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Old 14th November 2013, 09:17 PM   #11
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Quote:
Originally Posted by Palustris View Post
Antique Electric Supply lists them as "in stock."
They have 272X which is plentifull, no 372X though...
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Old 17th November 2013, 01:34 AM   #12
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Quote:
It is obvious to me that 115V trafo should be replaced ASAP as well as 2A3 filament transformer. I am simply destroying my tubes!
Perhaps it's time to be "creative". A $38.50 AnTek AS-05T280 toroid might get the job done for you. Use 1 of the 6.3 V. windings to energize the heater of a 6BY5 dual damper B+ rectifier. Use the other 6.3 V. winding to power the small signal tube(s).

BFD, if you have to fabricate a bracket on which the toroid mounts.
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Old 17th November 2013, 01:42 AM   #13
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Thanks, Eli.
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Old 25th November 2013, 08:10 PM   #14
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I replaced PT with Hammond 272BX. These transformers have 115 and 125 V taps on the primary. Direct replacement resulted in the voltage drop that allowed for removal of those 470ohm resistors. All voltages are as per original specs - 250V across 2a3...
2a3 filament transformer was connected to 115V tap (in a bucking fashion) resulting in more or less precise 2.5V AC.
It is a big improvement over the original transformers.
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Old 27th November 2013, 12:41 AM   #15
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After running the amps for several hours I sat down and gave it a good listen. The amps now sound "faster" with better attack edges on the bass and better defined highs. Previously these amps sounded a bit colored that could be described as "romantic", now that coloration seems to be gone. Transformers are dead silent and running much cooler.

Extremely happy with modifications.
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Old 27th November 2013, 01:27 AM   #16
mr ed is offline mr ed  United States
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I have a pair of later amps with the better transformers.
I bought them a few months back, but got no information with them.
So far the I am pretty impressed, but feel like it may be time to try some mods.
Thinking caps maybe first.
From this thread I gather there are no published schematics, it that true?
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Old 27th November 2013, 01:43 AM   #17
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Quote:
Originally Posted by mr ed View Post
I have a pair of later amps with the better transformers.
I bought them a few months back, but got no information with them.
So far the I am pretty impressed, but feel like it may be time to try some mods.
Thinking caps maybe first.
From this thread I gather there are no published schematics, it that true?
Correct, there are no official published schematics of these amps. It is not difficult to reverse engineer and draw your own schematics though - the amps are very simple.

The first thing to replace on these amps are power supply capacitors, chances are they are old (what is the assembly date on the labels on your amps?). Original coupling cap is Orange Drop which could be replaced with something better.

I replaced all caps with good quality ones, and all resistors with Mills and Kiwame. I also installed hum pots.

These are wonderful little amps with some unique design features.
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Old 27th November 2013, 02:24 AM   #18
Kyle K is offline Kyle K  United States
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George often used surplus parts, especially the capacitors. I've seen power supply caps on brand new amps that had ten year-old date codes, but they worked fine over the long-term. From what I've seen, early production used mainly Panasonic for the coupling caps, but even here, he sometimes used surplus. George did not believe in boutique parts, although he would put them in if you requested. To me, his gear sounded fine with common industrial parts; one of the things I admired about his designs.
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Old 28th November 2013, 02:16 AM   #19
mr ed is offline mr ed  United States
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I do find these amps sound quite good running my Lowther open baffle speakers as is. I just keep thinking they are begging for mods and look really simple to work on. P/S caps were my first thought too.
I would say that George was wise not going to deep into the boutique parts thing, its not the dollar amount that gives joy, but the synergy of the parts.

Cheers
Ed
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Old 17th December 2013, 11:30 AM   #20
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Replaced stock zip-cord power cords with good quality grounded ones - big improvement.
Next - binding posts. The stock ones are too short for banana connectors, will replace them with Cardas copper or similar.
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