ClassicTone Customer Service is Excellent!

[Gregg]

The PT manufacturers need to make adjustments for modern voltages.
I think they still wind Transformers like when we had 110V.

Maybe it would a good idea to include several primary taps in their PTs like 115, 120 and 125V (or 110, 120 and 130) for example. This way everyone will be able to adjust their voltages according to the mains line voltage.
If you have higher voltages for the specified mains voltage you could switch to the higher voltage tap and this way lower all secondaries' voltages.

[bob p]

I emailed CT about their excessive B+.
They basically said that, this is what we make, use them or don't!

Wow. I received a courteous, prompt and friendly reply from them, and they bent over backwards to help me. I wonder why anyone would give you the brush off.

Looking at the numbers with a 5AR4 rectifier:

CT 40-18016 is rated 422V @ 100mA
Test results yielded 455V @ 18mA

That's a difference of only (455-422)/422 = +7.82% from the 100mA load rating, with the transformer virtually unloaded. Like Tom said, transformers are rated under load conditions. Unloaded voltages don't tell us much. The voltages posted under low-load conditions don't seem out of line at all.

So can we compile a list here of measured B+ in our own experience with specific amps or builds? It might help visitors decide to buy a ClassicTone amp. I would like to know how high their B+ voltages are...

That would require people to draw schematics of their builds, and document everything in a build thread, like we used to do here in the old days. People don't seem to be willing to do that any more.

Creating a list of measured B+ would be a great idea if we could compile a data set that accurately reflects the transformer characteristics, but I don't think we've got very good data yet. In contrast, CT is already publishing the V=f(load) data on their spec sheets; there doesn't seem to be any point in creating a duplicate list unless we prove that the CT spec sheet is unreliable. In the big scheme of things, the spec sheet tells the builder what he needs to know, and the builder just needs to properly interpret the specs.

It would be interesting to clamp an ammeter around the B+ line, drive the amp to loads of 100mA and 120mA, and report the voltage numbers.

Idle voltages aren't very meaningful.

[Steve A.]

So can we compile a list here of measured B+ in our own experience with specific amps or builds? It might help visitors decide to buy a ClassicTone amp. I would like to know how high their B+ voltages are...

That would require people to draw schematics of their builds, and document everything in a build thread, like we used to do here in the old days. People don't seem to be willing to do that any more.

By "specific amps and builds" I was referring to the Fender amps as listed on the CT site for the PT that Terry referenced, whether restoring a vintage amp or building an exact clone. The schematics for the various tweed, brownface and BF/SF Fender amps are readily available on the internet. Plus the classic Marshall amps that CT handles. Just mention line voltage, VAC output of PT and B+ measured at plate of power tubes and we're good to go...

It would be interesting to clamp an ammeter around the B+ line, drive the amp to loads of 100mA and 120mA, and report the voltage numbers.

I've had at least a half-dozen AC clamp-on ammeters but none that handle DC. Here's an Amazon listing for one for $59.99... ain't technology great?

https://www.amazon.com/Auto-ranging-.../dp/B001VGND88

Steve Ahola

[bob p]

Sorry if I misunderstood you, Steve. But the amp we've been talking about isn't a standard Fender or Marshall amp. It was referred to as a 6V6-based JTM-25. So the water has been clouded a little bit. A schematic would help to clear things up.

With that in mind, if anyone wants to know what voltages a PT will supply under load, it's not necessary to go through the trouble to clone one of the amps listed on the CT site. All that you need to do is to build a test jig and take the measurements. I think that the underlying problem here is that people have false expectations that an amp should idle at the voltage spec'd for the transformer under full load. That's just not realistic.

Please ignore my previous clamp-on comment, I said it without thinking. When it comes to measuring B+ current, it's simple enough to just measure voltage drop across a resistor and do simple ohm's law math.

[Steve A.]

Sorry if I misunderstood you, Steve. But the amp we've been talking about isn't a standard Fender or Marshall amp. It was referred to as a 6V6-based JTM-25. So the water has been clouded a little bit.

