The last couple of days I've been contemplating output transformer size. In the old days of tube gear, it was generally accepted that bigger is better. I've read a lot of opinions recently and would like to hear from the tube gurus here on this, and any personal experience.
The problem with output transformers is that for good bass in an amp with lots of power, you need a lot of iron in it. For good treble, you need very little iron and very careful winding. In a low power amp, a smaller tranny can be used because it won't be saturated as easy because of not being enough power to do it. So, high power trannys have a real balancing act to do seeing as good bass and good treble have conflicting requirements. Having it high powered makes things even worse.
I had, in the past, always went with the bigger is better crowd because I couldn't get good bass with a small tranny. Now enter my Bell amp. I've had this for about 15 years. When I played it for a while after I first aquired it, I was unimpressed, as the bass was just mud. The mids and treble were to die for, but I couldn't get decent bass at all. I replaced the tranny's with some bigger ones I had and got great bass, but the mids and highs lost some of that magic sparkle. I put it back stock and forgot about it.
Enter the present. Now that my main fullrange speakers have a fs of around 100 Hz with nothing to speak of below 80 Hz, I decided to try this amp again. The mid and treble magic is still there! It's even better then my Heath SA-2 with the more expensive Stancor trannies in it. The Bell has very small trannies about 2/3 the size of the Heath's Stancors. And, with my subs hooked up to a ss amp tied off the Bells output, the bass is still tight and clean.
Harvey Rosenberg once wrote that for delicate sounding mids and highs, the less iron the better, that low powered amps were superior. I didn't agree with him then, but I'm starting to see what he meant.
I wonder if this could be why so many people are finding push pull amps to not have enough transparency. Maybe it has to do with, at least in part, the fact that most PP amps are trying to get that deep bass punch and are using massive tranny's to get it. Most companies even brag about how massive there tranny's are. Could it be that PP could be much better then we thought if they were made low power with small output trannies?
Any thoughts on this, or theories?
Long winded Dave
The problem with output transformers is that for good bass in an amp with lots of power, you need a lot of iron in it. For good treble, you need very little iron and very careful winding. In a low power amp, a smaller tranny can be used because it won't be saturated as easy because of not being enough power to do it. So, high power trannys have a real balancing act to do seeing as good bass and good treble have conflicting requirements. Having it high powered makes things even worse.
I had, in the past, always went with the bigger is better crowd because I couldn't get good bass with a small tranny. Now enter my Bell amp. I've had this for about 15 years. When I played it for a while after I first aquired it, I was unimpressed, as the bass was just mud. The mids and treble were to die for, but I couldn't get decent bass at all. I replaced the tranny's with some bigger ones I had and got great bass, but the mids and highs lost some of that magic sparkle. I put it back stock and forgot about it.
Enter the present. Now that my main fullrange speakers have a fs of around 100 Hz with nothing to speak of below 80 Hz, I decided to try this amp again. The mid and treble magic is still there! It's even better then my Heath SA-2 with the more expensive Stancor trannies in it. The Bell has very small trannies about 2/3 the size of the Heath's Stancors. And, with my subs hooked up to a ss amp tied off the Bells output, the bass is still tight and clean.
Harvey Rosenberg once wrote that for delicate sounding mids and highs, the less iron the better, that low powered amps were superior. I didn't agree with him then, but I'm starting to see what he meant.
I wonder if this could be why so many people are finding push pull amps to not have enough transparency. Maybe it has to do with, at least in part, the fact that most PP amps are trying to get that deep bass punch and are using massive tranny's to get it. Most companies even brag about how massive there tranny's are. Could it be that PP could be much better then we thought if they were made low power with small output trannies?
Any thoughts on this, or theories?
Long winded Dave
The high frequency response is primarily determined by the primary leakage inductance. While a higher-wattage transformer may generally tend to have more leakage than a lower-wattage one, this is just a rule of thumb. Core topology, size and composition; winding technique; etc will greatly affect leakage inductance.
I'm not an output tranny expert but I'd guess this is at best a rule of thumb. There will be many exceptions.
I'm not an output tranny expert but I'd guess this is at best a rule of thumb. There will be many exceptions.
