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 Post subject: How does a 6H6 tube work!
PostPosted: Apr Thu 19, 2012 2:16 am 
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Hi, Working on an RCA radio that used a 6H6 tube for the audio detector. While going through the Riders diagam on voltage measurements I see only a couple volts across the tube! How can it work with such a small voltage? :?

Corby Dawson


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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Thu 19, 2012 2:59 am 
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Its a detector diode it only takes a couple of volts to bias it on .

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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Thu 19, 2012 3:03 am 
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Think of that little workhorse as a dual diode. In fact you could substitute a 1N34 germanium diode for each section when in this service at lower frequencies. Higher frequencies, not.

Tube could also be used as a rectifier for very small amounts of current within it's boundries, sometimes found in old precision instruments.


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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Thu 19, 2012 6:06 am 
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The 6H6 (and its 7 pin minature clone the 6AL5), work pretty well with low voltages on them.
I seldom have had to replace one.
I have seen them used as rectifiers over the years also. Mostly in some VTVM's and signal tracers as diode detectors in probes and IIRC, some home brew projects from the radio projects magazines from the "good old days".
I have also seen projects using them as bridge rectifiers in metering circuits (2 tubes).

You would be amazed at how little voltage is really required in some projects to make the tubes work. I made a radio using a 6J5 in a regen circuit and got down to 6VDC on the plate with it still working!

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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Thu 19, 2012 9:34 am 
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You could try hooking only the heater voltage to the 6H6 and see if there is any voltage between
cathode and plate, with a DVM or VTVM on DC.

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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Thu 19, 2012 11:25 am 
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Here's a data sheet that includes the plate characteristics:
http://frank.pocnet.net/sheets/093/6/6H6.pdf

It seems that it will work even with a plate voltage less that 1v. Most of the data sheets just show the in-circuit performance.

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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Tue 24, 2012 9:02 pm 
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The 6H6 was designed from the start to have high "perveance"; that is, it needs hardly any voltage to get some current moving. That's what you want in a detector. It so happens that they also have high enough emission and breakdown voltage that they can be used as a power rectifier if you don't need much power, but that's a secondary application.

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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Tue 24, 2012 10:24 pm 
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A 6H6 or 6AL5 contains very small plates which are very close to its cathodes. Consequently, they begin conducting at much lower voltages than a power rectifier. The trade-offs for this is that the tubes can only handle a few mA of current, and the peak inverse voltage is also pretty low.

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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Tue 24, 2012 10:47 pm 
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Which means you always blow one out if you exceed max AC voltage in a VTVM. Same 6AL5.


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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Wed 25, 2012 1:28 pm 
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I hooked up a 6AL5 in place of the crystal in a crystal set awhile back and it makes a fair detector.

-Dennis


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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Mar Thu 26, 2015 6:00 am 
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codefox wrote:
Think of that little workhorse as a dual diode. In fact you could substitute a 1N34 germanium diode for each section when in this service at lower frequencies. Higher frequencies, not.

Tube could also be used as a rectifier for very small amounts of current within it's boundries, sometimes found in old precision instruments.


-I do not have any spares -I am working on a Crosley Moel 86CR console. The FM did not work-I replace the 6H6 FM detector and it started to work but the Audio is garbled then it fades out-My question is could I subsitute with a pair of 1N34??? I need to check all the componets first.. I belive this is a Foster Seeley Discriminator circuit.


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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Mar Thu 26, 2015 6:43 pm 
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If the 6H6 you installed is also bad, it could possibly have something to do with the garbled audio, but it is really unlikely that it would have anything to do with fading. Both of the symptoms you mention have lots of causes, and there isn't really a lot of information to go on. For starters, is the garbled audio and fading only on FM? How does the set play on AM and short wave (if it has short wave bands)? What work has been done on it so far?

