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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Those Magnificent Television Tubes

Eli is correct. Grounded grid, not cascode.

<snip>

I am not sure why you are splitting this particular hair.

The important consideration, (when applying these triodes to an audio application) is that the PC86 is characterised for fixed anode voltage [175V] - and shows striking linearity in this case.

Such characteristics are the making of an excellent cascode stage, preferably shunt-cascode for performance. If series cascode suits your application, you can also use the PC86 in the upstairs position - "grounded grid" - but any old bipolar transistor (300V+ rated) will perform and sound better... the excellent triode would be wasted.
 
JohanB wrote:
[special=If you have made an amp or other things with these tubes, please give a hint or schematic diagram in this thread.]%[/special]

PL504-PCH200%20Amplifier.png
 
Thanks JohnTubeamp

This is an extremely good example of "scavengineering"
A very well and straigt forward designed amp.
Old transformers at hand were used, even connected back to back to get the right voltages.
I´m a little curious of the output transformer configuration. Are they actually scavenged combination of power or vertical TV transformers?
The use of the absolutely zero-valued PCH200 in the input is excellent!! Only problem is to find that 10 pole special socket????
(but with old TV:s at hand, no problems)

Only a small remark. The heater of the PCL200 should be first in the heater chain, starting at ground. But that is probably only a misstake made in the drawing........

Johan
 
Hi Johan,
Thanks for the comment.
Yes I have used power transformers I had handy at the time I was building the amplifier. As regards the output transformers I didn't had an audio transformer available, but I found one (T1) which gave good results in match and sound, although I don't know what was originally used for. The ratio of the windings is 1:1 . The T2 output transformer is a modified 100V line audio transformer. Output power is around 20 W.
Tell you the truth I don't remember how I have connected the heaters..I will check it later on, although maybe is the reason of the hum I have in the output. Of course you must be very close to the speaker to hear it.

I have also build a SE tube amplifier using a Russian 6P36S deflection tube. 9 W per channel.
 
OK, sorry. I now see there is a bridge rectifier in the bias supply and the PCH200 heater is correctly balanced in the middle.
But better to use a half wave rectifier, like the one not connected in upper right corner, so you can connect one side of the heater winding to ground and then the PCH200 first in the string on the grounded side.
This will give lower hum from the heater.

Johan
 
Rod Coleman said:
I am not sure why you are splitting this particular hair. . . the PC86 is characterised for fixed anode voltage [175V]
Grounded grid and cascode are different circuits. In a grounded grid circuit the anode is not at constant voltage; it carries signal.

The 'upstairs' position in a cascode has a grounded grid, but it does not operate like a normal grounded grid circuit because the driving impedance ('downstairs' anode) is much higher.
 
Grounded grid and cascode are different circuits. In a grounded grid circuit the anode is not at constant voltage; it carries signal.
I am fully aware of the difference.

The 'upstairs' position in a cascode has a grounded grid, but it does not operate like a normal grounded grid circuit because the driving impedance ('downstairs' anode) is much higher.

It remains a grounded-grid circuit, regardless of this largely irrelevant distinction.

None of this has any impact on the fact that the excellent fixed anode-voltage characterisation of the PC86 makes it ideal for Cascode duty - and Cascode connexion makes excellent gain-stages for audio amplification.

the same triode may also work in grounded-grid - but here it offers few, if any advantages - and is easily surpassed by ordinary bipolar transistors. I spent quite a while designing & building these circuits, and the performance differences were very easy to distinguish.
 
Rod Coleman said:
It remains a grounded-grid circuit, regardless of this largely irrelevant distinction.
No, highly relevant as the interaction between the source impedance and the non-linear cathode input impedance can be a major source of odd-order distortion in a true grounded grid circuit but it has almost no effect in the upper part of a cascode.
 
Relevant to an audio amplifier? If you can show us a valve audio circuit that is actually compromised by such a (drive impedance) distinction, in a amplifier that you, or somebody has built (and performs well enough to be worth discussing) - we might have a discussion worth having.
 
Could be relevant if a grounded grid was used to get a low input impedance - MC preamp?
And run the cathode current into the cartridge?
With MC, the current-swing will be tiny, and impedance looking into the cathode will be almost constant, anyway. Before we mention that a valve is too noisy for MC.
I don't want to divert this useful thread any more, so let's drop it.

Good idea.
 
