I'm looking at some Hammond transformers that are all described as 325-0-325V or 650VCT at 170-180 ma for a 300B build (Tubelab TSE-II, 5k outputs, seeking just under 400V B+ on US line voltage with maybe a 70-80 ohm choke, like a 193J).
Candidates include the 273CZ, 290CX, and 260J. Am I right to assume that I'd get very different voltages out of these even though they are all described similarly in the top line specs? Under the "electrical data" on the spec sheet the 273CZ shows 686.6V with a 125V input. The 260J shows 701V with only 120V. The 290CX shows a whopping 714V on only 120V. (All 60hz.)
The DCRs of the secondaries also get significantly lower in the order of ascending voltage. They are different weights, ranging from the 260J at 5 lbs to the 290CX at 6.8 lbs. The 260J has an amp less capacity on the 5V winding that I'd often think may cause it to sag a bit more if all are loaded the same, but because it is a much newer design and the primary set up is more like the 300 series than the 200 series, I'm not so sure. I haven't run anything through PSUD or another simulator.
I'm contemplating giving the 260J a shot for packaging reasons (under a cheap auction site cover). But one gets a lot more iron for the money with the 290CX (like $30-40 cheaper than the other two), presumably because of economies of scale related to guitar things. I'm tempted by it, but a little worried that I'd end up with more B+ that I'm looking for.
Regardless of my circumstances, unless there is something I don't know about how to interpret these datasheets, one needs to look a bit closer at the actual measurements to be sure of what they are getting with Hammond.
Paul
Candidates include the 273CZ, 290CX, and 260J. Am I right to assume that I'd get very different voltages out of these even though they are all described similarly in the top line specs? Under the "electrical data" on the spec sheet the 273CZ shows 686.6V with a 125V input. The 260J shows 701V with only 120V. The 290CX shows a whopping 714V on only 120V. (All 60hz.)
The DCRs of the secondaries also get significantly lower in the order of ascending voltage. They are different weights, ranging from the 260J at 5 lbs to the 290CX at 6.8 lbs. The 260J has an amp less capacity on the 5V winding that I'd often think may cause it to sag a bit more if all are loaded the same, but because it is a much newer design and the primary set up is more like the 300 series than the 200 series, I'm not so sure. I haven't run anything through PSUD or another simulator.
I'm contemplating giving the 260J a shot for packaging reasons (under a cheap auction site cover). But one gets a lot more iron for the money with the 290CX (like $30-40 cheaper than the other two), presumably because of economies of scale related to guitar things. I'm tempted by it, but a little worried that I'd end up with more B+ that I'm looking for.
Regardless of my circumstances, unless there is something I don't know about how to interpret these datasheets, one needs to look a bit closer at the actual measurements to be sure of what they are getting with Hammond.
Paul
All power transformers depend directly on the AC line voltage for their secondary voltage values.
The actual current drawn by the circuit(s), and the rectifier topology, also affect the output voltages.
Only order the transformer that fits your application properly.
The actual current drawn by the circuit(s), and the rectifier topology, also affect the output voltages.
Only order the transformer that fits your application properly.
That's what I'm trying to do. The question is what this data means, if anything at all. If it does, folks should confirm on the datasheet before plunking down the $$ rather than assuming that the catalog description is indicative of the actual secondary voltage.
If these sheets imply loading to capacity, then normalizing to the same primary voltage, the 273CZ and 290CX, though described as the same 650VCT in the catalog, are actually going to be more than 50V different.
This is especially wild because going on the catalog description, Looking at the catalog specs, the 273CZ is described with a 117V primary and the 290CX as 120V. Based on that, I assumed the complete opposite--that with a given input voltage, a transformer rated at 117V/650VCT would give you a higher output voltage than a transformer described as 120V/650VCT.
Heck, if you look at the top line specs, one might think the 273CZ, at a rated 650VCT, would give you a higher voltage than the 274, which is called 640VCT. But on the data sheets, while the "650V" 273CZ says you get 686.V at 125v in, the "640V" 274 claims 693V!
