12GN7 makes a great driver tube. I was running one in Triode Mode with a Gyrator for the anode load, driving a 300B with very low distortion from select 12GN7s. Everything is packed up right now as I am moving so I can't find my notes on specifics. I did see quite a spread in distortion over several manufacturers. I think I had around 50 tubes and deemed 20% to be unacceptable.
The only issue I have with the 12GN7 in triode mode (with a IK screen resistor) and lowish 10K anode resistor #20mA running current is the hefty input capacitance, aggravated with the triode mode Miller cap thrown in. Using these tubes as diff driver for push pull stages as I do; the cathodyne as Williamson style phasesplitter, the resistor values have to kept low to reduce the HF Miller loading onto the cathodyne higher anode impedance. A diff driver using a CCS can avoid much disparity, but even so with Miller I calculated roughly 180pF equivalent loaded input capacitance of the 12GN7.
With push pull, above 10Khz I noticed rapidly increased output transformer distortion. This leads me to the following conclusion that for optimum performance for push pull, don´t use Cathodyne phasepsplitter with driver tubes exhibiting high Cg1 with g2,3 strapped to Anode. Use LTP, again with lowish anode resistors and CCS in joint cathodes for better HF balance and performance. The gain will be lower but there are other ways of making it up.
BenchBaron
.
With push pull, above 10Khz I noticed rapidly increased output transformer distortion. This leads me to the following conclusion that for optimum performance for push pull, don´t use Cathodyne phasepsplitter with driver tubes exhibiting high Cg1 with g2,3 strapped to Anode. Use LTP, again with lowish anode resistors and CCS in joint cathodes for better HF balance and performance. The gain will be lower but there are other ways of making it up.
BenchBaron
.
Interesting. Perhaps the very high intrinsic gm and the needed frame grid are not consistent for some manufacturers (a lot more difficult than the grids from 300B or 4P1L...) not a good news for people who not bought it when are cheap...
The first several years of my illustrious (ha ha) career in consumer electronic repair involved the descendants of many old B&W sets I had taken apart as a kid.
Flash forward 55 years. At ye olde thrifte store, for all of four dollars, I ran across a small diathermy device from the sixties. A piece of medical equipment used for physical therapy by deep-heating with a low-RF transducer. Molecular vibration, same physics principle as a microwave oven, except at the upper end of the audio spectrum. A spiky waveform with its rise and fall time in the megahertz range was what I think did the actual heating. It was called "shortwave" diathermy even though but its fundamental frequency was relatively low.
Opened up said device, and along with the power supply transformer, oscillator board, etc., therein sat a pristine, virginal-looking 6DQ6. The horizontal output tube of choice for countless 21" black & white TVs from the Twilight Zone era. It evoked a certain kind of nostalgia - specifically the odor of human flesh being burnt at 15.75 KHz. The "skin effect" starts somewhere around that frequency, so when you accidentally brush the plate cap with the back of your hand, (they were often uninsulated back then) along with the weird, nasty jolt, a a tiny bit of you gets cremated. It's a smell you never forget.
Flash forward 55 years. At ye olde thrifte store, for all of four dollars, I ran across a small diathermy device from the sixties. A piece of medical equipment used for physical therapy by deep-heating with a low-RF transducer. Molecular vibration, same physics principle as a microwave oven, except at the upper end of the audio spectrum. A spiky waveform with its rise and fall time in the megahertz range was what I think did the actual heating. It was called "shortwave" diathermy even though but its fundamental frequency was relatively low.
Opened up said device, and along with the power supply transformer, oscillator board, etc., therein sat a pristine, virginal-looking 6DQ6. The horizontal output tube of choice for countless 21" black & white TVs from the Twilight Zone era. It evoked a certain kind of nostalgia - specifically the odor of human flesh being burnt at 15.75 KHz. The "skin effect" starts somewhere around that frequency, so when you accidentally brush the plate cap with the back of your hand, (they were often uninsulated back then) along with the weird, nasty jolt, a a tiny bit of you gets cremated. It's a smell you never forget.
In my early youth I've found two of such diathermy devices, both Made by Siemens, both equipped with a RS1006B power triodes and a pair of 866 alike mercury rectifiers. Operation frequency was 27.12 MHz. In the meantime all these tubes were sold.
Best regards
Best regards
I grew up with a GE TV set from the fifties. It had a 6BQ6GT, and one of my favourites pass time was using a long screw driver to poke the top cap and the CRT anode. You could see the plasma flowing. It's a miracle I did not get electrocuted!
