#1
So I recently bought a tube stereo receiver amplifier (McIntosh 225 for $50) and I was going over its specifications and I had some questions about the tube specifics. Here's what each of the tubes are
Voltage Amplifier:1 each 12AX7
Phase Inverter:2 each 12AU7
Drive Amplifier: 2 each 12BH7
Output: 4 each - 7591
What are these sections of tubes and how do they affect the sound of the amplifier. How would changing [a] tube(s) out for another tube of a different model change the sound (for example a 12AU7, the phase inverter tube, gain of 19-20, switched with a 12AT7, gain of 60)

I am looking to fix, mod, and build other tube receivers and tube guitar amplifiers eventually but I wanted to know what each of these sections were and what the did for the circuit.

Thank you
#2
ok here

Voltage Amplifier:1 each 12AX7 - amplify voltage
Phase Inverter:2 each 12AU7 - inverts phase
Drive Amplifier: 2 each 12BH7 - drives the amplifier
Output: 4 each - 7591 - makes the output.
Prs se Holcomb is the answer
#3
Quote by AcousticMirror
ok here

Voltage Amplifier:1 each 12AX7 - amplify voltage
Phase Inverter:2 each 12AU7 - inverts phase
Drive Amplifier: 2 each 12BH7 - drives the amplifier
Output: 4 each - 7591 - makes the output.


nailed it.
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#4
Quote by AcousticMirror
ok here

Voltage Amplifier:1 each 12AX7 - amplify voltage
Phase Inverter:2 each 12AU7 - inverts phase
Drive Amplifier: 2 each 12BH7 - drives the amplifier
Output: 4 each - 7591 - makes the output.


There you go again making sense... You must stop this once and for all.

That's like telling people the gain knob controls the gain and the volume knob controls the volume.

Oh wait you do that too never mind
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Right now, there are six and a half billion people on earth who don't care what kind of tubes you have in your amplifier
#5
Quote by Willowthewitch
There you go again making sense... You must stop this once and for all.

That's like telling people the gain knob controls the gain and the volume knob controls the volume.

Oh wait you do that too never mind


i dont understand any of this.
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#6
Quote by Willowthewitch
There you go again making sense... You must stop this once and for all.

That's like telling people the gain knob controls the gain and the volume knob controls the volume.

Oh wait you do that too never mind


hi what does the gain knob do? and also what doe the volume knob do?
Prs se Holcomb is the answer
#7
Quote by Willowthewitch
There you go again making sense... You must stop this once and for all.

That's like telling people the gain knob controls the gain and the volume knob controls the volume.

Oh wait you do that too never mind


What are you trying to say?
#8
It's stereo amp, and I don't think it's tube. However, for a stereo amp, it is very good. Don't plug guitar into it; just use it as hi-fi if it works.
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#10
Quote by Willowthewitch
There you go again making sense... You must stop this once and for all.

That's like telling people the gain knob controls the gain and the volume knob controls the volume.

Oh wait you do that too never mind

If we want some info on fender mustang amps, we'll call you

But seriously...are you agreeing or trying to be a smartass? Because you clearly said "There you go again making sense"
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#11
if the op wanted a short treatise on the history and usage of thermionic valves i believe he should have have asked for one.
Prs se Holcomb is the answer
#12
Ok, all very funny but those terms assume a fair bit of background knowledge.

The first two take the miniscule input signal and amplify its voltage enough for the power amp to work with. This section will also contain tone shaping components.
The phase inverter is a device that splits the signal into two parts; the positive half and the negative half of the signal. This is necessary because of the way an A/B amplifier works. One power tube drives the positive half of the signal and the other drives the negative. It's a stereo amp so there are two phase inverters, one for each side.
The drivers are a bit of an oddity peculiar to this amplifier. The signal coming out of the phase inverter still isn't strong enough to drive the power tubes so they have added an extra stage to do it. Normally we use a phase inverter with enough output to do the job. For some reason they have decided to use a 12AU7 as the phase inverter and it's output is insufficient so they have added a couple of 12BH7's to overcome that.
The 7591's are the power tubes that actually produce the signal required to drive the speakers. It's a stereo amp so two drive left and two drive right.
It's actually quite an odd little circuit you have there.
http://www.tubebooks.org/file_downloads/McIntosh/MC225_sch.pdf

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Last edited by Cathbard at Oct 31, 2011,
#13
thats like exactly what I said man.

"The first two take the miniscule input signal and amplify its voltage enough for the power amp to work with. "

Voltage Amplifier:1 each 12AX7 - amplify voltage

see.

and really if we split hairs here does it really help the op? does it really help to have knowledge that you can't use?

I mean we could say well no your analysis of the driver stage is incorrect. It is not simply about drive. The 12bh7 follows the 12au7s in order to make up for the non linear characteristics of a phase inverter.

