And yet another one... this time for
@Tigerjones of this parish. Only took a few pics as it neared completion this time as plenty of A21 pics already now!
A very late one here from 1973. The commission was for not as far as a complete rebuild including all resistors and transistors this time... but as can often happen with such old gear, more work was required than at first apparent...
Above can be seen the completed amp. On initial testing over 20 mins or so some problems raised their ugly head which were traced to the small signal and driver transistors (power amp boards) and so all 5 per channel ended up being changed anyway... I reckon this will be de rigueur for any others I do.... the BFY52/53 devices do not seem to last well particularly. A few of the resistors which were well out of tolerance were changed.
I have a suspicion that this example may have had a channel imbalance from new! Sugden fit a select on test resistor to one channel as required to even the gain out and make sure the balance really is central with the control central... Now, it was a fair bit out with this one and removing the fitted 82K resistor from the channel on the left in the top photo made it considerably better... so I fitted a temporary trimmer resistor to the right channel and used it to properly equal the two channels... guess what value was optimum? yep, 82K! My suspicion is the value had been worked out in the factory but then a slip of the mind after a tea break or whatever and it was fitted to the wrong channel... Anyway the new 82K can be seen top right in the above pic at the input from the coax... the original can be seen in the first pic on the left board before I removed it.
And the finished article above.
It's been on about 18 hours so far of the 48 hour soak test I do and has been sounding bloody marvellous, as these do.
One often sees posts asking for recommendations for a SS amp that sounds like a valve amp.. . these are the best example of such a thing I've ever known
