Need help,I want to replace ECG7581a with the original EL37's

[sean sweeney]

I would say that helps plenty! Thanks!

Voicing is highly dependent on the characteristics of the output transformers used. You will likely need to adjust the feedback amount as well as the feedback capacitor. You will also likely need a step filter (sometimes called a shelf filter). Step filters perform the same function as a Zobel (limits HF extension as to avoid instability) but it's done on the small signal amplification stage rather than on the high current output of the transformer secondary, so smaller wattage parts can be used.

I have never used the 1650HA, so I can't really comment on them. I have used the 1650H in several builds, and it's very good to excellent in the LF region (below 100 Hz) and produces a fine sounding amplifier. But the 1650H is only "so-so" in the HF region (above 10KHz). Some focused tuning is needed to limit HF extension to not create an oscillator in to arbitrary speaker loads when global feedback is applied. This is the one big weakness of the 1650H and by extrapolation to all of Hammond's line of 16xx push-pull line of transformers that do not have the "A" suffix. Specifically, I've used the 1608, the 1650H, and the 1650R, and they all exhibit this same issue in the HF region.

I assume the same desirable LF characteristics exist for the 1650HA as the 1650H. But I really don't have experience with these so I can't comment further. Here's what I can say: I have no desire to use the 1650H (or any other Hammond non A suffixed transformers) in any new builds I might do. I would be willing to try the the "A" suffixed transformers if I were in the mode of building another amp and I didn't have any other better options. My hunch is the 1650HA is a better overall performer than the 1650H, but that's only a hunch.

Hope that helps.

 

[sean sweeney]

There's a guy on reverb that has i believe, 4 ADC 315G OT's. I know ADC has a very good rep for studio monitor amps. I also think the OT's in question are 30w, and very adaptable. They supposedly work well with 6L6, and i believe i read the primary resistance was 5k, vs the 6k that the crown has. If you know of those, or if you can find specs, i apologize, I wasn't able to find anything that helped me figure this out, but i think i can get 2 for 400, new 60s vintage in the boxes.

Voicing is highly dependent on the characteristics of the output transformers used. You will likely need to adjust the feedback amount as well as the feedback capacitor. You will also likely need a step filter (sometimes called a shelf filter). Step filters perform the same function as a Zobel (limits HF extension as to avoid instability) but it's done on the small signal amplification stage rather than on the high current output of the transformer secondary, so smaller wattage parts can be used.

I have never used the 1650HA, so I can't really comment on them. I have used the 1650H in several builds, and it's very good to excellent in the LF region (below 100 Hz) and produces a fine sounding amplifier. But the 1650H is only "so-so" in the HF region (above 10KHz). Some focused tuning is needed to limit HF extension to not create an oscillator in to arbitrary speaker loads when global feedback is applied. This is the one big weakness of the 1650H and by extrapolation to all of Hammond's line of 16xx push-pull line of transformers that do not have the "A" suffix. Specifically, I've used the 1608, the 1650H, and the 1650R, and they all exhibit this same issue in the HF region.

I assume the same desirable LF characteristics exist for the 1650HA as the 1650H. But I really don't have experience with these so I can't comment further. Here's what I can say: I have no desire to use the 1650H (or any other Hammond non A suffixed transformers) in any new builds I might do. I would be willing to try the the "A" suffixed transformers if I were in the mode of building another amp and I didn't have any other better options. My hunch is the 1650HA is a better overall performer than the 1650H, but that's only a hunch.

Hope that helps.

 

[kward]

I found a pair of ADC 315G's for sale on eBay. Here is a snapshot of what box says for specs:




For decent HiFi transformers, I would be expecting something like 30 Hz to 30 KHz frequency response. You might be able to increase that with some global feedback, but how much feedback you can add before the amp goes unstable is the question.

Also the 315Gs say 2500 ohms impedance. Maybe there's a way to get 5000 ohms out of it. I think you could make 5000 ohms primary work with 6L6s. On the other hand 2500 ohms is too low for 6L6s. I'm not familiar with these transformers so I can't say much more.

