| Johan Potgieter |
Jaime
No reason. On the contrary, there is a varying potential difference between parts of the filament and the control grid, so what is the actual bias? - etc. It is sometimes a little intriguing how, years after some developments have taken place and had been universally accepted as improvements, some visionaries would suddenly pop up and cause doubt as to which direction in audio is actually forward.
The F1 421A certainly looks neat, but I find the description too loaded with typical promotional fodder to mean much. (I mean: "When simple is best, that's the only ticket to bliss in valve land." Please!) Or simply swapping 6SL7s with 6SN7s?? I personally have a problem with exorbitant costing flea-power amplifiers - I built enough of them myself, and never found a good reason for using multibuck ultra-scarce tubage. Unless for collector's value, of course ...... But it is your money.
Regards. |
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| amperex |
| Usually older direct heater tride power tubes are better. It is the low plate resistance that is desireable in home entertainment amps. |
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| Giaime |
| quote: | Originally posted by amperex
It is the low plate resistance that is desireable in home entertainment amps. |
Now tell me between trioded EL36 and 2A3 (absolutely the same dynamic characteristics) which is better.
:D |
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| Jaime |
Amperex:
Plate resistance 6AS7G : 280 ohms
Plate resistance 421A : 330 ohms
Plate resistance 2A3 : 800 ohms
You said : 6AS7G and 421A are better than 2A3 ? |
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| kmtang |
Hearing is believing.
If you don't believe it, try it out yourself.
I won't say which one is better. It is up to you to decide.
Johnny |
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| SY |
| Or (as I've found), there's no consistent sonic advantage of one over another as a general case. But a DH tube certainly is more of a pain in the posterior to set up and run correctly, which may be its real attraction. |
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| Geek |
| "Better" is too subjective in audio. Kmtang and the correct answer :) |
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| vax9000 |
I believe DHT is better. the low impedance and high linearity combined, is better. 6AS7 has very bad linearity.
My theory:
DHT are old; thus primitive tech; thus big distance between cathode and grill; thus better linearity.
newer diode's problem, newer tech; thus closer cathode and grill (for higher amplify factor); thus worse linearity.
If we can move the grill of new triode away from its cathode, we may get a triode that is better than those old DHT. |
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| rdf |
| quote: | Originally posted by vax9000
6AS7 has very bad linearity. |
How so? |
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| poobah |
Looks pretty squashed between -60 & -80 Vkg.
:xeye: |
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| jlsem |
| quote: | | But a DH tube certainly is more of a pain in the posterior to set up and run correctly, which may be its real attraction. |
Why would that be an attraction? |
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| poobah |
difficult = better... First law of audiophooldynamics.
;) |
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| jlsem |
| quote: | | difficult = better... First law of audiophooldynamics |
Maybe you could clarify further. What do you mean by "audiophool"?
John |
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| poobah |
I guess in this case audiophool would refer to someone who believes that something must be better if, and only if, it is more difficult.
:) |
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| rdf |
| That definition needs work if it's not to include everyone save for the guys in the chip amp forum. |
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| poobah |
| I knew you were lurking... I did say "if, and only if". |
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| Eusebius |
I think the question to ask is whether builders who have used DHTs for a fair time (months, and with a really good filament supply) - and particularly small tubes like the 26, 12A, 01A etc - have gone back to using directly heated tubes and stated that they preferred the sound. I don't know any who have.
There are plenty of people who make comments about DHTs WITHOUT having had them in their own system (with a really good filament supply - RonanRegs, current sources etc) for enough time to get used to the sound, which is fairly generic in the case of the small DHTs. DHTs (like other things) aren't something you can evaluate without hearing them properly in a system you know well with your usual demo CDs or LPs.
Of course all evaluation of this kind is subjective, but so far I made a simple DHT preamp with a decent power supply and have taken it round to three friends. It was audibly more transparent with better timbre and tone than a 12b4, a 417a and a passive preamp. When these guys heard it in their own systems they could hear the difference.
I'm in London and we have an Audiocircle here, and one by one the members are going over to DHT small tubes. We all know the value of 845s, 300bs and 2a3s but the small tubes are something else and give a distinctive sound signiture right at the start of the amplification chain.
Why they do so construction-wise I don't know - wish I did. But the sound of the small DHTs has a distinct family resemblence - a certain clarity, sparkly top end, delicacy and good timbre to stuff like cymbals, grand piano, voice and woodwind. Once you identify it it's like women and chocolate - a craving that has to be satisfied. So something about them is different and quite distinctive. |
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| Tweeker |
With bigger stuff I tend to wonder whether its really just heater v filament or if some of it is triode v stapped multigrid tube.
Though I cant think of many power triodes with oxide heaters that are intended for high linearity AF service. |
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| Geek |
| quote: | Originally posted by Tweeker
Though I cant think of many power triodes with oxide heaters that are intended for high linearity AF service. |
Outside of kilowatt-level AM modulators anyway ;) |
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| Tweeker |
| Stuff for <110Mhz tends to be directly heated. :spin: |
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| rdf |
| quote: | Originally posted by Geek
Outside of kilowatt-level AM modulators anyway ;) |
The low mu ones are especially nice. According to the Eimac sheets on hand two of the early 3x3000a1 DHTs in push-pull will swing 6000 watts at 1.8% THD. |
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| Shoog |
| quote: | | Looks pretty squashed between -60 & -80 Vkg. |
Most people seem to use the 6080's at high bias points where it may show poor linearity. I am running mine at -30Vkg for 100V on the plate and 100mA current. Works very well. This is a high current enabled tube and works very well at these high current low voltage settings. Infact in a push pull configuration it is the best amp I have made so far.
Shoog |
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