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Why are people still touting the Mullard 5-20 circuit?

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#21
Kay Pirinha said:
Remember, the goal for Mullard fpr publishing the 5-20 and 5-10 designs was to advertise their then new tubes ECC83, EF86, EL34, EL84, GZ34 and EZ81. Hence these amplifiers had to be easily reproducible, and their performance surely could well compete with other designs of those days, given that apt iron was used. I guess they were, and still are, built by the millions.
Best regards!
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Those guys at Mullard knew their stuff. Much more than most experts today, thats for sure. And they would never have published amp designs that are of only mediocre or bad quality because they wanted to show whats in their tubes regarding quality of sound and lifetime.


What has changed is the music mind of the people today, which think that any transformer that couldn't reproduce 50K Hz isn't usable for a tube amp and that every tube amp should sound like a tubed version of their PC soundcard or better, the actual Iphone. A gold standard for most youthfull people in audio.
 
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#22
Schmitz77 said:
You have auditioned an amp thats 50 years old with worn out electrolyts and wonder why it performs badly and has hum?
Do you ever have one idea that this might not be the appropriate method to test something and rate it? Or do you simply have no clue about whatsoever in old tube amps could make them sound worse?
Your rating is simply false and I bet even the speakers and the source didn't match the setup that you used for a qualified rating of components.
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Pease don't make assumptions about what I did and didn't do. The electrolytic capacitors were replaced, there was no significant hum but there was some hiss and the input sensitivity of 50 mV at overload was ridiculously high for modern sources. The 5-10 (and 5-20 I believe) was designed to be used in conjunction with lossy tone controls which dropped the sensitivity to 600mV.

The amplifier came with appropriate speakers using high sensitivity wharfedale drivers from the same era.

I deliberately didn't make any comments about sound quality which is obviously subjective, so no "rating" was implied. Some simple changes can keep the topology essentially the same but improve SNR and make it more usable. The original design goals were appropriate for the time but times change.
 
#23
In a forum board, someone can write anything about the oh-so perfect circumstances that this amp would had when auditioned.
Of course, the amp was in a perfect condition, totally rebuild to original standards (even when those original parts are long gone after 50 years, but you managed, for sure) and yes, the speakers were even perfect ones, the best of the best at those time. And still it wasn't good enough, because today everything is better, of course. The circuits are so much better, the parts are better and the listeners have such a higher level of listening experience.
What I think in the end of all those "perfect" circumstances? No comment. The reality looks in almost any cases much different, but forum writing is easy...and nobody can proove the real facts.
 
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#24
tikiroo,
I'm with you on using donor parts in circuits more appropriate to todays requirements. I've used "harvested" iron from two Heathkit amps to good affect. An EL84 set in a Tubelab.com SPP amp and in 7591A set in an amp using those tubes with a Dynaco Doctor ST70-like driver front end. Both turned out very listenable.

S.
 
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#25
Ruining an all time classic tube amp for donor transformers because under non optimal conditions it played not at maximum level of performance?
The same are the guys who took loudspeakers from old tube radios and throw the rest in the garbage because they can sell them at ebay. What a waste of potential, what a loss on high quality tube amplification.
 
#27
Just to be clear:
1. I think saving good parts from an old amp with crumbling circuit boards and a bunch of out of spec resistors and caps, a service to future tube lovers and a way of honoring what is still good in these parts. I can't think of a better use than giving old trannies, and even some old, but still good tubes, a new and better life. It's a heck of a lot better than having them wind up melted down for scrap or useless in a land fill.
2. I wouldn't think of doing it to a classic Quad, Mac, H-K Citation, Leak or the like. Monetary value aside they are almost works of art in some ways and deserve to be kept whole. Second or third string amps like Heathkits and the like, not so much.

S.
 
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#28
According to the member "tikiroo" this was a classic and all original Mullard tube amp in MINT condition that he decided to rob parts and put in the trash.
As prices of those amps still rise, this will end naturally and will only be done by audio-fools that didn't notice what they are owning and what value it has.
 
#30
Schmitz77 said:
If you may think so, then its highly subjective thinking.
I think exactly the opposite way. With me, there is no case for transistor amps anymore. Build a few of them and owned some more. Always sterile sounding, up to the highly famed Mark Levinson & Co. models. No life or any life sucket out of those mega buck models, best thing is to switch them off and enjoy the silence.