The input rating on the data sheet confuses me even more by specifying a current. On the 273CZ, it lists that 125V at 159ma while the 274 shows 236ma. If that number was indicative of load, I'd think it'd make more sense if it was the other way around. I don't care about regulation for my Class A application--I just want to get the voltage in the ballpark.
Finally, if you look at different portions of the catalogs, you see very different things. I see a description now of the 290CX as 207ma on the secondary.
I suspect the answer is "you pays your money, you takes your chances." The catalog is a vague guess. While the 274 or 260J would be the easiest physical fit for me, unless folks know something about the "guitar" transformers I don't, I'm tempted to get the 290CX. It is more iron for less money, both in weight and voltage on the PDF. I don't lack for ways to get rid of some extra volts, but the converse isn't true.
Probably should have also just ordered the PT from Monolith when I ordered the OPTs.
Paul
If these sheets imply loading to capacity, then normalizing to the same primary voltage, the 273CZ and 290CX, though described as the same 650VCT in the catalog, are actually going to be more than 50V different.
This is especially wild because going on the catalog description, Looking at the catalog specs, the 273CZ is described with a 117V primary and the 290CX as 120V. Based on that, I assumed the complete opposite--that with a given input voltage, a transformer rated at 117V/650VCT would give you a higher output voltage than a transformer described as 120V/650VCT.
Heck, if you look at the top line specs, one might think the 273CZ, at a rated 650VCT, would give you a higher voltage than the 274, which is called 640VCT. But on the data sheets, while the "650V" 273CZ says you get 686.V at 125v in, the "640V" 274 claims 693V!
The input rating on the data sheet confuses me even more by specifying a current. On the 273CZ, it lists that 125V at 159ma while the 274 shows 236ma. If that number was indicative of load, I'd think it'd make more sense if it was the other way around. I don't care about regulation for my Class A application--I just want to get the voltage in the ballpark.
Finally, if you look at different portions of the catalogs, you see very different things. I see a description now of the 290CX as 207ma on the secondary.
I suspect the answer is "you pays your money, you takes your chances." The catalog is a vague guess. While the 274 or 260J would be the easiest physical fit for me, unless folks know something about the "guitar" transformers I don't, I'm tempted to get the 290CX. It is more iron for less money, both in weight and voltage on the PDF. I don't lack for ways to get rid of some extra volts, but the converse isn't true.
Probably should have also just ordered the PT from Monolith when I ordered the OPTs.
Paul
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You do need to normalize the secondary voltages to your typical AC line for comparing the models,
and to consider the transformer regulation due to loading. Most are rated for VA at their full loading.
Too high VA rating, compared to what you actually need, will cause the secondary voltages to rise,
same as the rectifier circuit type and load current can.
and to consider the transformer regulation due to loading. Most are rated for VA at their full loading.
Too high VA rating, compared to what you actually need, will cause the secondary voltages to rise,
same as the rectifier circuit type and load current can.
Transformer manufacturers rate secondary voltages at full rated current. So if you draw 3A from a 6.3VAC secondary, you will see 6.3VAC across that secondary provided that you have applied the rated primary voltage. Off-load, expect to see higher voltages. As a very rough rule of thumb, you can expect 10% regulation from a 100VA transformer, so that means secondary voltages will be 10% high off-load.
Hammond have for their PT technical sheets which include loaded voltages, no loaded voltages, winding resistances etc. Just acces the "download" not "product specification pages". To make a choice you need yo know what kind of rectification you use. Look at Hammond page " Design guide for rectifier use". Is not only the voltage matter. Look a AC secondaries current capability. For instance, for " bridge capacitor input" the ideal choice will be I.AC to be double than max I.DC you circuit demand. Anything less will be translate in more voltage sag and extra heat- still the PT may be pretty usable till the max dissipation limit with the price of poor regulation. For "full wave capacitor input load" I.AC = max I.DC. If you choose the PT correct in respect with type of rectification you use the regulation will be under 5 percent ( usually 3% around).
