doucanoe
Registered Audio Abuser
I could use some help on this one. Im getting ready to have my Allen #75 mono blocks recapped and modded a little. What I mean by modded is this.
The Allen's reportedly have too much gain so people (from what I understand) are "bypassing" one of the tubes, adding a resistor and that is supposed to take care of the gain issue. Im going to attach a link to the schematic and list bits and pieces of what I pulled from the archives of some other boards regarding the mod. The triode part, Im not interested in.
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Allen Organ Model 75's
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From: pkeller - view profile
Date: Tues, Oct 5 1999 12:00 am
Email: pkeller <pkel...@ix.netcom.com>
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Where can I get a schematic for Model 75 Allen Organ amplifiers?
These things can be spectacular in triode mode with teflon caps.
Reply
From: Tim H - view profile
Date: Wed, Oct 6 1999 12:00 am
Email: "Tim H" <t...@ma.ultranet.com>
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I'd start with a call to The Allen Organ Company in Macungie, PA.
610-966-2202 FAX 610-965-3098
Tim/
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pkeller wrote in message <37FAE10A.BFDD0...@ix.netcom.com>...
> Where can I get a schematic for Model 75 Allen Organ amplifiers?
>These things can be spectacular in triode mode with teflon caps.
Reply
From: Raymond Koonce - view profile
Date: Wed, Oct 6 1999 12:00 am
Email: Raymond Koonce <rkoo...@zzztyler.net>
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See http://www.triodeel.com/allen001.gif on Ned's site. It claims to be
a Model 75.
pkeller wrote:
> Where can I get a schematic for Model 75 Allen Organ amplifiers?
> These things can be spectacular in triode mode with teflon caps.
--
Reply
From: Paul Gustafson - view profile
Date: Wed, Oct 6 1999 12:00 am
Email: Paul Gustafson <gusta...@att.net>
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Were you the guy that bought the pair on ebay about a week ago??
Those were sure nice looking, there were three of 'em there !
Good snag!
Paul G
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pkeller wrote:
> Where can I get a schematic for Model 75 Allen Organ amplifiers?
> These things can be spectacular in triode mode with teflon caps.
Reply
From: pkeller - view profile
Date: Wed, Oct 6 1999 12:00 am
Email: pkeller <pkel...@ix.netcom.com>
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Actually no. But I did bid on them. When I got outbid, I took option #2 and
bought
a pair from a fellow who failed to get any bids for his model 75's a couple
weeks prior.
I have heard Allen 75's played through Lynn Olson Ariels and was
astounded
at the strong low frequency response as compared to other tube amps. These
are beefy amplifiers even in triode mode. My Dynaco MKIII's were no match
through the same speakers. Much of the superb mids and highs are directly
attributable to replacement of the coupling caps with teflon caps. I've
also heard that silver foil in oil couplers work well if you can stand the
cost.
These things are not well known and I consider them quite a value.
pkel...@ix.netcom.com
- Hide quoted text -
- Show quoted text -
Paul Gustafson wrote:
> Were you the guy that bought the pair on ebay about a week ago??
> Those were sure nice looking, there were three of 'em there !
> Good snag!
> Paul G
> pkeller wrote:
> > Where can I get a schematic for Model 75 Allen Organ amplifiers?
> > These things can be spectacular in triode mode with teflon caps.
Reply
From: pkeller - view profile
Date: Wed, Oct 6 1999 12:00 am
Email: pkeller <pkel...@ix.netcom.com>
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The friend of mine who has the Allen 75's that I've heard got the
instructions for trioding them from a guy that lives outside of Chicago
and is supposed to be an Allen aficionado. I'm a little leery about
giving out a name without prior permission. It's someone I've never
talked to. I don't have the method yet myself, but I will within the
next couple weeks when my amps arrive.
I don't know what the post triode power output is but it's plenty
for my high end needs.
Regards: pkel...@ix.netcom.com
- Hide quoted text -
- Show quoted text -
Blaine wrote:
> Where can you get a schematic showing how to convert to triode
> operation? What power can you expect in triode operation?
> Thanks,
> Blaine Ricketts
> Sent via Deja.com http://www.deja.com/
> Before you buy.
