Question from a transformer-disabled person....

[hopy]

This has been bothering me for a long time. When looking at tube amp schematics, why is the transformer info usually left out? I mean all the resistors, caps, tubes, etc, are usually clearly identified, but the transformer is hardly ever ID'd. (except for Fender) Your lucky if the output voltages are listed, but that's usually hit or miss too.

Does anyone know if there is a reference source, or just how do you, match transformers, or transformer voltages, to the tubes used in the circuit?

Example: I'm looking at a schematic with the following tube compliment.
6X4 rectifier.
12AX7 preamp.
12AX7 trem circuit.
6BQ5 or EL84 output.

And as usual, no information on what the transformers are. No numbers, no voltages, nothing. If I wanted to build a clone of this amp, how would I select the transformers?

Any help would be helpful to the helpless.....

Sincerely,
Frustrated

[loudthud]

Most big time manufacturers use custom transformers so at most you see their internal part number. If you can find who actually made the part, they usually won't sell one to you or disclose the specs. These days Fender has a parts list that gives the part number so you can order a replacement but you usually don't find the complete info online unless it's a big pdf file. Manufacturers don't want to give out the info needed to clone their products, they want to sell you one of theirs

[stingray_65]

Do you have a schematic?
any other info like output wattage?

The great thing about tube circuitry is how flexible it can be.
You don't nescassarily need EXACT voltages unless you are trying to make a perfect clone of a specific amp.

The few I've made I generally start with output CURRENT. this I've found to have the most affect on a design than the actual voltage (for the most part)

I'm pretty new to all this thermonic wonders myself and have made several power suppllys just to kind of get the hang of what is going on and how to manipulate them.

I have this Conn organ chassis with a HUGE hole for a transformer on it .
I keep one socket wired for a common rectifier (uses pins 2 and 8 and 6 and 4) I also have a Cap Can on the chassis from an old pull and a couple terminal strips for easy hook ups. I also have a terminal strip with 4 big diodes in a bridge formation.

I mockup all my transformers this way to make they are suitable for the circuit I'm using.

I keep thinking I'd like a big reostat mounted on it so I can check output current also, but havent quite gotten around to figuring that out. I mostly look at what the tranny came out of and reverse engineer from there.

[hopy]

I got a nice answer from another forum.... this makes good sense.

"Well, the power tubes usually dictate the maximum allowed voltage of the PT, and the output impedance of the OT.

6BQ5 with a rectifier, I'd say use 300-325V power supply, and an OT with 4000 to 8000 output impedence."


Now I'm tracking!

[Chuck H]

I got a nice answer from another forum.... this makes good sense.

"Well, the power tubes usually dictate the maximum allowed voltage of the PT, and the output impedance of the OT.

6BQ5 with a rectifier, I'd say use 300-325V power supply, and an OT with 4000 to 8000 output impedence."


Now I'm tracking!

Not necisarrily. When you consider that 300-325V is standard fare for a single ended EL84. I'd say that was a "likely" suggestion by the poster, at best. Some vinage amps that you may love the sound of are a bit higher voltage now because they used a 110V primary on the PT. And many vintage amps ran lower than the max too. Though most popular modern and vintage single ended EL84 amps ran about 300-325V on the plates.

And 4000-8000 primary (not output) impedance is the full range of variable for that tube in this operation. You could have gotten the same info looking at the tube data sheet. But at the very least you now have the working parameters. FWIW, if you can determine the plate volts, higher plate volts often mean higher primary impedance for these designs. At least in high end audio. For guitar amps the min primary impedance combined with the max allowable plate volts for the class of operation is the norm. Most often for AB1 push pull amps but Fender did make a couple of single ended amps that seemed to follow the same MO.

What is the vintage of the amp you wish to clone?

Better yet, what amp is it? Don't be shy. Someone here may already have the inside info on the design you want to build.

Chuck

[hopy]

What is the vintage of the amp you wish to clone?

Better yet, what amp is it? Don't be shy. Someone here may already have the inside info on the design you want to build.

Chuck

No amp in particular, I was just looking at a Kalamazoo Model 2 schematic, thought it was interesting, wondering what tranny would be a good fit. Then wondered why so many schematics are vague in this area. I've been building/repairing for a while now, the PT's, to me, always seem to be the most difficult to be sure about. I think maybe with more experience, I'll understand the whole concept better. I wish my real job was as much fun and thought provoking as tube amps are! Good stuff, this.

[Chuck H]

I wish my real job was as much fun and thought provoking as tube amps are! Good stuff, this.

Amen brother. I'm a painting contractor Good money when there's work. But not very exiting or creative.

Maybe better questions for you then would be 'what voltage and primary impedance would you good, experienced folk recommend for a single ended EL84?' or 'what's a good preamp for "X" style of music to go with a single ended EL84?'.

After that you still have some bugs to work out, but you'll be on the right track for an amp you have solid opinions on. Even if it's never been created before.

I've never built a single ended EL84 amp. So I can't give experienced opinion there.

FWIW most posters I read love their old Kalamazoo class A amps. And they've been cloned here before.

Chuck

[defaced]

I don't know if this will be of much help because it deals with sizing a transformer so it won't fry and really has nothing to do with the circuit, but I found it interesting and it may be of some help down the road:

The discussion I'm talking about starts at LT's post, #29.
http://music-electronics-forum.com/s...ad.php?t=11521