Not a miracle, but due to skin effect. I also loved to provoke arcs this way 🙂.
Best regards!
Best regards!
I had an old Zenith B&W with a 17DQ6 HOT and no insulator on the top cap. We used to hear the “sizzle” coming from the TV occasionally and couldn’t really figure out why. One evening I finally saw the very thin faint purple plasma stream coming from the CRT to the anode cap on the HOT. Yeah, the voltage there gets high, but it spends a lot of its time closer to ground. At 15.75 kHz intervals. Funny thing is that the path was curved, not going in a straight line.
You get the same smell being burnt at 2 GHz, too. I had a 10 watt 2GHz prototype on FR4 that was running a half dB low (ie, putting out 9 watts). Since FR4 is lossier than Rogers, I decided it see if that one watt was being lost in the RF output trace. I found more than one watt there with my finger when I tried to check the trace temperature. Hot as the blazes of hell and damnation, and stunk up the room.
The strange things kids do. Dunndat myself, but never got shocked and didn't poof any TV sets either.
6BQ6s also make some very fine audio finals, like 6V6s good for almost 40W.
In my youth the TV's are all IC's and semiconductors, but even so, sometimes I "put in danger" some Hout transistors making these irresistible arcs... I made it very fast, and almost all sets survived this... 😛
NOTE: arcs in the final HV terminal. In the collector of the HOT the amplitude is too low to make a decent show...
And, now I have a tube TV in collection, and now I understand the "anode arcs" heheh
NOTE: arcs in the final HV terminal. In the collector of the HOT the amplitude is too low to make a decent show...
And, now I have a tube TV in collection, and now I understand the "anode arcs" heheh
Far easier to poof a solid state TV. We had another B&W that seemed to last forever and was still in use till 1987 when it was finally replaced with color. All IC and transistor except the compactron HOT. Can’t tell you how many other people’s color sets I changed that stupid output transistor in in the meantime. That old all tube B&W eventually lost its vertical output transformer, and since it was so ancient no replacement was available. I tried a 120-24V power trafo (which was the right ratio), but without a proper air gap in the core the picture was pretty distorted at the bottom, and even rolled over.
Those 6BQ6’s however, are not Tubelab Approved for making crazy watts. The DQ6’s are. On paper you could get 80 watts out of a pair of 6BQ6, but they are not up to that task. Then again, 20-40 watt output transformers can be had for reasonable money and it’s enough watts for most uses.
80W from PP 6BQ6s as Class C RF finals. As Class AB amps, 80W out would really be pushing it.
Don't have any 6DQ6s, however, 6DQ5s can make some bigwatts, as can 6CB5s (older TV HD type) over 100W. Also have 36LW6s that can make really bigwatts and do it at reasonable (VPP= 350VDC) May have to do something with these some day. When you start talking such projects, you're gonna be needing custom wound OPTs. The project I did with 6BQ6GAs was able to use a junkbox Stancor OPT that looked to be designed for Class A 6L6s. It even included two tertiary windings that look to be for UL operation since 6L6s have a screen grid voltage limit. It did come up short on power rating, and so don't get more than 30W out, even if the 6BQ6s can do ~37W.
+1 for semiconductor hard voltage limit: they even not tolerate it pulse/tune cap goes a little low: voltage builds ups, and within some pulses, surpass the SOA of it and it explodes...
I don’t have any DQ6’s either, but several other similar types with the 1.2A heaters. They at least have the larger plate structure - that little bitty BQ6GT is cute, but not for crazy wattage. The innards aren’t any bigger than a 50C5. The DQ5’s are nice. With a 125V screen, they act like 6550’s. With the screen that low you don’t quite get 100W per pair, but you can clip the bejeezus out of it and not hurt the screens.
350 and 1000 watt PA amps are on the horizon, but I have another ~2 years to go on building this house. Then the tubes come back out again.
350 and 1000 watt PA amps are on the horizon, but I have another ~2 years to go on building this house. Then the tubes come back out again.
I just nabbed a quartet of 12GT5 sweep tubes. I may end up using them in a low power SE amplifier with some smallish Transcendar output transformers that I bought back when they were still making transformers. I may do a Schade setup with a depletion mode mosfet as an input device.
