Allen Organ 20 "Rondo" mono blocks

Rex Everything

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Well...after seeing the sweet work Jay is doing on the Allen 75's and knowing that 90's are probably out of reach I stumble across a set of Allen 20's with the "Rondo" markings.

These amps are no joke being built way over spec as has come to be expected from Allen. They have huge transformers and weigh in at a bit over 20 pounds each.

I'm having dreams of a sweet bi amped rig with the 20's on the high/mids and the 75's on the low end..... :drool:

I bumped up the schematic for these the other day. If any one has any suggestions on how to make these the best they can be please post them up.

And with out further adieu:

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If I was going to build them for say 500hz and up, I'd build the crossover into the input, dump the UL taps and run 5881s in triode mode and a 12At7 voltage amp and U7 splitter..:eek:
 
You could do two set of inputs like a couple of my amps, one set straight in, and one set through a passive xover. Then stick in the same triode / UL switch you want on your 35.

Gonna need a lot of hand holding to get though this.... :D
 
If you keep movin' all that heavy iron west,you're gonna cause a shift in the tectonic plates and it's goodbye California..:yikes:
 
I've got a pair of those working on now, when I do up the schem I can post it.

I'm doing 6S4 to 6CG7, doing away with the 12AY7 an possibly level pot as well.
(if the pot is really really nice I may incorporate a second input and use that to)
 
I've got a pair of those working on now, when I do up the schem I can post it.

I'm doing 6S4 to 6CG7, doing away with the 12AY7 an possibly level pot as well.
(if the pot is really really nice I may incorporate a second input and use that to)

I'd love to see that schematic. This one does not have a 6S4. The Rondo's appear to be different than the 20's in a few regards and these amps are both different from each other. Gonna have to find one curcuit and go the route.

I'm guessing the cleaner one as I assume it is the new unit having the higher serial number. It has 60uf caps in place of the 30uf in the other and a few more things different.

I notice on the turret board on these that they have a 30uf@25 volts that I have not seen on any of the non "Rondo" marked amps.
 
You misinterpreted my post.. ;)

No these do not HAVE 6S4, I'm changing the circuit.
(these amps are the same as yours)
 
You misinterpreted my post.. ;)

No these do not HAVE 6S4, I'm changing the circuit.
(these amps are the same as yours)

I getcha :thmbsp:

Here is an idea of the size of the Allen 20's. Here is one next to a Fisher 30-A. The Allen weighs in at 11 pounds more than the Fisher.

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I'd like to see a schematic on those Allen 20s... That fisher looks very nice too!

I don't see any chokes on the Allan 20. Maybe you can stuff one or two of those under each chassis.
 
This is the basic setup I'm shooting for, likely some tweaks when done. ;)

There is a choke in these amps, it is inside that power tranny can, and the
supply is choke input, with it's high voltage I suggest indirectly heated rect.
(the 12au7 can be, 6cg7, 12bh7, ecc99, 6gu7, 6n6p)

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This is the basic setup I'm shooting for, likely some tweaks when done. ;)

There is a choke in these amps, it is inside that power tranny can, and the
supply is choke input, with it's high voltage I suggest indirectly heated rect.
(the 12au7 can be, 6cg7, 12bh7, ecc99, 6gu7, 6n6p)

.
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So what would the input Z be Keg, or would depend on volume? Also what is the purpose of the 40k R to ground right after the choke? Thhanks, jay Is 390uf really the value of the first cap after the choke or a typo?
 
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The input Z yes would depend on volume. At fully open it would be roughly 90k.
(1meg in parallel with 100k pot, so 90k on either input)

The 2 inputs are stock, an if left that way I'd put that 1meg grid resistor there.
(again this was using what was "basically" setup originally)

The 40K is basically a bleeder an load, there is very high voltage on that power
tranny, it was already there stock and I just left it, 390uf is just a throw in, I'd
use between say 200-470uf there.
 
The input Z yes would depend on volume. At fully open it would be roughly 90k.
(1meg in parallel with 100k pot, so 90k on either input)

The 2 inputs are stock, an if left that way I'd put that 1meg grid resistor there.
(again this was using what was "basically" setup originally)

The 40K is basically a bleeder an load, there is very high voltage on that power
tranny, it was already there stock and I just left it, 390uf is just a throw in, I'd
use between say 200-470uf there.

Ah, I thought the 40k R may have been to keep the choke loaded so it would actually "choke". Thanks, jay
 
That was partly my assumption as well Jay, but I would not want to
run an directly heated rectifier with this tranny and setup, even with
that "load" you'd be at like 650+vdc to that first cap at startup! Ouch!
(the PT is 540-0-540)
 
That was partly my assumption as well Jay, but I would not want to
run an directly heated rectifier with this tranny and setup, even with
that "load" you'd be at like 650+vdc to that first cap at startup! Ouch!
(the PT is 540-0-540)

ooh, good point.
 
These are VERY nice amps. Here's one of two that I rebuilt around 4 years ago. The can cap got re-stuffed and pretty much all of the other passives replaced. I also added screen and grid stopper resistors. Not shown in this photo was the removal of the capacitive coupled input and the new RCA straight input jack.

Great frequency response, very smooth and best of all very quiet. Hmmm, that output transformer sure looks like an Acrosound....:scratch2:
 

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