The very best tube amp models can sound vibrant, full of life and swing, energy that proofs every transistor amp as a faulty model by design and with silky highs and thunderfull lows that no transistor is able to deliver until today. Its just a shame that this powerfull technology maybe hasn't been used to its edge and after all those fails people give their subjective rating on audio forums just showing their inability to use a given technology to its very best.


I don't know whats the best in transistor technology, but I studied electronics and know some of their state of the art circuits and they mostly sound boooooring to me, typical transistor sound. Technically speaking, the transistor was never invented to sound high quality audio like. It took decades before the first transistors were listenable in high end audio. Its exactly the same as with digital technology. It took years and years to crawl from the stone edge to something that is listenable, but with respect to the best analog sources still sucks because it contains the same design flaws like transistorized audio equipment.



Much too overengineered, much too complicated (look at all those dozens of negative feedback and regulator loops in every transistor amp) and invented with a theory behind it, that didn't worked out in real life like it was planned by the designers. Transistors were invented to safe energy and heat, to make things smaller and more comfortable and they have its own right in computers, mobile phones and all those electronic gear where its high priority to be small and low weigth with much computer calculation power. In high end audio they will never cut the edge of whats possible, even when people who have never touched this edge spread the sermon of the technically stone age tube technology.


Btw, to implement some technical equipment is often the same art like its to design a component. Most of the people claiming something sounds worse werent able to enjoy it 100% because of those poor matching with signal sources or other components.
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you mean all transistors is bad from first time until now ?
 
#31
tubes sound different, musical, euphonic and melodic, mosfets when run class A comes very close, bjt's? well that is too much hard work...

just look at how they chase ppm distortions.....while NP's mosfets are so simple and uncomplicated to build, much like tubes..
 
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#37
Steve Morley said:
If we believe Morgan Jones when he writes in "Valve Amplifiers" of the 5-20:

"The input stage is an EF86 pentode, which is responsible for the high gain but poor noise performance...."

"The cathode coupled phase splitter is combined with the driver with the driver circuit using an ECC83...... The output stage has an input capacitance of ~30pF, and combined with the 53k ohm output resistance of the driver stage, this gives a cut-off at ~100kHz, which is quite poor."

"....the driver stage has only 10dB of overload capacity. When the output stage gain begins to fall, for whatever reason - cathode feedback, input capacitance loading the driver, or primary inductance in the output transformer - the global feedback loop will try to correct this by suppling greater drive to the output stage, and the 10dB margin will be quickly eroded, raising distortion."

Jones goes on to discuss the output tube's individual biasing resistors and their bypass capacitors, "The capacitor is a short circuit to AC, and so prevents feedback, but its reactance rises at very low frequencies, so it is no longer a a short circuit, and allows feedback. Because the output stage is load matched, this feedback causes an immediate rise in distortion and reduction of power output due to the mismatch."

There are other points as well, I've just chosen a few.

Isn't it time we moved on from the Mullard 5-20?


Cheers, Steve
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Year's ago I had a pair of Audiomasters 5-20's all Partridge tx's and premium parts, as far as build quality goes these are some of the best ever produced in the UK, but it's not a great circuit, compared to a home built (Rankin) 45 se amp, it sounded terribly opaque ( so did Quad 2) I'm sure we can come up with something better now days
 
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#40
My current amp is a 5-20 circuit - 12AX7 front end, 6SN7 phase splitter, and 6AR6 output tubes in pentode - stuffed inside an old Eico ST70 chassis (using the original PT and OTs). It has been one of my favorite amps, especially with new caps, an added choke, and other minor upgrades. It's a - subjectively here - very "fast" amplifier with seemingly unlimited power into my KEF R500 speakers.

Another 5-20 circuit favorite is the Eico HF60 monoblocks using the EF86 on the front end.

My only complaint with the 5-20 is the high gain for most modern sources/preamps. I end up sticking a gain control on the front end to better match my preamplifier.

One a side note I've heard some old Heathkits W-series amps with the Williamson circuit and they sounded very colored, especially with aged original passive parts. A refresh of the stock circuit did wonders to improve the sound.
 
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