Peavey Classic 30

[blueswaite]

Got one of these real cheap because once in a while after it warms up it cuts out like when you have a bad guitar chord and shake it or move it around. It is a really nice sounding amp.
Can the tubes cause the problem. I noticed ont the 3 12AX7 tubes one glows pretty good one is very dim and one is balrely noticable that it is glowing.
Thanks for any input on what to check.

[sumgai]

bw,

Yes, those 12AX7's (and all the same-kind tubes) actually have two filaments in them. Depending on the manufacturer, the filaments may be easily visible, or not - there's no requirement that manufacturers place the filaments in the exact same place on every tube. ( )

One thing you can do right away is easy - just wiggle each tube within it's socket, and listen for break-up. If things are quiet, then you can eliminate dirty contact pins. (This doesn't happen often with pre-amp tubes, but you never know.... ) If the noise comes and goes in accordance with the wiggling, then you have dirty pins, either on the tube, or within the socket itself. Simply pull and replace the tubes a few times to wipe any crud off. Contact cleaner is not recommended - if it does the job, then there's a worse problem, things shouldn't have gotten dirty enough to need that much 'cleaning power'. Have a pro look at it, in such a case.

The next thing to do is equally simple - swap the tubes from one socket to another. (But keep track!) If the problem seems to get louder when the tubes are moved from Socket A to Socket B, or vice-versa, then you have a problem child on your hands - you know what to do about that, eh?

If all of that fails to pinpoint the problem, repeat the procedure with the power tubes.

Keep us posted on your progress!

HTH




sumgai

[blueswaite]

The static and noise is there when I turn the volume all the way down I have no control over the volume of the static and noise.
.

Ok i tunrned the amp around to see the tubes I let it cool down and turned it on. Left to right 1 2 3 4 I tapped the tubes with the back of my finger nail. 1 2 3 made a little ping noise but number four when I flick it it makes alot of noise the same noise when it starts acting up. Tubes all glow. Once the amp is warmed up ( been on alittle bit ) I can flick any of the tubes and cause the noise but when it has been off and cooled down only #4 does it.
Also left to right the the #3 12AX7 gets a loud pop over the other 2 when I flick it.

[sumgai]

bw,

Time for a tube job! Not that you need to replace every one of them, but I suspect #3 12AX7 is microphonic. The proof would be to swap it with #1, and re-test. But more to the point, if #4 is one of the power tubes, as I'm sure it is (after all, there are only 3 pre-amp tubes in there..... ) then you have a power tube going bad on you. Again, the proof is to swap it with one of it's brethren, and see if the loud pinging sound moves with it. Or even better, just pull it out, along with one of the other tubes, preferably #7. The amp will operate just fine like this, although at reduced power output.

If the pinging remains at #4 position, then suspicion reverts to the pre-amp tube in position #3. But be aware, you might have more than one bad tube!

Unlike pre-amp tubes, you should replace power tubes in pairs (or in full sets, to be more correct). This amp has a fixed bias setup, so it should be re-biased at that time. However, for testing purposes, you can simply stick the tubes in to make sure there's no further noise, before you go trotting off to the local Amp Tech store.

HTH



sumgai

[blueswaite]

Thanks. I read a post on the Peavey forum the the 12AX7 in V3 controls tone ect. to the power tubes. You are up on your knowledge. Thanks again.

[blueswaite]

Switched preamp tubes around. Then don't get a pop now.
there are 4 power tubes. Which one can i remove to try to see if one is bad. The second one fron the right when I turn it on for about 30 seconds gets some bad noise when I flick it. After it gets good a warmed up then they all do it. Does one bad tube affect the otheres.
I changed power tubes 4 3 2 1 V3 V2 V1
I swapped one with 3 and 2 with 4 and the noise flicking them was at 1 and 2 and now it is at 3 and 4 and 1 and 2 are ok. I think either 4 or 3 is bad.
ie seems 4 which was originally 2 is causing static and break up. Can I pull this tube out and run amp to see if it solves the problem. Thanks

[sumgai]

bw,

Well, I've seen one or two of these little buggers, from time to time.

And it doesn't hurt that I have a very complete set of schematics on the shelf above the bench, let alone several CD's of drawings... and then there's the innerweb itself, where I can find just about anything, eh?

