I have a pair of OP transformers, Hammond code 28185 – no, I don’t think they’ll be found an old catalogue because they are OEM, I pulled them out of an old church organ ~ 40 years ago, can’t remember the brand, possibly Gulbransen. Comparing physical measurements with those in an old Hammond cat. show the OPTs to be capable of 20 or 30W.
The amps used 6L6’s, measuring the trannie’s voltage ratio, I get 10:1, so a Z ratio of 100:1. The secondary has a C.T., so the only sensible way to use these with 6L6’s seems to be a 16 ohm speaker across one half of the secondary (to get a 400:1 Z ratio) for a primary a-a impedance of 6400 ohms (assuming my maths is correct).
However, I want to use these with 8 or 4 ohm drivers, and I’d like to not use 6L6’s either. Attracted by the elegance of the circuitry, I wanted to build an RLD, but these trannies don’t seem to be suitable. Perhaps I could use the same topology with a pair of EL34’s (3200:8) ? (This would probably suit the power transformer better too, it gives 350-0-350v, (the Hammond plate rates it at 125VA, 125V, 40Hz? What the?...)
The amps used 6L6’s, measuring the trannie’s voltage ratio, I get 10:1, so a Z ratio of 100:1. The secondary has a C.T., so the only sensible way to use these with 6L6’s seems to be a 16 ohm speaker across one half of the secondary (to get a 400:1 Z ratio) for a primary a-a impedance of 6400 ohms (assuming my maths is correct).
However, I want to use these with 8 or 4 ohm drivers, and I’d like to not use 6L6’s either. Attracted by the elegance of the circuitry, I wanted to build an RLD, but these trannies don’t seem to be suitable. Perhaps I could use the same topology with a pair of EL34’s (3200:8) ? (This would probably suit the power transformer better too, it gives 350-0-350v, (the Hammond plate rates it at 125VA, 125V, 40Hz? What the?...)
I never heard of an OPT with a centre-tapped secondary.
Why would you have 2 halves to a secondary and only use one? In an OEM transformer?
It just doesn't make sense.
Then there's RLD.
RLD Red Light District
RLD Rolled
RLD Rijksluchtvaartdienst
RLD Rashtriya Lok Dal (India, political party)
RLD Reference Listed Drug (drug used to compare effects and safety with trial drug FDA)
RLD Restrictive Lung Disease
RLD Ready-To-Load Date
RLD Relocation Dictionary
RLD Radar/Laser Detector
RLD Remote LAN Dial
RLD Remote Line Device
RLD Required Load Date
RLD Roni Lynn Deutch (Tax Debt Resolution Law Firm)
RLD Remote Location Device
?????????????????
Rotating Loudspeaker Doofer.
Is that what it was used for? 2 back-to-back speakers on a rotating thingie? For an organ. As in Hammond...
40Hz?
This post is like a cryptic crossword. Or a secret wartime code to the French underground.
w
In the beginners mind there are many possibilities. You're not Al Qaeda?
Why would you have 2 halves to a secondary and only use one? In an OEM transformer?
It just doesn't make sense.
Then there's RLD.
RLD Red Light District
RLD Rolled
RLD Rijksluchtvaartdienst
RLD Rashtriya Lok Dal (India, political party)
RLD Reference Listed Drug (drug used to compare effects and safety with trial drug FDA)
RLD Restrictive Lung Disease
RLD Ready-To-Load Date
RLD Relocation Dictionary
RLD Radar/Laser Detector
RLD Remote LAN Dial
RLD Remote Line Device
RLD Required Load Date
RLD Roni Lynn Deutch (Tax Debt Resolution Law Firm)
RLD Remote Location Device
?????????????????
Rotating Loudspeaker Doofer.
Is that what it was used for? 2 back-to-back speakers on a rotating thingie? For an organ. As in Hammond...
40Hz?
This post is like a cryptic crossword. Or a secret wartime code to the French underground.
w
In the beginners mind there are many possibilities. You're not Al Qaeda?
Most readers of this forum are quite familiar with the RLD since the thread is now nearly 700 posts long. It now has offspring, the WLD, the OLD, and the NLD.
It the organ was parted out 40 years ago, it must have been old enough then to destroy. A lot of old organs used multiple speakers. 16 and 32 ohms were fairly common. Assuming the tap is actually center (same voltage on both sides) I see two possibilities. It was somewhat common for one set of taps to drive an internal speaker and another set to drive the "extension speaker". It was also common for one amplifier to drive different sized speakers. I took apart some Hammond organ extension cabinets in the 60's that had 4 32 ohm speakers in each one.
