Help valve newb salvage some old TV tubes

[mr_push_pull]

Hi

First of all, I am completely new to valves. This means I know almost nothing about them.
A few days ago I remembered about an old valve TV I had in the closet, so I thought "maybe I could salvage a valve amp out of it".

Tracking the audio output cable I've come to the conclusion that the audio amp is made with two tubes: a PCL86 and a PL84. My first problem is: should I use the same schematic from the TV or should I use another one? Not that I am able to identify the exact part that is the audio amp, but maybe if I'll track where the wire from the volume knob goes I could identify the input and maybe that will help...
A thing I know about valve amps is that they should have an output transformer but the TV doesn't. I think that the output transformer is used as an impedance adapter, am I right? The TV's speaker was 700 ohms or so, but it is ruined, some have told me that those old elliptic speakers are not that bad at all as full-ranges, especially in horns.

The second problem is... The valves had that sticky dust on them so I thought I could wash them with soap. Great idea. The labels washed away with the dust... So now I don't know which is the PCL86! Anyone knows how to identify it?
Third problem... I've heard that valve TV's have some particularities that make those tubes not so suitable for audio amps. What is the exact problem?

Sorry for such newb questions, maybe someone could point me to some good webpage where I could learn about valve amps. Thank you.

 

[rpapps]

Identifying tubes

Hi MPP
I'm not a tube man but these links should get you started

http://www.r-type.org/exhib/aad0302.htm
http://www.r-type.org/exhib/aai0083.htm

Cheers
Rob

 

[EC8010]

Forget it. Salvaged valves from a television are of no use to you unless you want to treat them as a way of learning about valves. However, without an output transformer, you're stuffed. To avoid killing yourself, you also need a mains transformer. Oh, and the TV valves are probably worn out anyway. Sorry to be a wet blanket, but there's no point in you wasting your time.

One of the cheaper ways of learning about valves is to build a headphone amplifier - have a look at the headwize site. The TubeCAD site is good, but you'll run up a printer bill, so you might prefer to buy a book. Old Colony have a good selection of books about valve amplifiers.

 

[mr_push_pull]

Forget it. Salvaged valves from a television are of no use to you unless you want to treat them as a way of learning about valves.

And why is that?

 

[mcs]

The TV used an OTL (Output Transformer Less) amp. But an OTL amp with those tubes will only work with a 700-1000 Ohm speaker.

You can still use both the PL84 and the PCL86 in "normal" SE amps though - but then you'll have to find an output transformer.

New tubes of the same kind (or the 6V versions EL86 and ECL86) are not very expensive, but you could still use the old ones for testing.

You can tell them apart by looking at the construction. The PL84 only has tube inside. The PCL86 has a big tube and a small one next to each other.

Best regards,

Mikkel C. Simonsen

 

[EC8010]

Why it is...

Most of the valves in a television are designed for specific television uses. Yes, some can be used elsewhere, but it requires greater knowledge than you presently have, and you don't have enough of them. The PCL86 might be useful for playing with, but you mentioned that you had to wash a lot of muck off. Dust doesn't just fall into televisions, it's drawn in by the heat, so mucky valves tend to be ones that have seen a lot of service.

 

[powertriode]

As others have said, TV tubes are pretty useless for tube amps.
If you have some PCL82 you can build an amp based on the ECL82/6BM8 as they are the same tube but with different heater voltage.

 

[mcs]

As others have said, TV tubes are pretty useless for tube amps.

I would tend to disagree on that one... TV tubes are often a lot cheaper than the "normal" tubes, so why not use them?
They are every bit as good as the normal audio/radio tubes. You can often find ECC82, PCC88, PL84, PCL82, PCL86 tubes in TVs, and all are good audio tubes. You can often buy NOS TV tubes cheaper than Chinese junk tubes...

Best regards,

Mikkel C. Simonsen

 

[mr_push_pull]

People, hold on for a sec...
First of all I didn't say that I want to make a valve amp with a budget of $500. I can't afford it. And I'm not sure that I want that.

Second of all. Let's say that the valves are worn out. Since they aren't that exotic valves, I think I can get new ones for a low price. OK, maybe they're not the most appropriate valves for audio amps but then you can recommend some cheap ones that are more suitable.

All I want is build a cheap valve amp that's worth the effort. Someone I know likes to say "don't buy it if you can salvage it" and I agree to that. If I was to spend hundreds or thousands of dollars on DIY I would rather buy it from the shop.

So, it seems that my real question is: is building a very cheap valve amp worth the effort? By searching on the net I saw that very cheap valves are not considered that awful so I thought that maybe...

