• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Looking for high-voltage tubes

jan.didden

jan.didden

AX tech editor
Joined 2002
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I'm looking for a high voltage tube for my next gen ESL direct drive amp.
Basically Va(max) at least 6500V, with a Pa (max) of at least 50W.
Everything else is negotiable but preferable not one that requires me to take out a 2nd morgage ...

Jan
 
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ulibub

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Joined 2006
instagram.com/tubeampuli/
Hi Jan,
very interesting project... I also thought already about how to build such an amp... I would try a 4-125A (QB3/300). Max. plate voltage for RF power amplification should not exceed 3 kV (datasheet...), but from its construction its plate can take a lot more.... Max. screen voltage up to 600V, with such high plate potentials I would rather go quite a bit lower, 200-300V. Graphite plate and very rugged construction, so I think this would be a good beginning at least... But how do you plan to realize the plate resistances? Resistors, chokes?
In this way I also operated an EL81 with up to 1,2 kV DC plate voltage (and 70V screen) as a regulator tube for a power supply, which could be set from 800V to 1,2 kV output voltage using an EL519 as pass tube.
If it should be a triode, I would eventually try the former colour TV HV shunt regulator triodes like the PD500..... Maybe two or three of them in parallel?
all the best
Uli
@tubeampuli
 
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jan.didden

jan.didden

AX tech editor
Joined 2002
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Paid Member
Question again. If I look at say an 813, the max Va in the various modes is 2250 or 2500 V.
Yet, that is a DC spec, and if I use a SE choke loaded stage with say 2500V B+ (DC), the anode swings between close to zero and almost 5000V.
Does that then not violate the Va spec?

Jan
 
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RJM1

Member
Joined 2010
6BK4? only 25W but 27KV, two in parallel?
We used 4 of them in paralell for load testing 3ma 33KV power supplies for video projectors.
Lots of lead tape on that box.
 
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smoking-amp

smoking-amp

Member
Joined 2001
6HZ5 6000V 30W 300mA pk

6HZ5pic.jpg
 
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jan.didden

jan.didden

AX tech editor
Joined 2002
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Paid Member
That's an interesting tube.

I am wondering, those HV reg tubes with Va up to 25kV with Ia(max) 1.5mA.
Would they break if Ia was 25mA peak?
Is that 1.5mA a max because of the brittle fine wire/construction or is it 1.5mA to limit the Pa with those 25kV anode voltages?

Jan
 
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MarcelvdG

Member
Joined 2003
Two PL519's in parallel? They are actually specified for high voltage peaks rather than continuous high voltages, but hopefully they will survive. You could also ask @Lampie519 , he has used DIY direct-drive amplifiers for years.
 
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RJM1

Member
Joined 2010
I believe that it is to limit the Pa as they are HV regulator tubes, but there are no charts
on lower voltages.
I doubt that you cold make a wire thin enough to fuse at 1,5 or even 25ma and have it survive
as a lead in wire in a tube.
 
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smoking-amp

smoking-amp

Member
Joined 2001
I am wondering, those HV reg tubes with Va up to 25kV with Ia(max) 1.5mA.
Would they break if Ia was 25mA peak?
Click to expand...

Look at the heater power. 6BK4 6.3V 0.2 Amp , smaller than a 12AX7/ECC83
I have a 6BK4 here, and the cathode is miniscule.
That PD500 looks better though. 7.3V 0.3 Amp

The PL519 looks better than the 6HZ5 for continuous HV, since it has a plate cap. The Compactron socket (only) of the 6HZ5 would probably break down with continuous HV, unless you submerge the socket in silicone oil.
 
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RJM1

Member
Joined 2010
But yes the current from the filiment for the 6bk4 was also designed for 1.5ma. so no.
missed the edit time from my above post.
 
jan.didden

jan.didden

AX tech editor
Joined 2002
linearaudio.net
Paid Member
Tubes like the 20LF6 would be great if they had a bit more anode dissipation capability.

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://frank.pocnet.net/sheets/135/2/20LF6.pdf

Jan
 
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