The PT that Terry ordered is a drop-in replacement for a Deluxe Reverb amp. Wouldn't the CT PT for the JTM25 be more appropriate, especially the one with the multiple input voltages? (The 100VAC tap could be used if a higher B+ was desired than what was obtained using the 120VAC tap.)

http://www.classictone.net/40-18056.html

With that in mind, if anyone wants to know what voltages a PT will supply under load, it's not necessary to clone one of the amps listed on the CT site. All that you need to do is to build a test jig and take the measurements.

What I had in mind was the results from people here who have already used CT PT's in repairing or building the classic amps in the CT listings. And I'm not exactly sure how we could test the PT's without buying them first...

Steve Ahola

[bob p]

What I had in mind was the results from people here who have already used CT PT's in repairing or building the classic amps in the CT listings. And I'm not exactly sure how we could test the PT's without buying them first...

LOL, of course I can't take a measurement when I don't have the iron in-hand! That's why I contacted CT Customer Support over the holiday weekend to get the results of their measurements. The point of my starting this thread was to give them a positive review for excellent customer support by quickly getting me the numbers that I needed. I'm willing to trust the numbers that the engineer at CT provided in his spec sheet, I have no reason to suspect that his numbers are false.

In regard to the comments about idle voltages that are higher than the spec'd voltages under load -- that is to be expected. So far I haven't seen any data that refutes the data provided in the CT spec sheets, so I'm not ready to suggest that the CT products are anything less than what they are claimed to be. I think that more likely we have a case where the test conditions don't match the specified test conditions, which means that improper test conditions have to be suspected as the cause of the discrepancy.

As you suggested, maybe the wrong transformer was chosen, but that's not really CT's fault, is it? Regarding whether your suggested PT would be better, I don't see the V=f(load) specs in the 40-18056 data sheet. This would be a good opportunity for someone to independently re-test the CT customer support service by asking them to update the 40-18056 data sheet to provide a voltage vs. load table.

[loudthud]

And I'm not exactly sure how we could test the PT's without buying them first...

PSUD II will give pretty close results if you know the open circuit Voltage and the resistance of the windings. You have to know how to enter the data into the program and it calculates a lumped source impedance for the transformer. Then it's just a matter of setting the load current and the program calculates the load Voltage.

Unfortunately, the data sheet does not give the open circuit Voltage and resistance data.

Addendum: When you enter the open circuit Voltage, you can also correct for mains Voltage variations.

[bob p]

^^^ Yes. But the problem is like Steve said -- you typically have to have a transformer in-hand to take those measurements... because the data sheets almost never provide you with all of the numbers.

I have a 4-wire kelvin meter and an LCR meter. Back when I used Windows I used PSUD to do the types of calculations that you've suggested and it provided very accurate models when I was been able to give it the right input data. The problem -- as you noted -- is that just about nobody gives you all of the information that you need to accurately model their power transformers in-circuit. I'd sure like to see suppliers give full specs on their transformers, but virtually nobody does that. I thought it was a giant step in the right direction for CT to provide transformer voltage vs. load data with various rectifiers (diodes vs. various tubes), which allows people to estimate in-circuit performance using less "heroic" methods. I've never been able to get that kind of cooperation from any other suppliers. I do seem to remember Hammond providing DCR but not OCV in their spec sheets. Since I haven't used PSUD in quite a while, I haven't tried asking either Hammond or CT to provide those other numbers. I just went with the load tables which have put me in the right ballpark.

[big_teee]

If a PT is recommended for use in amps just for 6V6 Tube amps?
Then I expect the voltages to be in the range needed for all 6v6 tubes.
Regardless of the load on the PT.
The voltages IMO shouldn't be so high or so near the edge, that the load is that critical.
So with that said, on future builds?
I'm not likely to buy the Power Transformers, made by Magnetic Components Inc, ClassicTone, made in Chicago, Illinois, USA.
Anyway, I'm done with the amp and done with this Rant.
I recommend if you build a 6v6 amp, to do your homework.
It shouldn't be that big of a deal, and you shouldn't have to be a load engineer to pick a transformer set for a 6v6 amp.
GL
T

[bob p]

If a PT is recommended for use in amps just for 6V6 Tube amps?
Then I expect the voltages to be in the range needed for all 6v6 tubes.

