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Old 20th April 2006, 01:32 AM   #1
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Default 6HV5A Single Ended Amp

I'm currently working on a single ended amp using screen driven 6CD6GA sweep tubes. While rummaging around in my collection of oddball tubes, I came across a 6HV5 compactron. I originally thought it was your usual beam power pentode sweep tube, but it turns out to be a beam triode with high transconductance, high plate voltage rating, 30W plate dissipation, and a very respectable peak current rating. They are also fairly plentiful and pretty cheap. I have a reasonable number of the GE version of this tube, and the plates are very husky.

This got me to thinking what it would take to use these in a single ended amp. Looking at the curves, it takes at least 1100-1200V to get a respectable current swing. The plate resistance is also pretty high, at around 6k. It looks like the way to possibly use them to best advantage with standard iron would be to parallel a pair and use a 10k impedance output transformer. I would drive the pair with a common cathode stage using a 6005 triode-strapped, as I have a lot of these tubes on hand. One question, though - looking at the base diagram, the beam plate is brought to the outside on pins 3 and 10, and not hooked up internally. Does anyone know how these would be connected in a typical application for this tube?
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Old 20th April 2006, 03:01 AM   #2
mwiebe is offline mwiebe  United States
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A mu of 300 suggests spud amp, which I've tried with the similar 6HS5. But currently I'm runing it with the grid positive driven by the cathode of a 6E5P trioded tetrode, and greatly prefer the sound. B+ on the 6HS5 is 600V at about 65ma plate current. AC on the filaments on both tubes. Worth playing around with.
Matt
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Old 20th April 2006, 05:01 AM   #3
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My implementation will be almost as simple, but my question at the moment is, how do you hook up the beam plates on a 6HV5A? There is no internal dedicated connection, they just get brought out to the pins. And yeah, if you are running with a plate voltage as low as 600V, you need to drive the grid postive to get any current, if the curves on the 6HS5 are anything like the 6HV5. I was trying to avoid positive grid drive, though I admit the lower plate voltage would make my mind rest a little easier. At 1kV+, the stored energy in the filter caps gets really, really deadly.

At any rate, I'm going to finish my other amp before thinking too hard about this one, or I'll never get anything done. It would be nice to figure out how to hook up the beam plates properly though....
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Old 20th April 2006, 05:29 AM   #4
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Well duh, I answered my own question just looking a little closer at the data sheet. The beam plates are connected to the cathode at the socket. I bet you can get all kinds of antisocial behavior if you hook them up in a roundabout fashion... I also took a peek at the 6HS5 specs at tubedata.org and it looks pretty similar to the 6HV5A, though the Sylvania data sheet there didn't have any curves.
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Old 20th April 2006, 12:45 PM   #5
mwiebe is offline mwiebe  United States
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I tied the beam to the cathode, pins 3,4 10 tied together. Kind of surprised me when I checked since I would have been tempted to tie them to the plate whatever the data sheet said. I expect I probably did this at some time but I must have prefered everything to the cathode. By the way I'm using a 10K output trans.
Matt
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Old 24th April 2006, 06:03 AM   #6
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Two small questions - how much power are you squeezing out of the thing, and how does it sound (subjective impressions)?
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Old 24th April 2006, 08:47 PM   #7
mwiebe is offline mwiebe  United States
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I would guess at I'm getting around 8 watts or so. As to sound, A2 amps sound different but I don't really know how to describe it, looser. So much of an amp's sound is quality of iron that its hard to go further than that.

If you have the parts needed I think it is very well worth building and having a listen yourself. If you don't like what you hear give A2 a try, you can use the primary of an unused output trans to stand the cathode driver on without having to use a neg. supply. That makes it simple. But I suggest using a bench supply for B+ as plate current is hard to predict without good positive grid plate curves. So you will need to watch things as you dial plate current up.
Matt
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Old 24th April 2006, 09:53 PM   #8
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I don't mind negative supplies - the ones I use are small enough to fit nicely under the chassis, out of sight. I would tend to shy away from using choke loading, as the amp will be bulky and heavy enough without the extra iron. I don't have any extra iron to spare anyway - any dollars I spend in that direction will go to output transformers.
I also have no problem with characterizing the 6HV5A for positive drive if I decide to go there. I just finished doing a set of curves for a screen driven 6CD6GA to determine what I need for bias. Using that basic setup, all I'd need to do would be to wire up another socket and go to town... If I end up doing this, I'll post the curves just like I did for the 6CD6GA.
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Old 26th April 2006, 12:32 AM   #9
mwiebe is offline mwiebe  United States
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If you do 6HV5 positive curves I would love to see them so please post back. Good luck playing around.
Matt
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Old 29th April 2006, 02:35 AM   #10
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The high voltage and high current capability of the 6HV5A, along with its 35W plate dissipation may make it possible to get a lot of power out of a Class A setup if the output iron and power supplies are willing. I did a few numbers based on using the tube at 560V or 1120V B+ (a 400V secondary with full bridge or doubler), and was astonished at the results. However, a lot will depend on the current capability of the tube at the lower plate voltages (100-200V). with positive grid drive. A rarallel pair of these might be able to do awesome things with the higher plate voltage, even if they aren't biased and driven all the way. Time and effort will tell. If someone wants to nip in and scoop me on this, feel free - I'm still working on my screen driven sweep tube SE amp with cheap Hammond output transformers.
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