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A pure sine wave of 120VAC has 169.7V Peak.
At 3% Distortion of some Typical Power Mains 120VAC (120VAC True RMS), it will be truncated (slightly clipped). That may only be 164.6V Peak.
You will not get a consistent B+ voltage from a Typical 3% Distorted Power Mains; versus from a Pure Un-distorted Power Mains (good luck finding an Un-distorted Power Mains).
I use choke input filters for my B+. Then, if I need just a little bit more voltage, I put a 1uF, 2uF, 3uF, or 4uF capacitor in front of the choke.
Of course, you need more secondary voltage to drive a choke input filter. But the power transformer runs Cooler for the same load current, versus a capacitor input filter.
A 10uF to 60uF capacitor input filter really causes very large peak currents from the power transformer secondary and rectifier (especially important for tube rectifiers). It is all about I-squared heating.
Learn to do the best you can, and live with that.
Then you can sleep at night.
At 3% Distortion of some Typical Power Mains 120VAC (120VAC True RMS), it will be truncated (slightly clipped). That may only be 164.6V Peak.
You will not get a consistent B+ voltage from a Typical 3% Distorted Power Mains; versus from a Pure Un-distorted Power Mains (good luck finding an Un-distorted Power Mains).
I use choke input filters for my B+. Then, if I need just a little bit more voltage, I put a 1uF, 2uF, 3uF, or 4uF capacitor in front of the choke.
Of course, you need more secondary voltage to drive a choke input filter. But the power transformer runs Cooler for the same load current, versus a capacitor input filter.
A 10uF to 60uF capacitor input filter really causes very large peak currents from the power transformer secondary and rectifier (especially important for tube rectifiers). It is all about I-squared heating.
Learn to do the best you can, and live with that.
Then you can sleep at night.
Software Fans,
Does your power supply software allow you to enter your power mains distortion into the program,
Or do you have to measure the mains distortion, crest factor, peak voltage, or other means to enter the proper voltage?
(like entering 116.4Vrms into the software field, for a 120Vrms 3% distorted power mains).
Does your power supply software allow you to enter your power mains distortion into the program,
Or do you have to measure the mains distortion, crest factor, peak voltage, or other means to enter the proper voltage?
(like entering 116.4Vrms into the software field, for a 120Vrms 3% distorted power mains).
No, PSUD assumes sine wave input. I don't think that input waveform distortion will have much effect on loaded voltage - the distortion at the rectifier is much higher due to the pulsed current flow.
I have heard of others power mains with distortion exceeding 7%.
That does make a difference.
If you pick a power transformer that is twice the VA and Current Ratings that you need . . .
Then, typically the primary DCR and secondary DCR are lower; and the increased Laminations size reduces saturation with the lighter load;
. . . You will have more voltage out.
Skimping on a power transformer has its own rewards.
That does make a difference.
If you pick a power transformer that is twice the VA and Current Ratings that you need . . .
Then, typically the primary DCR and secondary DCR are lower; and the increased Laminations size reduces saturation with the lighter load;
. . . You will have more voltage out.
Skimping on a power transformer has its own rewards.
With these data sheets there is pretty much all that is needed to simulate the power supply and get very accurate predictions of output voltages.
They are actually very detailed and my simulations normally come with in 5% or less error.
They provide open circuit voltages that allows turns ratio to be calculated.
They provide DCR so winding resistance loss can be taken into account.
They even provide magnetizing current to allow the primary inductance to be estimated (saturation effects limit the accuracy)
Only thing missing is leakage inductance and I have found it low enough in Hammond units not to be a significant error at 60Hz.
However as 6A3sUMMER pointed out...
Your power company needs to provides clean power.
Many today do not as equipment to support the green grid (Dc to AC switching inverters) are not required to provide the sort of power line waveform purity old school rotating generators provided.
As well modern loads are now normally far from resistive.
