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TV Horz. Output Tubes used as Output Audio

Denis

Member
2001-10-13 2:25 pm
EL509

The sweep tubes are really excellent performers. This is particularly true for EL509/6KD6/6Pi45S. This seems to be the only such tube in current production. Extremely high emission current makes it possible to use this tube even in OTL amplifiers, and this is currently the best tube for such application. But it is better to use EL 509 with good output transformer in PP configuration. Look at http://www.cortmi.com.ua/omak.
Another example is 8417 tube. Quicksilver manufactured some quite good monoblocks using these tubes in 1970s.
 
Denis posted:

Another example is 8417 tube. Quicksilver manufactured some quite good monoblocks using these tubes in 1970s.

Denis - my experience with the 8417 is 100% opposite to that of the Russki sweep tubes. The 8417 has to be the most UNRELIABLE output tube ever used in audio-good perhaps but UNRELIABLE!

While the EL509s are the most reliable I know.

Allen
 

Denis

Member
2001-10-13 2:25 pm
EL509

Nothin to say about 8417 as the EL509 seems to be the only tube of such tupe currently manufactured. I use only EL509 produced in St. Petersburg by Svetlana, and I dare say this is simply excellent power pentode from any viewpoint. For example, it is possible not only to get about 40 watts of class A power from a PP pair of EL509s, but the transition from class A to class AB is smooth and does not add higher harminics to the distortion spectrum. Of course, it is possible to find similar modes of operation for other pentodes, but there always will be less power, even with 6550.
 
Hey-Hey!!!,
With sweep tubes, one can treat petodes plate Z the same as one would a triode's...it's high, but get the right OPTx, no?

Take the 6CB5A, octal base, anode cap, 2.5A of heater. Plate Z is ~5kOhm. As a triode, its plate Z is 430R. Go 2.5 this number for approx U-L and we're at 1k.

There are other valves that perform in a similar fashion. High gm, low u-g1g2...

Take a good 3k a-a OPTx and apply a little bit of plate-to-grid NFB and you'll have a sweet amp that has power output from 20-40 wpc depending on the valve chosen. No way I am going to build with 845's when it's this easy.
cheers,
Douglas
 
Most sweep tubes have very low G2 maximum voltage ratings compared to the plate voltage rating. My favorite, the 6LW6 has a plate voltage rating of 990 volts, but a G2 max of 275 volts. You can't get a lot of power in triode mode if you follow the published ratings. I have run them at 400 to 425 volts without the "glow of death". You get about 12 to 15 watts deprnding on load. Needs a lot of drive though. There was an article in Glass Audio that demonstrated a 90 watt per channel amp using sweep tubes. It is still on their web site:

http://www.audioxpress.com/reviews/media/GA399MA.pdf

A while back there was a thread asking about the 6AV5, a medium power sweep tube. I put a pair of those through some severe testing, in triode mode. These sounded far better than I would have expected.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=37403&highlight=

I find no information in any of my books on a 12BQ7. The 6BQ7 is a small twin triode made for TV tuners. The 12BQ6 is a horizontal output tube of about the same size as the 6AV5 that I tested in the above mentioned thread. These can often be found cheap, so it doesn't cost much to " find their true limits".

The 8417 was originally developed for audio applications. It was touted as the ultimate audio output tube, borrowing technology from other audio tubes as well as sweep tubes. The cathode to G1 spacing was reduced to lower its drive requirements. Notice the Mu in triode mode, 16.5. Unfortunately, as many users have discovered this led to unreliability. Some of these tubes lived long happy lives, but many more came to an early death, often by fire!
 
Hey All:

Have I got sweep tubes! At least I have a bunch and I'd sure like to do something with them. I have 6BM8, 6CG7, 12BZ7 and even 50EH5.

I asked earlier in this thread about 12BQ7 and someone suggested a link which, I followed and couldn't make head or tail out of. Not their fault, but I'm kinda new to tubes. I can read a schematic, but I still can't read the plots in a tube spec sheet.

Most of you fellows talk about tubes like they are friends and acquaintances. I'd love to get to that point - long ways away yet :xeye:

Also, several links in posts point to svetlana.com - this site is off the air (at least I can't get it). Can anyone point me to a currently available example schematic that uses this class of tubes for either preamp or small power amp?

Thanks

Jess Gordon
Alert Bay, BC
 
The "LW6-180" is the amp design that I refered to previously. No need to google, the schematic is on the AudioXpress web site.

http://www.audioxpress.com/reviews/media/GA399MA.pdf

I modified this design to fit parts that I had, used a 770 volt power supply that I had, and got 140 watts per channel at 1 KHz. The 80 watt OPT's (I alread had them) saturated heavilly below 100 Hz causing the death glow to appear.
 
OK, thanks, guys. I got that one.

I guess I was hoping for something simpler - a line stage or simple p-p power amp using these tubes as finals, but I will study this schematic.

Question: Is it reasonable to think about making a small amp out of one of the triode/pentode tubes, like the 6BM8? I sort of imagine a 2 tubes per channel amp using the triodes as input buffer and phase splitter and the pentodes in p-p for output. Is this possible?

Looking forward to your (various) replies :nod:

Jess
 
Take a look at my web page on using compactrons in AM tube radios: http://pw2.netcom.com/~wa2ise/radios/compaa3.html
Swap out the misused power transformer with some good for SE audio transformers, and this simple circuit should work well. The damper diodes in the 38HK7s I used make good rectifier diodes. In a SE stereo amp, the two damper diodes would be used for the B+ power supply as a full wave rectifier circuit when used with the usual centertapped power transformer B+ secondary winding.

Any cheap horiz output tubes you can lay hands on should work well as audio outputs. Also note that tubes with strange heater voltages can usually be had cheaply. And other tubes like 8CG7s. You can power an 8V heater nicely with an unfiltered rectifier diode like a 1N4004 in series with the heater from a 12VAC source. Remember, power is volts squared over the resistance, and half of 12 squared/R = 8 squared/R (close enough for heaters). The diode gives us the "half".
 
JesseG said:


Question: Is it reasonable to think about making a small amp out of one of the triode/pentode tubes, like the 6BM8? I sort of imagine a 2 tubes per channel amp using the triodes as input buffer and phase splitter and the pentodes in p-p for output. Is this possible?

Looking forward to your (various) replies :nod:

Jess

The 6BM8 is a fine valve to use. Two at a time in PP would be my suggestion. LTP from the triodes, and U-L rig the pentode section across ~10k a-a.
cheers,
Douglas