Reply
From: Blaine - view profile
Date: Thurs, Oct 7 1999 12:00 am
Email: Blaine <ricke...@my-deja.com>
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Where can you get a schematic showing how to convert to triode
operation? What power can you expect in triode operation?
Thanks,
Blaine Ricketts
Sent via Deja.com http://www.deja.com/
Before you buy.
Reply
From: Ned Carlson - view profile
Date: Thurs, Oct 7 1999 12:00 am
Email: Ned Carlson <postmas...@triodeel.com>
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Blaine wrote:
> Where can you get a schematic showing how to convert to triode
> operation?
Schematic? We don't need no stinking schematic!
1. Disconnect wires going to pin 4 on the 6550 sockets, tape
them up.
2. Install a 100 ohm 1/2W resistor between pins 3 & 4 on each
6550 socket.
3.Reset the bias. I believe on the Allen amps it's supposed to
be 1/4 volt between the bias test points and ground.
Oh, you want real triodes? Try this:
http://www.triodeel.com/allen005.gif
and compare it to this:
http://www.triodeel.com/allen001.gif
>What power can you expect in triode operation?
Triode connected 6550's, 25-30 watts.
300B's, about 40 watts if fixed biased.
I'm sure it would be easier to use Sovtek 6B4-G's,
I'd expect to get 30 watts or so out of them,
but they might do better than that.
What are the modifications that have been made to this point?
Have the 12AY7's been bypassed yet?
As for output tubes, I like the Svetlana 6550c's. I have not tried the Svetlana KT-88's yet, but hope to soon. KT-90's sound much too fat to me. The bass is not in balance with the mids or highs and I believe is not a good match for Allen #75's. If your speakers are weak in the bass region, this might compensate nicely though. GE-6550A's are a little sterile for my tastes, and TungSol 6550's are nearly the same sounding as the Svetlana 6550c's, but cost more and are difficult to find in reliable matched pairs. I actually prefer the Svetlanas.
I use Sylvania black plate 6SN7's with good luck.
Allen Organ #75's are very dynamic amplifiers with enough power to drive low efficiency speakers. They probably have the most stout power supply of any amplifier I've seen or heard. The PS choke is huge and free flowing. 15hy, 45 ohm.
The output transformers are incredible. I have one pair (I own seven #75's, + a pair of Allen #90's) that say "ACRO products" on the top. I believe these might be Acrosound TO-330's that have been dressed up as proprietary Allen products. The others are as good or better with 3300 ohm impedance.
I am going to experiment with some snubbers on the fillament supply as well as before the PS rectification bridge. Those old top hat diodes can be improved upon as well. There is a small bit of hiss that needs to be tamed, and I think it's from the fillament supply.
As for coupling caps, the best I have tried are "Custom" Teflon 1.0uf.
These were designed for "down the hole" oil field measurments. Very expensive. I've been thinking of trying those RelCap teflon's, but thats still a lot of dough for an unproven result.
Check that your tube plate resistors are still in spec. as they take a big voltage hit and change over time.
You will find that if your 12AY7 has not been bypassed, the gain will be way too high. The inputs are nearly mic level and need to be brought into useable range.
You have some amplifiers with incredible potential. I have not heard better imaging and soundstage from any amplifiers except for the "really rare" Allen #90's.
Allens were designed with commercial customers in mind and designed them to be very reliable. Conservative design decisions meant fewer service calls to pissed off customers, and therefore, better reputation and increased sales to theaters and churches. Remember, the speaker/amplifier cost was only a small percentage of the total organ package. This was often just a portion of the entire building construction cost.
Most Organ amplifiers don't sound very good when used for audio because they were built on a cost per watt basis. Allen had a completly different market.
I can't believe the #75's and #90's are not the "Holy Grail" of push pull tube amplifiers. I guess there are not enough around to propogate their audio reputation.
Paul Keller
It's easy Mike, just bypass the 12AX7 on the
front end and go straight into the EF86 (don't
forget to put in a grid resistor to ground on
the EF86).
Here's the diagram:
http://www.triodeel.com/allen001.gif
The Allen's reportedly have too much gain so people (from what I understand) are "bypassing" one of the tubes, adding a resistor and that is supposed to take care of the gain issue. Im going to attach a link to the schematic and list bits and pieces of what I pulled from the archives of some other boards regarding the mod. The triode part, Im not interested in.