Here's a snippet from the 6L6GC data sheet from GE that shows possible operating points and their associated primary impedance recommendations:


Of course, those are just three of the many possible options. And note these assume pentode mode (screen connected to a fixed voltage source), not distributed loading where the screen voltage fluctuates as a percentage of the plate voltage, as is shown in your schematic diagram in post #13. If you're looking for "more or less" a direct replacement for the transformers shown in your schematic diagram, you will want to find some output transformers with screen taps and in the vicinity of 5K to 6K primary impedance. The Hammond 1650HAs fit that bill if you don't mind re-tuning the amp for those specific transformers. Most other old stock transformers you'll find will very likely require you to re-wire the output stage for pentode mode since they likely will not have screen taps, and that will of course necessitate retuning the amp for those transformers as well.

 

[kward]

One more thing, if you are using or want to use EL37s in the output stage of your amp, the EL37 data sheet says you'll want to use output transformers with primary impedance of around 3500 ohms. In other words, in my mind, the EL37 curves resemble more the EL34 curves than they do 6L6 curves. But in the sense of max current they seem to be more in line with the 6L6-GC.

So, one thing that may work in your case (if you want to use EL37s) is to use the 1650HA, but run in half impedance mode. I.e., run 8 ohm speakers on the 16 ohm tap. That will get you effectively 3300 primary impedance and could work out nicely. There's a lot of "could's" in there. It's an interesting idea anyway.

Not trying to muddy the waters here, just pointing out some things for you to study and/or be aware of.

 

[sean sweeney]

I found a pair of ADC 315G's for sale on eBay. Here is a snapshot of what box says for specs:

View attachment 3721069


For decent HiFi transformers, I would be expecting something like 30 Hz to 30 KHz frequency response. You might be able to increase that with some global feedback, but how much feedback you can add before the amp goes unstable is the question.

Also the 315Gs say 2500 ohms impedance. Maybe there's a way to get 5000 ohms out of it. I think you could make 5000 ohms primary work with 6L6s. On the other hand 2500 ohms is too low for 6L6s. I'm not familiar with these transformers so I can't say much more.

Here's a snippet from the 6L6GC data sheet from GE that shows possible operating points and their associated primary impedance recommendations:
View attachment 3721087

Of course, those are just three of the many possible options. And note these assume pentode mode (screen connected to a fixed voltage source), not distributed loading where the screen voltage fluctuates as a percentage of the plate voltage, as is shown in your schematic diagram in post #13. If you're looking for "more or less" a direct replacement for the transformers shown in your schematic diagram, you will want to find some output transformers with screen taps and in the vicinity of 5K to 6K primary impedance. The Hammond 1650HAs fit that bill if you don't mind re-tuning the amp for those specific transformers. Most other old stock transformers you'll find will very likely require you to re-wire the output stage for pentode mode since they likely will not have screen taps, and that will of course necessitate retuning the amp for those transformers as well.

Thank you for that! I actually have already contacted the seller. I'm thinking of getting all four of them from him, and using them to replace all the outputs in the crown amps... that way they'll all have the same audio signature and I'll be able to have a very nice monitor system. Any idea what a good offer would be for all of them? Just wondering, as it's a very unique offering, but I would imagine the overall traffic they get will be low... as people would have to he both hip, and then also having a system that needs these... or building one. what do you think?

 

[sean sweeney]

One more thing, if you are using or want to use EL37s in the output stage of your amp, the EL37 data sheet says you'll want to use output transformers with primary impedance of around 3500 ohms. In other words, in my mind, the EL37 curves resemble more the EL34 curves than they do 6L6 curves. But in the sense of max current they seem to be more in line with the 6L6-GC.

So, one thing that may work in your case (if you want to use EL37s) is to use the 1650HA, but run in half impedance mode. I.e., run 8 ohm speakers on the 16 ohm tap. That will get you effectively 3300 primary impedance and could work out nicely. There's a lot of "could's" in there. It's an interesting idea anyway.

