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Old 25th Oct 2018, 10:51 pm   #1
Tyso_Bl
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Default Mullard π class AB Amplifier circuit

I've found a reference to a design of amplifier attributed to Mullard, (Transistors, Clement Brown), 3rd edition. I'd like to see the original design article, can anyone help please?

T
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Old 26th Oct 2018, 5:12 pm   #2
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Default Re: Mullard π class AB Amplifier circuit

Follow up from last night, forgot to attach the circuit, ooops.
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File Type: pdf classa.pdf (139.2 KB, 363 views)
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Old 26th Oct 2018, 10:15 pm   #3
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Default Re: Mullard π class AB Amplifier circuit

I have got a Mullard book with a silicon NPN version of that circuit in it with component values.
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Old 27th Oct 2018, 9:45 pm   #4
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Default Re: Mullard π class AB Amplifier circuit

Hiya Refugee,

I'd love to see that, It sort of appeals to my sense of aesthetics, complementary works, just never looked right to me, only found out about this technique by accident in the local used charity bookshop,

T
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Old 27th Oct 2018, 10:25 pm   #5
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Default Re: Mullard π class AB Amplifier circuit

I have had a quick look for my book however it was not where I was expecting it to be.
We will have to be patient.
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Old 27th Oct 2018, 10:44 pm   #6
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Default Re: Mullard π class AB Amplifier circuit

That circuit has some similarity with Linn's format:
https://www.americanradiohistory.com...cs-1956-09.pdf
I've come across two early amps now with all-pnp output stages - there was a short period when power level npn didn't seem to be available, and germanium was dominant. One amp was from Newmarket Transistors - they had a range of small amp modules for OEM's to use in commercial products. The other amp was an early solid-state PA amp that used a driver transformer before an all pnp darlington type output that drove an output transformer.
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Old 27th Oct 2018, 10:48 pm   #7
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Default Re: Mullard π class AB Amplifier circuit

OK no worries....


T
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Old 28th Oct 2018, 8:34 am   #8
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Default Re: Mullard π class AB Amplifier circuit

Checked my "Mullard Reference Manual of Transistor Circuit's", nothing. All the audio amps in there are earlier and use driver or OP tfmr's. Also checked several other Mullard books, again nothing.

BTW, what does the pi symbol signify? What date was the book published you mentioned?

Andy.
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Old 28th Oct 2018, 6:40 pm   #9
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Default Re: Mullard π class AB Amplifier circuit

Hi Andy,

The book according to the inside blurb was first published in 1966 by George Newnes, third edition in 1969, with the third impression in 1976, Green cover which is the one I found.

Odd really as by 1976 Transistors were hardly a new technology, and the text in the book would have been out of date in the late 60's early 70's anyway.

I don't know what the π designation is about, but looking at the biasing arrangement from the emmiter of the lower output transistor, it does sort of look like a π network shape, I'd assume its a low pass filter feeding the grounded base driver transistor, adjusting the bias according to the output level, at least that the way it looks to me without having the part values to hand.

T
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Old 28th Oct 2018, 6:57 pm   #10
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Default Re: Mullard π class AB Amplifier circuit

Intriguing - it uses a sort-of "long-tailed-pair" phase-splitter, but it's purely AC-coupled rather than the more usual version which uses a common, undecoupled emitter-resistor for both 'halves'.

Must admit I am fascinated - and may try out a version of this as an alternative to the usual centre-tapped driver-transformer in a little push-pull amp (a pair of AC153 as output) I'm building in my mind.
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Old 28th Oct 2018, 7:12 pm   #11
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Default Re: Mullard π class AB Amplifier circuit

Hello,

From memory this circuit appeared as an article in Wireless Word around 1963/64.

There is a chance is also featured in the Mullard trade publication "Outlook" around the same time.

Regards
Terry Bateman
Southend, Essex.
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Old 28th Oct 2018, 7:48 pm   #12
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Default Re: Mullard π class AB Amplifier circuit

Hello,

I’ve found an article in my collection of Mullard Outlook publications for the ‘PI mode’ amplifier. I’ve taken a scan of the article and attached it.

It also mentions the 'PI mode' amplifier article in the May 1963 issue of Wireless World.

Try this link.....
https://www.americanradiohistory.com...ld-1963-05.pdf

Hope this helps.

Regards
Terry Bateman
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File Type: pdf Mullard_Amp.pdf (610.8 KB, 184 views)

Last edited by Valvepower; 28th Oct 2018 at 8:07 pm. Reason: Add link
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Old 28th Oct 2018, 11:53 pm   #13
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Default Re: Mullard π class AB Amplifier circuit

That latest circuit looks more like the one in my book except mine is all NPN except one and is silicon transistors.
It will have to be tomorrow for another search for the book. The book I have got is a couple of years later.
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Old 29th Oct 2018, 7:26 pm   #14
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Default Re: Mullard π class AB Amplifier circuit

Hello,

I've attached a scan of a circuit I've located in the second edition Mullard Transistor Audio and Radio circuits book. Is this the later SI NPN version you were thinking about?

Regards
Terry
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File Type: pdf Mullard_PI_Later.pdf (118.2 KB, 230 views)
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Old 29th Oct 2018, 10:08 pm   #15
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Default Re: Mullard π class AB Amplifier circuit

That is exactly the same circuit as in my book.
I have also found my copy too but no longer need put the image up.
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Old 30th Oct 2018, 10:33 am   #16
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Default Re: Mullard π class AB Amplifier circuit

Thank you Terry,

I've got some homework now I know where the pi thing comes in!

T
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Old 30th Nov 2020, 9:22 pm   #17
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Default Re: Mullard π class AB Amplifier circuit

Thread reopened at Peter.R.M's request.
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Old 30th Nov 2020, 9:32 pm   #18
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Default Re: Mullard π class AB Amplifier circuit

I suspect that the original design predated the widespread availability of complementary transistors. Now such complementary devices are freely available the additional complexity is probably not worth the bother
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Old 7th Dec 2020, 8:28 pm   #19
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Default Re: Mullard π class AB Amplifier circuit

Hello everyone,

I was interested to read the posts about the Mullard pi AB amplifier design.

I have the original Mullard Technical Publication describing this and will attach a scan of it to this post. This is probably the souce behind the article uploaded by Terry Bateman.

I built this amp in the mid 1960s and still have it in the attic. I built it as a mono amp and used it to drive a home-built 2 cubic foot speaker to Wharfedale design, with a W12FRS bass driver and Super 5 mid/high driver. It all sounded very sweet to my ears.

The only slight drawback of the amp design was a little background hiss from the germanium transistors.

The PCBs for the design were offered, along with other parts, by a company called Hart Electronics, if I recall correctly.

Mullard had other audio designs around the same time -I have designs for a 5 watt class A amplifier using a single AD140 output transistor and a six-channel mixer design. I have scanned these too and can upload if anyone is interested.

Rather off-post, I also have Mullard publications for solid state oscilloscope circuits from the late 1960s.

All the best,

Peter
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Old 8th Dec 2020, 12:23 am   #20
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Default Re: Mullard π class AB Amplifier circuit

Quote:
Originally Posted by Peter.R.M View Post

I have the original Mullard Technical Publication describing this and will attach a scan of it to this post.
All the best,

Peter
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