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Old 9th April 2003, 09:00 PM   #1
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Question Interesting challenge:GU 50 output stage!

I'm wondering if any of you ever tried to build an output stage based on the Russian GU 50 tubes.
For the newbies,this tube is a military pentode,used mainly in mobile HF applications.It's,in fact,the contemporary Russian rugged version of the famous LS 50,a WWII German HF pentode.
For unknown reasons,despite of their very high reilability,this tube has been ignored by the most brands (as I know,only Manley Laboratories build an output stage whit them).
Strange enough,because if someone only looks at a GU 50 comparing it with a EL 34,there's,really,no competition....
Well,my intended application might seem a bit odd.
I'm playing electric bass in a fusion-jazz trio,and lately I bought an ultimate synth for bass guitar,namely Roland V-Bass.This monster is,by far,the most advanced processor-synth-pedal ever made for basses,a real dream come true.The first thing I noticed was that this synth is a "high-end" one,meaning that is totally different from any other processor I ever tried.The real problem occured when I played it through my crappy Fender 60W combo amplifier (transistor....).If used directly,the Fender sounds acceptably,but in combination with the V-Bass....just awful and pathetic.
So,I thought about building a real ,tube-based amp.I choosed a pair of GU 50 for making the honors as PP output tubes,taking into account B+ around 1000 V,and Ia aprox.40 mA/tube.
OK,here comes the challenge:what about the previous stages,especially the driver?
I already have planned some reliable configurations,but I'm interested what do you guys think!
The preamp/correction stages are not an issue,this is the easiest thing to decide about.
Thanks!
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Old 9th April 2003, 10:31 PM   #2
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Post a link to a datasheet and we might be able to comment. The one at tubes.ru comes up without the graphs.

How much are the tubes?
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Old 9th April 2003, 11:22 PM   #3
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Sorry,Brett,I'm not sure I understand what you're saying...
What do you mean by "how much are the tubes"?
Their price,maybe?
As for the graphs,I have to find all those curves,I know that have to be somewhere,and I'll scan them for you.
In the meantime,you could use the LS 50 data & graphs,there aren't big differences between the granpa and the nephew....except that the younger took some steroids....
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Old 10th April 2003, 12:16 AM   #4
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Quote:
Originally posted by Le Basseur
[B]Sorry,Brett,I'm not sure I understand what you're saying...
What do you mean by "how much are the tubes"?
Their price,maybe?{/B]
Yes, I was asking about the prices, as the only reference I has was the tubes.ru page which didn't have one. Just curious.

Quote:
As for the graphs,I have to find all those curves,I know that have to be somewhere,and I'll scan them for you.
In the meantime,you could use the LS 50 data & graphs,there aren't big differences between the granpa and the nephew....except that the younger took some steroids....
I'm downloading it from Franks page now, but I'd still like to see the Russian ones.

Cheers
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Old 10th April 2003, 12:45 AM   #5
Colt45 is offline Colt45  Serbia
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data:
http://oldradio.qrz.ru/tubes/russian.../gu-50_2.shtml

I can obtain them quite cheap too.. problem is, where the hell are you going to find sockets for them?


converting to octal base:
http://www.jogis-roehrenbude.de/Lese...red/Alfred.htm
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Old 10th April 2003, 07:16 AM   #6
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1.The GU 50's I have were dirty cheap....I got a dozen or so for the price of a beer/piece.
The most common sources for the GU's are ex-Eastern Germany sites and the Baltic countries,as it happens to have huge reserves,you guess why...I'll post some links for you,in case you're interested.The average price shouldn't be more than 10-12 Euros/piece.
2.Dont' worry,I also have the original bases.From where?Well,this is a question of luck,to be at the right time at the right place.Actually,I got them some years ago from some original devices,thrown away by the responsibles for the sake of "modernization".Aside from the original use of those devices,wich it isn't interesting at all,I found out that they were brand new....just think about it!
Honestly,it was a real pain-in-the-.... to get them out....I also learned a lot of things ant tricks on how to make the sturdiest tube-based device ever build by man.
So,your comments and ideas about the configuration,gentlemen?
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Old 10th April 2003, 07:18 AM   #7
TG is offline TG  Ukraine
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Hi, guys!

GU50 is really good, but... ONLY in triode mode, with both 2nd and 3rd grids connected to plate. In pentode mode the only advantage of GU50 is its price .

I've built class A2 PP with this tubes... 400V B+, 100 mA per tube, 7 kOhm Ra-a... Output of about 35 W (18-20 W in A1). The driver is 6N8S (Soviet 6SN7) SRPP, gives clean 120 V.

BTW, Uamax (continuous) for GU50 is 600 V... 1000 V is permissible only in pulse mode.
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Old 10th April 2003, 11:59 AM   #8
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Default Back to the point,folks....

I understand that there are serious doubts on using GU 50's with Ua 1000V.
This decision is based on some other things,not necessarily the specs.Therefore:
1.There are a number of schematics and,of course,real-life working amplifiers made around EL 34 and 807 tubes,the most notable cases being a couple of Marshalls and some Geloso's (the late is an Italian brand,famous in the '60-70' mainly because their RF engines).
All of these amps use the EL 34 tube FAR beyond the recomended regime...I have a Geloso schematic in wich EL 34's have a B+ of 1000V !
Of course,taking in the account the internal construction of the EL 34,it's not the happiest case,and I'm convinced that in those days,someone would replaced once a week the output tubes.
BUT,if in this cathegory,there is somewhere a tube wich can withstand 1000 V,I'm pretty shure that only GU 50 might be the one.
Yes,TG,I agree that the most common use of GU 50 is in triode mode,and I've written the specs,too.But,don't forget,please,it's an instrument's amplification what I'm going to build (therefore,I need more than 30-40W),and,(let's stay between us),I saw a couple of times those GU's on work in an infernal regime,the maximum anode disipation being overruled by 30%,in a pure class A operation.And,remember this,NOT EVEN A RED SPOT ON THE PLATES!
2.The re-basing is not an option,at least not in the way I saw on the link you mentioned.There are two reasons for that:
a.The GU 50 pins are unusually short (due to RF necessity to minimize internal capacitances),and made of a strange material,resembling some kind of steel.So,there are two critical issues,one regarding the quality and durability of soldering,and the second,the probability of messing up the thing by over-heating the legs...in other words,one could further expect possible glass cracks,event though it's Nonex.
I'd surely try re-basing on some average,precious,NOS tubes if I didn't find the appropriate socket,but not in this case....GU 50 runs VERY HOT...

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Old 10th April 2003, 12:22 PM   #9
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TG,if you can,please post me the schematic of the AB 2 PP you said you made.I'm especially interested in the the driver section!
Thanks,
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Old 15th January 2004, 01:28 AM   #10
anannra is offline anannra  Canada
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Here's me SE amp that uses 2 GU50s in parallel. I get a good 25W RMS per channel. A buddy of mine owns the audio circuit. I simply added a MOSFET plate regulator.

Sounds great, but the Hammond SE transformers start to roll off at around 18KHz. Need to save up some money and get me some Plitron transformers.

The power transformer is from Plitron.


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