The 12au7 is chosen specifically for very little voltage gain. That gain is further clamped down by the large amount of negative feedback at the output.

blah blah blah who cares.
Prs se Holcomb is the answer
#14
I was trying to keep it simple and tbh I didn't analyse the circuit, I just had a quick glance at it and tried to provide a simple explanation that he might have understood.
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Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#15
Quote by Cathbard
I was trying to keep it simple and tbh I didn't analyse the circuit, I just had a quick glance at it and tried to provide a simple explanation that he might have understood.


i know.

the circuit is interesting though.

however, it's not like a guitar amp where you can sub tubes.

there's too much nfb around the entire amp.
Prs se Holcomb is the answer
#16
Quote by Cathbard
Ok, all very funny but those terms assume a fair bit of background knowledge.

The first two take the miniscule input signal and amplify its voltage enough for the power amp to work with. This section will also contain tone shaping components.
The phase inverter is a device that splits the signal into two parts; the positive half and the negative half of the signal. This is necessary because of the way an A/B amplifier works. One power tube drives the positive half of the signal and the other drives the negative. It's a stereo amp so there are two phase inverters, one for each side.
The drivers are a bit of an oddity peculiar to this amplifier. The signal coming out of the phase inverter still isn't strong enough to drive the power tubes so they have added an extra stage to do it. Normally we use a phase inverter with enough output to do the job. For some reason they have decided to use a 12AU7 as the phase inverter and it's output is insufficient so they have added a couple of 12BH7's to overcome that.
The 7591's are the power tubes that actually produce the signal required to drive the speakers. It's a stereo amp so two drive left and two drive right.
It's actually quite an odd little circuit you have there.
http://www.tubebooks.org/file_downloads/McIntosh/MC225_sch.pdf

Better?


tldr.
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#17
Quote by greeny23
tldr.

Good thing I wasn't talking to you then, huh?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#18
Quote by Cathbard
Ok, all very funny but those terms assume a fair bit of background knowledge.

The first two take the miniscule input signal and amplify its voltage enough for the power amp to work with. This section will also contain tone shaping components.
The phase inverter is a device that splits the signal into two parts; the positive half and the negative half of the signal. This is necessary because of the way an A/B amplifier works. One power tube drives the positive half of the signal and the other drives the negative. It's a stereo amp so there are two phase inverters, one for each side.
The drivers are a bit of an oddity peculiar to this amplifier. The signal coming out of the phase inverter still isn't strong enough to drive the power tubes so they have added an extra stage to do it. Normally we use a phase inverter with enough output to do the job. For some reason they have decided to use a 12AU7 as the phase inverter and it's output is insufficient so they have added a couple of 12BH7's to overcome that.
The 7591's are the power tubes that actually produce the signal required to drive the speakers. It's a stereo amp so two drive left and two drive right.
It's actually quite an odd little circuit you have there.
http://www.tubebooks.org/file_downloads/McIntosh/MC225_sch.pdf

Better?

thank you for being the ONLY one to answer the question. this helped me a lot to understand it better. how are these tube amps different than guitar tube amps?

p.s. i mean that he/she answered it as in actually explaining wut the tube stages were doing not just rephrasing the titles of the section
#19
Quote by Denkigan
What are these sections of tubes and how do they affect the sound of the amplifier. How would changing [a] tube(s) out for another tube of a different model change the sound (for example a 12AU7, the phase inverter tube, gain of 19-20, switched with a 12AT7, gain of 60)


well, this is the world of HI-FI, we guitarists go around changing out 12AX-7's for 12AT-7's all willy nilly and don't really worry about the consequences too much. but as for the engineering aspects each tube has it's particular specs beyond gain factor (stuff like plate voltages and current draws) and when you design an amplifier and choose the tubes it will use then you will also run particular values of components (resistors and capacitors and the such) to optimize factors (like current being feed to the anode and cathode of the tube).

so, if you design an amp to run 12AX-7's and you throw in a tube with a different spec then you are effectively running your amp in suboptimal conditions. sometimes these suboptimal conditions are acceptable (like pulling a 12AX-7 for 12AT-7), but sometimes components can be more incompatible (like you can't just pull out a 6L6GC and throw in a couple of 6V6's)

i'll briefly go over the tubes you listed
Quote by Denkigan

Voltage Amplifier:1 each 12AX7
Phase Inverter:2 each 12AU7
Drive Amplifier: 2 each 12BH7
Output: 4 each - 7591


12AX-7 - is actually a 'dual triode' tube, it contains the innards of two vacuum tube components inside one glass envelope. this allows a single tube to perform two tasks and take up less space overall. this tube is generally used in preamps, noted for a high gain factor. there are other versions of the tube with the same spec but go by different names because of regional naming conventions or because they are high end versions of the tube. so a 7025, ECC83, ECC803, or a 12AX-7A are all aliases of a normal 12AX-7 and are completely interchangeable.

12AU-7 - kinda rare to find these in guitar amps. this is also a dual triode tube. primarily used as phase inverters or as buffers for effects loops or reverb tanks. evidently these tubes have provide a high current at output. in the HI-FI world they have a reputation among the cork sniffers (especially as phase inverters) which may be why you find them in your amp

12BH-7 - another dual triode, i am not too familiar with these tubes but i do know they have been used in power sections of very small 'tube' amps.

7591 - output tubes. these are beam tetrode and work quite a bit different than the preamps tubes. these tubes were fairly common as HI-FI power amp tubes and i wanna say ampeg ran them in their amps as well.
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