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GU50 SE vs 300B SE tube amp??

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6

6NS

Member
Joined 2013
Dam, I was hoping for a bunch of great news about the GU.
I have a pair of 300Bs running two tubes a side SET Triode. I like them but they never find themselves on my mid-base woofer. I have them on my compression driver which seams a waste to me. One of my SET EL34s has a problem and I'm no tech.
I'm trying to replace my stereo EL34 PP class A. I like it too but I have this bug, I've had it for 35 years. There must be something better!!!
If anyone has more news, good or bad about the GU50 please through it out here.
Thanks you guys,
 
Globulator

Globulator

Member
Joined 2004
cutestudio.net
I found the main problem with the GU50 was buying valve bases that didn't crack the tubes if you turned the chassis on it's side (so the tubes where horizontal). I lost 4 GU50's this way - they just cracked at the base.

Some naked sockets are ok - I have some that work fine, but I think the ebay variety stress the pins radially and the loading change finishes them off.
The official GU50 holders are available and look rather military but are very safe for the tubes.

Soundwise - I ran mine with local feedback within the driver+output tube section (GU50 anode to triode driver cathode) and they sounded fantastic. Look at the curves - they are pretty solid and good up to 800V too. I actually get one glowing red too when a bias voltage broke, the tube took it all in it's stride!
 
M

multi

R.I.P.
Joined 2011
Thanks Globulator;
I am hoping to make an amp using GU50's triode Push pull, so good to know to watch the Sockets.
VV30B At $850 each??? Who can afford to use them!! When were they last made.?
Are the currently available 300b's as good.?
I recently repaired an amp using VV30B Se sounded good, but I prefer the sound of my Push pull KT88 triode connected amps driving Altec & JBL compression drivers horn loaded speakers.
With any 300B SE amp and the 6-8 watts output the most important thing is your speakers 7 the type of music you enjoy.
Phil
 
E

enzoastro

Member
Joined 2010
I got some Chinese 300b's for £60 delivered and they are ok, best midrange I've ever built. Def better than a gm70. The gm70 bass I had was far better. Loaded with 11k so the damping factor was good. Weight with a gm build is the biggest issue. Even my 300b is a real struggle to lift the 5' up to its wall shelf, out of the kids way.
 
6

6NS

Member
Joined 2013
Hello Art,
How are the GUs after a couple of years of play?
Impressions impressions, I'd like your please.
I like that there cheap old stock. There very likely, (in the right design), as good sounding as many of the renowned tubes out there, KT88, EL34, 300B, 6C33C etc. but with more rugged build.
I'd like to try 4 per channel.
Thanks for dropping in again,
 
artosalo

artosalo

Member
Joined 2010
6NS said:
How are the GUs after a couple of years of play?...

...I'd like to try 4 per channel.
Click to expand...

I have not used GU50's for such long periods that I could have personal experience of their useful life.
However, GU50 is originally designed (by Telefunken) for very demanding military service and it clearly is a non-consumer grade tube.
Therefore I am quite sure that when used in an amplifier which is properly designed, the lifetime will be longer than with typical audio output tubes.

Would you like to build a PP-amplifier with 4 tubes ?
That would deliver some 150 W:confused:
 
6

6NS

Member
Joined 2013
No I don't need 150 watts. I have 2 EL34s a side in PP class A and think I need double that. 75 watts would be plenty but would that be ultra-linear then, not class A? I hear some think GU50 are nicer in ultra-linear. You may be one of them. The woofer I'd be running for mid-base is 95db efficient. It's just that its tough to find people who have lived with this tube.
Thanks again,
 
Globulator

Globulator

Member
Joined 2004
cutestudio.net
multi said:
Thanks Globulator;
I am hoping to make an amp using GU50's triode Push pull, so good to know to watch the Sockets.
VV30B At $850 each??? Who can afford to use them!! When were they last made.?
Are the currently available 300b's as good.?
I recently repaired an amp using VV30B Se sounded good, but I prefer the sound of my Push pull KT88 triode connected amps driving Altec & JBL compression drivers horn loaded speakers.
With any 300B SE amp and the 6-8 watts output the most important thing is your speakers 7 the type of music you enjoy.
Phil
Click to expand...

I'm not sure the GU50s have much of a 'sound' in my amp - it's an SE with the punch of a push-pull because it uses a great deal of feedback in the driver/GU50 loop to give the primary a very good quality signal. No other feedback is used. This is a technique espoused by Thorsten Loesch (on this forum in fact) and means I not only get the sweet sound of an SE but for rock music it just seems effortless and dynamic. My speakers are only about 87dB/watt and I can't be more than 9W power but it behaves like a far more powerful amp.