Approaching a 10% DC voltage error with the correct RMS AC is very possible.
See thread "B+ dropped 15%"
So planning to allow a way to "tweek" you finial DC voltage is always nice.
I op for a selection of rectifier tubes with various voltage drops and several values of NTC resistor (startup current surge suppressors) to allow some adjustment of the finial B+.
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Hi pjanda1
If you want nearly 400v B+, and wish to use choke input with full-wave valve/tube rectification, you will need to select a mains transformer with higher VAC output than the ones noted in your first post. I mention this because many seem to favor this power supply topology for single-ended amplifiers.
If you decide upon a bridge instead of full-wave (and not use the center tap) beware that the secondary power rating of the transformer will need to be double what is quoted. The power ratings on the Hammond specs sheet assume full-wave rectification.
One thing about choke input supply is that you can get away with selecting a mains transformer where the secondary rating is only 110% of the required current. If you chose cap input supply then it will need to deliver at least 140% of the required current.
Like 6A3sUMMER noted, skimping on the power transformer is not so wise. If my SE 300b budget was constrained, then I would rather skimp on the OPT's and not skimp on the power supply. This would allow you to 'upgrade' the OPT's with relative ease when more budget is available.
Tip: You can extend the usable life of your 300b by building a power supply which has a soft start.
If you want nearly 400v B+, and wish to use choke input with full-wave valve/tube rectification, you will need to select a mains transformer with higher VAC output than the ones noted in your first post. I mention this because many seem to favor this power supply topology for single-ended amplifiers.
If you decide upon a bridge instead of full-wave (and not use the center tap) beware that the secondary power rating of the transformer will need to be double what is quoted. The power ratings on the Hammond specs sheet assume full-wave rectification.
One thing about choke input supply is that you can get away with selecting a mains transformer where the secondary rating is only 110% of the required current. If you chose cap input supply then it will need to deliver at least 140% of the required current.
Like 6A3sUMMER noted, skimping on the power transformer is not so wise. If my SE 300b budget was constrained, then I would rather skimp on the OPT's and not skimp on the power supply. This would allow you to 'upgrade' the OPT's with relative ease when more budget is available.
Tip: You can extend the usable life of your 300b by building a power supply which has a soft start.
...and be aware: small input capacitor trick was mentioned above on choke input filter works only for constant current loads anything else will make output voltage dependent by input ripple which is function of current load of course.
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catalin gramada,
True.
Using a 1 - 4uF capacitor in front of a choke input filter, does have a couple of tradeoffs:
1. Those capacitor transient peak currents "I-squared x time" will be there again, but at a lower level than a 10 - 60uF first cap.
2. If the load current varies, then the B+ voltage will vary more than for a true choke input filer circuit.
Single Ended Amplifiers:
Since they are Class A, and are most often listened to at less than clipping levels (the extremes of saturated current, and cutoff current), the Average load current is just that . . Average.
I solve the varying voltage versus load this way:
Filter: 1-4 uF, 5H choke, 500uF cap, series resistor from there to the next 500uF filter cap. (*)
The 500uF takes care of the Low Frequency transient currents (amplifier not operated with the output stage at cutoff, and not operated at max current that would saturate most output transformers).
I do not like the sound of SE amplifiers that either go into output tube cutoff, or clip at max current, or both; this is Hi Fi, not a Hard Rock guitar amplifier.
Class A push pull has fairly constant load current.
Similar B+ design as SE B+ design works.
Class AB push pull Has widely varying load current.
This requires the B+ to deal with that.
The simplest way is to make sure the amplifier input signal is low enough to keep the amplifier in Class A operation (easy to calculate what power level that is; or to measure the push cathode current, and the pull cathode current to see that they are not going into cutoff).
Then, use a power supply that will deal with the large current variations of Class AB (this is where some decide to use regulated supplies).
I seldom listen to 20 second sustained 30 foot organ pipe notes, so the dual 500uF brute force filtering above works for me. (*)
Your Mileage May Vary
All of this comes back to two things:
It is a System Design problem, not an isolated design problem.
