• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Those Magnificent Television Tubes

Interesting, they sure look bigger than a typical 15 Watter.

I opened about 25 or the 100 boxes. I only found one old style tube ans it looks like it could eat about 15 watts, maybe a little more. All the others have the same size plates as the 24 watt tubes.

I asked how long this sale would run. The answer is that tube numbers will be removed from the list as their inventory returns to "normal". Their inventory system can tell them just how many of a given tube they have sold in the past 15 years and how many they have. The 6HJ5 sold 5 or 10 per year until someone stuck them into the red board and extracted a few watts. They sold almost 250 of them last year.
 
It looks like a 6CD6 with different grid spacing. Higher gm and g2mu, lower Va at high currents than the 6CD6. It does look like a 20 or 23 watt plate, not the 15 or 17 watt one.

The heater would need to be 600mA to work in a series string so I doubt they changed it like they did the 6146B...

These high power heater tubes have the advantage in cathode emission and peak cathode current, which makes them super candidates for high power g1+g2 drive amps. You need high peak cathode current to avoid cathode saturation on signal peaks with high plate current + grid current.
 
These high power heater tubes have the advantage in cathode emission and peak cathode current

By the way, ESRC has an interesting 24 Watt sweep for $3, the 26DQ5.

The 26DQ5 is the clear winner here, if you are building an OTL or something else that needs big cathode current peaks. The plate in both tubes looks the same.

I was sitting at the ESRC table at the Dayton hamfest a few years ago when a guy walked up and asked for some 6DQ5's. He only wanted RCA's and then looked at the guts for a particular construction. He said he was building OTL's and these were the only ones that worked. He bought a few tubes and left without explaining what he was looking for. Maybe he knew something, or maybe he was just superstitious.......
 
AM modulator

Once I made an AM modulator using a power transformer as a modulation transformer (plate to +B secondary and output to TX valve from 220V primary, and NFB from 6.3V) with two 6KD6 12 pin compactrons, and work very nice. It only used +330V in AB1, drived by a 12AX7 phase spliter and a 6CB6 as CCS from a -100V line (Long tail pair).
 
I have a Mullard GY501 on the shelf.
It has CAUTION X-RAYS What is that telling me?
It's telling you that when operated at rated high voltage of around 25KV, it can produce X-rays, albeit soft X-rays. This tube, and those like it, were always operated in a shielded enclosure. As the voltage level increases, there is an upward sliding scale for the X-ray level or hardness. But there are no X-rays produced when unused.
 
Mullard GY501....It has CAUTION X-RAYS....What is that telling me?

In the late 60's there was a full scale panic when someone determined that a color TV set produced high levels of X-rays. it was determined that the high voltage circuit was the source. The tube that you have is a rectifier designed to operate with 25 KV on its plate. Any tube operating at this voltage level can generate X-rays. The GY501 and others like it have zero use in audio and little other use so it sits on your shelf. It doesn't emit anything harmful unless 25 KV is applied!

It was discovered that the rectifier tube wasn't the main X-ray source. The high voltage shunt regulator was. Tubes like the 6BK4 were high voltage triodes running with 25+ KV on the plate. It's purpose was a shunt regulator across the 25 KV supply to regulate the voltage during dimly lit scenes when the CRT's beam current was low. There were many attempts to redesign the shunt regulator to minimize X-rays including leadded glass, but eventually the shunt regulator was moved from the secondary side of the flyback transformer to the primary side where it only had to deal with 1 to 2 KV.
 
It was discovered that the rectifier tube wasn't the main X-ray source. The high voltage shunt regulator was. Tubes like the 6BK4 were high voltage triodes running with 25+ KV on the plate. It's purpose was a shunt regulator across the 25 KV supply to regulate the voltage during dimly lit scenes when the CRT's beam current was low. There were many attempts to redesign the shunt regulator to minimize X-rays including leadded glass, but eventually the shunt regulator was moved from the secondary side of the flyback transformer to the primary side where it only had to deal with 1 to 2 KV.

Correct! Have a look at the GY501 curve and see that there's a plate-cathode voltage of far less than 100 volts at the typical current needed for a colour TV CRT of ~1 mA. That's too less for generating X-rays!

Best regards!
 
Correct! Have a look at the GY501 curve and see that there's a plate-cathode voltage of far less than 100 volts at the typical current needed for a colour TV CRT of ~1 mA. That's too less for generating X-rays!
Actually in the case of television HV rectifier tubes X-ray generation had very little to do with the anode to cathode potential differential, but much more to do with the Bremsstrahlung effect from the high voltage applied. And since this HV potential was high frequency pulses (15.750KHz in the U.S.), it's effect was less then the DC high voltage applied to the shunt regulator tube.
 
