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The mighty Allen Organ 75

I've had several pair over the years. Still have one pair I've mostly restored. Need to eliminate that first triode and replace a few resistors and they will be completely rebuilt and ready.
 
Could use some help here,I have an opportunity to purchase a pair of the Allen 75 amps, that have been in the possession of a tech of 40+ years. My question is what is the watt output on the 16 ohm side? They will be in series on a pair of Altec A7’s any input would be greatly appreciated.
 
Power on the 16 ohm taps will be the same as power on any other tap, assuming its working into a 16 ohm load. Based on @Brice's results that looks like right about 68 watts.
 
finding the resistors is proving to be the most difficult part of building the AO75. "R35 3830 OHM 1/2W" has minimum orders on mouser of 1000 for either 4000+ dollars or 400+ dollars. thinking of just putting several 1/2 watt resistors together in series to make the odd or difficult to find ones.
 
any reason you can't use a 3.9k ? Those should be very available and cheap. All those oddball values do is get you a high precision resistor, which isn't always needed. If you need them matching amp to amp or within a channel because of what they do its not that hard to get a few very close matches out of a bag of common 5% or 2% parts if you sit with an ohm meter for a few minutes. Bag of 100 metal film 3.9k is probably like 5 bucks.
 
Agree with gadget, 3.9K is within 2% of 3830 ohms. Looking at Brice's original schematics, the tolerance for this resistor is 5%, so well within. It's that or parallel resistors.
 
Made a little headway,but far to go(putting in a muffler system now). Gave up years ago when unable to locate resistors. Will evaluate values, as I have plenty of 1watt metal films. Hope to not throw my back out on this build; almost went in my pants picking it up last night....
 

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Man, those are some awesome Amps, Brice. Allen equipment was certainly well made. I found this T50 at a flea market and it sounds great. Sorry if a little off topic.. no tubes.. :dunno:DSCN0040.JPG
 
nice unit.
this is what I came-up with as estimates for replacements if actual values can't be found/ sourced, in parenthesis:


ALLEN MODEL 75 RESISTOR SHEET (from diyaudio member)
R 1,2,9,10,22,23 510K 1/2W (512, 515, 520k)
R3,4 1470 OHM 1/2W (1480, 1490, 1500 ohm 1/2 w)
R5,6 100K 1/2W
R7,8 500K POT
R11 180K (190k)
R12 10K
R13 100 OHM
R14 2.5K (2.7, 2.8, 2.9, 3k)
R15 ----
R16 178K (179, 180k)
R17,19 1MEG
R18 17.8K 1W (18, 19k 1w)
R20,24,25 33.2K ( 33.5, 34k)
R21,27,43 28.7K (29k)
R26,28 5K POT
R29,30 23K 10W (24k 10w)
R31,32 2200 OHM 1/2W (2.3, 2.4, 2.5k 1/2w)
R33,34 5 OHM 3W
R35 3830 OHM 1/2W (3.9k)
R36,38 700 OHM 3W (710 ohm 3 w)
R37,40,41 3.2K 20W (3.3, 3.4, 3.5k 20w)
R39 5K 20W
R42 12.1K
R43 28.7K (29k)
 
I don't know if this is the place to put it or what, but I seem to remember reading that an Allen Organ oscillator was used for decades as a tone generator by WOR 710 in New York (every hour on the hour, a ~757.5 Hz tone for :00.5 second duration). If not this, what model would they have used, and what other radio stations, if any, used such machines to set off when the next hour arrived?
 
W.B. said:
I don't know if this is the place to put it or what, but I seem to remember reading that an Allen Organ oscillator was used for decades as a tone generator by WOR 710 in New York (every hour on the hour, a ~757.5 Hz tone for :00.5 second duration). If not this, what model would they have used, and what other radio stations, if any, used such machines to set off when the next hour arrived?
Click to expand...
One dual section tube and a stable resonant circuit would be all that is required. The station engineer could easily construct it.
 
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