Yet another "what to do with those tubes?" topic

[balkanizeyou]

Hi everyone!
By an accident I just got my hands on some pretty old (most of them are from the 60s I think) tubes and I'm wondering what can I do with them. I've never worked with valves before, but I think that is the perfect time to start now that I have some of them at hand. So I wonder whether there's some guitar related use for those tubes - a preamp? power amp? overdrive pedal maybe? Or some other pedal? I have a few of each:
ECC81 (a lot of those) - dual triode, equivalent to 12AT7
ECC82 - dual triode, equivalent to 12AU7
ECC85 - dual triode, equivalent to 6AQ8
STR85 - it's a voltage stabilizer I suppose
QQE03 - twin beam tetrode
EL42 - output pentode
EL84 - power pentode, equivalent to 6BQ5
EF95 - pentode, equivalent to 6AK5
ECH81 - triode-heptode, equivalent to 6AJ8
5763 - beam tetrode

Does anyone have any suggestions what to do with these?

[whoisalhedges]

I've never worked with valves before...

<snip>

...Does anyone have any suggestions what to do with these?

Find a circuit that's already built, and needs replacement tubes, and pop them in. Or sell them.

That's a glib answer, I don't mean to come off like a jerk - but for 99% of valve applications, we're talking about voltages that can make you very, very dead if you don't know what you're doing.

That disclaimer out of the way, there's only one way to learn what you are doing, and that's to do it. The ECC81s, ECC82s, and EL84s are in loads of guitar amps. I think that for the ECC82 specifically, you can find some low-voltage boost circuits here - just search for "12AU7". 12AX7/ECC83 are more popular, but you can build a complete amplifier just with 81/82 in the preamp and EL84 as the output. Either guitar or hifi amp.

I've never heard of the QQE03 before, but as a *twin* tetrode it might (I'm not looking at the datasheet, and might not understand it adequately if I were) be usable as a single-tube push/pull output stage of a low-power guitar amp. Could be fun.

[amptramp]

Preamp stages can use a 12AX7 as the main voltage amplifier, a 12AU7 as the cathode follower and a 12AT7 can do both.
The STR85 is a voltage regulator tube with a strike voltage of 115 and a regulated voltage of 85±2 volts for a current variation of 1 to 10 mA.
QQE03 is a transmitting tube for VHF and low UHF frequencies with relatively low power.
EL42 is a Rimlock base power amp that puts out about 2.5 watts single-ended.
EL84 is a good output tube with good sensitivity.
6AK5 is an RF pentode that should also be usable for audio.
ECH81 Since the heptode has two control grids, it could be the basis for a good tremolo using the triode as an oscillator.
5763 is a beam tetrode that can put out 4.15 watts into an 8500 ohm load using 175 ohm cathode bias.

A lot of us grew up working on tubes and high voltages and we are still here.  Actually, unless the circuit is on when you are soldering it, there is no reason for tube circuitry to be any more dangerous than battery-powered circuitry, but burns from tubes are a bit more common.

[rutabaga bob]

You don't say whether they are used or NOS (new old stock).  If they are new, and you decide you want to sell, there are companies that will buy them...I have sold many to Antique Electronic Supply in Arizona.  12ax7a is going for $16 each, 12at7 fetches $4.50, EL84 brings $15.  If you're interested, email greg@tubesandmore.com

[balkanizeyou]

Some of them are NOS, some are used - I know I could probably make some money selling them, but I'd rather keep them and make something cool out of it - I got them from a friend whose grandfather worked on one of the first polish computers https://en.wikipedia.org/wiki/Odra_(computer)

Thanks for the replies! I appreciate the warning, I'm well aware of dangers I'm going to face when working with valves. I've built a few solid stade amps and know how to handle mains voltage, so that's something to start with at least. But I'll surely read much more about safety before even attempting to build anything.

That aside, thanks for the suggestions! At least now I know most of them have some musical use. It appears that I can build a preamp using ECC81 and ECC82 or EF95 (6AK5) with ECH81-based tremolo, then make a low-power power amp using EL42, EL84 or 5763. Sounds like a good place to start.