I've been aware of the value of TV and Transmitter tubes for some time; hence the reason, I bought a stock of NOS Military 807 tubes many years ago in many different styles.
The old 807 for example, I believe, there were around 3 billion of these devices made over the years, made in many different package styles. It was the tube that won the 2nd world war and was the workhorse of the Military for decades. Based on the 6L6 and using the 1930's Beam Tube Technology; in class AB2 on 750 volts it puts out more than a pair of KT88's, 6550's and EL34 tubes - that being 120 watts RMS. From the 6L6 & 807 the famous KT66 was born.

I don't mind using top-cap tubes, as long as they are cheap to buy and sound good. Looks and safety are not as important to me as they are to super rich Audiophiles who buy their audio equipment. When I say safety - I'm all for it - but I don't care if I need 1,000 volts on the top-cap to make the tube run better. Hence I also like the 833A power triode, which mounts on 4 large pins, instead of a traditional socket.

TV sweep Tubes like the 6CM5 run as low as 150 volts on the screen and lend themselves to possible OTL designs, supply regulator pass tubes and certainly power output tubes. Though not as pretty as the EL34; 6 tubes can deliver 100+ watts in push-pull on a mere 300 volts B+. It's believed the EL36/6CM5 is a baby EL34 when you look at the physical construction and data specs.

Any UHF triode used for industrial and commercial TV work, and built in the later years of the 1950's/60's will use the FRAME GRID technology. This grid technology is far less microphonic, more stable and tighter with GM and other specs; as well as giving better overall noise and gain figures.

Standard audio tubes lack this type of frame grid construction. Not even the 300B - the supposed "King of all triodes" uses it.

Realistically - if a tube works at audio frequencies then its worthy of further research.
 
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TV tube amps

I've been playing with TV tubes for a couple years and almost prefer them for audio amps. It started with 6U10 triple triodes for the front end and LTP splitter and 6JN6 (6GV5) for outputs. I did my 12 pin amp variants ( 6LB6) for several more designs and played with the 9 Pin variants. I'm still playing with the 9 pinners.

http://www.diyaudio.com/forums/tube...cheap-highish-power-pp-amp-4.html#post3543207

KEGGER inspired me to do a PCB for the 6L6 family of tubes with a little 9 pin driver tube, the 6JT8 and its variants. it was a fun project and I decided to modify it with 6JT6 output tubes and try N-Mosfet grid drivers. :rolleyes:
I'm currently listening to the little 17JT6 PP amp and it is all the amp that I need for my listening setup and room. I'm running 40 watt hammond 6.6KRa iron and the output tubes in pentode mode, 160V on the screens. ( second last pic).
The last pic is a 6LU8 PP amp that I did and it is a great little amp and was my main listening amp for many months. It had enough power for most listening, but ran out of steam when it was cranked up. ( only 14 watt tubes...)

I've asked Edcor if they would be interested in a multiple heater configuration PT for the sweep tubes to allow the outputs to be 6, 13, 17 volts that does leave the 21, 30 and 40 volters out. I was targeting 410V on B+ to use 450V caps with out stacking. 20 watt output tubes it seamed about right. Time will tell if they are interested.
 

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but the 6CL6 is another good one . I'm sure George has some other secret sauce that I don't (yet ) know about

The 6CL6 was first used in military radar units and other RF stuff, but it did find its way into some TV sets.

Good CHEAP TV tubes.....

The 6HB6 is on the dollar list at two Florida tube sellers. It has the construction of the EL84 but G1 is wound a bit tighter for higher Gm. The pinout is the same as the 6EJ7, not the same as the EL84. Works in most EL84 circuits with socket rewiring and less bias. I have also mad it work in some 12BY7 designs....different heater wiring. I already have plenty.

The 13GB5 is a little horizontal sweep tube that can make a lot of power. It is also on the dollar menu. Good for 100+ watts per pair. It will work from two 6.3 volt windings in series...like what's found on most Antek toroids. Yes, got plenty of these too.

There are still a few horizontal sweep tubes out there in the under $5 range that can make big power, but they aren't being made any more so they won't last forever.
 
6CL6 and 6KD6 are a good output pentode. They was also used in class AB parallel in some SSB tranceivers for Ham Radio Amateurs (Like the old Yaesu FT400).

I had used them in push pull using a reversed wired tube-TV power transformer to modulate an AM transmitter. I used two of them in a new state to modulated other two but slightly used. So, as the modulator need about 50% of the carrier, the full power from the push pull audio stage is not necessary. I did some contacts with it. (Audio in Class AB operation and RF in Class C).

I also used the rare 6BN6 FM demodulator as an audio limiter followed by a low pass filter, to enhance modulation percentage.
 
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