Is there such a thing as an output tranny that does it all well, or do we just choose the best compromises, or just what we can afford?
The amp I'm using seems to be very well thought out and well built. I'm contemplating whether or not upgrading the trannies would make a worthwile difference. The trannies are smallish, no brand name, no outer covers. Mids and highs are wonderful. Is trying to get taunt bass without affecting the mids and highs asking to much, or can it be done at reasonable cost?
My previous amp, A modified 1959 Heath SA-2 EL84 PP amp w/Stancor OT's seemed to have it all, but this amp I'm using now, a 1961 Bell 2420, has noticably better imaging and (sparkle?) in the mids and highs. More "magic" then I've heard yet. When used with a speaker with low bass, it is "mushy". Both sound much better in the mids and highs then my previous 1962 Fisher 500C.
Any advise is greatly appreciated.
Picture of amp on my site.
http://www.geocities.com/the_hurdy_gurdyman/
Dave🙂
The amp I'm using seems to be very well thought out and well built. I'm contemplating whether or not upgrading the trannies would make a worthwile difference. The trannies are smallish, no brand name, no outer covers. Mids and highs are wonderful. Is trying to get taunt bass without affecting the mids and highs asking to much, or can it be done at reasonable cost?
My previous amp, A modified 1959 Heath SA-2 EL84 PP amp w/Stancor OT's seemed to have it all, but this amp I'm using now, a 1961 Bell 2420, has noticably better imaging and (sparkle?) in the mids and highs. More "magic" then I've heard yet. When used with a speaker with low bass, it is "mushy". Both sound much better in the mids and highs then my previous 1962 Fisher 500C.
Any advise is greatly appreciated.
Picture of amp on my site.
http://www.geocities.com/the_hurdy_gurdyman/
Dave🙂
I would suspect some of the more expensive transformers are able to "have it all" due to more attention spent on R&D and more money spent on materials. I think we need a transformer expert who has listened to the high-end models to answer.
It's far too great a simplification to say things like "bigger transformer=better bass and poor midrange", etc. It's just one part of the system. The Rp of the output tube, for example, will have a dramatic effect on bass response.
I just got done building a parafeed 6080 amp, using a tiny Hammond 125BSE output transformer. The bass is "slammin", as they say.
The same thing goes for assuming that a large-cored transformer - or one with a high DC saturation limit - will have high interwinding capacitance, and therefore poor high freq response in the audio range. A 1628SE is flat beyond 20k, and it is 5"x5" and weighs 11lbs!
Choose the right transformer for the right tube and the system will have predictable results at both ends of the spectrum.
I just got done building a parafeed 6080 amp, using a tiny Hammond 125BSE output transformer. The bass is "slammin", as they say.
The same thing goes for assuming that a large-cored transformer - or one with a high DC saturation limit - will have high interwinding capacitance, and therefore poor high freq response in the audio range. A 1628SE is flat beyond 20k, and it is 5"x5" and weighs 11lbs!
Choose the right transformer for the right tube and the system will have predictable results at both ends of the spectrum.
Could you recommend a decent transformrer for a PP 6V6 amp that is not real expensive?
Also, would a transformer being used with EL84 tubes be suitable for 6V6 use? I could try my Stancors, but don't want to waste time rigging up a way to mount them if they won't work right anyway. Thanks.
Dave🙂
Also, would a transformer being used with EL84 tubes be suitable for 6V6 use? I could try my Stancors, but don't want to waste time rigging up a way to mount them if they won't work right anyway. Thanks.
Dave🙂
hurdy_gurdyman said:
Try the Hammond 1609. It's about $30, and sounds great to my ears. It has ultralinear taps as well, which is how I would prefer to run them.
Thanks! Where is a good place to shop for these. Never bought any OT's by themselves before.
Dave🙂
Dave🙂
Ok, lemme see if I can get this right...
It's false logic to think that all those parameters are determined strictly by the size of the transformer.
The primary parameters controlling LF response are saturation and inductance. Generally, more turns = more inductance, but more turns means more amp-turns, so the core will saturate at a lower current. You also have to deal with the larger mass of wire. HF is determined by contruction; if the primary and secondary are well interleaved, with low-capacitance insulation between sections, you can easily get well over 100kHz.