Used run and repair (Mechanically & load reload software when it crashed often) an XRF machine which ran 50KV. Changed a few of those big tubes. cooled with deionized H2O. Tubes would last about 2 yrs. The first machine I worked with was a Seimens from '69 with ticker tape software loading and big floppies back in the mid 80's. It was horiz.laid out and about 10 X 4 ft with a zillion tubes & many nice looking transformers. Those tubes never gave any problem! If I had only known , that the tubes were useful when it was scrapped in the late 80's! . It had some nice big transformers too!

Later machines were reliable and automated. Easier to repair and smaller. Vacuum was always an issue as it was necessary to have a perfect one in the chamber where the sample was zapped and many sensors picked up the results, so we were always working on pumps and seals.

Randy
 
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In the late 60's there was a full scale panic when someone determined that a color TV set produced high levels of X-rays. it was determined that the high voltage circuit was the source. The tube that you have is a rectifier designed to operate with 25 KV on its plate. Any tube operating at this voltage level can generate X-rays. The GY501 and others like it have zero use in audio and little other use so it sits on your shelf. It doesn't emit anything harmful unless 25 KV is applied!

It was discovered that the rectifier tube wasn't the main X-ray source. The high voltage shunt regulator was. Tubes like the 6BK4 were high voltage triodes running with 25+ KV on the plate. It's purpose was a shunt regulator across the 25 KV supply to regulate the voltage during dimly lit scenes when the CRT's beam current was low. There were many attempts to redesign the shunt regulator to minimize X-rays including leadded glass, but eventually the shunt regulator was moved from the secondary side of the flyback transformer to the primary side where it only had to deal with 1 to 2 KV.

This shows the irresponsibility of some manufacturers.
No matter what is said, NOBODY knows what the safe level of radiation to a human.
 
This shows the irresponsibility of some manufacturers.
No matter what is said, NOBODY knows what the safe level of radiation to a human.

True, but modern society has become much more aware of product safety than they were 50 years ago. Yes, some TV's emitted X-rays, but radios had the power line connected to the chassis such that a broken plastic knob could kill you, cars didn't all have seat belts (and some burst into flames), and doctors thought that cigarettes were good for calming the nerves without hazard. Sometimes you have to learn what is bad before you can fix it.
 
Actually in the case of television HV rectifier tubes X-ray generation had very little to do with the anode to cathode potential differential, but much more to do with the Bremsstrahlung effect from the high voltage applied. And since this HV potential was high frequency pulses (15.750KHz in the U.S.), it's effect was less then the DC high voltage applied to the shunt regulator tube.

The CRT is like a small particle accelerator.
Acting on the electrons principally two forces: The due to electric field of high voltage and the due to magnetic field of the deflection yoke, and do so over a relatively large distance, then, the electrons collide with anode at high energy levels.
Precisely, CRT is designed to produce Bremsstrahlung effect, and then radiation in the visible spectrum allows us to watch TV, but radiation exceeds the visible spectrum and reaches the X-ray level.
Fortunately he agreed to put lead in the glass formulation.
 
True, but modern society has become much more aware of product safety than they were 50 years ago. Yes, some TV's emitted X-rays, but radios had the power line connected to the chassis such that a broken plastic knob could kill you, cars didn't all have seat belts (and some burst into flames), and doctors thought that cigarettes were good for calming the nerves without hazard. Sometimes you have to learn what is bad before you can fix it.

In my country there are still TVs with live chassis ! and are not very old !
Whenever repair one, I ask if they have children.
 
...but radios had the power line connected to the chassis such that a broken plastic knob could kill you...

True enough, but radios and TV sets weren't the major offenders. A rectified mains DC PS isn't such a big deal for this application since the only thing the end user need connect is an antenna which can be isolated from potentially dangerous voltages with a suitably insulated coupling transformer. If built right, the end user will never come into contact with a hot chassis. (Of course, you can't guarantee that some end users won't perform "surgery" on the unit to add some feature like a headphone connection that will defeat the protection.)

The A Number One problem occurred when the same power supply topology was used with audio amps. Low powered guitar practice amps, or amps like that Lafayette 5W kit that was introduced in 1959, resulted in electrocutions and near electrocutions. They also destroyed equipment, as there aren't many computer sound cards, CD and DVD players, or tuners that can stand up to 120Vrms. Even some "insulated" radios and TV's weren't so well insulated if the chassis was mounted to its wood or plastic case with exposed screw heads, which was all too common a practice.