BTW you can by the original 'dustbin' style sockets and simply cut them down to just use the naked bases. IMO it's the safest way.

Tube construction is top class - these would be very expensive tubes IMO if made today.
 
G

gaborbela

Member
Joined 2005
Globulator said:
I'm not sure the GU50s have much of a 'sound' in my amp - it's an SE with the punch of a push-pull because it uses a great deal of feedback in the driver/GU50 loop to give the primary a very good quality signal. No other feedback is used. This is a technique espoused by Thorsten Loesch (on this forum in fact) and means I not only get the sweet sound of an SE but for rock music it just seems effortless and dynamic. My speakers are only about 87dB/watt and I can't be more than 9W power but it behaves like a far more powerful amp.

BTW you can by the original 'dustbin' style sockets and simply cut them down to just use the naked bases. IMO it's the safest way.

Tube construction is top class - these would be very expensive tubes IMO if made today.
Click to expand...

Were I can see you GU50 schematic :D Please let me know.
Do you think your GU50 would stand firm in compared to a well built 300B amplifier
Your opinion needed
Thank you
Greetings gabor
Thank you
 
DrRoyal

DrRoyal

Member
Joined 2013
gaborbela said:
Were I can see you GU50 schematic :D Please let me know.
Do you think your GU50 would stand firm in compared to a well built 300B amplifier
Your opinion needed
Thank you
Greetings gabor
Thank you
Click to expand...

You can find a lot different schematics in the internet for SE or PP GU50
You decided to make it again ?

SE: easy for copy https://sites.google.com/site/moiusiliteli/Home/zvukotehnika/lampy/gu-50---vzroslaa-tema

or this one Sergei Klimanski Blog Archive ????? ?? ??????? ??-50 ( GU-50 ) ? ???????? ????????? ? 6?23?. - Personal web blogwith 6DJ8 and GU50

If you like clear real sound you should like SE one or two stage

Regards
 
Globulator

Globulator

Member
Joined 2004
cutestudio.net
gaborbela said:
Were I can see you GU50 schematic :D Please let me know.
Do you think your GU50 would stand firm in compared to a well built 300B amplifier
Your opinion needed
Thank you
Greetings gabor
Thank you
Click to expand...

Here is the thread here - it's a mod on the Sweet Peach a cheap unassuming Chinese amp which sounds surprisingly good with the right mods :D

http://www.diyaudio.com/forums/tubes-valves/163459-trying-make-sense-sweet-peach-17.html

The schematic is there but also here: (note this is my one, not the original layout!)
184143d1281867982-trying-make-sense-sweet-peach-sweetpeachpppmodz.png


The SRPP driver has since been modded to a tubelab style optimised one - it works very well as a powerful and energetic drive for the GU50s.

With this feedback arrangement I can't see why the 300B would be any better TBH - I suspect the main 'sound' of the amp comes from the input tube which as I recall is an Amperex Bugleboy in mine.

There is a hiatus in my tube soldering while I have a house extension so most info about the amp is now from memory. Before it was tucked out of the way of the building the tube regulators did make the whole thing look very pretty though :). Also if I did a clean design with better transformers etc I'd also do the tubelab mod of feeding back PSU noise into the amp - it's a quiet amp but PSU rejection goes beyond noise into signal correction - however good the PSU (this one was a simple choke+caps) the music will always imprint itself on there.

BTW I didn't realise goldenbeer had a Peach until I looked at the thread just now!
 
DrRoyal

DrRoyal

Member
Joined 2013
artosalo said:
Both of the designs you linked have THD more than 5 % at >5 W.
Do those represent clear real sound ?

Then what would be the sound if THD is dropped with more advanced design to 1 % at the same power level ?
Click to expand...

If you'll use CCS you'll get lower distortion and I send first schematic which i found
One more . Again if you'll use in pentode high power in triode sweet sound.
SRPP not the best schematic for driver GU50 or 300B.
Anyway, it's not too hard try it and only after it you can told - I like it or NOT, not before.

I've PP KT120, SE300B and looking for something new for myself.

Regards
 
Celsius

Celsius

Member
Joined 2011
Rod Coleman said:
I think the ГУ-50 (GU-50) is a splendidly made power tube. But the linearity in triode will be similar to the triode-connected KT-88.

This is no surprise: most indirectly heated power tubes in triode produce curves like this (see below for ГУ-50 triode curves).

If you really like the ГУ-50, it may be better to design an amplifier that uses some kind of local feedback to improve its high-voltage linearity.

Since the OP question is a direct comparison in a SE amp, the 300B has the greater potential. But only if the B+ and filament supplies are implemented to a high standard.
Click to expand...
Rod, in your experience how do you implement the local FB in two stages amp ?
thanks
 
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