When you pull ONE power tube out of a set, you unbalance things. This is hard on the amp in general, so we don't advise that. Fortunately, there is a standard way of laying out the power tubes in an amp. If you see a pair, you can't pull just one, that unbalances the output section. (More on this below.) If you see a quartet of tubes, you can pull either the outermost pair, or the innermost pair, and the amp will remain in balance. (Ditto for those with 6 output tubes.)

In this case, balance refers to the fact that voltage is going through two halves of the transformer's primary, and each half goes to one tube. (Or a pair, if it's got four tubes.) If you pull one tube, the other half is now doing all the work, and it can't - it simply wasn't meant to do that, and the circuit won't allow it. Thus, you end up with unacceptable tone. (There are cases where the owner does accept that tone, but the life of the amp and/or the tube is at great risk.)

For a short test, you could pull the suspect tube, let it warm up, and check for noises. Don't try to run a signal into the input at this time, that's what causes problems. When all's quiet at the input jack, you can safely do testing like this for short periods of time. How short? Couple of minutes is OK, which should be sufficient for testing purposes.

If 2 was the suspect, and you moved it to 4, where it now is the strongest suspect, then do this: From your original setup (before you swapped anything), pull 2 and 3. Test. If either 1 or 4 ring out/make noise, pull them and insert the tubes you just pulled. (After cool-down, of course!) Re-test. Now swap one of the known good tubes (it doesn't give you any grief) with one of the suspect tubes. Re-test. That should tell you which one is bad. ;D

In summary, if you have four tubes, it'll take three tests to find the bad one, no matter which method you use. But always bear in mind that you may have more than one bad tube.

HTH



sumgai

[blueswaite]

Thanks for the help. A friend had a new set of 3 Sovetek 12AX7 I got from him and put them in.No noise when I ping the tubes.
Changing the sequence of the power tubes helped. I don;'t get the noise any more. But if I pink the fourth tube I can get the noise out of it. So I'll be changing all four and be totally retubed.
I can play for quite awhile and don't get any problems.
Again thanks for helping me with this.

[sumgai]

bw,

You're welcome!

Generally, a total re-tube is not needed for solving problems, but it never hurts (except maybe the wallet ).

You should be good to go for quite awhile, those amps are as close to bullet proof as it gets.



sumgai

[blueswaite]

Put 4 new Mesa Boogie EL84 power tubes in. Don't know who makes them for mesa but they are nice. Really happy with this amp now.

[mr_sooty]

Ive had a Classic 50 for 9 years. It rules. I just hate carrying it. I'd get something smaller if I didn't love it so much.

[sumgai]

mrsooty2 said:

Ive had a Classic 50 for 9 years. It rules. I just hate carrying it. I'd get something smaller if I didn't love it so much.

They make casters for that kind of thing, you know.

[ux4484]

sumgai said:

Contact cleaner is not recommended - if it does the job, then there's a worse problem,

Yes....a MUCH worse problem....
modern contact cleaner will ruin the plastic in many tube sockets.
The old stuff was even worse. I saw someone use Tri-Chlor on an old Grundig radio and the sockets disintegrated.

Back in H.S. we used to make money in electric shop replacing tube sockets for folks who tried to clean 'em themselves (there was still gobs of tube equipment in those days). It was easy money ;D .
I saw a blues band with the lead using a Peavey Classic 30 this weekend, He had it buried behind him on the small stage (it was mic'd), but during the break I caught a glimpse. Sound-wise, I was sure it was a Fender Blues Jr. until I saw it.

[mr_sooty]

sumgai said:

mrsooty2 said:

Ive had a Classic 50 for 9 years. It rules. I just hate carrying it. I'd get something smaller if I didn't love it so much.

They make casters for that kind of thing, you know.

Actually (mr. smarty pants) I have put castors on it, and side handles. It's much better, but still a bit of a pain. For example, castors aren't much use up and down stairs.

[nomadh]

Mar 2, 2008 23:19:19 GMT -5 sumgai said:

bw,

Well, I've seen one or two of these little buggers, from time to time.

And it doesn't hurt that I have a very complete set of schematics on the shelf above the bench, let alone several CD's of drawings... and then there's the innerweb itself, where I can find just about anything, eh?

