McIntosh C220, C2200, C2300 tube configuration

[jdandy]

My C2200 preamp has four 12AX7 tubes in the line stage, and four 12AX7 tubes in the phono stage. The C220 has only two 12AX7 tubes in the line stage and two 12AX7 tubes in the phono stage, and the C2300 has the same tube configuration as the C220 plus two additional 12AX7 tubes for the moving coil phone stage.

Why does the C2200 use four 12AX7 tubes in the line and phono stages? Is one design superior than the other, or quieter?

NOTE: TUBE CONFIGURATION CORRECTED BELOW.

 

[vintage_tube]

My C2200 preamp has four 12AX7 tubes in the line stage, and four 12AX7 tubes in the phono stage. The C220 has only two 12AX7 tubes in the line stage and two 12AX7 tubes in the phono stage, and the C2300 has the same tube configuration as the C220 plus two additional 12AX7 tubes for the moving coil phone stage.

Why does the C2200 use four 12AX7 tubes in the line and phono stages? Is one design superior than the other, or quieter?

Regarding the C2200 -- I thought it utilized:
2 each 12AX7A's in phono
2 each 12AT7A's in phono
2 each 12AX7A's in higher level circuitry (tone bypass, bass/treble control)
2 each 12AT7A's in higher level circuitry (tone bypass, bass/treble control).

The C2200 does not have a dedicated tube pair for preamp in/out as does the C2300. C2300 slots are:

2 each 12AX7A for MM phono
2 each 12AX7A for MC phono
2 each 12AX7A for MAIN in/out

The C220 is similiar in utilization of it's tube to the C2200:
2 each 12AX7A for phono
2 each 12AX7A for higher level circuitry (bass/treble controls)

 

[jdandy]

Pulled the cover off the C2200 to look again, and you are correct. Two 12AX7 and two 12AT7 in phono and line level circuits. I was hasty in my original observation. What are the 12AT7 tubes doing in the C2200 that are not required in the C220 and the C2300?
New avatar......Cool!

 

[jdandy]

The 12AT7 is a triode, right? Why was the 12AT7 not used in the circuit design of the C2300? What advantage did the 12AT7 provide in the C2200 design?

 

[Vintage Pete]

Curious

I know this is off topic, but I have to ask...Vintage, what kind of R-R is that in your cool new Avatar? And, is it yours? Almost looks like a Teac..but I don't remember any Teacs with blue meters...

Pete

 

[jdandy]

I know this is off topic, but I have to ask...Vintage, what kind of R-R is that in your cool new Avatar? And, is it yours? Almost looks like a Teac..but I don't remember any Teacs with blue meters...

Pete

Bob and I discussed that reel to reel machine. It is his Akai GX-400. Very rare machine. Three speeds, too, 3 3/4, 7 1/2, and 15 ips. He told me there were only 200 of them made with the black bottom and blue meters. He said he bought it new in Okinawa, carried it all around the world, and now has it home. It's a good looking machine. Wold look nice in a rack full of other blue meters.

 

[vintage_tube]

I know this is off topic, but I have to ask...Vintage, what kind of R-R is that in your cool new Avatar? And, is it yours? Almost looks like a Teac..but I don't remember any Teacs with blue meters...Pete

Hey Pete -- had several questions regarding the R-R. I had to pull the original receipt --bought it on 19 Nov 1974 at Gakiya Radio Electric Co, LTD in Ginowan City, Okinawa.

It is an Akai GX-400D with 3 3/4, 7 1/2 and 15ips and from what I can research, it is one of 200 made -- and only a handful (less than 25 or 50 at the end of the production run) that have huge blue VU meters and the lower half is black (Serial Number 00190). The other units are entirely silver w/yellowish VU meters. It is written that is it the 2d best deck overall that Akai built (the GX-1000 Pro tops the list). It does not have dolby but an Akai in-house designed similiar unit (considering the times--just when dolby units like the Teac AN/180 were coming out--which I also had mated to this deck).

Paid $708 back then for it w/the 25 foot "cable" remote. Took me 6 months to save up for that deck. Works perfectly to this day but I am interested in finding a shop on the east coast to do a thorough 35 year checkup. Original boxes, R-R and remote are in mint condition - along w/the deck -- not one scratch, ding or dent. It could do for a thorough cleaning/polishing (was going to do that today -- but got caught up in honey-do's this weekend).

There are a few more pics on the tape forum.

