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Topic: 250 watts Parallel S.E. advises

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Posted by devo_yan on 05-16-2018
Hello every body, I live in France and I'm new on this forum.

I'm thinking to build (some months) a mono big Single Ended amplifier (200-300 watts) made with triodes (IDHT or DHT doesn't matter for me) for outdoor professional audio.

Have you got an online store to advise to me for custom output transformers and power transformers ? (I have to admit that I'm more looking for cheap price than high grade =s)

On internet I found "toroidy" that seem to be good.

After many thinking, for final stage I think to use
- 10 parallele 845 (psvane) running at something like 1000V (24 watts per tube in A1). (any other advise ?)
- 2 or 3 845 for driver (running at 1000V too (choke and capacitor coupled))
- 1* 300B (choke and capacitor coupled )for to drive the driver stage (with it's own power supply (400V))
- 1* 6J5 (half 6SN7) (or 6sn7GT with both triodes in parralele) carbon resistors/capacitor coupled to drive the 300B (they will share the same power supply than the 300B)

both power supply with
- center tappered tranformer and full wave tube rectified (5Z3 for 400V, 836 for >1000V)
- LCLC filtered (no solid state regulated)

Every tubes will be self bias and without negative feedback.

How much can I expect it weight ? 100Kg ? More ?
Any advise welcome = )))


I often read that S.E. are not good for to properly drive big basses speakers, do you know why ?

I mean why for example a 300B S.E. could produce wonderfull basses when driving a 5" basic sealed speaker and can't properly drive bigger speaker ? Is it because of the poor damping factor ? (I mean the speakers drive more the amp than the amp drive the speakers ^^)

If yes how to increase it ? Someone told me that I need very high current (like plenty 6c33 in parralele or solid state). But why ? with the output transformer the speaker should already see low impedance, right ?

Posted by xandcg on 05-16-2018
I am far from the best person to comment on it but your biggest problem would be the (huge/gigantic) power supply. And I confess I do not know if it is possible to parallel more than two output valves on SET fashion, I never saw it but the ultralinear amplifiers.

For behemoths SETs you are looking for, you will need to choose between some big transmitters valves like 833A, Eimacs, QB5/1750, or ever GM100 (among others).

There is this thread about a related subject:

Posted by devo_yan on 05-16-2018
Hello, thank you for your answer,
I already read this very interesting link (this how I knew about this forum (like "yes ! there is weird people too"))
I never saw too much parellele things too (excepte for solid states); I hope nothing is wrong doing it

I hope some other peoples will answer to this thread
The question is:
"if you really really would love to do a big S.E. amp with triodes for to power four 18 inch Band Pass Horn bass speaker, that can drive them very well, what will you do ?"
(I want S.E. because from my few experiences I have an ever better feeling with S.E. (I have nothing against P.P. don't worry), and the same for triode instead of triode connection penthode (even if I didn't tested so much pentodes in triode connection))

I would like to do it cheap (it will be a kind of usable test), let say 3000e (I have nothing against less, (no I will not use Tango Hirata transformers for this project)) and at least 100 watts in A1 (because my bed is very long and I want to be sure to hear the bass when I'm in my 13m2 bedroom with 106dB/1watt/1meter speakers (I'm joking))

I don't speak english very well so don't hesitate if you don't understand something..

Posted by xandcg on 05-16-2018
Beyond those well know "audiphiles" transformers  there is the Ogonowski also. This is the transformer Lapizator use.

That should not be cheap, and I think you may have problems to find a cheap (probably) custom transformer for you project

You may also look for some info at the Thomas Mayer blog.

Posted by devo_yan on 05-16-2018
Nice thank you for the link, see the "lo SE100-1", 169.0 USD for 7Kg, it's cheap and they look good.

So I was Happy with my choice of parallel 845 (I was hesitating with GM-70 but after a difficult decision I decided that the GM-70 filament consume twice the power of the 845 (and all of a sudden I felt concerned by power consumption (as much as someone wanted tube class A can be)).
But now that I read "How to get a LOT of SET power" again, I'm thinking about
but because I will need to run her with 2500V plate, the Output transformer and the power transformer will need to be far bigger than parralele 845-GM70 right ?

or 833
but the need to run her in A2 scary me

what about 50 parallel
6as7 ? (maybe after soldering 10 of them I will hate me)

If someone could explain me what is the secret for to have good basses with S.E. amp (without negative feedback) ? Does it have something to do with the low impedance of the final stage tube(s) ? So would parallele 845 drive better big bass speakers than GM-100 for example ? or does it have absolutly nothing to deal with ?