 

[EC8010]

If you want to build an amplifier from salvage you need to start looking at the free advertisements in your local newspaper, scavenging skips, going to radio fairs, and going into junk shops. You'll also want to look in the adverts in the radio magazines. With a bit of luck, you may pick up some transformers - these are the important bits. Transformers cost, but they last a long time. You will need to buy a cheap multimeter so that you can test things.

 

[mr_push_pull]

Hmm... It's not like I don't know ohm's law, it's just that I don't know anything about valves, not electronics. I don't think that every electronist has the obligation to be a valve guru. And I have to admit that I don't feel the greatest temptation to become one.
After all, hasn't anyone ever built an audio amp with these tubes?

 

[mcs]

After all, hasn't anyone ever built an audio amp with these tubes? [/B]

Of course. Just look for circuits with EL86 and ECL86 - they are the "radio" versions of your tubes. The EL86 was often used in Philips radios, and the ECL86 is quite common also. I could probably dig up some circuits for you, but try Google first...

Best regards,

Mikkel C. Simonsen

 

[mr_push_pull]

Just look for circuits with EL86 and ECL86 - they are the "radio" versions of your tubes. The EL86 was often used in Philips radios, and the ECL86 is quite common also. I could probably dig up some circuits for you, but try Google first...

Best regards,

Mikkel C. Simonsen [/B]

So ECL86 is the radio version of PCL86 and EL86 (not EL84) is the radio version of PL84?

 

[mcs]

So ECL86 is the radio version of PCL86 and EL86 (not EL84) is the radio version of PL84?

Yes, the E, U and P tubes with the same number are often the same, but not always. I guess the PL84 was made for TV use first. And then it was decided to make an E version, but the 84 number was already in use - but that's just a guess. The EL84 is not available as a P tube for some reason.

Best regards,

Mikkel C. Simonsen

 

[powertriode]

Here are some links for you. Have fun.

http://www.mcamafia.de/tubes/keksdose/cookiebox.htm

http://www.lh-electric.4t.com/projects/tiny3w.htm

http://www.bonavolta.ch/hobby/en/audio/ecl82_1.htm

http://www.avanwaarde.freeler.nl/id13.htm

http://www.albertkreuzer.com/recycle.htm

http://www.tubebuilder.com/images/s...d/ecl82_se2.gif

http://nmwilliam.tripod.com/ecl82.html

http://www.svetlana.com/docs/products/glass/6BM8.html

Also search for the 'tube gainclone' thread

 

[EC8010]

Hmm... It's not like I don't know ohm's law, it's just that I don't know anything about valves, not electronics...
...After all, hasn't anyone ever built an audio amp with these tubes?

Aha! I beg your pardon, I had rather assumed that you knew little about electronics. My mistake.

Line scan valves: PL504, PL509/PL519 are popular as output valves in Output TransformerLess (OTL) amplifiers. You probably know the output stage as "totem pole".

Field scan valves: 6BX7, 6BL7 have a following, but you won't get much power out of them. European field scan tended to use pentodes. In neither case was linearity a primary concern.

Audio valves: Push-pull ECL86 in ultra-linear mode makes quite a nice little amplifier. SE pentode ECL86 gives 3W with lots of distortion. SE triode-strapped ECL86 probably < 2W.

 

[mr_push_pull]

Originally posted by EC8010 Aha! I beg your pardon, I had rather assumed that you knew little about electronics. My mistake.

What did you think my nickname and location meant? Didn't you know what I am and what I do?

Originally posted by EC8010
Line scan valves: PL504, PL509/PL519 are popular as output valves in Output TransformerLess (OTL) amplifiers. You probably know the output stage as "totem pole".

Field scan valves: 6BX7, 6BL7 have a following, but you won't get much power out of them. European field scan tended to use pentodes. In neither case was linearity a primary concern.

Audio valves: Push-pull ECL86 in ultra-linear mode makes quite a nice little amplifier. SE pentode ECL86 gives 3W with lots of distortion. SE triode-strapped ECL86 probably < 2W.

OK, so what about ECL82 valves? I can get two unused EL86's and two unused ECL82's. It would be nice if you took a look at the links above and make a recommendation for an amp that can be built with these valves. I'd really appreciate that
And the output transformer is not such a concern. I think I can get one at a junk shop and rewind it.

 

[EC8010]

ECL82 is fine, and some people get quite enthusiastic about them. EL86 is a rather different kettle of fish and is meant for driving high impedance loudspeakers directly (have a look at the data sheet on Frank's site) - it can be used for headphone amplifiers. Any of thos amplifiers in the links should be fine - they're all derivatives of the Mullard design.

Toroidal mains transformers have been successfully used as output transformers in push-pull amplifiers, but the anode currents need to match exactly to avoid core saturation.