Of course it is possible to use diodes in a discriminator circuit rather than a tube, but it is not as simple as just popping in a couple of diodes and dumping the tube. Realignment of the discriminator will likely be necessary, and it may be necessary to make other modifications in addition. So it would be easier to get the radio working the way it was designed, with a 6H6. Putting diodes in now would only add more variables and make it more difficult to solve the actual problem.

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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Mar Sat 28, 2015 11:39 pm 
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Using the diode function on a DMM will tell you how much drop there is across the diode with whatever the DMM uses for test current.

You can get the voltage pretty low, rivaling germaniums even, if you give it 9 or so volts on the heater.

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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Mar Tue 31, 2015 2:03 pm 
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For replacing a diode used as a detector a 1N5711 works great and maybe it would work good to replace the diodes in a discriminator.


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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Mar Tue 31, 2015 3:54 pm 
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Location: Powell River BC Canada
A 6H6 works well as a power supply rectifier , especially for battery tube circuits.
Instead of the doorbell transformer, two 6.3 filament transformers could be used
back-to-back for isolation.

Attachment:
6H6 LOW COST POWER  SUPPLY S.jpg
6H6 LOW COST POWER SUPPLY S.jpg [ 103.21 KiB | Viewed 425 times ]
Attachment:
6H6 LOW COST POWER  SUPPLY SC.jpg
6H6 LOW COST POWER SUPPLY SC.jpg [ 122.05 KiB | Viewed 425 times ]

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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Mar Tue 31, 2015 4:48 pm 
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codefox wrote:
Think of that little workhorse as a dual diode. In fact you could substitute a 1N34 germanium diode for each section when in this service at lower frequencies. Higher frequencies, not.

Tube could also be used as a rectifier for very small amounts of current within it's boundries, sometimes found in old precision instruments.

10.7 MHz is well within a 1N34A germanium diode's efficient switching frequency. The output voltage on a 1N34A doesn't begin to drop substantially until about 250 MHz or more, depending on circuit impedance.


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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Mar Tue 31, 2015 10:15 pm 
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re 6h6s common as detectors in tube radios? I note my sx28 uses a 6b8, likely due to it also being used to develop smeter voltage. Is the 6h6 superior in the world of thermionic detectors?


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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Fri 03, 2015 12:57 pm 
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db gain wrote:
re 6h6s common as detectors in tube radios? I note my sx28 uses a 6b8, likely due to it also being used to develop smeter voltage. Is the 6h6 superior in the world of thermionic detectors?

It is an excellent small signal detector and was used in many early vacuum tube voltmeters for the AC rectifier, as well as FM detectors/discriminators but was pretty much replaced by the miniature 6AL5 twin diode tube later on, and then by crystal rectifiers like the 1N34, 1N60, etc., when they became less expensive. They all do pretty much the same job as well as all the others.


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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Sat 04, 2015 6:56 pm 
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too-bamp wrote:
db gain wrote:
re 6h6s common as detectors in tube radios? I note my sx28 uses a 6b8, likely due to it also being used to develop smeter voltage. Is the 6h6 superior in the world of thermionic detectors?

It is an excellent small signal detector and was used in many early vacuum tube voltmeters for the AC rectifier, as well as FM detectors/discriminators but was pretty much replaced by the miniature 6AL5 twin diode tube later on, and then by crystal rectifiers like the 1N34, 1N60, etc., when they became less expensive. They all do pretty much the same job as well as all the others.



Wow-great input, it opens my eyes for that little work horse called "6H6". So it is frequency sensitive tube in the hi area.l will replace all the componets around the circuit with no subsitutes & use exact ohmages ,capacitaces----I will try later with 1n34s solder into a broken octal male shocket, just to see if it works. Come to think of it the audio is not too great when in the AM & Sw operation Thank you all : Too-bamp, db gain, radiotechnician, tube radio, dkjones96 & Cris108--- In America, The Chief.


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 Post subject: Re: How does a 6H6 tube work!
PostPosted: Apr Mon 06, 2015 1:59 pm 
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