• 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.

6 volt recifier tubes

None of the diodes mentioned here will deliver the power that a 5AR4 can except for the damper diodes.

The 6BY5 needs a rather small input cap to survive and they will spark out if you use the typical 47uF. The 6X4 is a wimpy 7 pin rectifier, the 6X5 is the same thing in an octal package. The Bendix 5993 is a bit better, but specced at only 70 mA, and blows up at about 140.

That leaves damper tubes. These are designed to run as a pulse rectifier in a TV set. Many have a very high heater to cathode breakdown rating so they can run off of the same heater supply as the other tubes. They come in many flavors and ratings in 7 pin, octal, 9 pin miniature, and 9 or 12 pin compactron. Two tubes are needed for a FW rectifier. Several are on the ESRC dollar menu. Look for type numbers ending in 3 (sometimes 4).
 
None of the diodes mentioned here will deliver the power that a 5AR4 can except for the damper diodes.

That leaves damper tubes. These are designed to run as a pulse rectifier in a TV set. Many have a very high heater to cathode breakdown rating so they can run off of the same heater supply as the other tubes. They come in many flavors and ratings in 7 pin, octal, 9 pin miniature, and 9 or 12 pin compactron. Two tubes are needed for a FW rectifier. Several are on the ESRC dollar menu. Look for type numbers ending in 3 (sometimes 4).

Old color TV damper tubes are the best choice: they are very robust, have very high maximum H-K and P.I.V voltage ratings , slow warm-up and (last but not least) are dirt cheap and available. You can use any in the 6CL3/6CM3/6CK3/6DW4,... family. For safety reasons,avoid European types with cathode topcaps (EY88,EY500..) Some disadvantages are that you'll need NOVAR tube sockets and there are no dual (full wave) versions of these tubes. Tube manufacturers usually doesn't recommend using damper diodes as (50/60 Hz) power supply rectifiers,probably because they were designed for short pulse type operation at TV horizontal line frequency (15.75 KHz) ,though I never had any reliability or reduced lifetime issues with damper diodes used as power rectifiers. Maybe some (maximum peak cathode current) derating is needed at 50/60 Hz. TV damper diodes were also used in some old HAM equipment power supplies and were very reliable .
 
I had a bad experience with one of those damper diodes -- wound up around 10 feet back and knocked on my derriere.

Used In a color TV set the damper diode has very high voltage pulses of 5 Kv (and more) on its cathode and that can really BITE !! Most old tube type TV schematics have a "do not measure" mention near the damper tube for some very good reasons. Used as a low voltage power supply rectifier a damper tube is no more dangerous than any common rectifier tube (5U4,5AR4,...),still better to avoid types with (cathode) topcaps like the EY88,EY500 etc...
With any tube circuits using potentially lethal voltages think SAFETY FIRST and keep your hands away...
 
Most old tube type TV schematics have a "do not measure" mention near the damper tube for some very good reasons.

Yes, but the reason is not what you would think. The DC voltage at the plate of the horizontal output tube and the damper tube is high (400 to 700 volts), with pulses into the several KV range. The flyback pulse is only a few uS wide with a very short fall time, and thus has a significant amount of high frequency energy. The high frequency content is enough that the skin effect comes into play. Assuming that you had a voltmeter capable of measuring 5KV at DC or 60Hz. Attaching it to the sweep circuit in a TV would force a significant portion of the energy to flow along the surface of the resistors in the voltage divider inside the meter. At best you would get an inaccurate reading. Usually you would get a blown meter. Yes, I blew the dividers in my Eico VTVM kit shortly after I got it in the mid 60's.
 
I bought a whole bunch of the 6CD3. The only problem is-where on earth do you get the sockets? I suppose it would not be impossible to make something. I have used the 6D20P that Wavebourne mentions. I had to solder to the cathode cap as the ones which I bought on ebay did not fit. The Loctal sockets that I bought from the same seller did not work either and I ended up making(rather ludicrous) connectors from them.The voltage drop across the 6D20P was really very low as I recall.
 
I bought a whole bunch of the 6CD3. The only problem is-where on earth do you get the sockets? I suppose it would not be impossible to make something. I have used the 6D20P that Wavebourne mentions. I had to solder to the cathode cap as the ones which I bought on ebay did not fit. The Loctal sockets that I bought from the same seller did not work either and I ended up making(rather ludicrous) connectors from them.The voltage drop across the 6D20P was really very low as I recall.

6CD3's needs 12 pin duodecar (also called "Compactron") sockets. These are still available from Antique Electronic Supply and from many sellers on the well-know auction site you mentioned.
 
Yes, but the reason is not what you would think. The DC voltage at the plate of the horizontal output tube and the damper tube is high (400 to 700 volts), with pulses into the several KV range. The flyback pulse is only a few uS wide with a very short fall time, and thus has a significant amount of high frequency energy. The high frequency content is enough that the skin effect comes into play. Assuming that you had a voltmeter capable of measuring 5KV at DC or 60Hz. Attaching it to the sweep circuit in a TV would force a significant portion of the energy to flow along the surface of the resistors in the voltage divider inside the meter. At best you would get an inaccurate reading. Usually you would get a blown meter. Yes, I blew the dividers in my Eico VTVM kit shortly after I got it in the mid 60's.

Yes I know.... the "do not measure" mention was not there for user safety but for test equipment safety: most VTVM's (and probably modern DMM's) would not survive to an attempt to measure a damper's cathode voltage. I didn't believed it... until I burned the expensive precision resistors in my VTVM. Since then I used the less accurate but much more meter-safe "screwdriver test" on damper cathodes and horizontal output plates.
And if the HF energy can burn resistors it can burn your skin too. Not deadly,but not a pleasant experience either... All this is history now.