Now, the problem is, that I have literally zero knowledge about designing valve-stuff, so I would be greatly appreciative if someone could point me in a direction of already working circuits - does anybody know a nice sounding pre-amp that uses my valves (or equivalents)? What about a some really simple preamp+poweramp in one circuit, like fender champ?

Another thing that crossed my mind is building a hybrid amp with a tube preamp and SS poweramp (say, a LM3886 chip running off a +-35V rails). The most problematic part would be probably building a power supply, but I'm wondering whether this approach would work in this case - I guess +105V is a respectable voltage for the preamp tubes?

[whoisalhedges]

The way I see it, there are so many circuits out there - you're not re-inventing the wheel. Look at a pretty basic cookie-cutter topology: something like a common-cathode preamp, long-tailed pair PI, push-pull (or single-ended, or parallel single-ended - have some fun!) output section. Just maybe consider using some of those oddball valves in place of the usual suspects. Do you know any old-school tube EEs who can go over the datasheets and let you know which could work in an existing circuit? They will have different pinouts, but that's part of the creative part. 

[balkanizeyou]

Unfortunately not, in fact this friend of mine who was the previous owner of those tubes gave them to me because I was the only person he knew that could possibly do something useful with them (even though I've never messed with tubes)  so I'm on my own, but hopefully with help of this forum something will come out of it.

I want to build something really simple first just to get started - I was thinking of a simple preamp-in-a-box build, here's something I found on the webz that looks simple enough for me to build and it uses only one valve:

It's also perfect because I have a couple of 12V secondary transformers laying around, so the only expensive parts I'd have to buy would be the filtering caps (but now that I've checked they cost like $1 each, so not really) and tube sockets (hey, there's only one tube in here)

Unfortunately I don't have the 12AX7/ECC83, will it work fine if I put there an ECC81 or ECC82? Maybe a slight resistor values change will be required?

I'm not going to mount them on the PCB so the pinout should not be too big of a problem.

[patricks]

Start reading here, then buy the book, it's fantastic and so easy to follow. Great for peeps who are noobs to toobs and lots of useful stuff even if you've already got some design experience

Preamp-in-a-box is a good starting point; you've got enough tubes to build a slightly modified version of one of the AX84 amps, too. Build the amp, read some data sheets and set up the 12AT7s the way you like them in the preamp section, and get your feet wet with a good build and some tinkering. AX84 is also a fantastic forum for tube guitar amp stuff.

Probably a bit ambitious to dive right in at the deep end and design your own amp from scratch using oddball tubes. Not outside the realm of possibility, but much more homework required.

[balkanizeyou]

I've already been to Valve Wizard site, but thanks, that's a great resource! I haven't bought the book yet but I'll surely do.

And thanks for the link to the AX84 amp, I think I'll make this project next in line after the one I mentioned above. One question - I don't have a rectifier tube, I guess I can use a solid-state rectifier instead without any problems right?

[patricks]

The book's fantastic!

And yes, a solid-state rectifier will slot straight in

[tubegeek]

Actually, unless the circuit is on when you are soldering it, there is no reason for tube circuitry to be any more dangerous than battery-powered circuitry,

There's a statement that is not a fact and which is very unsafe advice as well. Some tube circuits omit a bleeder resistor. In which case you might have many hundreds of volts left on the filter caps after turn-off, and I wager you'd easily be able to tell the difference between being bit by that and by 9V. If you survived the experiment.

[amptramp]

Actually, unless the circuit is on when you are soldering it, there is no reason for tube circuitry to be any more dangerous than battery-powered circuitry,

There's a statement that is not a fact and which is very unsafe advice as well. Some tube circuits omit a bleeder resistor. In which case you might have many hundreds of volts left on the filter caps after turn-off, and I wager you'd easily be able to tell the difference between being bit by that and by 9V. If you survived the experiment.

