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Allen Model 90 Schematic? anybody?

doucanoe

doucanoe

Registered Audio Abuser
When I had my Allen Model 75's gone over, I was fortunate enough to get a schematic from Allen Organ. Now I am looking for the same but for the Model 90 monos. I thought that I would check here first before bothering them again.

Anybody have a .pdf of it?

Thanks, RC
 
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Thanks Dave, I appreciate that.


You have a pair of these, what do you know about any needed mods for the 90's. Are they just gain concerns similar to the Model 75's?


RC
 
I have looked into possible upgrade paths a couple of times, but never thoroughly enough to feel comfortable passing on anything on. I take it you found a pair of these?

I do think you are right that there is probably unnecessary gain with the 12A*7 up front. Mine have non-matching chassis, so I was considering just using the iron and some other schematic. The only thing that worries me about the stock schematic is the very high B+. It's pushing the limits where the quality of tube is probably going to be very important.
 
I was fortunate enough to happen across some. Yours have non-matching chassis eh. Is it just cosmetic or a different amp circuit design?

You should really send me some pics of what you have as I might be able to fix that.

There seems to be more info. posted on the Model 75's than the 90's. These are a little grimey after sitting on the shelf for lord knows how long but I'm sure will clean up nicely.

Not sure what the answer is going to be for these yet. One thing though, I sure would like to hear them modded and as is.

RC
 
IMG_2330.jpg
 
Mine seem to be what you have on the left in the pic. Mine have those mystery (to me) dealie bobs at the front of the amp opposite the TX's. One has... Well, I will take a pic and show you. I have no idea what they are honestly.

RC
 
I didn't want to haul them out so I took the pics where thay sat. They are facing in opposite directions but I think you should be able to see the "dealie bob" difference. Other than that, I believe that they are the same.


RC
 

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Nice Hammond, too! :)

I'm not too concerned about matching, I'll probably be making new chassis for them. But thanks for offering to help make a match.
 
it could very well have to do with the exact models of tranny and choke used, the Allens that have all three pieces of big iron cased have been the heaviest IME.

I'm nearly positive mine weigh 40+.
Click to expand...
I don't for a moment doubt you, my 90's were Webster branded and all three pieces of iron were the open architecture type, smaller and lighter weight i believe. While my Allen 75's had all enclosed iron and weighed well over 100 lbs well packed as a pair, i'm pretty sure i net weighed them at 45-46 lbs each, but as i think about it more they may have been 50+ each net.:scratch2:
 
That's a pretty neat circuit Ron, and I don't think I'd change it too much. It's cool how they take the B+ from the CT of the 5v winding. You would definately want to protect that PT as muchg as possible as that bule/black tap makes it pretty special. I see the shcematic shows a 12AY7, while the chassis shows 12AT7, or am I looking at it wrong?:scratch2:
 
jaymanaa said:
That's a pretty neat circuit Ron, and I don't think I'd change it too much. It's cool how they take the B+ from the CT of the 5v winding. You would definately want to protect that PT as muchg as possible as that bule/black tap makes it pretty special. I see the shcematic shows a 12AY7, while the chassis shows 12AT7, or am I looking at it wrong?:scratch2:
Click to expand...

I just looked at them and they are 12AY7's in that position right in front of the 6SN7's.


"It's cool how they take the B+ from the CT of the 5v winding. You would definately want to protect that PT as muchg as possible as that bule/black tap makes it pretty special"


I guess I will have to take your word for that as I have no idea what you just said :yes:

What do you think about Daves idea about using the transformers in another circuit. Sounds intriguing to me but it would be nice to see what they sound like as they stand.

These are so dusty and dirty that I wasn't sure what condition the chassis were in. I started to clean one up and they are nice! Gold chassis with all the screen lettering just like new. I guess all those years of crap accumulating on them was acting as a protective coating :D
 
doucanoe said:
I just looked at them and they are 12AY7's in that position right in front of the 6SN7's.


"It's cool how they take the B+ from the CT of the 5v winding. You would definitely want to protect that PT as much as possible as that blue/black tap makes it pretty special"


I guess I will have to take your word for that as I have no idea what you just said :yes:

What do you think about Daves idea about using the transformers in another circuit. Sounds intriguing to me but it would be nice to see what they sound like as they stand.

These are so dusty and dirty that I wasn't sure what condition the chassis were in. I started to clean one up and they are nice! Gold chassis with all the screen lettering just like new. I guess all those years of crap accumulating on them was acting as a protective coating :D
Click to expand...


Ya know, I've found that "crud" does make an outstanding preservative (as does tar and nicotine).:yes: If they were mine, I'd probably try them fairly close to stock, with the exception of some obvious PS upgrades and making sure that there are no low or high pass type filters in there anywhere. Sometimes those old engineers seemed to hit on "good stuff" as far as design values and such. Too often though, their designs didn't get to be their best do to production cost issues, and quite simply, poor lead dress. Apparently a certain amount of hum was acceptable back in the golden years of Hi-Fi.:D I betcha I've got a bunch of those Y7s in NOS somewhere around this mess. All that being said though, I decided to go with a completely different circuit for Terry's Conns. It will be a lot closer to an HK 250 than an organ.:D Lemme study on that schematic some more.:scratch2:
 
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