Note that all these parameters add up: you need a larger core to handle more flux, more turns of heavier wire and to accomadate the 'wasted space' of insulation between windings.
Tim
It's false logic to think that all those parameters are determined strictly by the size of the transformer.
The primary parameters controlling LF response are saturation and inductance. Generally, more turns = more inductance, but more turns means more amp-turns, so the core will saturate at a lower current. You also have to deal with the larger mass of wire. HF is determined by contruction; if the primary and secondary are well interleaved, with low-capacitance insulation between sections, you can easily get well over 100kHz.
Note that all these parameters add up: you need a larger core to handle more flux, more turns of heavier wire and to accomadate the 'wasted space' of insulation between windings.
Tim
Hurdy-Gurdyman,
You mention that you have Stancor, can you tell us the spec, or where was it pulled(if it was actually pulled)? The reason I asked is that I built a PP EL84 while back with a Stancor Transformer from an old Heath Amplifier, dont remember the number on the tranny, but there was a number stamp on it. The amp that I built sounded really good, I was totally suprised by its performance. If what you have is the same as mine, TRY THEM, they are good.
Alex Deveza
You mention that you have Stancor, can you tell us the spec, or where was it pulled(if it was actually pulled)? The reason I asked is that I built a PP EL84 while back with a Stancor Transformer from an old Heath Amplifier, dont remember the number on the tranny, but there was a number stamp on it. The amp that I built sounded really good, I was totally suprised by its performance. If what you have is the same as mine, TRY THEM, they are good.
Alex Deveza
EL84 is very similar to 6V6, a 6V6 is a bit more grunty though. (12W vs 14W) You should be able to use your Stancors.
FALSE LOGIC INDEED.
Hi,
Agreed.
And second Joel's point too.
However there are limits:
Don't expect thunderous bass from a mini-jupe.
Don't expect extended highs from a huge xformer either.
Have I seen rather small OPTs with good bandwidth?
Yes, sir.
But than they sported unobtainium core materials or winding techniques that cost a fortune too.
So, when asked to generalise, yes, most of the time size does matter.
Cheers,😉
Hi,
Agreed.
And second Joel's point too.
However there are limits:
Don't expect thunderous bass from a mini-jupe.
Don't expect extended highs from a huge xformer either.
Have I seen rather small OPTs with good bandwidth?
Yes, sir.
But than they sported unobtainium core materials or winding techniques that cost a fortune too.
So, when asked to generalise, yes, most of the time size does matter.
Cheers,😉
>You mention that you have Stancor, can you tell us the spec, or where was it pulled(if it was actually pulled)?<
Hi Alex,
The Stancors are the factory tranny's in a SA-2 that I have. The numbers are 51-29. In the Heath, they sound great! Unfortunately, the Heath needs a complete rebuild, as it's full of tarnished solder joints and weak caps. It hums, the two channels change levels unevenly when adjusting the volume, just to name a few problems. The Bell I have is in excellent condition. I've even converted the power supply to a CLC type. Nice. The only problem with using the Stancors is jury rigging a way to mount them. I wasn't sure if they'd work with 6V6's, so didn't want to put forth the effort. Sounds like it may be worth it, though. The Bell is all triode vs the Heath having tiode-pentode drivers. The Bell may be the better amp.
Dave🙂
Hi Alex,
The Stancors are the factory tranny's in a SA-2 that I have. The numbers are 51-29. In the Heath, they sound great! Unfortunately, the Heath needs a complete rebuild, as it's full of tarnished solder joints and weak caps. It hums, the two channels change levels unevenly when adjusting the volume, just to name a few problems. The Bell I have is in excellent condition. I've even converted the power supply to a CLC type. Nice. The only problem with using the Stancors is jury rigging a way to mount them. I wasn't sure if they'd work with 6V6's, so didn't want to put forth the effort. Sounds like it may be worth it, though. The Bell is all triode vs the Heath having tiode-pentode drivers. The Bell may be the better amp.