Isolation PTX's are still a very good idea, and the extra voltage for the DC rail improves headroom. It's also a good deal safer, especially if you include third wire grounding to divert dangerous voltages to ground if there's a fault. Really no excuse not to include a PTX for any audio design. A PTX is still cheaper than a computer, CD player, a trip to the emergency room, or a funeral.
 
Interesting, they sure look bigger than a typical 15 Watter. Will be interesting to see what your "stress test" will produce.

HD pents have very conservative ratings, as these were intended for an application that produced max power continuously with a signal with one constant waveform: max RMS power. This is just about the most brutal type of operation, and these HD finals had to do it for hours a day, and do so with a decent service life.

The 6BQ6s that I used for audio power finals are rated with Pd= 12W -- same as a 6V6. As audio finals, I run the bias to ~50mA/plate at 350Vdc so the operational Pd= 17.5W. This spec busting doesn't produce red plates, even when observed in the dark. The RCA grey plate 6BQ6s will show a trace of color if you increase the plate current to 70mA. The Sylvania black plate 6BQ6s still aren't showing any color, though the actual plate dissipation is 24.5W -- spec busting by over 100%.. A 6V6 would probably melt down under those conditions. It's a good thing too, in that the hotter biasing definitely improves sonic performance, nor does it seem to seriously impact service life for this much less demanding application. I'm still using the original 6BQ6s and the bias hasn't changed in five years of almost daily use.
 
True enough, but radios and TV sets weren't the major offenders.

I found a somewhat different story. I worked in TV repair from 1967 to 1970 and ran the service department in an Olson Electronics store in 1971 and 1972. This was in Miami and many houses still didn't have air conditioning. A lot of houses had terrazo floors (ours did). Terrazo is a Portland Cement based mixture with colored stones that is highly pollished. It was common in old Florida houses and used from the 1940's to the 80's. Standing on that with bare feet is like standing on wet concrete. Touch a live circuit, prepare to die!

Many old radios had lost their paper or cardboard back covers, their chassis were often connected DIRECTLY to one side on the power line. Everything had a two prong plug, and so did most houses. As stated many old radios had exposed screws or broken plastic knobs.

Some TV sets had power transformers, with the death cap wired from one side of the line to the chassis. Some (old Sylvania color sets) had metal cabinets, WITH the death cap. Some TV's had hot chassis with plastic cabinets....and a metal whip antenna on top. THe antenna was isolated by a balun transformer wound on a cardboard former. A year or two in the Florida humidity and the former was conductive enough to zap the owner.

Rabbit ear antennas were also common in Miami. At least once a week we got a call because a customer was getting shocked by the TV or the antenna.

Yes ther were guitar amps that regularly zapped their owners, I got zapped a few times by my old Fender. Standing berefoot on the floor and touching the guitar with a sweaty hand (we didn't get AC until I was in high school) evoked the use of bad language. I eventually could tell which way to orient the plug by the faint hum in the speaker when the guitar was plugged in. Still, there were far more TV's and radios in use by the general public than guitar amps.

The PC86, and other tuner triodes are designed for cascode operation.....Eli is correct. Grounded grid, not cascode.

The EC/PC86 does look like it was designed for grounded grid oeration. There are many tubes designed for VHF TV and FM radio use that were designed for cascode operation. They are all dual triodes though. The 6BQ7 and 6BK7 are common type numbers. Many were designed with a variable Mu characteristic so that AGC could be applied to the top tube. They work well for audio LTP stages, and gain stages in guitar amps.

I have explained the operation of TV sweep tubes in other threads, but it has been a while. A TV has two sweep circuits.

The vertical (or frame) output tube operates as a linear amplifier. It is basically an audio amplifier designed for a single frequency, 60 Hz US B&W or 59.97 Hz US color or near 50 Hz in the rest of the world, and a uses sawtooth waveform. The vertical output power in a small black and white TV may be 1 to 3 watts usually provided by a SE triode. Common types are the 6SN7, 6BL7, 6BX7, 6EM7, 6DN7 and triode wired 6V6 types.

A large color TV may need up to 10 watts and it is usually a SE pentode. The most common were the 6LU8 and 6LR8. A vertical output transformer applies this signal to the deflection yoke. The deflection yoke is a set of electromagnets that bend the electron beam up or down to control the vertical aspect of the TV picture. It "sweeps" the electron beam across the screen in the vertical direction. If the linearity isn't perfect, round things aren't round. They become egg shaped. When the power output dropped the picture shrank from top to bottom. Really old TV's had vertical height (gain) and linearity (cathode bypass feedback adjust) pots.