This stuff must be really old. Today most power in North America is 60Hz while much of the world is 50Hz. Not too long ago there were isolated power companies scattered across the US that did whatever they wanted. Odd voltages and frequencies did occur. The 40Hz rating was the minimum and the transformer would work just fine on 60Hz. The military used (and still uses) 400Hz power in aircraft to cut down on transformer weight. Never plug a 400 Hz transformer into an ordinary wall outlet unless you like some really stinky smoke!
If the transformers are in good shape (doubtful) you can build a RLD using 6CW5 tubes. These want a 3200 ohm load but use a lower B+ voltage (about 250 volts). EL34's could be used, but I doubt that your power transformer could power two channels, and the 12AT7 may not drive them to full power.
New member here, and hopefully I can shed some light on your transformer question.
It is very possible your transformers came out of a Hammond Organ product as they manufactured many tone cabinets in the early days of electronic organs, and even wound their own transformers for a period of time as well.
Going down that road then, in the earliest Hammond models, the power amplifier proper (usually located in the tone cabinet) consisted of nothing more than a push-pull output stage, preceded by a push-pull driver stage. The amplifier was driven by a balanced to ground transformer originated signal from within the organ, so no electronic phase inverter in the power amplifier was necessary. As for the output transformer and it's center tapped secondary, it was very common for Hammond to apply push-pull feedback from the secondary of the output transformer to the cathodes of the output tubes (PPP in the largest designs), as that was the easiest and cheapest way to do it. Hence, the requirement of the secondary being center tapped. The speakers were always connected across the full secondary. This was often 16 ohms, but hardly always. Sometimes it was 32 ohms. When it was 16 ohms of course the CT would represent 4 ohms, and an 8 ohm CT if it was a 32 ohm secondary -- although the transformer was typically not wound for that purpose or service. If it were, the low ohm winding portion would have been wound with wire gauge that was more appropriate for the current flow that impedance required.
In those days, two 6L6s were often used in 20 watt tone cabinets, while four were used in the 40 watt models. Is it possible that your transformer came from a 40 watt unit? If so, it would have been appropriate for use with PPP 6L6s and a 32 ohm load, based on the turns ratio your unit offers.
In any event, the old organ transformers were hardly a high-fidelity grade product, often with a very limited frequency response and power bandwidth. That may or may not be a problem depending on your application. I hope this helps.
Dave
It is very possible your transformers came out of a Hammond Organ product as they manufactured many tone cabinets in the early days of electronic organs, and even wound their own transformers for a period of time as well.
Going down that road then, in the earliest Hammond models, the power amplifier proper (usually located in the tone cabinet) consisted of nothing more than a push-pull output stage, preceded by a push-pull driver stage. The amplifier was driven by a balanced to ground transformer originated signal from within the organ, so no electronic phase inverter in the power amplifier was necessary. As for the output transformer and it's center tapped secondary, it was very common for Hammond to apply push-pull feedback from the secondary of the output transformer to the cathodes of the output tubes (PPP in the largest designs), as that was the easiest and cheapest way to do it. Hence, the requirement of the secondary being center tapped. The speakers were always connected across the full secondary. This was often 16 ohms, but hardly always. Sometimes it was 32 ohms. When it was 16 ohms of course the CT would represent 4 ohms, and an 8 ohm CT if it was a 32 ohm secondary -- although the transformer was typically not wound for that purpose or service. If it were, the low ohm winding portion would have been wound with wire gauge that was more appropriate for the current flow that impedance required.
In those days, two 6L6s were often used in 20 watt tone cabinets, while four were used in the 40 watt models. Is it possible that your transformer came from a 40 watt unit? If so, it would have been appropriate for use with PPP 6L6s and a 32 ohm load, based on the turns ratio your unit offers.
In any event, the old organ transformers were hardly a high-fidelity grade product, often with a very limited frequency response and power bandwidth. That may or may not be a problem depending on your application. I hope this helps.
Dave
Yes they WERE "high-fidelity", very much so. but they did it different then we do today. Hammond would place multiple amplifiers in the tone cabinet. One would be for bass, another amp would handle treble and a third would be for the output from a spring reverb unit. Each amp would then drive it's own set of speakers.
