New Thomas Mayer 845 Amplifiers

Ron Resnick

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After the introduction of the 845 amplifiers with an indirectly heated driver, here is Thomas Mayer's new top of the line single ended 845 mono amps with a directly heated driver. The Elrog ER887 is a completely new tube type especially developed for these amps by Deutsche Elektronenröhren Manfaktur GmbH.

As the 845 requires a large voltage swing at its grid an amplifier with all directly heated tubes would normally require minimum stages due to the low amplification factor of directly heated triodes.

The all-new ER887 is a big directly heated triode with thoriated tungsten filaments. No similar tube type was ever made so far. It shares the identical glass bottle/Jumbo 4 pin base as the 845 and operates at similar plate voltages.

The power supply uses a hybrid bridge with two ELROG ER274A and two 6AU4 TV dampers for the rectification of the plate voltage. The complete set of four chassis takes a whole square meter of floor space.




http://vinylsavor.blogspot.com/2018/07/the-new-845-mono-amplifiers.html?m=1
 

Zero000

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Jul 28, 2014
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Any more info anywhere Ron?

EDIT: Ah - resolved now.
 
Last edited:

LL21

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Ron Resnick

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I saw the amplifiers first on Mono and Stereo.

ZeroStarGeneral may have some insight into these new amplifiers.

I am curious about the output power myself.
 

astrotoy

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Ron Resnick

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25W per channel. Although up to 30W can be squeezed out of a single 845 I design for best possible sound rather than max power.


Thomas

Thank you, Thomas. We are very honored to have you here!
 

VinylSavor

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They are a bit below your self-imposed power limit. :)

I have not really imposed any power limits. I just don't want to make compromises in sound quality below a certain level in order to achieve higher power. Cost, size and weight pretty much go up linearily with max power if the sound quality should remain at the same level. That's why this set of 4 chassis has a combined weight of 150kg. Higher output power is possible with larger tubes like the 212. Er even more with a beast like the 851. See photo with a 211 besides it. With a single 851 about 150W would be possible in single ended mode, no feedback and pure Class A1. But the weight of such an amp would be staggering, also the heat it would produce.

BTW this set of 845 amps are the first prototypes which I built to prove the concept and test the ER887 driver tube which was specifically developed for this amp. Two sets of this amp with all silver transformers are now in the making. The copper prototypes will be on demo at the upcoming Hong Kong Hifi show in August

Best regards

Thomas



851.jpg
 

Ron Resnick

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Dear Thomas,

Please don’t tease us! :eek:

I think you could sell to WBF members alone several pairs of 150 watt SET amplifiers!

Purely out of curiosity why do you prefer the 851 tube over the 833 (used by Wavac and AM Audio) and the GM-100 (used by NAT)?
 
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LL21

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Dear Thomas,

Please don’t tease us! :eek:

I think you could sell to WBF members alone several pairs of 150 watt SET amplifiers!

Purely out of curiosity why do you prefer the 851 tube over the 833 (used by Wavac and AM Audio) and the GM-100 (used by NAT)?

Agree!!!...most intriguing.
 

VinylSavor

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Hi!

So far I have not built an amp with either of these tubes so everything is theory at this point.
The 833 requires Class A2 drive to get these kind of powers and this brings a whole lot of problems to be solved.
Class A2 operation is something I avoid.
I have not looked closely at the GM100 tube yet.
I bought a couple 849 and 851 tubes in the past because of their extreme linearity. But admittedly no amp built be me yet with them.

In general I recommend to stick with as little power as really needed and implement that in the best possible sound quality. At power levels beyond the 845 it is easier to replace the loudspeakers for a more efficient one. In the past I have powered a one off installation of a speaker at one of the ETFs (European Triode Festival) to ear shattering levels in a room which hosted 100+ people. And that with 5-10W. So far my customers requested power amps in the range up to 25W from me and most amps I sold are in the single digit power range.

But if someone is interested and commissions a larger power amp, I will build it. But it would be a monster and require 6 chassis. One for signals section one for the high voltage supply and one for the filaments.