Topic in rec.audio.tubes - view in Groups BetaNew!
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Allen Organ Model 75's
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From: pkeller - view profile
Date: Tues, Oct 5 1999 12:00 am
Email: pkeller <pkel...@ix.netcom.com>
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Where can I get a schematic for Model 75 Allen Organ amplifiers?
These things can be spectacular in triode mode with teflon caps.
Reply
From: Tim H - view profile
Date: Wed, Oct 6 1999 12:00 am
Email: "Tim H" <t...@ma.ultranet.com>
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I'd start with a call to The Allen Organ Company in Macungie, PA.
610-966-2202 FAX 610-965-3098
Tim/
- Hide quoted text -
- Show quoted text -
pkeller wrote in message <37FAE10A.BFDD0...@ix.netcom.com>...
> Where can I get a schematic for Model 75 Allen Organ amplifiers?
>These things can be spectacular in triode mode with teflon caps.
Reply
From: Raymond Koonce - view profile
Date: Wed, Oct 6 1999 12:00 am
Email: Raymond Koonce <rkoo...@zzztyler.net>
Groups: rec.audio.tubes
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See http://www.triodeel.com/allen001.gif on Ned's site. It claims to be
a Model 75.
pkeller wrote:
> Where can I get a schematic for Model 75 Allen Organ amplifiers?
> These things can be spectacular in triode mode with teflon caps.
--
Reply
From: Paul Gustafson - view profile
Date: Wed, Oct 6 1999 12:00 am
Email: Paul Gustafson <gusta...@att.net>
Groups: rec.audio.tubes
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Were you the guy that bought the pair on ebay about a week ago??
Those were sure nice looking, there were three of 'em there !
Good snag!
Paul G
- Hide quoted text -
- Show quoted text -
pkeller wrote:
> Where can I get a schematic for Model 75 Allen Organ amplifiers?
> These things can be spectacular in triode mode with teflon caps.
Reply
From: pkeller - view profile
Date: Wed, Oct 6 1999 12:00 am
Email: pkeller <pkel...@ix.netcom.com>
Groups: rec.audio.tubes
Not yet ratedRating:
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Actually no. But I did bid on them. When I got outbid, I took option #2 and
bought
a pair from a fellow who failed to get any bids for his model 75's a couple
weeks prior.
I have heard Allen 75's played through Lynn Olson Ariels and was
astounded
at the strong low frequency response as compared to other tube amps. These
are beefy amplifiers even in triode mode. My Dynaco MKIII's were no match
through the same speakers. Much of the superb mids and highs are directly
attributable to replacement of the coupling caps with teflon caps. I've
also heard that silver foil in oil couplers work well if you can stand the
cost.
These things are not well known and I consider them quite a value.
pkel...@ix.netcom.com
- Hide quoted text -
- Show quoted text -
Paul Gustafson wrote:
> Were you the guy that bought the pair on ebay about a week ago??
> Those were sure nice looking, there were three of 'em there !
> Good snag!
> Paul G
> pkeller wrote:
> > Where can I get a schematic for Model 75 Allen Organ amplifiers?
> > These things can be spectacular in triode mode with teflon caps.
Reply
From: pkeller - view profile
Date: Wed, Oct 6 1999 12:00 am
Email: pkeller <pkel...@ix.netcom.com>
Groups: rec.audio.tubes
Not yet ratedRating:
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The friend of mine who has the Allen 75's that I've heard got the
instructions for trioding them from a guy that lives outside of Chicago
and is supposed to be an Allen aficionado. I'm a little leery about
giving out a name without prior permission. It's someone I've never
talked to. I don't have the method yet myself, but I will within the
next couple weeks when my amps arrive.
I don't know what the post triode power output is but it's plenty
for my high end needs.
Regards: pkel...@ix.netcom.com
- Hide quoted text -
- Show quoted text -
Blaine wrote:
> Where can you get a schematic showing how to convert to triode
> operation? What power can you expect in triode operation?
> Thanks,
> Blaine Ricketts
> Sent via Deja.com http://www.deja.com/
> Before you buy.
