YBA-1 Guitar amp makes a chirp sound

[J M Fahey]

But seriously, if your feedback polarity is correct, the presence pot should be effective. Check for a 4K7 resistance to ground from the feedback yellow wire going to the pot, check the pot, the capacitor, etc... The entire phase inverter network depends on that 4K7 to ground resistor(R20).

Agree, this is true ... on the unmodded YBA1 (or the original Bsassman for that matter), but in this one, I think a PPIMV master volume was added ("dual gang master volume" ... "220K bias resistors replaced") .
The presence control works, basically, as a "reverse tone control" by killing mid/highs from the feedback signal, letting the amp become open loop (a.k.a. "maximum gain possible", whatever that is) at high frequencies.
How much can it boost?
Maximum: whatever gain was attenuated by the NFB loop.
Since guitar amps usually have low NFB, in the order of 6/8dB , that's the max. "boost" you can have.
Now, the PPIMV is *within* the amp gain stages, right between the PI and the output tubes (duh !); as soon as you lower it a little, you kill your presence pot, since there is no extra gain free for it to act.
In my "Angus" JTM45 cousin, I added a "Rage" switch which killed NFB for a looser, dirtier sound , and had to warn users that it killed the Presence pot too.
So, in a nutshell: don't worry, it's normal.

[jmaf]

A switch to turn off or just change the value of the feedback resistor value is an interesting idea, thanks for sharing.

[soundguruman]

The first thing I see is the amateur capacitor installation. The solder joints on the can capacitors are looking pretty superficial.
The reason for this is that it is nearly impossible to heat the galvanized chassis to a suitable soldering temperature (without special equipment) to bond the capacitor can, with a clean solder joint.
Also the solder used, I'm going to need to question the method. It's mickey mouse.
I would imagine because of the bad grounding of the capacitors, you have really crappy grounds.
The can caps should have been mounted with clamps. A ground jumper, down to a screw with a lock washer, etc... is much more reliable than what you have there.

In case you are interested, first the galvanize must be completely removed from the steel. then the steel is heated pretty dog-on hot before the solder is applied. You never got that far.
And, the capacitor cans are made of aluminum, making it impossible to bond with solder. No matter how hot you make it.

The capacitor cans have tabs, which insert into a special Bakelite / plastic mounting flange. The tabs are then twisted to secure the cap to the flange. The tabs were never intended to be soldered. You can't solder to aluminum.
The flange is then screwed or riveted to the chassis. Then you connect your wires to the terminals.
In other words, this capacitor job is a complete botch job. It has to be taken apart and done over the right way.

[yba-1 user]

Hmmm....Surprising to hear that.
That is exactly how Traynor attached the Caps cans to the Chassis back in '72.
If you are familiar with Traynor amps of the 60's and 70's you will notice that this is the way they attached the cap cans to the chassis.
Like it or not .....that is the way it was done from the factory.
As with any vintage tube amp, it would be a shame to completely alter from the original - for a "better Idea".
A few resistor replacements and cap changes are easily reversed and are a fun way to experiment with the tone.
I appreciate your input but I will probably keep it close to original.

[soundguruman]

except that traynor used steel cans, not aluminum.
you can solder to steel.
It looks like someone trapped the aluminum tabs under mounds of cold solder. cute, but ineffective.
does a magnet stick to your cap cans? that tells it all.

[g1]

Seriously, where do you get your info from? Wherever you read about biasing in the dark to just before redplating?

The first thing I see is the amateur capacitor installation. The solder joints on the can capacitors are looking pretty superficial.

Looks like the factory connections were resoldered, what is superficial about it?

The reason for this is that it is nearly impossible to heat the galvanized chassis to a suitable soldering temperature (without special equipment) to bond the capacitor can, with a clean solder joint.

Like a BASI (big a** solder iron)? You don't have one?

Also the solder used, I'm going to need to question the method. It's mickey mouse.

You can tell the type of solder that was used?

I would imagine because of the bad grounding of the capacitors, you have really crappy grounds.

What bad grounding?

The can caps should have been mounted with clamps. A ground jumper, down to a screw with a lock washer, etc... is much more reliable than what you have there.
In case you are interested, first the galvanize must be completely removed from the steel. then the steel is heated pretty dog-on hot before the solder is applied. You never got that far.

Pure speculation, if that were the case I think it would look more "blobby"

And, the capacitor cans are made of aluminum, making it impossible to bond with solder. No matter how hot you make it.