Dave🙂
Hurdy_Gurdyman,
Thats it, 51-29, that the same on I have in my amp, well, my suggestion is if your heath is kaput, maybe just salvage the transformers and just get yourself an aluminum chassis and rebuilt it from scratch. There are a lot of circuit using EL84 on the Net, or you can use the same circuit as the heath. I have a 12AU7 and a 12AX7 in a concertina configuration and it work great.
Good Luck...
Alex Deveza
Thats it, 51-29, that the same on I have in my amp, well, my suggestion is if your heath is kaput, maybe just salvage the transformers and just get yourself an aluminum chassis and rebuilt it from scratch. There are a lot of circuit using EL84 on the Net, or you can use the same circuit as the heath. I have a 12AU7 and a 12AX7 in a concertina configuration and it work great.
Good Luck...
Alex Deveza
My old Bell uses all 12AX7 tubes and is a real funky looking piece of early sixties gear. It is also one of the infamous Joe Rosen's chosen few that he likes, if that is worth anything.😉
I think I'll try it in this amp to see what it happens. It sounds very good with the small no-name trannies that are in it now. A pic of the Bell is on my site. Click on the Hi-Fi link.
http://www.geocities.com/the_hurdy_gurdyman/
Dave🙂
I think I'll try it in this amp to see what it happens. It sounds very good with the small no-name trannies that are in it now. A pic of the Bell is on my site. Click on the Hi-Fi link.
http://www.geocities.com/the_hurdy_gurdyman/
Dave🙂
I installed the Stancors last night in my Bell amp. It seems to be working fine. It's now ultra-linear. Haven't had time to do a lot of critical listening yet, but first impressions are favorable. Nothing in the mids and highs sound worse, so that's a good sign.
Dave
Dave
Hello
I have an old Heathkit EL84 output transformer (I don't know the model, just that it's a mono amplifier AA). On it, I can see 51-29 and 549-6352. I think it is a Stancor 51-29
But I have a doubt about wiring.
I have a green/yellow , green , blue/yellow , blue and a yellow wires on primary.
If I look old heathkit schematics I can find on the web,
- blue/yellow and blue are plate 1 and plate 2,
- green/yellow and green are UL tap 1 and UL tap 2
But normally B+ is red, and on my transformer it is Yellow ???
Does somebody could confirm that it's possible ?
Between yellow (B+?) and blue/yellow (plate1?) = 146 ohms
Between yellow (B+?) and blue (plate2?) = 143 ohms
Between yellow (B+?) and green/yellow(UL1?) = 67 ohms
Between yellow (B+?) and green (UL2?) = 55 ohms
Between green/yellow(UL1?) and blue/yellow (plate1?) = 80 ohms
Between green(UL2?) and blue(plate2?) = 87 ohms
Could you help to confirm that :
- blue/yellow and blue are plate 1 and plate 2,
- green/yellow and green are UL tap 1 and UL tap 2
- Yellow is B+
Thank you very very much in advance
Cordially
Pascal
I have an old Heathkit EL84 output transformer (I don't know the model, just that it's a mono amplifier AA). On it, I can see 51-29 and 549-6352. I think it is a Stancor 51-29
But I have a doubt about wiring.
I have a green/yellow , green , blue/yellow , blue and a yellow wires on primary.
If I look old heathkit schematics I can find on the web,
- blue/yellow and blue are plate 1 and plate 2,
- green/yellow and green are UL tap 1 and UL tap 2
But normally B+ is red, and on my transformer it is Yellow ???
Does somebody could confirm that it's possible ?
Between yellow (B+?) and blue/yellow (plate1?) = 146 ohms
Between yellow (B+?) and blue (plate2?) = 143 ohms
Between yellow (B+?) and green/yellow(UL1?) = 67 ohms
Between yellow (B+?) and green (UL2?) = 55 ohms
Between green/yellow(UL1?) and blue/yellow (plate1?) = 80 ohms
Between green(UL2?) and blue(plate2?) = 87 ohms
Could you help to confirm that :
- blue/yellow and blue are plate 1 and plate 2,
- green/yellow and green are UL tap 1 and UL tap 2
- Yellow is B+
Thank you very very much in advance
Cordially
Pascal
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