Some may not realize that the pinout of the 6DQ6 and 6BQ6 tubes is the same as the typical audio tubes like the 6V6 and 6L6 if you connect a plate cap to pin 3. My first real DIY guitar amp came in my pre-teen years when I cloned a friends 5C1 Fender Champ amp (6SJ7 driving a 6V6 powered by a 5Y3). It used parts collected from dead 1940's and 1950's TV sets that had been dumped in a dry lakebed near my house where people dumped their trash. Yes, the 6V6 was used as the vertical sweep (frame) output in some really old TV sets. The Dumm Blonde Kid never figured out why the 6BQ6GT screamed like a modern "metal head" amp and got quite loud, but the larger 6DQ6 just glowed red, made some parts smoke, and produced a weak distorted sound. I mean bigger is better right? I wouldn't understand things like bias, impedance, and load lines until I got into a three year long high school vocational electronics program several years later. It was the late 60's in Miami. Our textbooks were from the 1950's. The lab in that school was where I really learned to make things glow. Can you make the outer metal envelope of a metal 6L6 glow red? No, but you can stink up one whole wing of the school trying. The paint had peeled, and the base was beginning to burn when the tube lost its vacuum and died.
As a kid we had walkie talkies from the Lafayette Radio Electronics store. Every afternoon we got this loud buzzing that seemed to dance across every channel in the 27 MHz unlicensed Citizens Band. We didn't know what it was but there were two hospitals within a couple miles of our neighborhood. 30 some years later I met a guy that fixed electronics for medical offices, and I met the diathermy machine. Some ran at 13.56 MHz and some ran at 27.2 Mhz, both of these frequencies are in ISM bands where just about anything goes including MRI machines with multi kilowatt level pulses. Many of the older low powered diathermy machines did use a TV sweep tube. I saw a couple big ones that used a 211 transmitting triode! Most ran the tube on raw AC, or rectified, but unfiltered DC. Some of the big ones used the tube as half of a voltage doubler much like a microwave oven does today.
Sure they are......how long do you want them to last? Back in 2008 AES decided to reduce their stock of "NOS" tubes with a sale that went on for a while with lower prices every week. Some of the NOS tubes were not so NOS, so a pair of crusty oldies got the hot seat for a "life test." These were run in SE for a total of a few hours before they didn't work so well any longer. I think I was on the 20+ watt per channel region when they still sounded good. The sound quality degraded as the vacuum got contaminated. I ended the experiment when one of the tubes started to run away to save the OPT's.
I grabbed a box full of "NOS 6BQ6's" from the AES sale and then got another from the dissolution of Angela Electronics. I still have a bunch of these tubes. The 6BQ6GT (small plate) will live in a HiFi amp at about 80 WPC since it only sees that power level on loud musical peaks. Life is shorter in a cranked guitar amp. The 6BQ6GA/6CU6 (large plate) will live at 100+ watts in a HiFi amp, and I also got ample life out of them in a guitar amp at 100 watts. I graduated to the 6AV5 for most of my LOUD experiments when I got a box full of them. They are the same tube with a different pinout and no plate cap.
I recently fetched the box of 6AV5's for a requested "blast from the past" involving UNSET in SE. I did a quick push pull experiment that made 68 watts before a funny smell killed the fun. It turned out to be my old Fluke 407D power supply. I never planned to test P-P so I didn't use the big supply. I'll get back to it sometime soon. See post #563 and those that follow here:
There are many extreme experiments scattered throughout the "Tube Sale At AES" thread. Understand that these happened about 16 years ago when I had a little less knowledge and a lot less restraint. How many tubes can one guy blow up in a lifetime?
Attachments
Here a friend of mine are wanting some of my PL509 since he got one machine using it (several years ago)...
Telefunken (or Siemens, which actually were Telefunkens) EL156's also were candidates here in Germany.
Best regards!
Best regards!
https://www.nadotornado.com.ua/foru...-lampovyj-usilitel-khronologiya-izgotovleniya
20 Watts in Class A
fine tuning - using a spectrum analyzer
the entire process of creating and setting up an amplifier is shown without hiding anything
instead of output tubes 6p41s you can use
6p36s
6p42s
6p44s
GU50
changes are minimal - the main thing is fine-tuning and selection of tubes according to parameters
output audio transformer - TOroidal - with an overall power of 80 or more Watts
all this so that at a volume of 5 Watts the distortion was at 1000 Hz at a level of 0.028% with a feedback depth of no more than 4 dB