Not trying to muddy the waters here, just pointing out some things for you to study and/or be aware of.

well, I'm using TWO of these amps... and summing the outputs... so I'm wondering what that would mean in this case? Also, there are two ADC output tyranny's on Reverb, and Ebay, as another member just wrote me about them on here! lol. I'm wondering if these would be as cool as I think and what would be the best way to do this, if any different than what you've stated. I ran both amps in summed mode, using 6L6GC quartets, as I have so many of the Sovtek ones lying around from various projects, most of which are new... and the sound was pretty amazing on both, once I dialed in the bias... which was a bit wonky, leading me to believe these crown output tranny's are a bit biffed... people have said on here that they either work, or don't... but considering the intense age, that they were sitting in a very hot rack, and used for many tens of thousands of hours, I do believe the sound of these transformers, even the primary ohmage, has been greatly affected, or they just sounded kind of MEH to start with. two of those NOS ADC transformers may be just the ticket. I have the quartet of NOS EL37's... and since they'll likely not be doing me any good, I'll maybe sell them for the money to get those ADC's... lol

 

[sean sweeney]

I found a pair of ADC 315G's for sale on eBay. Here is a snapshot of what box says for specs:

View attachment 3721069


For decent HiFi transformers, I would be expecting something like 30 Hz to 30 KHz frequency response. You might be able to increase that with some global feedback, but how much feedback you can add before the amp goes unstable is the question.

Also the 315Gs say 2500 ohms impedance. Maybe there's a way to get 5000 ohms out of it. I think you could make 5000 ohms primary work with 6L6s. On the other hand 2500 ohms is too low for 6L6s. I'm not familiar with these transformers so I can't say much more.

Here's a snippet from the 6L6GC data sheet from GE that shows possible operating points and their associated primary impedance recommendations:
View attachment 3721087

Of course, those are just three of the many possible options. And note these assume pentode mode (screen connected to a fixed voltage source), not distributed loading where the screen voltage fluctuates as a percentage of the plate voltage, as is shown in your schematic diagram in post #13. If you're looking for "more or less" a direct replacement for the transformers shown in your schematic diagram, you will want to find some output transformers with screen taps and in the vicinity of 5K to 6K primary impedance. The Hammond 1650HAs fit that bill if you don't mind re-tuning the amp for those specific transformers. Most other old stock transformers you'll find will very likely require you to re-wire the output stage for pentode mode since they likely will not have screen taps, and that will of course necessitate retuning the amp for those transformers as well.

I meant that I had actually contacted the gent before I saw this. lol. Don't know if that was clear. I saw the same ad on Reverb. But thanks for looking out!

 

[sean sweeney]

I found a pair of ADC 315G's for sale on eBay. Here is a snapshot of what box says for specs:

View attachment 3721069


For decent HiFi transformers, I would be expecting something like 30 Hz to 30 KHz frequency response. You might be able to increase that with some global feedback, but how much feedback you can add before the amp goes unstable is the question.

Also the 315Gs say 2500 ohms impedance. Maybe there's a way to get 5000 ohms out of it. I think you could make 5000 ohms primary work with 6L6s. On the other hand 2500 ohms is too low for 6L6s. I'm not familiar with these transformers so I can't say much more.

Here's a snippet from the 6L6GC data sheet from GE that shows possible operating points and their associated primary impedance recommendations:
View attachment 3721087

Of course, those are just three of the many possible options. And note these assume pentode mode (screen connected to a fixed voltage source), not distributed loading where the screen voltage fluctuates as a percentage of the plate voltage, as is shown in your schematic diagram in post #13. If you're looking for "more or less" a direct replacement for the transformers shown in your schematic diagram, you will want to find some output transformers with screen taps and in the vicinity of 5K to 6K primary impedance. The Hammond 1650HAs fit that bill if you don't mind re-tuning the amp for those specific transformers. Most other old stock transformers you'll find will very likely require you to re-wire the output stage for pentode mode since they likely will not have screen taps, and that will of course necessitate retuning the amp for those transformers as well.

I would think these ADC transformers are from the 60s... and they should be ultralinear shouldn't they? I would think so as they were designed for hifi, and the Crown amp that I have from 1956 has ultralinear screen taps... but do you think these don't? Just curious.... as I would have thought they did... it mentions screen voltage on the spec sheet, so doesn't that mean screen taps? Or were you thinking the crown was too early for the screen taps?

 

[sean sweeney]

One more thing, if you are using or want to use EL37s in the output stage of your amp, the EL37 data sheet says you'll want to use output transformers with primary impedance of around 3500 ohms. In other words, in my mind, the EL37 curves resemble more the EL34 curves than they do 6L6 curves. But in the sense of max current they seem to be more in line with the 6L6-GC.

So, one thing that may work in your case (if you want to use EL37s) is to use the 1650HA, but run in half impedance mode. I.e., run 8 ohm speakers on the 16 ohm tap. That will get you effectively 3300 primary impedance and could work out nicely. There's a lot of "could's" in there. It's an interesting idea anyway.