 

['cisco]

My C2200 preamp has four 12AX7 tubes in the line stage, and four 12AX7 tubes in the phono stage. The C220 has only two 12AX7 tubes in the line stage and two 12AX7 tubes in the phono stage, and the C2300 has the same tube configuration as the C220 plus two additional 12AX7 tubes for the moving coil phone stage.

Why does the C2200 use four 12AX7 tubes in the line and phono stages? Is one design superior than the other, or quieter?

NOTE: TUBE CONFIGURATION CORRECTED BELOW.

hey Dan, don't have an answer for ya...but I recently turned "off" the phono tubes as I'm not a vinyl person. That should save on my tube life...:thmbsp:

I could have responded, (using your line).....but I did stay at a Holiday Inn.....:lmao:

Hey Pete -- had several questions regarding the R-R. I had to pull the original receipt --bought it on 19 Nov 1974 at Gakiya Radio Electric Co, LTD in Ginowan City, Okinawa.

It is an Akai GX-400D with 3 3/4, 7 1/2 and 15ips and from what I can research, it is one of 200 made -- and only a handful (less than 25 or 50 at the end of the production run) that have huge blue VU meters and the lower half is black. The other units are entirely silver w/yellowish VU meters. It is written that is it the 2d best deck overall that Akai built (the GX-1000 Pro tops the list). It does not have dolby but an Akai in-house designed similiar unit (considering the times--just when dolby units like the Teac AN/180 were coming out--which I also had mated to this deck).

Paid $708 back then for it w/the 25 foot "cable" remote. Took me 6 months to save up for that deck. Works perfectly to this day but I am interested in finding a shop on the east coast to do a thorough 35 year checkup. Original boxes, R-R and remote are in mint condition - along w/the deck -- not one scratch, ding or dent.

There are a few more pics on the tape forum.

vintage_tube, That's a sharp looking RR you got there :yes: any chance of posting a separate pic of that baby? :scratch2: Would love to have it in my little archive...oops I didn't see your last comment

 

[jmprest]

I'm hoping that some of our more technically oriented folks will chime in on the design difference between the two units (c2200 vs c2300), besides the obvious tone meters ect features. Seem like the c2300 is more like 2 c220 put together with 2 extra tubes for MC.

 

[jdandy]

I'm hoping that some of our more technically oriented folks will chime in on the design difference between the two units (c2200 vs c2300), besides the obvious tone meters ect features. Seem like the c2300 is more like 2 c220 put together with 2 extra tubes for MC.

It has been said to me that the C2200 is really a solid state preamp with a tube tone control circuit, and a tube phono stage. Looking at the block diagram in the C2200 Owner's Manual, it shows the 12AX7/12AT7 as a 15dB gain amp. The block diagram triangle symbol is labeled main amp. Not being an electronics tech, I'm not certain what I am seeing in the block diagram.

It would seem to me that if the C2200 were a solid state preamp, then I should be able to pull the tubes, and the preamp would still work. I haven't done this, of course, don't want to screw anything up. McIntosh literature states , "The C2200, which utilizes vacuum tubes to provide all signal amplification, delivers an unsurpassed sonic experience." That's right off their web page for the C2200.

Some technical feedback on this issue would be appreciated.

 

[Victor]

The 12AT7 is a triode, right? Why was the 12AT7 not used in the circuit design of the C2300? What advantage did the 12AT7 provide in the C2200 design?

I'm not a tube expert but I'm pretty sure the 12AT7 and 12AX7 tubes are both dual triode tubes. So each tube can perform 2 different functions. And the difference between the 12AT7 and 12AX7 is the 12AX7 has more gain.

 

[dshoaf]

I've got the service manual for the C2200 but not the C2300 - I own the C2200 only.

While the manual is out in Arkansas and I'm in California right now, I'll operate from memory. The 12AX7s in both the phono and the line-level preamp of the C2200 operate as gain stages as befitting their abilities a la Victor's comments.

The 12AT7s, IIRC, operate as impedance buffers or, in more proper terms, cathode followers. These stages are intended to provide low output impedances but have no gain of their own. If you really want to get into this further, here's a long technical discussion.

FWIW, I also see lots of discussions about adding this same sort of tube circuit, the cathode follower, to digital sources and are supposedly there to add 'tube warmth' to the digital playback unit. Ha!

BTW, another famous preamp that used 12AT7s in this configuration was the HK Citation I.

Cheers,

David

 

[Vintage Pete]

Sweet!

