Question about el 84 tube amp............

[jstich]

Hi, I'm a first timer.Here's a question for tube amp freaks: I have a 6eu7 pre, (2) El- 84 pwr amp that was in an old record player.The question is, it has a knob labeled bal on the back. It acts as a balance control, but also seems to direct most of the power to which ever "channel' the bal knob is turned to.Does this knob have anything to do with the bias of the amp? Thanks!

[loudthud]

Not very likely.

[jstich]

Thank you, Loud thud! Here's another question:My amp has a 6eu7 preamp tube. Like a goon, I tried to put a 12ax7 in the socket.Amp wouldn't work with it; put 6eu7 back in, amp once again worked, but the pilot light connection doesn't work anymore. Can anyone help a moron? Thanks!

[Regis]

I would gently suggest you stop experimenting with this amp before something bad happens, worst being you end up dead, best being you fry the amp. Try to learn a little more about tube amps before you continue. Sorry if you take offense to this, but it needs to be said.

About the pilot lamp, you probably shorted it out, maybe did some damage to the heater supply.

[Enzo]

A lot of record players were "hot chassis" types, which meant there was no isolation from the mains. These can be deadly to work on if you don'r know what you are doing. You probably burnt out the bulb when the wrong tube pins caused certain things to be connected that didn't want to be.

[jstich]

Thanks for responding.It may not sound like it, but I do take precautions.I maybe sound like a dumb kid, but I'm 36.Of course, 250 volts DC doesn't care how old you are, do they? No offense taken. Safety HAS to be the #1 concern when dealing with tube amps.I did successfully re- cap this amp, and it sounds better than I thought it would. I monitored it for many hours afterward, to make sure it didn't start a fire or die.

[jstich]

Thanks for the info.If I could find a schematic for this amp, it would save a lot of 'hands on ' work.Tried for hours to get the schematic, but no luck.I will go back and review some safety guidelines.Thanks again!

[Joe6v6]

Yea the 6eu7 has a diffrent pin out than a 12ax7, looks like you put plate voltage on the heaters. Use this page here to check out tube pin out & voltage info befor any more ill advised tube substitutions.
http://tdsl.duncanamps.com/tubesearch.php
In general a 6xxx can not be used in place of a 12xxx the diffrent first number means diffrent heater voltage. However 12ax7's,ay7's etc. can be and usually are wired to run on 6 volts because they have a heater center tap , (pin 9).
Just be careful continue to learn & have fun, With a little more knowledge it looks like you could rewire that socket to accept a 12ax7.

JOE

[Enzo]

This is a very simple amp. Why not take a piece of paper and a half hour of your time and draw out the schematic? I do it all the time. In fact last night I saw so many differences from the published schematic in an ancient GIbson GA30, that I drew out the schemo from the unit.

[jstich]

I've tried making a schematic of circuits, but even simple ones like this seem a lot more confusing than a regular schematic.But, what the heck, I think I'll try it anyway.It's been a while, maybe I can make it less complicated looking this time. Thanks for the idea, I never thought of that! This forum is filled with a lot of nice people.

[jstich]

This amp also has flying lead terminals.What a mess!

[Steve A.]

I've tried making a schematic of circuits, but even simple ones like this seem a lot more confusing than a regular schematic.But, what the heck, I think I'll try it anyway.It's been a while, maybe I can make it less complicated looking this time. Thanks for the idea, I never thought of that! This forum is filled with a lot of nice people.

Even if the result isn't a schematic that makes sense to anybody else, it is a good idea to draw up where everything goes. With a tube amp, you can start off with the tube sockets, the pots and the jacks... that could easily be half of the parts inside the amp, and those connections are often the ones that get screwed up. If a wire drops off when you are working on something else it can be next to impossible to figure out where it came from unless you took the time to make a drawing first (or take some shots with your digital camera before you start taking things apart!)

If you can find a schematic for an amp with a similiar configuration it can make things go much easier...

--Good luck!

Steve Ahola

P.S. Hopefully you already replaced the bulb and the new one works... I have a hunch that the old bulb acted a fuse and protected your amp from further damage.

[jstich]

Hi, Steve, thanks for helping.You're right, I just have to try to make a schematic.Also, after putting the 6eu7 back in, the amp works great, especially after the cap job, but, strangely, the pilot light terminals don't have any voltage at all.I just checked again. Weird, isn't it?

[sbluestubes]

I don't mean to sound insulting but did you set your meter to AC volts ?

[jstich]

You're not gonna tell me there's ac here, are you?! I've been thinking it has dc for the pilot light.Great. I just checked, and it doesn't show any polarity.Do I have ac there? And if so, how many volts? If it has ac, I'm gonna feel like an idiot. Thanks..............

[jstich]

Just checked, and I got a reading by putting the meter on ac. Must be 6.3 volts ac, then? Thanks..................

[sbluestubes]

Yes those filaments are AC the voltage will be around 3.6 volts per side reading to ground.
Mike

[sbluestubes]

Replace the bulb the filament acted liked a fuse as someone mentioned in a previous post.

[jstich]

In my defense, I only had terminals and not an actual bulb in there.Yeah, there is no defense for this. I sincerely thank all of you for your help. Jamie