There's a problem in relying on a transformer that's recommended as a "generic 6V6" transformer, because different 6V6 amps have voltages that can differ by over 80 VDC. As an example look at the Fender Deluxes. The old Fender schematics show voltages that ranged from 332 (5c3) to 415 (DR) VDC. That's an awfully wide range, so a builder has to know exactly what he wants, and he has to pay a lot closer attention to the actual transformer specs to get the right voltage, instead of just taking a manufacturer's application recommendation on blind faith.

The range of voltages for other applications are even more widely discrepant. I've seen 6L6 and EL34 designs that go up to 525 and 600 VDC, respectively. It' s just not realistic to expect one generic transformer to be in the range needed for every application that uses a specific tube.

If a PT is recommended for use in amps just for 6V6 Tube amps?
Then I expect the voltages to be in the range needed for all 6v6 tubes.
Regardless of the load on the PT... [emphasis added]
It shouldn't be that big of a deal, and you shouldn't have to be a load engineer to pick a transformer set for a 6v6 amp.

Well, that's the problem. Once you've decided not to be a kit buyer, and you decide that it's time to start building your own designs, then you have to become a little bit of a load engineer. It's just the nature of the beast.

Many manufacturers like to sell transformers that are "good for a 6V6 amp" to people who don't want to think too much about what they're buying. To those customers, "mojo" is the primary marketing theme. Rather than buying into mojo marketing, and buying "magic mojo parts", users have the option to make their purchase decisions logically, based upon the laws of physics and electrical performance characteristics instead of mojo. That's what the concept of "better tone through mathematics" is all about.

Unfortunately it's very easy to fall prey to the marketing charlatans if you decide to ignore the numbers. I've found that by taking the extra steps to do a little math (or run a simulation if you don't like doing the math) all of those headaches go away. Sure, it adds some extra steps, but to me taking the extra steps is part of the fun in reaching the right answer.

[Justin Thomas]

I agree with you Bob, on much of this. I guess my only thing is, there's a nice middle ground between "kit novice" & "engineer" that a lot of us probably fall into... I'm one. I can't fathom the math, but I can build my own design without blowing it up (usually).

I think the main thing here is, that perhaps tranny manufacturers should make a "6V6 amp" PT that will put out an ABSOLUTE max of 440V of rectified B+ under practically any load circumstance. It's widely believed that the Deluxe/Princeton/Champs w. 420+ B+ are VERY borderline for any 6V6 but JJ anyway... So if the tranny won't put out any more than 440V unloaded, that will allow use of ANY 6V6, pretty much. Couple that with a stated tolerance of +/-20%, then I'd much rather have 20% LOW all over than high...

My last build puts 470 on the plates of the 6V6s, so I used JJs. But lucky for me, I plugged in 6L6s and it did jus t fine after an hour. But that was originally a 6973-equipped organ chassis... the whole venture was an adventure.

I guess the best compromise is to use these "vintage clone" trannies for restoring vintage amps; anything original, gotta do some homework... me? I try to stick with what came in the reclaimed chassis or close alternative... in my case, the 6973s seemed a sorta-decent load match for the OT too... even if I am stuck using JJs.

Justin

[bob p]

FYI: I was editing post # 25 while you were writing post # 26. I edited the deluxe voltages listed in the first paragraph.

I guess all threads get hijacked eventually, and this one is no exception. Honestly, I like the way the hijack has gone in this thread, because you and Terry are addressing the same concerns that I've dealt with many times. These are the types of problems that has had everyone banging his head on the desk at one time or another.

I can't fathom the math, but I can build my own design without blowing it up (usually). I think the main thing here is, that perhaps tranny manufacturers should make a "6V6 amp" PT that will put out an ABSOLUTE max of 440V of rectified B+ under practically any load circumstance.

I agree that it would be GREAT if manufacturers could do that, but the problem is that the voltages must change as we progress from no-load to full-load conditions because we can't violate the laws of physics. The result is that we're forced to be aware of the problem and to take measures to identify it, understand it and compensate for it.

Skimpy underbuilt, cheapo iron is the worst offender in this regard. Sags can be huge. The differences between OCV, minimal load/idle and full load sag can be tremendous. Hefty overbuilt iron with good regulation doesn't change as much under load. Looking at the spec sheets can help you get a handle on this, but unfortunately most of the spec sheets always leave off some of the parameters that we need to know about if we're into doing the math. That's why I was so happy when CT gave a quick answer to my questions.