Wrong, then the solder wouldn't stick to the ground tabs. Some caps have aluminum cans, the cans are never used for grounding and the negative leads are isolated from the can.

The capacitor cans have tabs, which insert into a special Bakelite / plastic mounting flange. The tabs are then twisted to secure the cap to the flange. The tabs were never intended to be soldered. You can't solder to aluminum.

Wrong on both counts, see above.

The flange is then screwed or riveted to the chassis. Then you connect your wires to the terminals.
In other words, this capacitor job is a complete botch job. It has to be taken apart and done over the right way.

Factory installation, nothing botched about it. I won't comment on some of the other chassis connections but the cap ground tabs don't look bad.
If this is the first time you've come across metal caps soldered to chassis maybe "green" would be a good sub. for "guru".

[soundguruman]

From the pictures, clearly the solder did not flow, but was caked on.
I also see a ground connection in the foreground of the picture, that is a mound of built up cold solder. Clearly, the person who soldered this did not have enough heat to make solder flow.
Does not look factory to me.
As I said, prehaps you missed the point, you can't bond aluminum to steel with solder. The old caps were steel, not aluminum.
The new caps? well I'm not there with a magnet to check that, but it looks like aluminum.
And if it is, and its soldered, it won't bond.

[soundguruman]

If this is the first time you've come across metal caps soldered to chassis maybe "green" would be a good sub. for "guru".

A. I have been repairing guitar amps since before you were born.
B. I have repaired more guitar amps than you have ever seen, in your entire life.

I have seen many attempts to solder can caps to the steel chassis, and most of them are a complete failure. If you grab the can and twist it, the solder pops right off the zinc. Cause, it did not bond to the metal.
You wanted to know what was wrong and I told you. Sorry you could not accept the reality.

[yba-1 user]

Wow................this thread was going so well at first.
If you want to teach - then teach.............. If you want to simply criticize everyone then that doesn't really help.
I thought that this forum is to ask questions and get repair advice .....and NOT "MY words are law and I am the Solder king"

[pdf64]

I have seen many attempts to solder can caps to the steel chassis, and most of them are a complete failure. If you grab the can and twist it, the solder pops right off the zinc. Cause, it did not bond to the metal.
You wanted to know what was wrong and I told you. Sorry you could not accept the reality.

You may have a valid point but currently no one here knows the reality, so the above is assumption rather than fact. It would be beneficial to make this clear, rather than attempt to create a false impression of omniscience.

A. I have been repairing guitar amps since before you were born.
B. I have repaired more guitar amps than you have ever seen, in your entire life.

Your omniscience seems to extend to g-one's DOB and resume.
Pete.

[J M Fahey]

Earlier I had answered something similar, referring to the adivinatory powers (or free access to FBI files or whatever) implied, but pulled it, considering it a waste of time.
After all, my questions to the guru about how a unity gain Op Amp, passing 1V peak signal, could be "the" main distorting element in a signal chain, are still unanswered. Mesa V Twin problem.
Well, after seeing his helpful answer to a first time builder First Amp Build

You are ignoring the obvious application, as either a door stop, or a boat anchor. Don't forget, not all of us can build an amplifier ....

I should have known better.

Oh well, let's say it adds a little spice in an otherwise too knowledgeable and polite Forum.

OK, ok, don't stone me !! I was just trying to say something nice about this situation.
I love this Forum.

[g1]

A. I have been repairing guitar amps since before you were born.
B. I have repaired more guitar amps than you have ever seen, in your entire life.

A. So you are enjoying your seniors discount. How long have you been retired?
B. You chose to use "seen" rather than repaired. So you have repaired more amps than anyone on this forum, the internet, or the planet. Congratulations!
You are making the resident rocket scientist seem somehow...humble.

I have seen many attempts to solder can caps to the steel chassis, and most of them are a complete failure. If you grab the can and twist it, the solder pops right off the zinc. Cause, it did not bond to the metal.

We were talking about aluminum:

As I said, prehaps you missed the point, you can't bond aluminum to steel with solder. The old caps were steel, not aluminum.
The new caps? well I'm not there with a magnet to check that, but it looks like aluminum.
And if it is, and its soldered, it won't bond.

