13-09-2015, 07:41 AM
That is a really professional job you have made of the re-build.
Mike
Mike
Mullard 10W High Quality Stereo Amplifier
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13-09-2015, 12:01 PM
(This post was last modified: 13-09-2015, 12:02 PM by pamphonica.)
Well done Joe - sharp eyes! Yes, the input is via a socket wired the same way as the Leak Stereo 20 input is wired. I have a couple of stereo 20s and thought it would be fun to compare them to this amp at some stage. I have not bothered to take the HT etc to the input socket as the preamp is essentially built in now. I expect it will be fed from a CD player or similar. Currently I am playing tracks from my phone!
As for the hiss, yes it is the classic hiss that peaks in mid travel of the volume pot. I may have to reduce the value of that pot to get the hiss down.
Jeremy. G8MLK. BVWS Secretary. British Vintage Wireless and TV Museum Friend.
Pamphonic Website ______________ BTTT OB Truck Restoration
13-09-2015, 04:30 PM
Happiness is a warm valve... The little ECL82 and ECL83 valves are good (and still cheap) for a quick lash-up of an iPod player. Single-ended they give enough volume for local listening and the triode stage allows for lower-level inputs. But a 741 and an EL84, now there's a lovely "what's available" solution!
Jeremy. G8MLK. BVWS Secretary. British Vintage Wireless and TV Museum Friend.
Pamphonic Website ______________ BTTT OB Truck Restoration
13-09-2015, 04:56 PM
They compliment each other nicely as the 741 looses gain as the frequency increases which off-sets Pentodes tendency to scream.
High quality it isn't but it sounds very nice to my, admittedly cloth, ears. - Joe
13-09-2015, 08:14 PM
I have seen the circuit for hybrid amp on your web site Jo and intend to build one 10 out of 10 for a great idea.
Rob T
if its made by hand it can be repaired by hand
16-09-2015, 03:14 PM
By the way, I have diagnosed the problem with the balance control. It was my error. I failed to specify the pot fully. The pot as delivered from Blore-Ed had the antilog section at the rear. But the anti-log section was meant to be for the Right-hand channel. As laid out by Mullard, the front pot sections control the Right-Hand channel. I have re-wired the balance pot so the rear section controls the right channel.
By the way, the symptom of a back-to front log/antilog control is a distinctly low-level mid position, with each channel increasing significantly in volume if the control is rotated in that direction. This cobbled-together diagram illustrates the problem. A properly-wired standard log/antilog balance control gives about 75% volume on both channels at mid-point. A mis-wired control gives 25% at mid-position. Of course, the purists will say that you don't need tone or balance controls, but Mullard specified them in about 1962 and who am I to quibble! Jeremy
Jeremy. G8MLK. BVWS Secretary. British Vintage Wireless and TV Museum Friend.
Pamphonic Website ______________ BTTT OB Truck Restoration |
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