The issue is further complicated if you don't have any spec sheets to work with. Those kinds of builds require you to either adopt the math approach or the trial and error approach. When no specs are available, the math approach is complicated by the fact that you have to generate your own performance parameters to use as input data. In that respect re-purposing old gear is harder than building from a kit.

[bob p]

It's widely believed that the Deluxe/Princeton/Champs w. 420+ B+ are VERY borderline for any 6V6

Yes, but I think that can be traced back to purposeful propaganda. It must have been close to 2 decades ago I was a member of a private forum that was an invitation-only sort of place. I had posted a thread where I was giving praise to the robust nature of the JJ 6V6. Prior to that I had been getting Teslas from Czechoslovakia for quite some time, and when the state owned company was dismantled after the Velvet Divorce I began to get tubes from the new company that Jan Jurcho had formed using Tesla's old equipment. I was an early adopter of the JJ tubes because I had contacts in the country and I was using them long before Eurotubes came along and began importing them.

When the JJ started being imported there were a lot of 6V6 failures in Fender circuits because most people hadn't figured out the primary voltage problem that we're so familiar with today. Someone else (who ultimately started a boutique company selling reproductions of pre-Rola celestions) vociferously bashed every brand of 6V6 except NOS Mazda as being failure prone in DR type circuits. He was sitting on a stockpile of NOS Mazda at the time, he clearly had an ulterior motive, and I think he was the primary spreader of rumors about the failures of anything that wasn't a NOS Mazda 6V6 in 420V applications.

I commented that my experience was quite the opposite -- that if you paid attention to the amp's operating conditions, and if you bothered to get a handle on input voltage many of those problems went away. I mentioned that screen failures were occurring because people were blindly tube-rolling without paying attention to screen dissipation, and that merely making minor changes to operating conditions would make the problems go away.

Of course, this kind of information was NOT what he wanted people to hear. He made a point of spreading as much FUD as he could in order to drive up the value of his NOS Mazda inventory. He started his speaker company at that time, which he used to leverage his credibility. He put out a lot of disinformation which persists to this day as sticky internet lore. Over a decade later there is still invalid internet lore about Fenders as tube killers, all because some people would rather not be bothered by looking at data sheets and making sure that the tubes were operating within their design limitations.

[bob p]

My last build puts 470 on the plates of the 6V6s, so I used JJs. But lucky for me, I plugged in 6L6s and it did jus t fine after an hour. But that was originally a 6973-equipped organ chassis... the whole venture was an adventure.

I used to build a lot of conversions based on old gear, but that was a long time ago. In the 90s you could buy a lunchbox PA head for $5 at a flea market, and you could stop along the roadside to pull a Hammond chassis and a Jensen speaker out of an organ that was being thrown away. That was back in the days of the old Ampage site, long before internet forums became popular and amp building became so widespread. Back in those days I always used to drive around with a pair of dykes in my back pocket.

If you're building off of old iron where you don't have specs, then none of this debate over spec sheets is going to help you. In that case you're left with doing the math. but like Loudthud said, PSUD will really help you in that situation, and it's modelling features will spare you from getting bogged down in the math. If you measure the PT open circuit voltage and impedance then you can plug that data into PSUD along with the estimated load and it will accurately model the voltages for you. It's a great tool, but you definitely have to know how to use it to get the best results.

[Stratz]

As an example look at the Fender Deluxes. The old Fender schematics show voltages that ranged from 332 (5c3) to 415 (DR) VDC. That's an awfully wide range, so a builder has to know exactly what he wants, and he has to pay a lot closer attention to the actual transformer specs to get the right voltage, instead of just taking a manufacturer's application recommendation on blind faith.

Hi Bob.
In defense of people such as myself (first time build and I chose the Mojo Tone Deluxe Reverb kit) Classic Tone lists their 40-18016 as a replacement for the Fender (Schumacher?) 025130 and125P23B PT's.
Thats what I read on the CT site. I saw 330-0-330 so I bought it. What I have for voltages (at idle) is quite different than their posted voltages.

I cant get into a tech discussion because I'm not an amp builder and only have one kit build under my belt but I sure enjoyed building my first kit.
Cheers
Rob.