Not trying to muddy the waters here, just pointing out some things for you to study and/or be aware of.

ok, I think I misread your comment. These amps are definitely wired UL, so we know that, you were saying that most old tranny's wouldn't be, but that the ADC's most definitely ARE... which is a good thing. OK... I have to get these tubes listed so I get get those tranny's... lol and then sell a hammond C3.... lol. thanks and let me know what you think. I think all four is the way to go, of course.

 

[gadget73]

monitoring what? If you want decently flat response, this really doesn't seem like the right iron for the job since it has limited response. Also do you need the 70 odd watts you might get with these in mono mode? I'd be real tempted to leave the amp with the good transformers alone and use it as it was meant to be used. Put something else on the other amp and make it work if needed.

age of the iron is entirely unrelated to whether or not it will have screen taps.

 

[sean sweeney]

monitoring what? If you want decently flat response, this really doesn't seem like the right iron for the job since it has limited response. Also do you need the 70 odd watts you might get with these in mono mode? I'd be real tempted to leave the amp with the good transformers alone and use it as it was meant to be used. Put something else on the other amp and make it work if needed.

age of the iron is entirely unrelated to whether or not it will have screen taps.

It's for primarily a pair of 604-8G Altec Duplex speakers in Altec 614 cabs, so yes, I will likely need the 70 or so watts at times. I will have two discreet systems for louder stuff. So you're saying the ADC OT's are not likely to be decently flat? I thought that was their claim to fame? That they were used for many studio installations back in the day. If you can tell different from the specs, I'm curious to what you see that confirms this. Not that I doubt you, I'm just getting into the transformer tech of these and want to be a little more fluent. thanks!

 

[sean sweeney]

I found the data sheet on the auction for the transformers in question, though. Here is the data sheet, or the only one I could get. I could ask for more, though.

 

[gadget73]

I have no idea what their supposed claim to fame is, but if they only rate flat within 1.5 dB from 50 to 10k, its not really full range. Fair bet the stock Crown specs are better. Feedback can help that but if the transformer is too limited there is only so much that can be done. Zero experience with these.

And an altec 604 is around 100 db efficiency. Thats single digit power territory. That should be uncomfortably loud at 30 watts, another 3db is just overkill

 

[sean sweeney]

Well, a lot of that gets eaten up with bass program, honestly, and sometimes when recording, the speakers will double as a PA cab, and if you're tracking bass live, without headphones, you need more than 30 watts. So it will definitely be necessary. I know my rigs. When mixing drums and bass, there should be no natural compression happening, either, because that won't give you an accurate mix. That's why i opted for the stanley screamers, and put the most compliant kits in them. I'll need every watt. And the amp with the replaced transformer was very much different in this way, using the 6L6 tubes, as I'll likely be using. I just don't think they were prioritizing bass with these amps. The crown decks weren't really so much for recording music, in this era. The pro decks were likely for making basic commercial recordings for AM radio. This is from the advice of a former Crown employee i spoke with. So it's not like i'm comitting heresy. These amps have unrealized potential.

I have no idea what their supposed claim to fame is, but if they only rate flat within 1.5 dB from 50 to 10k, its not really full range. Fair bet the stock Crown specs are better. Feedback can help that but if the transformer is too limited there is only so much that can be done. Zero experience with these.

And an altec 604 is around 100 db efficiency. Thats single digit power territory. That should be uncomfortably loud at 30 watts, another 3db is just overkill

 

[sean sweeney]

Sorry to bombard you with questions, but this transformer is made in California, and available for about $100 a piece by pacific transformer. They seem very sincere, hand wound, and lots of atention to original details.

One more thing, if you are using or want to use EL37s in the output stage of your amp, the EL37 data sheet says you'll want to use output transformers with primary impedance of around 3500 ohms. In other words, in my mind, the EL37 curves resemble more the EL34 curves than they do 6L6 curves. But in the sense of max current they seem to be more in line with the 6L6-GC.

So, one thing that may work in your case (if you want to use EL37s) is to use the 1650HA, but run in half impedance mode. I.e., run 8 ohm speakers on the 16 ohm tap. That will get you effectively 3300 primary impedance and could work out nicely. There's a lot of "could's" in there. It's an interesting idea anyway.

