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Old 19th August 2007, 08:52 AM   #1
noyan is offline noyan  Turkey
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Default sound comparison of Class A1 vs A2 amps

Hi,
I have a GM70 SET Class A1 all triode 2x30watts tube amp. Sound very very good. What i want to know, what is the sound difference between Class A1 and A2 tube amps. Is the difference in only little nuances or there is big difference. Also, which triode gives me the highest Class A1 power? For example, 833 very powerful but, gives only Class A2 sound only due to positive grid supply requirement. For example big tube GM-100 works in Class A1 or A2 mod ???
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Old 19th August 2007, 09:30 AM   #2
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Hi,

In theory, if your driver is capable of sourcing the grid current (cathode follower, MOSFET or IST), you should be able to hear little difference.

In practise, the harmonic composition does change and depending on your speakers, the difference could be quite noticeable.

I don't like SE (T or P) A2 in general for HiFi (though I haven't heard that particular tube), so I'm a bad one to ask. Just laying out some info for you

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Old 19th August 2007, 10:00 AM   #3
noyan is offline noyan  Turkey
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Default A1 A2

Hi Geek,
Thank you. I m agree with you. I recently intended to build a 833 SET 75watts amp but, it will give me sound in only A2 mode. It means that, i will have more power but less sound quality (i don't know how is the sound of Class A2 but anyway) when compared with GM70 A1 - i am not acceptable this- Due to this reason, i changed the mind about 833 tube amp project. GM70 tube also can give me about 62,5watts (125/2=62,5w) of power in Class A2. Perhaps better idea for more power in class A1 mode, to build a parallel SET GM70 amp. Then i get 62,5watts of power in A1. Also, when i want to make economy in power consumption, i can remove one of the GM70 from it's socket then i have half of the power. In the other hand, i want to learn if there is any other big power triode which can give me beautiful sound (like GM70) and more than 30 watts in Class A1 mode. Do you have an idea, is there any big triode tube like i want?
Noyan
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Old 19th August 2007, 12:01 PM   #4
7N7 is offline 7N7  United Kingdom
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Default Re: A1 A2

Quote:
Originally posted by noyan
Hi Geek,
Thank you. I m agree with you. I recently intended to build a 833 SET 75watts amp but, it will give me sound in only A2 mode. It means that, i will have more power but less sound quality (i don't know how is the sound of Class A2 but anyway) when compared with GM70 A1 - i am not acceptable this- Due to this reason, i changed the mind about 833 tube amp project. GM70 tube also can give me about 62,5watts (125/2=62,5w) of power in Class A2. Perhaps better idea for more power in class A1 mode, to build a parallel SET GM70 amp. Then i get 62,5watts of power in A1. Also, when i want to make economy in power consumption, i can remove one of the GM70 from it's socket then i have half of the power. In the other hand, i want to learn if there is any other big power triode which can give me beautiful sound (like GM70) and more than 30 watts in Class A1 mode. Do you have an idea, is there any big triode tube like i want?
Noyan

I should think that budget permitting, the 4212E/V1505/MY3-275 is the one for you. Frank has the data:

http://datasheets.electron-tube.net/.../m/MY3-275.pdf

Alternatively, a much cheaper option, if your driver stage can drive the capacitance, would be to run a pair of valves in parallel. A pair of triode-strapped 813s would do nicely. At say 900V and 90mA they would be easy to drive (bias about -80V) and anode resistance would be about 900 ohms.

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Old 19th August 2007, 12:07 PM   #5
noyan is offline noyan  Turkey
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Thank you. I don't like to use any capacitor on signal path. I use interstage. I have westinghouse 813 tubes in stock but, instead of them why not use the GM70's parallel? Any comment?
Noyan
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Old 19th August 2007, 02:00 PM   #6
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Quote:
Originally posted by noyan
Thank you. I don't like to use any capacitor on signal path. I use interstage. I have westinghouse 813 tubes in stock but, instead of them why not use the GM70's parallel? Any comment?
Noyan
Well capacitors are not obligatory and I didn't mention them! By capcitance I meant the Ca-g of the output valve(s). I imagine your transformer will drive this with no problems.

Yes why not parallel your GM70s? I have no knowledge or experience of GM70 so beyond that I cannot comment. I do have experience of 813s; as triodes they are excellent (and probably excellent as beam tetrodes too).

Of course you will need a bigger (i.e. capable of more power) output transformer, but the advantage is that you can have a lower primary impedance. You should get better bass if you do not halve the existing impedance

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Old 19th August 2007, 02:36 PM   #7
noyan is offline noyan  Turkey
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Thank you. I read good things about 813 triode connected in internet like you wrote. Later, i will try to make 813 set amp too. I have a pair of 6k. output transformers, tubes and sockets. 813 Is very beautiful tube for me with the head cap.
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Noyan
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Old 19th August 2007, 04:03 PM   #8
7N7 is offline 7N7  United Kingdom
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Quote:
Originally posted by noyan
Thank you. I read good things about 813 triode connected in internet like you wrote. Later, i will try to make 813 set amp too. I have a pair of 6k. output transformers, tubes and sockets. 813 Is very beautiful tube for me with the head cap.
Regards,
Noyan
Serefé!

7N7
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Old 20th August 2007, 01:35 AM   #9
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Sir 7N7,
Have you any experience with the metal anode 813's of US make? any comparison to the usual graphite type?
Best Regards,
Douglas
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Old 20th August 2007, 07:37 AM   #10
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Default 813 - Metal Anodes

Hello.

All the 813s I used, had graphite anodes.

I was once shown (at Colomor) some very late RCA 813s; these had metal anodes, but they are the only ones I have ever seen.

Sorry I cannot help more.

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