The entire vertical output circuit including the transformer can often be lifted right out of a TV set and used as an audio amplifier. I made guitar amps this way in the 1960's. The most popular "conversion" is the Bottlehead SEX amplifier. The early versions used a TV vertical output transformer for the OPT until the supply dried up.

The horizontal (line) output tube has a much tougher job. It "sweeps" the electron beam left and right across the CRT face. OK, that easy. The magnetics work like the vertical sweep, but at 15,750 Hz (US B&W) or 15,734 Hz (US Color) Again up to 10 watts are needed for a 25 inch color TV.....but wait theres more..... the horizontal output tube has three more tasks.

It must produce the high voltage that accelerates the electron beam toward the face of the CRT. This little task alone needs serious power. How much? THe typical 25 inch color CRT can draw over 1 milliamp......at 25 to 27 KILOVOLTS. So 1 mA at 27 KV is 27 watts. Some is also consumed by the previously mentioned shunt regulator, but it draws more current when the CRT doesn't draw much in an attempt to keep the total draw constant. We will assume the total HV power is 30 watts.

The horizontal output must produce the focus voltage to focus the beam so that it is a single point as it hits the CRT screen. Typical here is 3 to 5 KV at 500 micro amps. Another watt or two are needed here.

The average large color TV has a B+ supply of 350 to 375 volts. How do we get big power from a fairly low B+ voltage without half an amp of current? Simple we DON'T. The TV's power supply may deliver 350 volts, but we rectify some of our horizontal sweep and use it to boost (bootstrap) our power supply into the 500+ volt range. This is a seperate supply generated by the horizontal sweep circuitry, rectified by the damper tube (we like these too) to make "BOOSTED B+" often called just "BOOST". We are adding 150 volts or so to the B+ at up to 200 mA , so we need another 30 watts. In large TV's the BOOST may feed the vertical sweep section and the video output stage.


What? We need 10 + 30 + 2 + 30 = 72 WATTS!!!!! How do we get this from a single tube that fits inside a TV set. Obviously a linear SE amplifier isn't going to work. So, the horizontal output tube is NOT operated as a linear amplifier. It is actually a constant current sink that is switched on and off. The tubes we use for RF and audio linear amplifiers were never intended to be used in this manner. Most of them just happen to be good at it though.

The "drive" voltage is applied to G1. This is an asymmetrical square wave (short off time) that switches G1 between 0 volts and cutoff. The voltage applied to G2 sets the current through the tube when it is switched on. This is why most horizontal sweep tubes have screen grid curves with G1 at zero volts.

The B+ is applied to the plate of the damper tube (a rectifier). The cathode of the damper tube is connected to a tap on the primary of the flyback transformer. The plate of the horizontal output tube (HOT) is connected to another tap on the primary, while its cathode is grounded. The deflection yoke is wired across two more taps on the primary. There are other taps used for synchronization, focus voltage (rectified by tube or SS) and other functions. There are one or two secondaries on the flyback. One has thousands of turns and generates the high voltage. The other (if present) lights the filament on the high voltage rectifier tube. Later tube TV's used solid state HV and focus rectifiers. Some flybacks are wound as one big autotransformer except for the heater winding(s) which much float.

When the HOT is switched on a constant current flows from the B+ through the damper tube, through the flyback transformer, into the HOT's plate and out through the cathode to ground. From basic electronics theory we know that a constant current through an inductor (flyback/yoke) generates a ramp (sawtooth) voltage which is what we need to sweep the beam across the CRT face. The ramp continues until the beam reaches the edge of the CRT. At this point the HOT is cutoff causing the beam to "fly back" to the other edge of the CRT. We know what happens when the current through an inductor is abruptly cut off, the voltage rises. The rising voltage pulse is coupled to the secondary where it is rectified and filtered. THe flyback operates at 15.75KHz, but it is usually resonant in the 100KHz region. This creats ringing at switchoff, which is captured by the damper tube (damping the ringing and recovering the energy) and added to the B+ creating the boost.

This is a rather ingenious scheme that evolved over a period of years, and continued to evolve into the SS era. From this we see that the HOT was the big boy from the receiving tube era and thats where the last of the improvements in receiving tube technology were focused. THe last tube in the TV to be displaced by silicon was the HOT. THe damper tube was the king of rectifiers too. Its cathode ran directly off the flyback seeing 500 volts or so of DC and several more volts of high frequency energy.