20W cathode follower amplifier

[tubelab.com]

I do agree. There are several disadvantages to doing a cathode follower output stage, including the large drive voltage requirements. I don't think that I would build one for normal amplifier service (except maybe an SE OTL).

I need a BIG cathode follower for one piece in a much larger design. It is a big experiment far into uncharted teritory. Success or failure it will all be written up in November.

The 13E1 looks like an ideal tube, but they are extremely rare in the US. I have run dozens of tubes in cathode follower service under my unique conditions. The best were large sweep tubes, and the higher Gm regulator triodes, 6336A, 5998A, and 7236. The usual 6AS7 - 6080 is OK but not as good as the previously mentioned tubes. For smaller designs some of the dual dissimilar triodes made for vertical amplifier service (6EM7, 6DN7, 6DE7, 6DR7) work OK.

I tested the 6HS5 and its brothers including the 6HV5. They need too much B+ for my particular needs, but I think these guys are good for the ultimate "spud" amp. All you need is the tube, the OPT and a power supply, further details later.

[coresta]

I don't think that I would build one for normal amplifier service (except maybe an SE OTL).

Exactly Tubelab That's the reason why I think OTLs being a better solution for more than 3 watter amps

[Shoog]

A third option? http://www.mif.pg.gda.pl/homepages/.../084/6/6HS5.pdf

Thats one amazing valve. It would be interesting if they attached curves as well.
Do you think there are many out there ??

Shoog

[tubelab.com]

These tubes came at the very end of the vacuum tube TV era. They were an attempt to eliminate the 6BK4 shunt regulator which worked directly on the 25KV supply. Think about what a shunt regulator across 25KV goes through. They had a short life, and generated some pesky X rays, so after 15 or so years they were designed out. Then tubes were designed out of TV sets.

GE (and others) moved the shunt regulator onto the primary side of the flyback transformer, so in only has to deal with 2500 volts. These tubes were made for only a few years, and I don't know if the idea was ever adopted outside the US. Most of the US tube sellers have some in stock for fair prices. There are a few different type numbers for these, and they come in two dissipation sizes. The 6HS5 is rated at 30 watts, and the 6HV5A is rated at 35 watts. I have seen 30 watt 6HV5's and 35 watt 6HS5's with and without the "A" suffix.

There was a thread devoted to these tubes about a year ago. I never got to making any sound with them, but that is about to change.

6HV5A Single Ended Amp

The 6HV5 data sheet has curves, but they don't cover the "nornal" range of operation.

http://www.mif.pg.gda.pl/homepages/f...23/6/6HV5A.pdf

[rdf]

Originally posted by tubelab.com
I never got to making any sound with them, but that is about to change.[/url]

Rats, that's the signal to stock up. I have made sound with them, CF driving a transmitter tube. The cathode load was a 150H choke for max impedance in series with a resistor to set the operating point. It worked very well.

[Shoog]

I read those threads. Strikes me that these are types of valves which would be difficult to get to work in any description of "normal" operation.

Shoog

[7N7]

I have just had a look at the GE data http://frank.pocnet.net/sheets/123/6...23/6/6HV5A.pdf (why doesn't this work?) on Frank's site for this very interesting valve.

The data sheets are dated 10/69, so here is an good indication of the way development as going right at the end something that has always interested me. Apart from the very high gm of 65 mA/V (only equalled as far as I know by WE 416) extraordinary for a "consumer" product unlike 416, I found the description of the diffusion coated cathode fascinating.

As for using it in am amplifier, well the high anode resistance really rules it out for a conventional output stage, although for SE I suppose one might get away with a 10K transformer and as pointed out on the other thread referred to here, Miller capacitance would be a problem.

However, for a cathode follower output stage I would imagine it would be superb. I would love to build a p-p amplifier with output transformer using this type. Agreed that the driver stage would be challenging, but not impossible. Of course one would have to be careful about heater cathode voltages, but 6HV5A does offer a decent range.

7N7

[yan24]

Hi
Don't be astonishing,
I know Audiophile review and Guy Marec and I take his schema to do a SE.
Look at this

[URL=http://www.audiodesignguide.com/my/se.html]

What do you think about this disign but i think it'll be difficult to find a good intersage transfo

Yan

[tubelab.com]

What do you think about this disign but i think it'll be difficult to find a good intersage transfo

I am sure that this design would work, and sound good with good transformers. As you point out, a good IT transformer is hard to find. The specified Lundahl should be available. I will keep experimenting until I find a driver circuit that I like that can deliver 400 to 500 volts P-P. I will post it when I find it. So far the choke loaded 6V6 works good, but doesn't suit my needs.

I never got to making any sound with them, but that is about to change.

OK, last night I made sound with a 6SH5. My ultimate "spud" amp (a single tube amp) needed one resistor to work right. I set up a 6HS5 in common cathode using clip leads. No bias, driven directly from the headphone jack of a portable CD player, 5K ohm Edcor OPT, variable B+ supply. I had to add a 1K ohm resistor from grid to cathode (parallel with the CDP output) to provide a path for grid current. I had to switch to my 550 volt power supply and max it out to get enough plate current (30 mA at 550 volts). Power was about 2 watts limited by lack of drive.

I don't think that the sound would cause anyone to run right out and buy up all the existing tubes, but it was better than I expected. The bass was kind of "loose" due to the highish Rp. Highs were crystal clear, so Mr. Miller was stopped dead by the low source impedance. Would I build one of these? No, a chip amp would blow it away, and it needs a lot of voltage.

I may try these in cathode follower mode, but they would need a lot of B+, which would cause over dissipation, or they would need to run with a few volts of positive grid bias, where they may not be linear. Only time will tell.

[tubelab.com]

Today, I had some time to experiment with a cathode follower amp. I built a very simple driver that could deliver 490 volts peak to peak from a 550 volt supply. Then I started thinking (very dangerous). To make any serious power from a cathode follower, I'm going to need a lot of B+ voltage. The most my bench supply can give is 550 volts. I need an OPT, but the lowest impedance transformer that I have is 3K ohms, and it is rated for 110 mA max. If I want to be able to test at full current (and maybe more) I am going to need a tube that can dissipate about 50 watts. With the thinking part done, I went for the biggest tube in my junk box, the 6LW6. These will laugh off 50 watts.

So, I wire one up on my breadboard, and crank it up.