Hi,
Most owners of gear using this type of valve tend to replace them every 18 months.
In some so called high-end gear they are often dead after a year and even less...too high heater voltage, gives you a tad more detail for a while, too much of a twisted application...all of that makes sure that the pundit is sent to the till paying through the nose for a matched pair of candles.
Sorry to be sarcastic, my ECC88s haven't been replaced once in 20 years and they still measure 100% on the testers.
Same goes for all my tubes bar the 6080s...well those are the workhorses anyway.
Cheers,
Most owners of gear using this type of valve tend to replace them every 18 months.
In some so called high-end gear they are often dead after a year and even less...too high heater voltage, gives you a tad more detail for a while, too much of a twisted application...all of that makes sure that the pundit is sent to the till paying through the nose for a matched pair of candles.
Sorry to be sarcastic, my ECC88s haven't been replaced once in 20 years and they still measure 100% on the testers.
Same goes for all my tubes bar the 6080s...well those are the workhorses anyway.
Cheers,
The Philips data book here is the 1967 edition. The RCA Tube Handbook from 1957 also states 7V.
But you are right Frank, tubes designed for series connection (P types and U types) are best powered by constant current.
E types designed for constant voltage heater power certainly not, the heater of E types draw virtually a constant current by themselves at varying heater voltages.
Cheers
But you are right Frank, tubes designed for series connection (P types and U types) are best powered by constant current.
E types designed for constant voltage heater power certainly not, the heater of E types draw virtually a constant current by themselves at varying heater voltages.
Cheers
Interesting about the heaters - my Brimar manual says 7.6 volts but both Mullard and Tungsram say 7 volts...
I once read an article in an old radio mag which made great claims for the PCC88 as a small pp output stage. With fixed bias of -6v and a 200v on the anodes, output of 1.5w was claimed, and at its maximum ratings, with fixed bias of -5v and 210v on the anodes, output was supposed to be about 2.5w. The output tranny had a 10k anode to anode impedence. If I remember rightly the article warned of not exceeding the valve's limitations, or it deteriorates very quickly.
I saw this in an old Practical Wireless mag from about 1967-8, but I cannot remember the exact issue...if I find it out I'll post the reference.
I once read an article in an old radio mag which made great claims for the PCC88 as a small pp output stage. With fixed bias of -6v and a 200v on the anodes, output of 1.5w was claimed, and at its maximum ratings, with fixed bias of -5v and 210v on the anodes, output was supposed to be about 2.5w. The output tranny had a 10k anode to anode impedence. If I remember rightly the article warned of not exceeding the valve's limitations, or it deteriorates very quickly.
I saw this in an old Practical Wireless mag from about 1967-8, but I cannot remember the exact issue...if I find it out I'll post the reference.
fdegrove said:
I do this for almost everything now. I picked up a ton of LM317 and LT1083 for dirt so I do a voltage then current reg setup. The tubes come on slower and they're always set at just the right voltage. I haven't used series string tubes in a while, but I'd probably do the same, with the current as the set item.
Using this configuration on DHT fils is indistinguishable to my ears from AC, except without the hum. Use the LT's though.
So what would that need for a 2A3? 2.5V, 2.5A. Which LT108x regulator(s) should I use, how much voltage do I need from the filament transformer, what would you recommend for the rectifier and filter? I think I have a pair of 3300uF/35V Panasonics so I'd probably use those, but I'll probably have to buy everything else, I don't think I have anything else I could use.
I'm pretty sure there's a schematic for this in my Morgan Jones book, but if you could give me a head start on design and/or parts selection, that would be a big help.
Also, if I have AC on the DHT output tubes as well as the IDHT driver tubes, which one would contribute more to the hum? The drivers are 6SL7s, so that's 6.3V, 300mA (I think). Let's assume I've done a decent job with twisting the filament leads and routing the wires (which is a pretty big assumption
).Thanks,
Saurav
Hi,
Yes to some people, no to me...It's a bit more complex than that..