And as I said, aluminum caps have negative terminals, they do not ground through the cases. Have you ever tried to bend aluminum? It doesn't bend, it breaks. If those tabs were aluminum and you tried to bend them around the chassis like that they would break and that cap would be hanging from the wires. But they don't make aluminum caps with ground tabs to solder to. They put a negative terminal beside the positive terminals.
You said the caps "look like aluminum". What part of the filter cap cans are visible in the photo? The only thing I can see (from following the wires) is that there are no negative terminals, therefore the metal can is the negative and the can is NOT aluminum.
Of course, all this is just on my planet, otherwise all bets are off!

[J M Fahey]

Please let me correct this particular (very common) misunderstanding.
Let's start stating that electrolytic caps *do* have aluminum cans.
Never ever seen a steel can one (can't *swear* they don't exist, but in 42+ years still haven't seen a single one).
Referring to chassis mounted ones, you have:
a) Clamp mounted ones.
The clamp is just "mechanical", you have not only separate positive terminals, but independent negative ones too, not connected to the case.
This is the "modern" version, although it has been popular since the early Marshalls, early to mid 60's.
2) Twist Lock ones, where the can base shows some legs, which are the negative terminals, *connected to the case*, they look "one piece" with the case even to the trained eye.
Mystery: how can they, "being aluminum" , be safely twisted, plus being able to be soldered (and to boot, to a galvanized steel chassis?)
Mystery solved: they use a clever trick (at least the ones I have used): at the base they have an auxiliary ring, made out of tinned iron (at least the ring and legs attract magnets, the case does not).
How come almost nobody notices that?
Because the can base edge is crimped toward the inside, officially to grab the hard rubber disk which seals the capacitor and supports the terminal(s) .... but also cleverly gripping a tinned iron ring, which sports nice twist lock lugs ... or which in so-called "shielded electrolytics" (free translation of Spanish/Portuguese Language Siemens/EPCOS "Capacitores Blindados" terminology.) carries PCB solderable pins.
These Twist Lock types were the most popular throughout the 50's and 60's, specially American made equipment and billions of B/W TVs , PA equipment, you name it.
Just to show what we are talking about (click the image to expand it):

The caption reads:
From left to right, we have a LCR computer capacitor, an Elna Cerafine computer type (unfortunately no longer in production), a Panasonic TSHA snap-mount capacitor, a new-production Aero-M twistlock, a NOS Mallory twistlock, and a good-but-used Elna removed from equipment.
3) I live in Argentina, which follows Europe rather than USA standards and most popular here (say 99%) were Teslas (then Communist-Czechoslovakia) which universally had the negative aluminum can, one or more positives protruding from a central, externally threaded cylinder (about noval socket size) which was accompanied by a stamped iron or molded bakelite nut .
This way, you could tightly screw the aluminum can to the chassis, without any other hardware, making contact at the same time.
If you needed insulation, they offered a fiber washer plus a metal one, with a side terminal, so you could ground it wherever you wanted or , say, put a couple in series if needed.

[soundguruman]

Wow................this thread was going so well at first.
If you want to teach - then teach.............. If you want to simply criticize everyone then that doesn't really help.
I thought that this forum is to ask questions and get repair advice .....and NOT "MY words are law and I am the Solder king"

It's not my fault that I have fixed so many amps....I did it for rock and roll.
There's no need to be terse, if you keep fixing amps, someday you will be able to say so too, junior.

[jmaf]

As with any vintage tube amp, it would be a shame to completely alter from the original - for a "better Idea".

That is very true, IMHO. For every vintage amp out there you can probably find tens of places you'd "improve". The problem is, they're not meant to be "improved". How would a BMW rearview mirror look on a 1929 Ford Phaeton? Ridiculous.

I have a recent case of my own. A friend ordered an amp of mine earlier this year. Since it's not my job, a hobby only, it's still in the making 4 months on. It just happens that I built him a prototype so he could listen to the tone. It uses a turret board and is not exactly a hairball, I made it pretty neat for a prototype meant to be thrown away afterwards. Well the customer wants the prototype so badly, he's building his own wooden cabinet for it. He says it's part of the tube amp magic to have it laid back like that. So I gave it to him and he wants to pay me a few beers for it. I'm sitting my @55 here for hours a day, tired, into the night and after 9-5 work, to build him a neat amp, and he wants the prototype more than anything else. I said we can improve this, he said "don't f'n improve anything, this is a done amp". He's right, some things are not meant to be "improved". I found a bad solder on it BTW. Found it poking around with a chopstick.