Hi guys,
I was going to do some experiments with a high-voltage SRPP stage for my ESL direct drive voltage amp stage with 6HS5 tubes.
I got a quintet of Raytheon packaged and marked 6HS5's and yesterday I wanted to check out their heater current profiles. This is important as these will be fed with floating DC-DC converters with limited current surge capability. The nominal heater current is 1.5A @ 6.3V, but to my consternation, 4 out of five drew 2.4A @ 6.3V!
Interestingly, there are variants of the 6HS5 like the 6HZ5 with 2.4A @ 6.3V heater, and the 6HV5(A) with 1.8A @ 6.3V. They only differ in heater current, the rest of the data sheets are identical as far as I can see.
But the ones I have are clearly marked 6HS5. Do these things happen in tube country, that heater currents can vary so much, or maybe that marking is somewhat loose?
Jan
I was going to do some experiments with a high-voltage SRPP stage for my ESL direct drive voltage amp stage with 6HS5 tubes.
I got a quintet of Raytheon packaged and marked 6HS5's and yesterday I wanted to check out their heater current profiles. This is important as these will be fed with floating DC-DC converters with limited current surge capability. The nominal heater current is 1.5A @ 6.3V, but to my consternation, 4 out of five drew 2.4A @ 6.3V!
Interestingly, there are variants of the 6HS5 like the 6HZ5 with 2.4A @ 6.3V heater, and the 6HV5(A) with 1.8A @ 6.3V. They only differ in heater current, the rest of the data sheets are identical as far as I can see.
But the ones I have are clearly marked 6HS5. Do these things happen in tube country, that heater currents can vary so much, or maybe that marking is somewhat loose?
Jan
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It doesn't matter unless series heaters are employed, P type prefix, (100mA) on valves.
The heater current does vary with conditions but not normally beyond say 10% for the same valve type. Different and 'equivalents' will vary.
The heater current does vary with conditions but not normally beyond say 10% for the same valve type. Different and 'equivalents' will vary.
There are instances were the same tube was printed and sold under different names. Several PCC88 tubes draw the specified 300mA at exactly 6.3V, instead of the nominal 7V. Then they could have been labeled either ECC88 or PCC88 according to the market requirement. I have many replacement type tubes that have been factory labeled with multiple markings, as example 6BC5 / 6EC5 or 6GK5 / 6FQ5A. They fit both types. In your case, current draw value is not guaranteed on datasheet, so I guess that the manufacturer was labeling the tube as 6HS5 or 6HZ5 based on market demand.
So another data point: the 2.4A tubes are taller than the 1.5A tubes. Coincidentally, the taller tubes are the height of the 6HZ5, which is specced ... you guessed it: 2.4A.
Yet, ALL of them are stamped 6HS5 which is the smaller 1.5A type.
Sort of fake tubes or what?
Jan
Yet, ALL of them are stamped 6HS5 which is the smaller 1.5A type.
Sort of fake tubes or what?
Jan
Yes something like that seems to be going on. And indeed there is no tolerance on the heater current in the data sheet, but 2.4A for a nominal 1.5A seems a bit extreme.
It seems that if I buy more 6HS5's I also must specify the bulb height ... !
Jan
Hi
Looking at your reply on this thread, I wonder if you can cast some light on an issue with with a bigbottle phono stage using PCC88's
What prompted this post is you have said P prefix valves should be run at 100ma.
To explain what I'm getting at, we've recently had a discussion on this forum about what is the correct voltage on a PCC88, as they are specced at either 7 or 7.6 v, depending on the data sheet.
Having read up on it, it's become clear they are current, not voltage driven.
If you look at this thread
Bigbottle Phonostage Builders thread.
particularly post 936, you'll see what I'm asking, as I've measured current on the PCC88 heaters at just over 100ma, but was under the impression they should be 300ma.
Could you clarify this for me?
Many thanks.
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A PCC88 is specified for 300mA heater current. The voltage is secondary and may vary.
Just as in an ECC88 the voltage should be 6.3V, with the current being secondary and may vary.
If you measure less than 300mA in a PCC88, that means you have not enough voltage in your circuit to get up to 300mA. Ohms law.
Jan
Just as in an ECC88 the voltage should be 6.3V, with the current being secondary and may vary.
If you measure less than 300mA in a PCC88, that means you have not enough voltage in your circuit to get up to 300mA. Ohms law.
Jan
I think Jon mixed up P and U valves. U valves need 100 mA, P valves 300 mA. U valves were typically used in radios without supply transformer that could work on AC and DC (U stands for universal), P valves were for television applications.
Towards the end of the tube era the manufacturers started to re-use newer designs for old bottles. The lengthy TV tube thread explains it more in depth. For example an older tube designation with a dissipation of 18 watts might have the innards from a newer 24 watt design.
I also found out that on my '6HS5' tubes, pin 7 & pin 8 are interconnected making them 6JD5/6JH5s which is consistent with a 2/4A heater.
What a mess!
Jan
What a mess!
Jan