Reply
From: Blaine - view profile
Date: Thurs, Oct 7 1999 12:00 am
Email: Blaine <ricke...@my-deja.com>
Groups: rec.audio.tubes
Not yet ratedRating:
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Reply | Reply to Author | Forward | Print | Individual Message | Show original | Report Abuse | Find messages by this author
Where can you get a schematic showing how to convert to triode
operation? What power can you expect in triode operation?
Thanks,
Blaine Ricketts
Sent via Deja.com http://www.deja.com/
Before you buy.
Reply
From: Ned Carlson - view profile
Date: Thurs, Oct 7 1999 12:00 am
Email: Ned Carlson <postmas...@triodeel.com>
Groups: rec.audio.tubes
Not yet ratedRating:
show options
Reply | Reply to Author | Forward | Print | Individual Message | Show original | Report Abuse | Find messages by this author
Blaine wrote:
> Where can you get a schematic showing how to convert to triode
> operation?
Schematic? We don't need no stinking schematic!
1. Disconnect wires going to pin 4 on the 6550 sockets, tape
them up.
2. Install a 100 ohm 1/2W resistor between pins 3 & 4 on each
6550 socket.
3.Reset the bias. I believe on the Allen amps it's supposed to
be 1/4 volt between the bias test points and ground.
Oh, you want real triodes? Try this:
http://www.triodeel.com/allen005.gif
and compare it to this:
http://www.triodeel.com/allen001.gif
>What power can you expect in triode operation?
Triode connected 6550's, 25-30 watts.
300B's, about 40 watts if fixed biased.
I'm sure it would be easier to use Sovtek 6B4-G's,
I'd expect to get 30 watts or so out of them,
but they might do better than that.
What are the modifications that have been made to this point?
Have the 12AY7's been bypassed yet?
As for output tubes, I like the Svetlana 6550c's. I have not tried the Svetlana KT-88's yet, but hope to soon. KT-90's sound much too fat to me. The bass is not in balance with the mids or highs and I believe is not a good match for Allen #75's. If your speakers are weak in the bass region, this might compensate nicely though. GE-6550A's are a little sterile for my tastes, and TungSol 6550's are nearly the same sounding as the Svetlana 6550c's, but cost more and are difficult to find in reliable matched pairs. I actually prefer the Svetlanas.
I use Sylvania black plate 6SN7's with good luck.
Allen Organ #75's are very dynamic amplifiers with enough power to drive low efficiency speakers. They probably have the most stout power supply of any amplifier I've seen or heard. The PS choke is huge and free flowing. 15hy, 45 ohm.
The output transformers are incredible. I have one pair (I own seven #75's, + a pair of Allen #90's) that say "ACRO products" on the top. I believe these might be Acrosound TO-330's that have been dressed up as proprietary Allen products. The others are as good or better with 3300 ohm impedance.
I am going to experiment with some snubbers on the fillament supply as well as before the PS rectification bridge. Those old top hat diodes can be improved upon as well. There is a small bit of hiss that needs to be tamed, and I think it's from the fillament supply.
As for coupling caps, the best I have tried are "Custom" Teflon 1.0uf.
These were designed for "down the hole" oil field measurments. Very expensive. I've been thinking of trying those RelCap teflon's, but thats still a lot of dough for an unproven result.
Check that your tube plate resistors are still in spec. as they take a big voltage hit and change over time.
You will find that if your 12AY7 has not been bypassed, the gain will be way too high. The inputs are nearly mic level and need to be brought into useable range.
You have some amplifiers with incredible potential. I have not heard better imaging and soundstage from any amplifiers except for the "really rare" Allen #90's.
Allens were designed with commercial customers in mind and designed them to be very reliable. Conservative design decisions meant fewer service calls to pissed off customers, and therefore, better reputation and increased sales to theaters and churches. Remember, the speaker/amplifier cost was only a small percentage of the total organ package. This was often just a portion of the entire building construction cost.
Most Organ amplifiers don't sound very good when used for audio because they were built on a cost per watt basis. Allen had a completly different market.
I can't believe the #75's and #90's are not the "Holy Grail" of push pull tube amplifiers. I guess there are not enough around to propogate their audio reputation.
Paul Keller
It's easy Mike, just bypass the 12AX7 on the
front end and go straight into the EF86 (don't
forget to put in a grid resistor to ground on
the EF86).
Here's the diagram:
http://www.triodeel.com/allen001.gif