I use unregulated, yet well filtered DC on my 2A3s and compared to AC I feel they sound better, especially in the bass...other peoples' MMV.
I, and others, did some plotting on DHTs with AC and DC on DHT triodes and found that the curves alter when fed with DC.
No big deal but curious nonetheless, now if current regulation sets it straight then we're onto something...
Let's just wait for the verdict of someone with much more hands on experience on this than yours truly...
Cheers,
Yes to some people, no to me...It's a bit more complex than that..
I use unregulated, yet well filtered DC on my 2A3s and compared to AC I feel they sound better, especially in the bass...other peoples' MMV.
I, and others, did some plotting on DHTs with AC and DC on DHT triodes and found that the curves alter when fed with DC.
No big deal but curious nonetheless, now if current regulation sets it straight then we're onto something...
Let's just wait for the verdict of someone with much more hands on experience on this than yours truly...
Cheers,
Hi,
What I have experienced is that the dynamic resistance of the filament is quite high for indirect heated tubes that are intended for voltage drive. So driving it with a constant current source is not a wise idea. Probably tungsten is used for the filament, which has quite a high positive temperature coefficient. Manufactures (at least Philips, I know) recommend to drive such tubes with a voltage and not with current.
When the tubes are cold the resistance of the filament is quite low so when powering up it draws excessive current until heated up. When powering up you can notice that the short wires coming out of the cathode light up quite intense shortly. Although made for it I wonder how this affects lifetime. Also found once a note to make the heater transformer winding in such a way as to limit the inrush current in some way. In the same note: For tubes of different kinds it is largely advised against powering them in series. There is a serious risk of voltage imbalance between tubes and runaway conditions.
For a pre amp I used a voltage stabilised DC heater supply, current limited to app. 20% higher for what is nominal needed for the total amount of current.
A couple of years ago there was a debate in the DIY supplement of Hi-Fi World that there is a sonic difference between when the DC heater voltage is positive to ground and when it is negative to ground. Honestly I do not hear any difference. But the time between doing the mods changed my mood maybe too much to be able to hear such subtleties. And only I tried it with the pre amp and not with a power amp, the power amp heaters run at AC.
Tubes made for series supply are another matter. Heater resistance is more constant, probably Nicrome or the like is used for it. For these I agree with John, these are best powered with nominal current no matter what voltage develops. 12.6 V AC with a suitable series resistance is also an option for a PCC88.
Cheers
What I have experienced is that the dynamic resistance of the filament is quite high for indirect heated tubes that are intended for voltage drive. So driving it with a constant current source is not a wise idea. Probably tungsten is used for the filament, which has quite a high positive temperature coefficient. Manufactures (at least Philips, I know) recommend to drive such tubes with a voltage and not with current.
When the tubes are cold the resistance of the filament is quite low so when powering up it draws excessive current until heated up. When powering up you can notice that the short wires coming out of the cathode light up quite intense shortly. Although made for it I wonder how this affects lifetime. Also found once a note to make the heater transformer winding in such a way as to limit the inrush current in some way. In the same note: For tubes of different kinds it is largely advised against powering them in series. There is a serious risk of voltage imbalance between tubes and runaway conditions.
For a pre amp I used a voltage stabilised DC heater supply, current limited to app. 20% higher for what is nominal needed for the total amount of current.
A couple of years ago there was a debate in the DIY supplement of Hi-Fi World that there is a sonic difference between when the DC heater voltage is positive to ground and when it is negative to ground. Honestly I do not hear any difference. But the time between doing the mods changed my mood maybe too much to be able to hear such subtleties. And only I tried it with the pre amp and not with a power amp, the power amp heaters run at AC.
Tubes made for series supply are another matter. Heater resistance is more constant, probably Nicrome or the like is used for it. For these I agree with John, these are best powered with nominal current no matter what voltage develops. 12.6 V AC with a suitable series resistance is also an option for a PCC88.
Cheers
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