Hey Pete -- had several questions regarding the R-R. I had to pull the original receipt --bought it on 19 Nov 1974 at Gakiya Radio Electric Co, LTD in Ginowan City, Okinawa.

It is an Akai GX-400D with 3 3/4, 7 1/2 and 15ips and from what I can research, it is one of 200 made -- and only a handful (less than 25 or 50 at the end of the production run) that have huge blue VU meters and the lower half is black (Serial Number 00190). The other units are entirely silver w/yellowish VU meters. It is written that is it the 2d best deck overall that Akai built (the GX-1000 Pro tops the list). It does not have dolby but an Akai in-house designed similiar unit (considering the times--just when dolby units like the Teac AN/180 were coming out--which I also had mated to this deck).

Paid $708 back then for it w/the 25 foot "cable" remote. Took me 6 months to save up for that deck. Works perfectly to this day but I am interested in finding a shop on the east coast to do a thorough 35 year checkup. Original boxes, R-R and remote are in mint condition - along w/the deck -- not one scratch, ding or dent. It could do for a thorough cleaning/polishing (was going to do that today -- but got caught up in honey-do's this weekend).

There are a few more pics on the tape forum.

Hey VT,

That's a beautiful machine indeed...most machines of the day (not just Akai) had the yellowish meters, like you mentioned. That's how my Crown SX-724 is. Dan is right-your machine would look nice in a rack with other black panels/blue meters! (not to mention any brand names! )

Pete

 

[jdandy]

The 12AX7s in both the phono and the line-level preamp of the C2200 operate as gain stages as befitting their abilities a la Victor's comments.

The 12AT7s, IIRC, operate as impedance buffers or, in more proper terms, cathode followers. These stages are intended to provide low output impedances but have no gain of their own. If you really want to get into this further, here's a long technical discussion.

David

Thank you, David. So, you are saying that the 12AT7/12AX7 tubes in the line stage of the C2200 are part of the audio signal amplification, and not used soley as a tone control circuit. Is the C2200 a true tube preamp from signal input to signal output? There are some who have suggested that the C2200 is a solid state preamp with tube enhanced tone control circuits, but that the audio signal does not use the tubes unless the tone controls are introduced into the circuit. This is a question I would like a definitive answer for.

 

[JSCC]

Dan,

The C2200 is a trude blue tube preamp, thru and thru ... all the way ... from input to output! Not a hybrid at all! That was my understanding when I had my first one and now the C2200G version!

Cheers!

 

[dshoaf]

Dan, I believe (without looking at the C2200 Service Manual's schematics right now) that the tone controls are switched in/out with the front panel switch. This implies that there is a way for this to be done with logic gates of some sort - but those would not be in the signal path. I wouldn't fret about that at all. The signal path through both the phono and line stages are all-tube. Note: The only exception on the C2200 are the balanced inputs/outputs where there is a level converter used to get the signal into or out of the preamp. You'll see these in the schematic.

I have no idea where that other solid-state folk-lore is coming from. Get the service manual - its available from Mac for about $25.00 to debunk what's being cast around the net these days.

Again, I haven't checked on the C2300's circuit topology but I'm sure it will follow a similar set of gain stages. Whether it uses a specific set of tube types - and more importantly, the specific circuit topologies used - is more the issue of how the designer approached the set of preamp functions required for the market.

It would be helpful to understand why this is a big issue for some folks. I don't seem to get it......

Cheers,

David

 

[jdandy]

Dan, I believe (without looking at the C2200 Service Manual's schematics right now) that the tone controls are switched in/out with the front panel switch. This implies that there is a way for this to be done with logic gates of some sort - but those would not be in the signal path. I wouldn't fret about that at all. The signal path through both the phono and line stages are all-tube. Note: The only exception on the C2200 are the balanced inputs/outputs where there is a level converter used to get the signal into or out of the preamp. You'll see these in the schematic.

I have no idea where that other solid-state folk-lore is coming from. Get the service manual - its available from Mac for about $25.00 to debunk what's being cast around the net these days.

Again, I haven't checked on the C2300's circuit topology but I'm sure it will follow a similar set of gain stages. Whether it uses a specific set of tube types - and more importantly, the specific circuit topologies used - is more the issue of how the designer approached the set of preamp functions required for the market.

It would be helpful to understand why this is a big issue for some folks. I don't seem to get it......

Cheers,

David

Thanks, David.

Thanks, Jerry.

Guess I need to order the service manual.