new amp turns out nice.
My current project is a tubelab simple PP, it should be running within a week, be interesting to hear what it sounds like. It also uses a concertina inverter.
Gary, hope your new amp turns out nice.
My current project is a tubelab simple PP, it should be running within a week, be interesting to hear what it sounds like. It also uses a concertina inverter.
No Ian, I decided to go with more or less a traditional cathode resistor and bypass cap on this build.
I may try the LED array on a later build.
I went back and installed GNFB last night at about 8dB, and that has brought the gain down to where the volume pot is about half way at normal to slightly loud listening levels. Previously it was only at about 20%!
Gary, I know what you mean about tubes, I got the remnants of a TV repair shop and spent 6 months culling out the bad tubes. Most tubes I have one or two and a few three of a kind.
The only tube I have enough of to build a stereo and have spares is the 6BQ6 of which I have about 14. That would make for a big amp.
This little 6P1P PP amp is plenty loud enough for me.
I may try the LED array on a later build.
I went back and installed GNFB last night at about 8dB, and that has brought the gain down to where the volume pot is about half way at normal to slightly loud listening levels. Previously it was only at about 20%!
Gary, I know what you mean about tubes, I got the remnants of a TV repair shop and spent 6 months culling out the bad tubes. Most tubes I have one or two and a few three of a kind.
The only tube I have enough of to build a stereo and have spares is the 6BQ6 of which I have about 14. That would make for a big amp.
This little 6P1P PP amp is plenty loud enough for me.
I was just digging through some old boxes looking for my LED bar graph meter that I built in college around 1977. I found the receipt, manual and a photostat of the board layout. But, alas no meter.
However I did find three vacuum florescent bar graph meters and the data sheets along with three TL491CN 10 step analog level detectors and 12 MC3494P 7-segment VF drivers. Very similar to this one on u-tube:
YouTube - VFD VU Meter (Bargraph)
However I did find three vacuum florescent bar graph meters and the data sheets along with three TL491CN 10 step analog level detectors and 12 MC3494P 7-segment VF drivers. Very similar to this one on u-tube:
YouTube - VFD VU Meter (Bargraph)
I have done some experiments with my new lot of 6p1p´s and it looks that when powering some tubes do the same yours do, they went blue (almost a white blue), followed by the same lots of dumped current you reported, It seems that some of the 6p1p tubes went a little gassy, almost to several to make a thyratron tube of a normal tetrode.
I had the whole situation in my control, and before all those cute things exploded, I disconected the HT source, after a few thoughts I had the idea of a gassy tube, after some minutes with the heaters still conected, and thinking in the getter doing its cleaning job, I re-conected the HT and the thing looked ok, the thingy was in shape, and it sounded good!
So I advice you people to run the heaters from this kind of tubes before aplying plate voltages, because some of them had alredy 40 years old, and can be a little gassy, you can kill several things with a gassy one, including your self atempting to shut down the thing, so: be ready and be safe!
I had the whole situation in my control, and before all those cute things exploded, I disconected the HT source, after a few thoughts I had the idea of a gassy tube, after some minutes with the heaters still conected, and thinking in the getter doing its cleaning job, I re-conected the HT and the thing looked ok, the thingy was in shape, and it sounded good!
So I advice you people to run the heaters from this kind of tubes before aplying plate voltages, because some of them had alredy 40 years old, and can be a little gassy, you can kill several things with a gassy one, including your self atempting to shut down the thing, so: be ready and be safe!
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Thanks maton00. Interesting obervation.
Another alternative would be to bake them at 350F (177C) for a couple of hours to activate the getter. There is a thread about baking tubes which have been in storage for many years. There is sound data to back the proposal to elevate thetemperature to activate the getter.
The amp is still running after almost four years of regular usage in the dining room. It is used almost every day.
Another alternative would be to bake them at 350F (177C) for a couple of hours to activate the getter. There is a thread about baking tubes which have been in storage for many years. There is sound data to back the proposal to elevate thetemperature to activate the getter.
The amp is still running after almost four years of regular usage in the dining room. It is used almost every day.
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