Author Topic: Mullard 5-10 stereo  (Read 1193 times)

Offline Mars

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Re: Mullard 5-10 stereo
« Reply #15 on: May 26, 2018, 11:12:00 AM »
if you are DC coupling you probably don't need to use a negative supply

Let me try that. So with 300V B+.  I'll have one third of rail voltage over the ECC82 cathode resistor, one third across tube and one third across anode load resistors. That would be a 2 x 10k anode load and a 4700 ohm long tail resistor?
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Offline handsome

Re: Mullard 5-10 stereo
« Reply #16 on: May 26, 2018, 03:59:11 PM »
well it would depend on the plate voltage of your pentode......but 10k is a bit of a low load for an ECC82 try aim for more than 27k (plate impedance of an ECC82 ~8-10k load should be at least 2.5 times)

Offline Ampdog

Re: Mullard 5-10 stereo
« Reply #17 on: May 27, 2018, 02:21:57 PM »
Ah Karel .... exactly what one was trying to avoid - a 'redesign' of the original 5-10!

But since yopu are going to use a more suitable valve for the phase inverter: The more common load resistors are some 47K or such, with the tail resistor to suit (10K - 22K). You do not need a high amplitude output signal to the EL84s, thus not a high 'standing' anode current.

[Caveat: You may notice from published information on low-µ triodes in the Schmitt phase inverter (its real name) that the anode load resistor of the 'bottom' valve must be somewhat higher than the 'top' triode for equal signal amplitude to the power stages. Lets take that to PM after I have found some reading matter on that.]
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 #18 on: June 06, 2018, 09:47:55 PM »
Well, thanks to all the input, I tried Ampdog's suggested values: 47k load and 22k (shared) cathode resistors for the ECC82 phase inverter. I kept EF86 exactly like on the schematic. I changed the power supply for the stereo amp a little bit. First filter cap 47uF and two 22uF for the other nodes. NFB changed to 22k, but the sensitivity is still high. My cell phone on 50% and volume knob at 12h00 and the amp maxes out.

The sound is formidable! Rock solid and clear. This design is a keeper :dop:

Mullard-5-10 by Karel Mars, on Flickr

Mullard-5-10-stereo by Karel Mars, on Flickr
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Offline Qualityten

Re: Mullard 5-10 stereo
« Reply #19 on: June 23, 2018, 11:57:06 PM »
A beautiful build, as usual.  Thank you for sharing your work.

I'm listening to a very fine 5-10, with the best Partridges available, and it sounds amazing.  I got this one from a kind person who just wanted it to be restored and loved.  With good transformers, this design still sounds amazing.  This one doesn't have the EF86 triode strapped.

Offline Qualityten

Re: Mullard 5-10 stereo
« Reply #20 on: June 24, 2018, 04:36:28 PM »
More info about my OPTs.  They are marked P4014.

Offline Qualityten

Re: Mullard 5-10 stereo
« Reply #21 on: June 24, 2018, 07:19:39 PM »
Talking about Partridge OPTs, I also have a very high quality ultralinear Partridge transformer marked TD4832, which was a lucky find when I spotted it in a broken home built guitar amplifier.  I have since found out that this was supplied as an upgrade to the Parmeko P2642 for the Sterns 5-10 kit back in the late 50s.

Looking similar to the ones illustrated here, I have a Partridge OPT marked D7765, which I found as a replacement in a broken mono Beam Echo amplifier that I had that I have since sold.  It too does not have the 43% screen grid taps of the others.

The only reliable information on Partridge transformers I've found comes from the Mullard Tube Circuits book.  It would be great if someone found a reference guide to Partridge and Parmeko OPTs.

Coming back to the point in this thread, I tried the mods described by him on a mono 5-10 and got the same results, namely good sound but not much reduced sensitivity.  I'll be interested to see what 5-10 configuration Karel decides to build for clients.  Would it be worth triode strapping the EF86 as well?
« Last Edit: June 24, 2018, 07:31:00 PM by Qualityten »

Offline Family_Dog

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Re: Mullard 5-10 stereo
« Reply #22 on: June 24, 2018, 07:33:16 PM »
Good evening Dave, it's been a while since we last had a chat!

You might find Claus Byrith's paper interesting, I modified five Mullard 5-20 and one 5-10 with the ideas he expressed, bar the variable bias for the output valves, which I left at fixed bias.

https://www.google.co.za/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiky-v65-zbAhXlAsAKHRjqA5oQFggoMAA&url=http%3A%2F%2Fwww.lundahl.se%2Fwp-content%2Fuploads%2Fdatasheets%2Famplifier_30wpp.pdf&usg=AOvVaw1SBq-dOQYrpJRkQpzWlsyw



Regards,

-F_D



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Offline Qualityten

Re: Mullard 5-10 stereo
« Reply #23 on: June 24, 2018, 07:46:43 PM »
Hi Eric, I really should study that CB paper again. I have read it a few times, but never at the same time as when I'm tinkering with a 5-10 or 5-20.  Regarding the latter, there is an interesting thread on one over on Audiokarma tubes right now.  A stereo build of the 5-20 design, but using Acrosound OPTs, a separate power supply and few other refinements. 

Offline Family_Dog

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Re: Mullard 5-10 stereo
« Reply #24 on: June 24, 2018, 07:59:25 PM »
i haven't logged into AK for a while... hope they haven't sent me packing in the interim ;)

I will go have a peek at this.


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Offline Family_Dog

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Re: Mullard 5-10 stereo
« Reply #26 on: June 25, 2018, 06:44:43 AM »
We built a similar 5-20 Stereo monoblock for my business partner at work, main difference is we made everything mounted on one chassis. Heavy as hell, but it sounds sweet!

Must try get some pics if I remember, but will post in a new thread - don't want to hi-jack this thread unnecessarily.


_F_D



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Offline Mars

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Re: Mullard 5-10 stereo
« Reply #27 on: June 25, 2018, 12:23:35 PM »
Hi Qualityten

The amplifier was supplied with the EF86 in pentode mode, and NFB adjusted for enough sensitivity to take a cell phone input. I will hear from the customer again after the coming weekend. He listens to it in his beach house.

I am going to try out the triode strapped EF86 in the next build. It might be the way to go forward. Otherwise I might opt for a shared ECC82 for input voltage preamplification.
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Offline Qualityten

Re: Mullard 5-10 stereo
« Reply #28 on: June 25, 2018, 07:45:07 PM »
Thanks for the info Karel.  I really admire all your builds, and that you share your work here.  So did you change that 22k feedback resistor?

Listening to Abdullah Ibrahim via my stereo 5-10, playing into KEF 104/2 speakers which were intended for big SS amps, I am amazed at how good 12W (x2) can sound.  Just a little bass grip is lacking.

(F_D, you should feel the weight of the separate power supply to my 5-10s.  It has a huge PT and two big chokes.)

Offline Family_Dog

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Re: Mullard 5-10 stereo
« Reply #29 on: June 25, 2018, 07:56:34 PM »
Plenty of iron, eh? I can believe it will be *very* heavy!   :2thumbs:


-F_D



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