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GU50 SE vs 300B SE tube amp??

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Hello
I turn to the forum ( to some expert guys) about my SE tube project.
I start from the beginning so it would be easy to understand my case.
I wanted to build a GU50 SE triode tube amp, so I collected almost all the necessary parts, let say 90%
Power transformer 325V 2.5A, a pair 3.5K SE 10W 100mA continuous bias USA made transformer, driver and power tubes, sockets, choke, PS capacitors etc
Now I don't know do I complete the amplifier or to use those parts to build a 300B SE amplifier.
Do any one has experience with these two power tube, built or heard their sound?
I could use the same transformers, for the 300B , I have D3a tube to drive the 300B, only has one choke 200mA tested up to 2000V (may be I need two)..
What would be the best think build a 300B and sell the GU50 tubes or finish the GU50 and probably I never get close to the 300B performance??Any advise pro and contra welcome.
Also please keep in mind probably later I'll sell the amp because my wish to build a GM70 SE. I just do not want to start with 1000V now, last few years I built only SS amplifier.
Of course all depend the amplifier performance, if sound great I'll keep her.:)
Also if the amp sound better probably easier to sell in case/.
I do wanted to post pictures from the parts I collected but I have to charge my camera's battery.
So pictures will follow soon.
Thanks for your help
Happy New Year!
Greetings Gabor
 
Hello
Here is the two circuit I think about
First the GU50 what I planed to build but mean while I collected the parts I get several negative or just OK feedback on these tube using as SE...
http://sergeev21.narod.ru/gu50se.htm
The GU50 I like with the 6E5P driver tube but one power tube only..
The 300B is from Andrea reference amp all do I have to do several mode because he use higher primary OPT and almost dual mono PSU.
Right now I have only one choke 6H 200mA, he uses two choke. I don't know for start if I can connect both channel to one PSU.. At least to test the circuit.
After I would buy a pair choke because the two must be the same.
I wrote to Andrea to get some info about his amp but unfortunately I didn't got answer yet. Also one capacitor value missing from the circuit..
Please take a look the 300B circuit, can I use it with my 3.5K transformer and for start can I use only one choke in the PSU?? I know these is a great amp, I know if Andrea say is a reference amp that is not bad.
http://www.audiodesignguide.com/SE300B/index.html
I read good think about the 300B but... that how it was with the GU50 when I started. Now those guys who praised the GU50 tube they gave up and build something else.
To me 6 to 8 Watt it would be plenty to drive my speakers.
Thanks for the help.
Greetings Gabor
 

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Hello
If you look at the 300B circuit there is two arrow
First I don't know the capacitor value and voltage
second arrow - I'm not sure if I can leave out that part of the PSU and connect both channel for the one 400V.
These would be temporary until I would get some idea about the amp performance after I would buy two 10H choke. Also I plan to use SS bridge rectifier, not tube
Only I question the amp performance because my OP transformer has 3.5K primary. Probably I get higher distortion and higher bias with out mode.
Please let me know what would you do in my case.
About the GU50 tubes if I solder them (specially the socket cost more) I can't sell those..
Thanks one more time
Greetings Gabor
 
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I have built the GU-50... and I think it is pretty awesome.
You can try running it in triode mode, or switching to pentode mode but use some plate to grid feedback.
Since you already have all the parts you need, just proceed with the GU-50... you may end up liking it. I certainly do like mine.
It won't sound like a 300B, but I could say no 300B could ever sound like it, with the solid bass and bite and yet maintain a sweet midrange especially in pentode mode.
BTW, my driver stage is with 6E5P too but using 3 red LED bias bypassed with Elna Silmics2, and the GU-50 run in pentode mode with screen grid voltage regulated by neon lamp voltage reference at 210V.
 
i'd build the gu50 and when funds allow get some 300b's, the money is in the ps and opt's so swapping sockets and bias components is a pretty economic way to get a new amp. i would not fret too much re your choke, worst case you get a little cross talk and imho thats the least important spec when your listening.
p.s both those circuits could be much improved with 2 resisters and a dn2540 mosfet!
enzo
 
I don't like building with high voltages, so I see your point. I'd go up to 450v or so. But at that kind of HT you can use various big tubes at "low voltage" operating points. The 813 is one that many like. Looks like you can put up to 100mA through your OPTs so you may get enough power - what speakers are you driving?
Hello I did check up the 813 tube, in my case that is not a option. High voltage tube. Those tube need certain anode voltage to get out quality sound worth to build invest time, money energy. For example GM70 works 750V but if you go up to 950-1000V it will be another level.. Only two possibility I have put together GU50 amplifier or go for a 300B. quikie22 thanks for the circuit you posted but how Wavebourn wrote it is not correct so to me how is it useless. Sorry about that.. Also you wrote you would like to upgrade, it would be helpful to see your complete circuit what is in your mind..

To the Andrea 300B circuit I can get two 5H 100mA choke plus I use my 6H 200mA.. My question for the 300B the choke does need special air gap/ I see on the Ebay from Taiwan the mentioned choke for $24/PC plus shipping. It look nice but who knows the quality.. One think if I could know from the GU50 can get enough and quality bass in SE mode. That would be very helpful. I read many negative about these the tube. Some people wrote only good for PP if I want audio sound. The picture I got now (from all information get about the GU50 tube) if I want good SE sound with acceptable bass I have to use 300B tube or some transmitter high voltage tubes. Also certain PL TV tubes great but need 500V or more.. And pricey to.. These theory is true I will be not to happy because the GU50 tube price VS the 300B..:bawling: Al do if the extra invested money would ad up at the sound quality I would not mind. I do have the driver D3a tube for the 300B but not the power tubes. So before I will do invest more it would be good to know all that investment it will be for good use or in vain. I do make picture from my collected parts, I have the amp case also but I will tested on a PC of plywood at first.

Thanks one more time

Greetings
Gabor
 
Schade Feedback

Quikie

Plate to plate or "Schade" feedback works best with a driver that has a very high rp, that is tries to works like a current source. A triode on the other hand has a relative low rp and tries to work as a voltage source. There are basically three options for a Schade driver:

1. Use a high gm tetrode or pentode, (your 6E5P), but do not triode strap it.

2. Use a cascode with a high gm triode (6DJ8).

3. Use a depletion MOSFET (DN2540).

Either of these three options will out perform your 6E5P operating as a triode. Also operate the output pentode as a pentode as well.
 
Go build your 300B amp gaborbela :) and enjoy it.

That is very kind from you!
Thank you & Happy New Year.. I hope you will get help in the near future according to your willingness you help me here.:)
You know about the GU50, also probably compared with other amps to:eek:
I open these thread to discuss my option with the parts I already own & hoping to get some honest help, advise from some experienced guy.
If I made you upset in any way please forgive me.

Greetings
 
Quikie

1. Use a high gm tetrode or pentode, (your 6E5P), but do not triode strap it.

2. Use a cascode with a high gm triode (6DJ8).

3. Use a depletion MOSFET (DN2540).

Either of these three options will out perform your 6E5P operating as a triode. Also operate the output pentode as a pentode as well.

Hello
What do you think from the circuit I posted? All do I need a complete circuit to build something.
What I mean by a simple advise I can't mode the circuit or build it successfully. Probably I'll need a little more help like some simple advise.
Thanks
Greetings Gabor
 
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