Can I use an EL84 tube instead of JJ ECC82 (12AU7) ?

[eh la bas ma]

Hello,

The tube in my Bass Amuser circuit just died. It's been working since April 2020...

I wonder if I can safely use an extra EL84 tube I got for my Fender Blues Junior amp, as replacement ?

Bass Amuser doc : http://www.uk-electronic.de/Download/Beschreibung%20BassAmuser.pdf



Thank you for your help !

[theehman]

No.  Even though they have a similar base, they're completely different tubes with different pinouts and circuit requirements.
You can sub a 12AX7 or 12AT7 but their gain is different.

[eh la bas ma]

No.  Even though they have a similar base, they're completely different tubes with different pinouts and circuit requirements.
You can sub a 12AX7 or 12AT7 but their gain is different.

Ok, understood, thanks for your reply !

[mozz]

A 12AX7 will sound like crap in that circuit, it's got very low plate voltage. A 12AU7 or a 6211 is the tube of choice. If you are CONUS, let me know i will send you one.

[eh la bas ma]

A 12AX7 will sound like crap in that circuit, it's got very low plate voltage. A 12AU7 or a 6211 is the tube of choice. If you are CONUS, let me know i will send you one.

Thanks, it's very kind of you, but i live in France.

I understand tubes are harder to come by, at least on the european market, since the Ukraine/Russia conflict, most of them being manufactured in Russia.

I read somewhere some time ago that the western industries were recently considering some investments to develop their own tube factories, but they probably will be more expensive and worse quality than russian tubes, just like the non-russian tubes already available on the market ?

Is it true that Czech, British, Chinese and American tubes are either more expensive and/or worse quality, for economic and historical reasons ?

All I can find at my usual supplier are some expensive military-grade 5814A NOS tubes :

https://www.musikding.de/5814A_1

I guess it will be compatible with the Bass Amuser circuit ?

[PRR]

The tube in my Bass Amuser circuit just died. It's been working since April 2020...

Are you sure? Tubes like these should live 20 or 30 years without much trouble.

There are a lot of other parts in that box which may be the actual problem.

What does it do or not do?

[eh la bas ma]

Are you sure? Tubes like these should live 20 or 30 years without much trouble.

There are a lot of other parts in that box which may be the actual problem.

What does it do or not do?

I just tried to connect the stompbox again to answer your question, and now everything is back to normal !

Last time I tried to play with it, status led was ok, the volume was much lower than usual, and i noticed the bulb filament wasn't lighting up. I thought the tube was dead, but today it's lighting up again...

Not sure what happened, maybe a dodgy part somewhere but I never had any trouble with this effect before.

When I noticed the bulb wasn't lighting up, i shook the stompbox a bit to see if I could hear the filament rolling inside the bulb, like we do with regular light bulbs, to check if it's still good... Didn't hear anything, but i assumed the tube was out of order nonetheless.
I didn't know they were able to last 20 or 30 years, and i am using this effect quite a lot, so it didn't feel suspicious.

If this happen again, i will open the enclosure and look for issues.

Be that as it may, it looks like it was a false alert.

I offer my humblest apologies for the trouble, and thank you very much for your help.

[amptramp]

There are those of us who restore antique radios and one of the issues we often run into is tube sockets where the spring loading on the pins has gone away.  This shows up as intermittent operation of the "here one day, gone the next, back in operation the following day" sort.

Our usual treatment is to use contact cleaner on the pins (in case the problem is corrosion) and check the pin retention force.  We use contact cleaner on the tube pins as well.  If you have wafer sockets, you can use pliers to bend the socket pins slightly to get more tightness and get another few decades out of them.  In some cases, the problem affects so many pins that we just replace the socket.

[merlinb]

i shook the stompbox a bit to see if I could hear the filament rolling inside the bulb, like we do with regular light bulbs, to check if it's still good...

Tubes don't rattle, they are not like light bulbs.
You can buy news ones in any music shop, even in France.

[amptramp]

JJ Tubes from Slovakia should still be available.  They are regarded as one of the better sources for tubes with delivery to anywhere in Europe.  Their website is here:

https://www.jjtubes.eu/

[PRR]

Even when a tube "fails", it is almost never the heater. (They run MUCH cooler than incandescent lamps, thus "burn-out" much-much-much slower.)

Not counting series-string TV sets, I saw about two bad heaters in my days with tubes. One had been DUMPED into a disposal bin before I crawled in after it. I forget the other.

Bad joints are ALWAYS your best bet. Good solder joints are very reliable, but not all technicians make good solder joints (ideally a team effort with layers of inspection). Part of the impetus behind "integrated circuits" was to reduce the number of solder joints in computers and other big gear. Also Surface Mount moves more production away from manual and into automated processes.

Get a bright light and a magnifier in there. Learn what "bad" joints look like. I've seen many "rosin rim" joints hold-up for years, by incidental touch, before they fail.