Not trying to muddy the waters here, just pointing out some things for you to study and/or be aware of.

 

[kward]

I initially got excited when I saw this was an A470 clone…but it is not a clone. It’s apparently only matching the dimensions of an A470. Dead give away is the primary impedance of 5.5k.

Ask them if they wound it following the exact A470 interleave structure. If yes then it might be a decent transformer just with higher impedance than the original A470. If it’s their own winding method then it still might be okay. The all important specs are how the transformer behaves at the low end and high end of the audio spectrum. You want to be able to apply a decent amount of feedback without the amp going unstable, and in my experience that seems to be difficult to do for most modern transformer winders unless they have specialized skills and/or are copying a vintage winding design. I’m remembering a recent post where a winder out of India I think copied the Dynaco Z565 winding method and did a right decent job of it, but it took a lot of dedicated effort.

I can’t say if this one is better or worse than the Hammond 1650HA, which seems to be a close competitor.

 

[gadget73]

musicalpowersupplies may be another option. I have a set he made for my 6L6 amp that I'm pleased with.

 

[sean sweeney]

What do you think of the Thermionic Labs OT for the ST70? Then I could simply turn these into actual monoblocks with a bit of modifying. I have a bunch of old hammond amps with lots of big old chokes in them as well... I'm wondering if those will help the overall stability, since these amps have no chokes. I appreciate all the input. I wish I had time to read and read on these things, but I have to make this studio work and make music foremost, but I love to put a good rig together, and I know what I like. Also, if anyone has an interest in a quartet of EL37's, I'm putting mine up on Reverb. I got them from a fellow that helped design the current magnepan woofers and other things for them. we horse traded for a lot of stuff and I built him a custom guitar/organ Leslie, but if anyone wants what appear to be NOS tubes for a trade that would get me to where I'm trying to go, that's the only reason I'm bringing them up here. I don't know what the policy is for even mentioning things like this, but I am just tossing it out there.

 

[kward]

To post selling anything, you do that in the bartertown forum. You have access to it since you are a subscriber. Read the bartertown rules to guide you on how to formulate a post.

Any of these transformer choices are going to get you in the ballpark and you will very likely be able to make any of them work with not too much feedback and some HF and LF tuning.

If you are wanting to add a “decent amount” of feedback, say over 10 to 12 dB, I doubt you will be able to just slap in any random new production transformer with the correct primary impedance and just have it work well. If that’s a requirement (higher levels of feedback) then you will want to restrict your choices to known transformers that handle high levels of feedback. There are several old stock transformers that I feel comfortable recommending that would meet this requirement: Fisher 500C, 200KX. Heathkit AA-100, W5. Dynakit A431, A470, Z565. Harmon Kardon A500. Eico ST70, HF60.

Those are the ones I’m familiar with that I can recommend that I know can handle larger amounts of feedback.

If you can restrict the amount of feedback to 12 db or less, then the Hammond line or equivalent as discussed directly above would very likely also work.

 

[sean sweeney]

Thank you for your knowledge. With this latest one, though, I'm looking at a 70w transformer, one per amp, and just wondered if that would be better than having the two per amp, and would it be simpler, as i would need just one NFB, and what would i change in the current topography, otherwise? I'm quite sure the way these are laid out, that they would easily deliver 70wpc in mono. I'll head down to barter town! Thanks!

To post selling anything, you do that in the bartertown forum. You have access to it since you are a subscriber. Read the bartertown rules to guide you on how to formulate a post.

Any of these transformer choices are going to get you in the ballpark and you will very likely be able to make any of them work with not too much feedback and some HF and LF tuning.

If you are wanting to add a “decent amount” of feedback, say over 10 to 12 dB, I doubt you will be able to just slap in any random new production transformer with the correct primary impedance and just have it work well. If that’s a requirement (higher levels of feedback) then you will want to restrict your choices to known transformers that handle high levels of feedback. There are several old stock transformers that I feel comfortable recommending that would meet this requirement: Fisher 500C, 200KX. Heathkit AA-100, W5. Dynakit A431, A470, Z565. Harmon Kardon A500. Eico ST70, HF60.

Those are the ones I’m familiar with that I can recommend that I know can handle larger amounts of feedback.

If you can restrict the amount of feedback to 12 db or less, then the Hammond line or equivalent as discussed directly above would very likely also work.