When you pull ONE power tube out of a set, you unbalance things. This is hard on the amp in general, so we don't advise that. Fortunately, there is a standard way of laying out the power tubes in an amp. If you see a pair, you can't pull just one, that unbalances the output section. (More on this below.) If you see a quartet of tubes, you can pull either the outermost pair, or the innermost pair, and the amp will remain in balance. (Ditto for those with 6 output tubes.)

In this case, balance refers to the fact that voltage is going through two halves of the transformer's primary, and each half goes to one tube. (Or a pair, if it's got four tubes.) If you pull one tube, the other half is now doing all the work, and it can't - it simply wasn't meant to do that, and the circuit won't allow it. Thus, you end up with unacceptable tone. (There are cases where the owner does accept that tone, but the life of the amp and/or the tube is at great risk.)

For a short test, you could pull the suspect tube, let it warm up, and check for noises. Don't try to run a signal into the input at this time, that's what causes problems. When all's quiet at the input jack, you can safely do testing like this for short periods of time. How short? Couple of minutes is OK, which should be sufficient for testing purposes.

If 2 was the suspect, and you moved it to 4, where it now is the strongest suspect, then do this: From your original setup (before you swapped anything), pull 2 and 3. Test. If either 1 or 4 ring out/make noise, pull them and insert the tubes you just pulled. (After cool-down, of course!) Re-test. Now swap one of the known good tubes (it doesn't give you any grief) with one of the suspect tubes. Re-test. That should tell you which one is bad. ;D

In summary, if you have four tubes, it'll take three tests to find the bad one, no matter which method you use. But always bear in mind that you may have more than one bad tube.

HTH



sumgai

I have the classic 50 and this troubleshooting works fine in my and many other quad power amps. I don't have a cl30 but have it on good authority that the 30 has the power section is run in series. Pull 1 and the amp goes dead. To test or run at half power you need a tube modified by having a pin or 2 cut. See the peavey forum for more detail

[sumgai]

nomadh,

What you propose is not impossible, per se, in the general scheme of how to design a power amplifier. But in this particular amp, the Classic 30, such isn't the case. If you have an exact link to where you heard (read) about this alleged series connection, I'd like to see it, please.

And as for cutting pins to make things work as not designed, that I've got to see!


sumgai

[nomadh]

Couldn't find the thread I learned about this issue. The guy I learned it from even posted a picture of his modified tube. The big problem is when you're missing pins you loose your index position. If i were to do this I'd prefer to take an old 9 pin, break the glass, clip out the guts and hard wire the proper pins. Many people who know peavey including an authorized repair guy agreed that the c50 just pulls the set of tubes but the c30 /delta blues is a series circuit. The only amp I know of that does this. I think it was at the peavey forum but I can't find it. Anyone here with a 30 just pull a tube and see if it still works.
Here is a different ref to the issue.
www.fenderforum.com/forum.html?db=&topic_number=678420&offset=20
Classic 30 @ 15w

This absolutely can be done and it is probably the easiest mod you can make since there's no need to even pull the chassis. I've been running my Delta Blues at 15 watts for several years now. Here's how it works:

The Delta Blues/Classic 30 mainboard is wired with the tube filament heaters in series with each other. If you were to simply pull two tubes from the amp, the remaining tubes would shut down. The method to get around this is to modify two of the EL84 power tubes by cutting off all of the pins except for the two heater filament pins. Plugging these two "dummy" tubes back into the amp completes the heater circuit, allowing the amp to operate normally, yet the two dummy tubes no longer contribute to the power output.

[sumgai]

nomadh,

Well, I see your point, but I must ask that you see mine. Here's what you first contributed to the topic:

I ..... have it on good authority that the 30 has the power section is run in series. Pull 1 and the amp goes dead. To test or run at half power you need a tube modified by having a pin or 2 cut. See the peavey forum for more detail

Later you chimed in with the fact that you were speaking to the heater circuit of those power tubes. Now that fully I understand what you're talking about, I can agree with you, at least in principle. (Whew! )

Yes, Peavey did try a very odd approach to getting power to the filaments - they did this in order to save weight in the transformer, or at least the cost of the winding(s), but in the end, the idea backfired on them. It's been done before (anyone remember the All-American 5? ), and it gets dropped every time. The drawbacks don't sufficiently overcome the miniscule benefits, so sooner or later, everyone who tries it goes back to Plan A.

