Valve Amplifier Study 008: Mullard 5-10 Valve Amplifier
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- Опубликовано: 7 сен 2024
- This is a quick tutorial with our service technician taking you through the circuit of the Mullard 5-10 Valve amplifier, a British vintage classic from the late 50s, early 60s. Stay tuned for the Mullard Stern Mic Amp Mixer circuit using the EF86 screened pentode valve, which will be our next upload.
We have many more videos to upload covering a wide variety of vintage British & International audio circuits.
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Excellent video thanks 😊
Very welcome, we have lots more to post once we get through the edit stage. Paul
I built this amplifier recently. It took me some time to fix the oscillation and the hum at the beginning. It was rather annoying because it was not quite easy to fix it. Finally, I got it all done with completely stable and no more hum at all. I have it connected to the monitor audio Bronze II speaker, the sound is pretty good especially the bass that it produces, and I am very satisfied.
I'm restoring a well built one of these at the moment, one with a lovely Partridge output transformer. I managed to finally get the thing working today but am getting quite a bit of hum. I've replaced all of the electrolytic caps and all voltages are okay. I like your idea of fitting a choke I may well do that myself. I really love the sound of this amp the D.C coupling gives lovely bass reproduction.
Excellent video thanks
I really enjoy your videos. Very clear and helpful. Although not commercially available, have you considered examining the design of the late Gerry Well's Wadar amplifier? There is the circuit diagram and a write-up in the Autumn 2019 BVWS Bulletin - with a typo for the pre-amp valve! It seems to have a small cult following and sell for good prices when they come up at auction.
Hi yes I can do that for the near future, I nearly bought 3 of them to make a 3way active sound system several years ago,, they sounded pretty good.
@@vintageaudioworkshop That will be really interesting. The BVWS article doesn't really include any circuit analysis, but a breakdown of what Gerry did would be interesting, and to see any minor mods to improve it. I can scan a copy of the article for you guys if you're not in the BVWS.
Hi I have asked Phil if he knows any circuit details, he is not keen to cover this circuit for his own personal reasons with the museum organisers. Sorry
I am building the Mullard 5-20 amp which is very similar to the 5-10 . I am puzzled by the lack of a value for the resistor between the main t/f
and the rectifier valve . I have , in my circuit 100ohm here but the HT voltage is 100volts too high . What should I do to lower this .???
This is not an amplifier but rather a harmonics generator -) That phase inverter/amplifier is a great example of how to NOT use a differential stage.
It's not a floating paraphrase phase splitter, it is a long-tailed pair, and Mullard's notes state that the correct load resistor values for this circuit are 100K and 103K, and, considering that in 1954, when the circuit was published, 5% resistors were assumed. The 91+100K you mention is for the Leak Stereo 20 which has different operating conditions around the LTP, and are not correct for this design. The phase inversion in an LTP phase splitter takes place in the left hand (common cathode) triode, not the right hand (common grid).
This is correct about it not being the floating paraphase splitter so an apology can be added from me.
In 1954 the use of 5% resistors was NOT assumed: they would be
considered semi-precision.
The comments about using different anode load resistors remains true,
even though this is the Mullard not the Leak implementation of the
amp,
Phil Moss
@@vintageaudioworkshop The balance of a long tail pair is chiefly determined by the value of the tail resistor. Higher values improve balance but reduce the available output swing of the triodes. With 68k in the tail I would expect a fairly close balance. Balance can alternatively be achieved by reducing the value of the inverting triode's anode resistor, and, out of interest, I calculated the value which would (theoretically) result in perfect balance which turns out to be 97k, a reduction of 3%. The next lower E12 (10%) value is 82k and the next lower E24 (5%) value is 91k. To increase the value of the non-inverting triode's anode resistor by 3% would require a 103k resistor and the next higher preferred values are 120k (E12) and 110k (E24). In both cases 100k is closer to the 'ideal' values of 97k or 103k leading to the conclusion that, in this particular circuit, the closest balance possible with readily available preferred values is achieved with equal 100k resistors.
@@silasfatchett7380 thank you for your contribution, I plan to come back to this subject and cover more thoroughly in basic theory, the technicians are ready to get back after the bad spell with corona19 is over. Paul
Would you recommend building the Mullard 5-10 or the Williamson valve amp for today with a vinyl system?
Can you recommend where to buy transformers from and which ones? Many thanks
Hi I would recommend www.ilissus.com for decent valve amps designed in Britain with all British transformers sounding very decent and well tested, I have used the Pentode EL84 type single ended for the last two years and recently just bought the 6V6 version. I may need to sell them both if interested due to travel plans, they normally retail at $700 each I will take 250 each, both in excellent condition with vintage valves. I have a set of Lowther speakers also for sale!... Thanks
This is leak stereo 20 scheme?
The Leak amplifiers are a lot better. Paul
太老實啦，推挽就只得10W？淘宝的吹到輸出8欧姆接喇叭，有25W的啊！🤣🤣