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 ???
Thanks
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 ???
Thanks
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 😉
Cheers!
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 😉
Cheers!
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
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
Re: A1 A2
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/sheets/129/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.
7N7
noyan said:
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/sheets/129/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.
7N7
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
Noyan
noyan said:
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
7N7
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
Regards,
Noyan
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
Have you any experience with the metal anode 813's of US make? any comparison to the usual graphite type?
Best Regards,
Douglas
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.
7N7
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.
7N7
Hi , are the 803's a clone of the 813 ? I have some of these and would try .. are the worth the effort ?😕
I think it more likely that the 813 was developed from the 803.
The 813 is specified amongst other things for AF amplifier and modulator service whilst the 803 is not.
The 803 is more of what I call a "Class B" valve and I would think that it would have to be run with grid current - i.e. with a positive voltage on g1.
Strapped as a triode it would probably have quite a high anode resistance, but to be sure, you have to make the triode curves to find out.
The curves look nice though - you can find it on Frank's.
7N7
The 813 is specified amongst other things for AF amplifier and modulator service whilst the 803 is not.
The 803 is more of what I call a "Class B" valve and I would think that it would have to be run with grid current - i.e. with a positive voltage on g1.
Strapped as a triode it would probably have quite a high anode resistance, but to be sure, you have to make the triode curves to find out.
The curves look nice though - you can find it on Frank's.
7N7
noyan said:
So far I have built three prototype A2 amps using 3C24 , 826 and 809 . Very clear sounding and detailed but the bass sounded slow . With some anode to anode feedback this was somewhat improved as the output impedence was way in excess of the speaker imepdence . Depends on the speakers you use I guess . If you want a REAL valve for some serious A1 power , look up the WE308 . Apparently it's a current production valve 😉
cheers
316a
A2 when done correctly sounds forcefully bright but delightfully pleasant at normal listening levels......but forced grid drive with fixed bias can give higher thd..this is one trick that can be done when using a higher than normal prim Z, however be-careful when testing with cont sine/square wave as tube dissipation can rocket out of control.
I use A2 on guitar and trumpet for added rasp.
In normal use a pair p-p 6550 does like load Z around 3.5K a-a somewhat lower than a KT88's. Using 4.5K a-a, would under-power but forced grid A2 can easily give 50W from a pair of 6550's with only 360V, but watchout full load current of around 180mA per tube which will strain power supply and tubes. Perhaps I should try this with KT90's or other high current sweep tubes.
I seem to think there was an fixed bias 807 application circuit around on sim grounds using diodes strapped from grids to neg line. Any other ideas ?
richj
I use A2 on guitar and trumpet for added rasp.
In normal use a pair p-p 6550 does like load Z around 3.5K a-a somewhat lower than a KT88's. Using 4.5K a-a, would under-power but forced grid A2 can easily give 50W from a pair of 6550's with only 360V, but watchout full load current of around 180mA per tube which will strain power supply and tubes. Perhaps I should try this with KT90's or other high current sweep tubes.
I seem to think there was an fixed bias 807 application circuit around on sim grounds using diodes strapped from grids to neg line. Any other ideas ?
richj
Big triode
Thank you very much! I decided to connect parallel 2 x GM70 triodes for 62,5watts SET Class A1 sound. Because, i have good experience with GM70. By the way, do you have any comments about Hammond's 5k, 75watts OPT's ? They are not expensive (250usd-each) but, i could not find on internet any review or comment about their sound quality. In their internet site, specified that core material is M6 grain oriented silicon steel. It means that, thickness of the laminations is 0,35mm. Is it not too thick???
Regards,
Noyan
Thank you very much! I decided to connect parallel 2 x GM70 triodes for 62,5watts SET Class A1 sound. Because, i have good experience with GM70. By the way, do you have any comments about Hammond's 5k, 75watts OPT's ? They are not expensive (250usd-each) but, i could not find on internet any review or comment about their sound quality. In their internet site, specified that core material is M6 grain oriented silicon steel. It means that, thickness of the laminations is 0,35mm. Is it not too thick???
Regards,
Noyan
hey-Hey!!!,
If you're using grid drive to do A2, you have a step-change in the driven load when the grid goes positive. What is a decent driver for A1, makes some interesting effects on flow of grid current. Even one that can deliver A2 current sees an order( or two ) of magnitude change in the grid impedance.
So then how to get grid current with a constant load to the driver stage?
Drive the cathode.
The grid is now acting like a pentode's screen grid, so no Miller. The downside is for a 211/845 there is a ~250R load to drive, even w/o grid current flowing. This load takes power, but it remains constant...🙂
cheers,
Douglas
If you're using grid drive to do A2, you have a step-change in the driven load when the grid goes positive. What is a decent driver for A1, makes some interesting effects on flow of grid current. Even one that can deliver A2 current sees an order( or two ) of magnitude change in the grid impedance.
So then how to get grid current with a constant load to the driver stage?
Drive the cathode.
The grid is now acting like a pentode's screen grid, so no Miller. The downside is for a 211/845 there is a ~250R load to drive, even w/o grid current flowing. This load takes power, but it remains constant...🙂
cheers,
Douglas
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