Also having a tube factory at my disposal I would probably come out with a new tube rather than relying on extremely rare NOS tubes. A 212 could be built by my tube factory and could easily bring double the output power of a 845

Best regards

Thomas
 
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Audiophile Bill

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Wow Thomas. An Elrog 212 would be a beast of a tube.

Ron - I think you need the 6 chassis Mayer 212 with your Pendragon. You know it makes sense ;)
 

DaveC

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Nice to see your new amp, Thomas, and thanks for posting... I have been a fan of your blog for a long time! :)
 

zztop7

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Excellent statements from VinylSavor:

"In general I recommend to stick with as little power as really needed and implement that in the best possible sound quality. At power levels beyond the 845 it is easier to replace the loudspeakers for a more efficient one. In the past I have powered a one off installation of a speaker at one of the ETFs (European Triode Festival) to ear shattering levels in a room which hosted 100+ people. And that with 5-10W."

zz.
 

morricab

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I have not really imposed any power limits. I just don't want to make compromises in sound quality below a certain level in order to achieve higher power. Cost, size and weight pretty much go up linearily with max power if the sound quality should remain at the same level. That's why this set of 4 chassis has a combined weight of 150kg. Higher output power is possible with larger tubes like the 212. Er even more with a beast like the 851. See photo with a 211 besides it. With a single 851 about 150W would be possible in single ended mode, no feedback and pure Class A1. But the weight of such an amp would be staggering, also the heat it would produce.

BTW this set of 845 amps are the first prototypes which I built to prove the concept and test the ER887 driver tube which was specifically developed for this amp. Two sets of this amp with all silver transformers are now in the making. The copper prototypes will be on demo at the upcoming Hong Kong Hifi show in August

Best regards

Thomas



View attachment 42833

Not you Thomas, Ron. He didn't want to go below 150 watts or so for his speakers. Your amps power is fine :).
 

GMKF

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Hi!

So far I have not built an amp with either of these tubes so everything is theory at this point.
The 833 requires Class A2 drive to get these kind of powers and this brings a whole lot of problems to be solved.
Class A2 operation is something I avoid.
I have not looked closely at the GM100 tube yet.
I bought a couple 849 and 851 tubes in the past because of their extreme linearity. But admittedly no amp built be me yet with them.

In general I recommend to stick with as little power as really needed and implement that in the best possible sound quality. At power levels beyond the 845 it is easier to replace the loudspeakers for a more efficient one. In the past I have powered a one off installation of a speaker at one of the ETFs (European Triode Festival) to ear shattering levels in a room which hosted 100+ people. And that with 5-10W. So far my customers requested power amps in the range up to 25W from me and most amps I sold are in the single digit power range.

But if someone is interested and commissions a larger power amp, I will build it. But it would be a monster and require 6 chassis. One for signals section one for the high voltage supply and one for the filaments.

Also having a tube factory at my disposal I would probably come out with a new tube rather than relying on extremely rare NOS tubes. A 212 could be built by my tube factory and could easily bring double the output power of a 845

Best regards

Thomas

Hi and welcome to WBF.
I have been reading your blog about tubes for about one year. I always enjoy the tube of the month post :D
Whats your opinion on the 6C33C ? Do you have experience with tubes with "variable amplification coefficient" (varibalen µ)
(https://www.frihu.com/roehrentechnik/tube-non-grata/)

Danke und Grüße an den Bodensee :D
 

VinylSavor

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Thanks guys!

Whats your opinion on the 6C33C ?

Not really a fan of them. While I do use indirectly heated power tubes and am also not afraid to triode wire TV tubes like the 6CB5A, Those are for my budget level amps. In the top of the line amps I prefer to stick with the most linear tubes available. IME this gives the best sound quality or let's say the sound I am after.


Do you have experience with tubes with "variable amplification coefficient" (varibalen µ)

Not really, as stated above I prefer the linear tubes and a long as I have enough of those to use I do not need to resort to this kind of tubes. But I always admire people who build with uncommon tubes and bring them to a good use.

Danke und Grüße an den Bodensee :D

Greetings to Munich. I miss my old home.

Thomas
 

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