Quite true if you have large capacitors and limited circuit drain or if you are using directly-heated cathodes (and none of these tubes are).  I am used to the cathodes remaining hot for a couple of seconds, enough to drain the voltage from a radio but you are right - it may not be enough for a preamp.  In that case, add a bleeder resistor or ground the filter capacitors before you start work.

[rankot]

If anyone is reading this thread trying to figure out how to use EF95 tubes, here's the answer: http://www.diystompboxes.com/smfforum/index.php?topic=120117.0

[anotherjim]

For the 7806, I used a 7805 with 2 1N400x diodes in series with its ground pin for 6.4DC. This does mean the 7805 tab/can cannot be grounded at the heatsink. I'm sure the 7806 is fine, but I happen to have plenty of 7805 and diodes to use.

[Marcos - Munky]

You can build a Hi Octane with 2 12AU7 and a EL84, although it asks for 2 12ax7 so you'll have less gain. Excellent sounding amp.

There's a preamp using a ECH83 here in the forum, mayoe you can use the ECH81 in the same circuit.

[davent]

Start reading here, then buy the book, it's fantastic and so easy to follow. Great for peeps who are noobs to toobs and lots of useful stuff even if you've already got some design experience

And Merlin, the books author does pop in here and post every once in awhile.
dave

[bartimaeus]

I'd recommend picking up some cheap modern tubes to test out your circuits, then swap in the new ones once they're finished. It would really suck to destroy some 60 year old tubes because of a minor beginners mistake.

[TejfolvonDanone]

Preamp stages can use a 12AX7 as the main voltage amplifier, a 12AU7 as the cathode follower and a 12AT7 can do both.
The STR85 is a voltage regulator tube with a strike voltage of 115 and a regulated voltage of 85±2 volts for a current variation of 1 to 10 mA.
QQE03 is a transmitting tube for VHF and low UHF frequencies with relatively low power.
EL42 is a Rimlock base power amp that puts out about 2.5 watts single-ended.
EL84 is a good output tube with good sensitivity.
6AK5 is an RF pentode that should also be usable for audio.
ECH81 Since the heptode has two control grids, it could be the basis for a good tremolo using the triode as an oscillator.
5763 is a beam tetrode that can put out 4.15 watts into an 8500 ohm load using 175 ohm cathode bias.

A lot of us grew up working on tubes and high voltages and we are still here.  Actually, unless the circuit is on when you are soldering it, there is no reason for tube circuitry to be any more dangerous than battery-powered circuitry, but burns from tubes are a bit more common.

I made a tremolo/boost pedal with the ECH84 (really similar to the ECH81): https://www.diystompboxes.com/smfforum/index.php?topic=114688.msg1066515.
I'm currently waiting on PCBs to refurbish the pedal because it wasn't a really nice build and i'd like to implement couple of mods. Should be here next week.
The triode has a gain of 22 so it isn't easy to make a phase shift oscillator with it.

The 6AK5 is a sharp cut-off pentode so you could make a preamp with it.

The ECC85 has doesn't have a centre tapped heater but otherwise I think is similar to the ECC81 (?).

[anotherjim]

Another +1 for Merlin's info. Especially, read the grounding advice. Compared to a lot of SS projects, I find there is a higher risk of getting annoying levels of ground loop hum with tube projects. Getting the ground connection paths right solves it.

If you want to make a small amplifier and keep it cheap with "found" parts, it is possible to use mains supply transformers "backwards" for the output transformer. Google to find out how.

[amptramp]

One of my favourite types of output transformer is the distribution transformer.  It usually has an 8 ohm secondary and primaries rated by power level.  The most common ones are for a 70.7 VRMS line so a 1 watt tap is 5000 ohms, a 2 watt tap is 2500 ohms, a 1/2 watt tap is 10,000 ohms etcetera.  They may not have the gap needed for a single-ended output but I have never run into a problem using them.

As for power, get a couple of wall warts, say 6 VAC and use the 6 VAC for the heaters and connect the 6 VAC of the other wall to the 6VAC of the first and the primary will have power line voltage on it and you can use a bridge rectifier or a doubler to get the plate voltage you want.