Author Topic: Mullard 5-10 stereo  (Read 1075 times)

Offline Mars

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Mullard 5-10 stereo
« on: May 24, 2018, 10:07:03 AM »
Hi All
I am building a Mullard 5-10 stereo kit for a client. I am following the original circuit, but the usual issues will present themselves: how to reduce the gain on the amplifier and improve the sound etc.





I'll be posting some photos next.
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Offline Mars

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Re: Mullard 5-10 stereo
« Reply #1 on: May 24, 2018, 10:13:10 AM »
This schematic shows the ultra-linear connections I'll be using:



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Offline El Sid

Re: Mullard 5-10 stereo
« Reply #2 on: May 24, 2018, 10:18:43 AM »
Are you going to wind the transformers, Karel?

And if so, will you use your standard EL84 opt or will you try to emulate the original transformers as close as you can?

Nice project - look forward to the photos!

Offline Family_Dog

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Re: Mullard 5-10 stereo
« Reply #3 on: May 24, 2018, 01:50:11 PM »
Easy! Use this link...

www.lundahl.se/wp-content/uploads/datasheets/amplifier_30wpp.pdf

I've modded all my Mullard 5-20s and 5-10 accordingly and the results are excellent.

-F_D



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Offline Ampdog

Re: Mullard 5-10 stereo
« Reply #4 on: May 25, 2018, 01:49:37 AM »
Ah! The old 5-10!!

I have two of those, with Partridge transformers to boot (unfortunately not UL output capable).

There is however a slight caveat here :(  Resistors R12, R13 are at the high-limit for practical stability (secondary G1 emmision). After decades of use and come-backs, it appears that rather 680K and preferably 470K should be considered as safe values. This particulalrly so what with today's valves often deviating from specs. by as much as -20% to +15%.

(In particular the Leak Stereo 20 initially suffered from many returns, having used 1M resistors there and H.J. Leak took some flak before bringing those down to 680K if memory serves,)


Karel,
If you can tolerate another hint? :) :)

Rather than triode-strapping the input EF86 as triode for lower gain as per the Byrith alternative, consider using the original EF86 circuit but using a low µ valve like the ECC82 or another of the many available similar dual triodes as phase inverter/driver.  (I don't consider the ECC83 as a suitable valve for any service in a power amplifier!   :flame:  )  In defense of Mr Byrith: I think he suggested an alternative with the least changes to the original, not an optimal re-design.

But this is OT  (we can rather discuss this per PM should you be at all interested).

As always:  Good luck!
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Mars

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Re: Mullard 5-10 stereo
« Reply #5 on: May 25, 2018, 10:36:08 AM »
Are you going to wind the transformers, Karel?

And if so, will you use your standard EL84 opt or will you try to emulate the original transformers as close as you can?

Nice project - look forward to the photos!

El Sid, I will be using my transformers.

BTW: Do you have any information on the original Partridge OPT's for this project? Maybe core size and impedances.
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Offline Mars

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Re: Mullard 5-10 stereo
« Reply #6 on: May 25, 2018, 10:40:21 AM »
Ampdog, you are on target there! I looked at simulations of the Long Tail phase inverter on TUBECAD and noticed that the ECC82 like  proper voltages to work optimally. I am planning to use ECC82 with a -150V supply on the tail end. Your suggestion has given me the confidence to proceed :thumbs:
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Offline El Sid

Re: Mullard 5-10 stereo
« Reply #7 on: May 25, 2018, 02:00:14 PM »
El Sid, I will be using my transformers.

BTW: Do you have any information on the original Partridge OPT's for this project? Maybe core size and impedances.

Karel I'm afraid I don't, so I went on a mission off to the interwebs to see what I could find. Here is Mullard's spec for the transformers:


The Partridge transformers I have are marked D3098, and I can't find anything about them. They don't have UL taps. But (for what it's worth) they look identical to images of the P3667. I could measure the core for you as well as winding resistance. My R300 multimeter from Mica can't measure L. 

On this forum I found F_D has similar, which look like mine, even including the yellow varnish: (which model are yours, F_D, and maybe Ampdog can also check the model number?)


I am interested because I want to build an LSpice model for my amp.
 

Offline Family_Dog

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Re: Mullard 5-10 stereo
« Reply #8 on: May 25, 2018, 05:29:08 PM »
Sadly no numbers on mine, other than the primary of the OPT is 8k and there are no SG taps. The only number visible on the side of the transformer is hand-written and looks like D1661.

Good to see Photobucket is working again, I removed the browser add-ons and all is good.


-F_D



-Eric

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Offline handsome

Re: Mullard 5-10 stereo
« Reply #9 on: May 25, 2018, 05:38:33 PM »
Quote
I am planning to use ECC82 with a -150V supply on the tail end. Your suggestion has given me the confidence to proceed :thumbs:
if you are DC coupling you probably don't need to use a negative supply

Offline El Sid

Re: Mullard 5-10 stereo
« Reply #10 on: May 25, 2018, 05:57:58 PM »
Sadly no numbers on mine, other than the primary of the OPT is 8k and there are no SG taps. The only number visible on the side of the transformer is hand-written and looks like D1661.

Good to see Photobucket is working again, I removed the browser add-ons and all is good.


-F_D

I think that is the model - mine has the D3098 hand written, as does this P3667:


Offline Mars

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Re: Mullard 5-10 stereo
« Reply #11 on: May 25, 2018, 07:04:53 PM »
Nice photos of the Partidges!

Are those output transformers measuring 80mm from base to top? How thick is the stack laminations?
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Offline El Sid

Re: Mullard 5-10 stereo
« Reply #12 on: May 25, 2018, 08:51:44 PM »
The laminations on mine are about 36-37mm - cant measure exactly without taking the covers off. The core measures 91x63mm, and the tops and bottoms of the "E" are 13mm. I can't see the inside to measure the inner part of the E.

Here are photos of mine:




Offline Family_Dog

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Re: Mullard 5-10 stereo
« Reply #13 on: May 25, 2018, 09:10:16 PM »
The measurements on mine seem to be the same as yours, El Sid. Probably the same transformer.


-F_D



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Offline Mars

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Re: Mullard 5-10 stereo
« Reply #14 on: May 26, 2018, 11:05:26 AM »
That would be EI86 laminations with a tongue of 26mm and 38mm stack (1.5 inch stack) = 9.88 cm square core?

EI86 laminations are not available any more, so either EI76 or EI96 will do. EI76 tongue is 25mm wide, so a stack of 4cm would be a close, but bigger core. Or a EI96 with a 32mm tongue would need a 32mm stack. The EI76 transformer has lower copper losses, so it should be a close, if not better OPT than the Partridge?
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