Attention to Details
True.
Using a 1 - 4uF capacitor in front of a choke input filter, does have a couple of tradeoffs:
1. Those capacitor transient peak currents "I-squared x time" will be there again, but at a lower level than a 10 - 60uF first cap.
2. If the load current varies, then the B+ voltage will vary more than for a true choke input filer circuit.
Single Ended Amplifiers:
Since they are Class A, and are most often listened to at less than clipping levels (the extremes of saturated current, and cutoff current), the Average load current is just that . . Average.
I solve the varying voltage versus load this way:
Filter: 1-4 uF, 5H choke, 500uF cap, series resistor from there to the next 500uF filter cap. (*)
The 500uF takes care of the Low Frequency transient currents (amplifier not operated with the output stage at cutoff, and not operated at max current that would saturate most output transformers).
I do not like the sound of SE amplifiers that either go into output tube cutoff, or clip at max current, or both; this is Hi Fi, not a Hard Rock guitar amplifier.
Class A push pull has fairly constant load current.
Similar B+ design as SE B+ design works.
Class AB push pull Has widely varying load current.
This requires the B+ to deal with that.
The simplest way is to make sure the amplifier input signal is low enough to keep the amplifier in Class A operation (easy to calculate what power level that is; or to measure the push cathode current, and the pull cathode current to see that they are not going into cutoff).
Then, use a power supply that will deal with the large current variations of Class AB (this is where some decide to use regulated supplies).
I seldom listen to 20 second sustained 30 foot organ pipe notes, so the dual 500uF brute force filtering above works for me. (*)
Your Mileage May Vary
All of this comes back to two things:
It is a System Design problem, not an isolated design problem.
Attention to Details
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catalin gramada,
I added more information to my Post # 15 . . . my edits were . . . After you posted a "Like".
Re-read my post if you want to.
I added more information to my Post # 15 . . . my edits were . . . After you posted a "Like".
Re-read my post if you want to.
A lot of pre-production samples were given out to renowned manufacturers to get the critisim and input to fix it for the final (released) version. A lot of developers, technichians and storage inventory staff got access to the pre-production samples and nobody thought about them disapparing. Now these hidden stashes are weight in gold since they are the only available ICs nowadays but everyone disregards they do - for the most cases - not perform like the production examples. If they would have, they would have been sold off since they weren't distinguishable. So if you buy those pre-production samples, expect them to perform sub-par. A strong hint is the production date code but that might also be fake.
Both. And that's because lately there were a lot of prototype samples of IC and transformer prototypes being sold at eBay which did not fit the general specs from the manufacturer. But since the dramatical rise of the value of copper, you'd expect an exponentally rise of fakes like it did at many other items which were hyped into the sky.
First rules of purchasing something:
Caveat Emptor
Know the Vendor
Know the Product
Know the history of the product
Do not forget the bogus tubes that are marked with all the favorite tube type numbers.
Easy to sell, Easy to purchase, but hard to use the way you planned to.
"Cheap is not good, and good is not cheap" Frank Reps who built the Baby Ongaku 2A3 amplifier, designed by Gordon Rankin,
and published in "Sound Practices".
Free lunches went away right after the great depression's meal lines
Everything later has a cost (The gold there during the great depression, is now owned by other countries, not the US),
so taxes pay for everything that is "Free".
See how that works?
Caveat Emptor
Know the Vendor
Know the Product
Know the history of the product
Do not forget the bogus tubes that are marked with all the favorite tube type numbers.
Easy to sell, Easy to purchase, but hard to use the way you planned to.
"Cheap is not good, and good is not cheap" Frank Reps who built the Baby Ongaku 2A3 amplifier, designed by Gordon Rankin,
and published in "Sound Practices".
Free lunches went away right after the great depression's meal lines
Everything later has a cost (The gold there during the great depression, is now owned by other countries, not the US),
so taxes pay for everything that is "Free".
See how that works?