As for cutting pins, let me ask you this: Are you gonna cut up an otherwise perfectly good tube, or two? If you've got that kind of money to burn, I've got this hot property........ Or are you gonna cut up a perfectly bad tube, one that's no longer working? And who's to say it ain't working because the heater went South, eh Sparky? Seems either foolish or risky to me, how 'bout you?

Fortunately, there's an easier way to make a substitute device to place in the empty sockets - simply use a 2.7 ohm resistor of about 1 watt's worth of power capacity. You'll find that most of the time, the heater element of a tube will not measure nearly that much on a meter, but when it's actually hot, the resistance rises, sometimes quite a bit. Better to be safe and use a higher value to start with. If it's too high, all that will happen is that it drops more voltage across it, leaving less voltage available for the remaining tube filaments. Decrease the value accordingly, in small steps, until the measured voltage drop across the real heater is about equal to the drop across the fake heater element.

HTH




sumgai

[ChrisK]

From a theoretical perspective:

To replace the two tube's filament circuit,

1. The EL84 is rated for 6.3 V at 0.76 A for its filament.

2. This equates to 8.3 Ohms hot.

3. The power dissipated is 4.788 Watts.


I'd do the following;

Replace each tube with an 8.3 Ohm resistor. This can be made from a 10 Ohm 10 Watt resistor in parallel with a 50 Ohm 2 Watt resistor. I recommend using a 10 Watt and 2 Watt resistor as I never run a power resistor at more than half of its rated power.

One can also get 5 Ohm and 3.3 Ohm resistors. You could use one of each in series, each rated for 5 watts for 8.3 Ohms.

One can find power resistors at www.digikey.com

search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=CPA-3.3-ND

search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=CPA-5.1-ND

Since the filaments heat up and rise in resistance, the resistor replacements will limit the initial heater current and prolong both the warm-up time AND the tube's filament life.

[nomadh]

I'm not in an argument. I don't know enough to even point out it was the heaters we were talking about. The part below in my post was a quote. I forgot to point it out.
I thought it was a terrible idea to clip pins because you lose your index that way. I think the idea of wiring up an old tube with a resistor far superior. I'm not surprised at all that you guys here would figure out a better concept and exactly how to do it. I just wanted to point out that I hear pulling 2 tubes won't work. I don't even know that for a fact because I own the cl50 where it does work. Hope I didn't upset anyone. Specially thanks for the detail work on this. I thought this issue might effect my new crate V30 but it actually handles pulling 2 tubes just fine (as god intended . As I recall I believe that my 8 ohm speakers need to changed to a 4 ohm set when I do that. But once again I may be totally wrong.

[sumgai]

nomadh,

As I recall I believe that my 8 ohm speakers need to changed to a 4 ohm set when I do that. But once again I may be totally wrong.

No, you're not totally wrong, but you did err in which way to change your speaker's impedance. No worries, we'll fix that in a few paragraphs........

<lesson mode>
Tubes have high output impedances. Speakers have low impedances. Transformers take care of making one work with the other. Simple, no?

A transformer's ratio between the Primary and Secondary windings is not changeable after it's been built, so if you change the impedance connected to the Primary, the Secondary will follow suit. Thus, the speaker itself is now seeing a different impedance being presented to it.

For purposes of calculating tube impedances, their values are treated just like resistors - they add arithmetically when in series, and add algebraically when in parallel. To recap, the parallel formula is:

Impedance = V1 * V2 / V1 + V2

where V means "vacuum tube", and there are two of them.

If you have more tubes, then just add their values into the equation. Also, a simple shortcut is, if all the values are the same, then simply divide the value of one tube by the number of tubes, and Presto!, you have your magic number.
</lesson mode>

Now, it should be obvious that if you remove two out of four tubes, then the impedance presented to the speaker, through the transformer, is doubled, not halved. To keep the match correct, you should either add a second speaker in series, or disconnect one (out of a group) from a parallel connection. Do this if you're gonna keep the new tube configuration, if for no other reason than to keep your tone (at a lower power level). Chances of your components not going up in smoke are also increased by quite a bit. But for short-term testing, the mismatch is OK. Just be aware that the tone may not be what you want/expect/desire/will put up with.

HTH



sumgai

[nomadh]

I knew it was half or double. Thanks for the memory correction. That could have been an expensive memory slip. And thanks also for the explination why. Knowing why something is can make it easier to member it down the road. I'll have to plug it into my 4x12" Acoustic corp cab and see how it sounds.