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Another Mullard 5-20.
Another Mullard 5-20.
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Old 29th November 2004, 09:11 PM   #1
GeirW is offline GeirW  Norway
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Default Another Mullard 5-20.


Anyone here can comment on this one.
There have been various threads here about the 5-20,
so i assume the schematic of that one is well known.
I started to read a article by Claus Byrith, over at Lundahl site,
(5-20 . + the CB 4-30)
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Old 30th November 2004, 03:46 AM   #2
ray_moth is offline ray_moth  Indonesia
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Yes, I enjoyed reading Claus Byrith's article, with his explanations of his redesign of the Mullard circuit. I haven't tried building Claus's circuit but it seems to make sense. I think he could have improved it still further if he'd included a CCS in the tail of the phase splitter but that would have caused additional complication.

In his article, Claus suggests that there are basically two established designs to choose from when building a P-P amplifier, namely, Williamson or Mullard. He recommends avoiding the Williamson style, because its two stages of capacitve coupling carry the risk of instability with global feed back. I can't disagree with his reasoning on that point. Incidentally, the same criticism could be levelled at the H.J. Leak designs, which are basically th same as Mullard's design except that they don't have DC coupling between the first and second stages.

However, there are other design options that Claus didn't mention, including the all-differential three-stage design, in which the first stage is a long-tail pair phase-splitter with CCS in the tail, DC coupled (or coupled through a step network) to the second stage, which is is a differential amplifier. It incorporates aspects of both the Mullard and Williamson designs and is my own personal preference. The DC (or step) coupling between first and second stages is compatible with global feedback and the circuit has the added advantage of good PSRR.
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Old 30th November 2004, 07:59 AM   #3
raychak is offline raychak  Hong Kong
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Hi there!

I also planning to build a EL34 pp amplifier, probably a Mullard 5-20 amplifier too! But a friend of mine suggested me to replace EF86 with 6J7G which can enhance the performance, is that true?


newbie to *DIY*
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Old 30th November 2004, 01:45 PM   #4
adalin is offline adalin  Sweden
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I have built exactly that amp and it works fine.

I used outputtransformers from Hammond instead of Lundahl and a toroidal power transformer from Amplimo

It serves me every day

Tubes 4 ever
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