diyAudio

diyAudio (https://www.diyaudio.com/forums/index.php)
-   Tubes / Valves (https://www.diyaudio.com/forums/tubes-valves/)
-   -   The point of an 845, 211, 805 amp? (https://www.diyaudio.com/forums/tubes-valves/339572-845-211-805-amp.html)

samsdad 25th June 2019 02:52 PM

The point of an 845, 211, 805 amp?
 
Hello,

Iím trying to understand the point of an 845, 211, 805, etc. amplifier. Let me explain:

From what I understand, all things being equal, and assuming competent circuit design, parts quality, etc. the more gain stages an amplifier has, the less likely it is to be linear. And, from what I understand, generally speaking, the more transformers involved in a circuit, the more it will suffer from transformer-based distortion.

Iíve never heard such an amp, mind you, so maybe the proof is in the pudding. But as a general observation, all of the amps that Iíve seen that use these tubes in their power section are all preceded by something like an input tube such as a 6922 or 12ax7, followed by a 300b or 6L6 section (described as the driver section), then followed by an 845, etc. Or, it omits the input section and requires a separate preamp. In any event, all of such amps seem to have a veritable village of transformers stacked around these tubes, or because of weight and space limitations, stacked in a separate case.

Are these amplifiers really more linear than say, a El34 ultra linear amp running in class A designed with, again, a quality circuit, parts, etc.? Is there something super special that Iím missing in an 845 SET amp (line magnetic, for example) that canít be achieved in a 6p15 SET (Decware zen Torii, for example) plus a quality subwoofer?

analog_sa 25th June 2019 04:42 PM

Quote:

Originally Posted by samsdad (https://www.diyaudio.com/forums/tubes-valves/339572-845-211-805-amp-post5834201.html#post5834201)
generally speaking, the more transformers involved in a circuit, the more it will suffer from transformer-based distortion.


This may hold some academic merit bit is completely irrelevant in real life. Good transformers have negligibly low harmonic distortion and subjectively sound more transparent than capacitors. At least to some listeners.

Not sure why would you compare any of the big transmission valves to an EL34, at the very least they offer a much higher power compared to a triode strapped EL34.

As for the linearity, some very highly regarded amps are far from linear. Perhaps we should not overstate its importance.

As with everything else it all boils down to implementation. It is very easy to end up with a poor sound amp full of transformers, chokes and transmission valves.

FullRangeMan 25th June 2019 05:02 PM

Its beyond me why they use these expensive 845, 211, 805 tubes, when a GM70 or GK71 price is only $17
''GSTube.com''. Tubes, sockets etc. Search result for <u>gm70</u>
They use 12AX7 why is a ready available tube in China and have lots of gain 100x

Lingwendil 25th June 2019 05:29 PM

The "super special" that can't be acheived with a Decware or similar amplifier should be quite obvious- it isn't a big, huge, hot "statement" of an amplifier the same way the impractically heavy and large amps are. For some folks they have a biting desire to simply make something that way, so they do.

While the car they drive is different than yours, and the road they drive is different, they still aim to take the same journey to audio enjoyment. It's fun, it's ridiculous, and it's expensive. It's all valid to an extent.

multi 25th June 2019 06:26 PM

I think the price of $17 is for sockets not the tubes

schiirrn 25th June 2019 06:32 PM

Quote:

Originally Posted by samsdad (https://www.diyaudio.com/forums/tubes-valves/339572-845-211-805-amp-post5834201.html#post5834201)
Are these amplifiers really more linear than say, a El34 ultra linear amp running in class A designed with, again, a quality circuit, parts, etc.?


Quite on the contrary, winding an output transformer for such tubes is a nightmare if you aim at full range operation and just want +-3dB from say 25Hz to 40kHz.
But then again, for some people there might be more aspects to an amplifier than linearity.

GoatGuy 25th June 2019 06:36 PM

This may be both anecdotal and mathematically possible to formalize, but in my experience, one shouldn't ask each voltage gain stage to maximize its gain. Doing so seems to 'accentuate the triode/pentode distortion' of the stage.

For instance … whether one uses 6SN7s — hugely reputed to be marvelously linear — or 12AX7's or any of its socket substitutes of equally legendary quality, since the incoming signal to a main amp is relatively low (typically 700 mVRMS, allowing for Ī3000 mVPK) … having the first stage being “only” a 10◊ to 15◊ gain merit is a good balance between minimizing noise and stage distortion at the same time.

Now the signal is (say) 15 ◊ 700 mVRMS = 10 VRMS.

Great! As KodaBMX has posted in other fora, the next stage is optimally the symmetric signal inverter (supposing feed to a push-pull output section).

Higher current valves such as the 6SN7 seem to do well, tho' there's not a thing in the world wrong with low power pentodes. Not-exquisitely-matched anode and cathode resistors … plus a trimmer to dial in symmetry … then gives a nice pair of complementary VRMS ≈ 10 V signals.

THEN … each phase is voltage-amplified again.

Not much, maybe only 3◊ or 4◊ at the next stage. A single 6SN7 or other dual triode (or dual pentode) manages this well without a capacitor bypassed cathode resistor. Now with VRMS at about 35 V, there is a good strong drive for some powerful output valves in PP configuration.

Just saying,
GoatGuy ✓

samsdad 25th June 2019 07:14 PM

So, what Iím gathering so far is that Iím not missing anything other than perhaps a physical behemoth of an amp when compared to, say, your typical PP integrated El34-sized fare, all other things being equal.

I own both a Decware SE84 CKC (SET EL84, 2 watts) and Torii Junior (PP EL34 UL, 20 watts) and, imho, the Jr. outclasses the CKC in terms of soundstage depth (which apparently is an artifact of negative phase 2nd harmonicóhere somewhat adjustable, apparently, via the VR tubes in the circuitóat least thatís what my ears tell me) and power.

Iím thoroughly chuffed with the sound of the Jr. running it into Klipsch RB 81 mkii speakers (97 dB efficient supposedly), but, not having heard an 845, etc., was just making sure that there wasnít another nearly universally accepted higher level of enjoyment that Iím missing out on comparatively speaking, by moving to transmission-line-tube level amps.

FullRangeMan 25th June 2019 08:27 PM

Quote:

Originally Posted by multi (https://www.diyaudio.com/forums/tubes-valves/339572-845-211-805-amp-post5834428.html#post5834428)
I think the price of $17 is for sockets not the tubes

I confirm the GM70 tube price is $17.50 each graphite plate version its a impressive tube.
The socket for this tube has no price why its out of stock.
I had bough various GM70 and 6C33 tubes from Andrey.

Lingwendil 25th June 2019 08:30 PM

You've got to wade through a lot of ad-copy type of speak, even among the DIY side of tube and "audiophile" hobbyists. Everyone has a special idea that they swear by, and there are a lot of "spiritual" reasons behind design decisions, regardless of whether or not they're good engineering or financially sound.

If you like what you have, cool. Don't let it stop you from building/buying different amplifiers or speakers. Try different stuff, even wildly different. Step outside of your comfort zone and build something crazy, everyone should build a boat-anchor of an amplifier at least once. :)


All times are GMT. The time now is 03:20 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 17.65%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio

Wiki