Posted by xandcg on 05-16-2018
Just remembering I am not technically capable to do any actual statement.

About the GM-100 I guess so. NatAudio has an amplifier using GM100 but with solid state power supply. Magma.

As you certainly know the actual result will be a consequence of all decisions you did; however you are looking for an amplifier to work on narrow bandwidth, and so you would be better to use optimized output transformers, with narrow bandwidth. In this case, just for bass.

Search in the forums about the Romy Malquiades amplifer and the DSET concept, and you will probably answer your-self later about that (at least partially).

For those high powered transmitting triodes you may want to take a look on rectifiers like PY500 too, and they are cheap. :-)

Posted by devo_yan on 05-16-2018
I already have some PY500 (it's a sign =))) ) and I have 836 too.

I read about Malquiade amplifier threads.

So it seem peoples on this forum like horn speakers (I love them too) and are looking for fast transient response, it's exactly what I like.
But I'm not sure to understood all particularities of the Malquiade amplifier
Maybe it have a fast transient response sound because of:
- only two stages amplifier
- the driver is resistor/capacitor coupled, I guess it's faster than poor choke or interstage transformer.
- very low impedance final stage power supply (I like to do it too =))) )
- no automatic bias (I do it for convenient raisons =s), I guess the time the cathode capacitor charge and discharge we lost speed

And if I understood well, for the 6 channel system, each channel have a optimised bandwith output transformer right ? This is what mean Dedicated SET ?

But I still don't understand the secret for a S.E. amp drive well big bass speakers. To simply use a good output transformer, this is the key ? And it's more easy to build good O.T. for low impedance tube this is why I often read that low impedance final stage tube is better for bass ?
I mean with a very good output transformer, even a 45 DHT can properly drive 4* 18" bass speakers ?

I said that I want to build a S.E. amp for to drive 4 18" BPH speakers but in fact I would like to drive a full range system with passive filters:
- 4* 18" band pass horn
- 1* 10" horn speaker
- 1* 1.5" horn speaker

Is it possible to have good sound with passive filter or will I really need to do 1 amplifier per channel with active crossover (crossover before the amplifiers) ?

(I ask to much questions in the same time)

Posted by Romy the Cat on 05-18-2018
 devo_yan wrote:
So it seem peoples on this forum like horn speakers (I love them too) and are looking for fast transient response, it's exactly what I like.
Horns are not serving “fastest transient response” the direct radiators do. I do not feel that going after ONLY fastest transient response is a right direction to go. Idel your amplification more and you your have more transients. So what?

Posted by devo_yan on 05-18-2018
Ok, I said a mistake, I like direct radiator (sealed speakers) too, but I often noticed more dynamic with horn speakers (I like every speakers (if properly tunned) except speakers that radiate with both sight of the drivers (bass-reflex, tapped horn, horn-reflex, rear loaded horn...)) but it's not the subject.

About my project, I will probably chose GM-100 for final stage (I sent an email to in purpose to know if they would be able to build GM-100 power and output tranformer).
So someone know if we can get strong bass with a 10Y (VT-25) S.E. driving 4* 18 inch bass speaker for example, if yes what does it need, only good output transformer ? Or does too small S.E. amplifier not able to drive too big bass speaker ?

How should I run the GM-100, 3000 volt on the plate and -70 volt on the grid (that should give 300ma (900W plate dissipation)) ?
So 10 000 ohms output transformer (turn ration 35:1 for 8ohms)
so if the grid swing 140 Peak to peak it mean 48 volts RMS/35 (turn ratio)*18 (GM-100 approximative gain) ~= 24 volt in the 8 ohms speakers = 72 watts in A1. So I will need to run the GM-100 in A2 or to run her with higher plate, right ?
What is the recommanded plate voltage and negative grid voltage for to run a GM-100 at full power in A1 ?

I never played with 3000 volt power supply, and I all time used amplificateur case made by 18mm wood, is there any risk to don't use metal grounded case with such voltage ?

Thank you.

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