Also, and this explains the center tap, the amps were "balanced". basically this meant the schematic looed like two single ended amps on of the speaker. No phase splitters as the source itself was balanced.
What you likely have is a "bass output transformer" that is good for up to (guessing) about 800Hz or 1KHz. The typical setup from Hammond would have also two treble amps in the same box each with it's own "treble output transformer".
Today we would call this a "bi-amp'd active PA speaker".
I think the only reason Hammond's system was not used with home HiFi was cost. Their bi-amp balanced system hade about four time more parts. Thse old tome cabinets sold for more money than a new car cost. I have some old adds that $1,800 prices. That was a lot of money in 1950. These were not built cheap
What you need to do is learn to play bass guitar. This would make a really great pratice amp for a bass. I've been wanting a low poer 6L6 tube bass amp for a long time. (BTW, bass guitars players call 200W "small" and 40W would be a living room sized practice amp. Most would haul a minimum of 400W to a gig.
I think you should be able to test your transformers using a large solid state amp connected to the secondaries. Play test tones into a 5K ohm dummy load Turn the amp's power up and see how much bandwidth you get at 40W
Chris -- We'll have to just disagree on the what the term "high-fidelity" means then. I realize that the use of multiple amplifiers and reproducers can make for wonderful sound, and while an organ amplification system of the type we are discussing here does have to reproduce copious amounts of low frequency energy, it has to produce little to nothing over say 8 kHz. True high fidelity in the hey day of vacuum tubes came to be defined as a single piece of amplification equipment that could produce full rated power output over a 20 Hz to 20 kHz bandwidth, at typically less than a percent or so of THD and IM distortion within 1 db of rated power. None of the Hammond tone cabinet amplifiers or their output transformers were capable of that kind of performance. No doubt that if the OP wanted to use the transformer for a precise bandwidth application, it would work fine -- which I as much noted at the end of my post.
Also,when I referred to the "earliest" models, I was referring to models much earlier than you describe. I have an example of one of Hammond's earliest amplifiers (model A-20), employing PPP 2A3s. From the period it was manufactured up until the later 40s, there were no such things as "bass" amplifiers, "treble" amplifiers, "reverb" amplifiers or the like. There was just a power amplifier in a tone cabinet, that during that period typically employed electromagnetic speakers. Type "G" amplifiers were the first to employ push-pull feedback from a center tapped secondary to the output tube cathodes, and employed PPP 6V6s. This was done to maintain a low output impedance since these were among the first amplifiers to employ pentode output tubes. The type HR tone cabinet was the first to include reverberation -- but again it was only one amplifier producing all the organ output.
Against the backdrop of not knowing the age of his transformer, or the intended purpose of his build, I was simply offering a caution to the OP that it's extremely doubtful his transformer would produce high fidelity results as it generally became known to mean....the same performance level as that of say an Acrosound or Dynaco transformer would produce. It is general application information that would be worth knowing about an otherwise unknown transformer in the course of a project under consideration.
Dave
Also,when I referred to the "earliest" models, I was referring to models much earlier than you describe. I have an example of one of Hammond's earliest amplifiers (model A-20), employing PPP 2A3s. From the period it was manufactured up until the later 40s, there were no such things as "bass" amplifiers, "treble" amplifiers, "reverb" amplifiers or the like. There was just a power amplifier in a tone cabinet, that during that period typically employed electromagnetic speakers. Type "G" amplifiers were the first to employ push-pull feedback from a center tapped secondary to the output tube cathodes, and employed PPP 6V6s. This was done to maintain a low output impedance since these were among the first amplifiers to employ pentode output tubes. The type HR tone cabinet was the first to include reverberation -- but again it was only one amplifier producing all the organ output.
Against the backdrop of not knowing the age of his transformer, or the intended purpose of his build, I was simply offering a caution to the OP that it's extremely doubtful his transformer would produce high fidelity results as it generally became known to mean....the same performance level as that of say an Acrosound or Dynaco transformer would produce. It is general application information that would be worth knowing about an otherwise unknown transformer in the course of a project under consideration.
Dave
Tubelab, re:' you can build a RLD using 6CW5 (=EL86) tubes. These want a 3200 ohm load but use a lower B+ voltage (about 250 volts). EL34's could be used, but I doubt that your power transformer could power two channels, and the 12AT7 may not drive them to full power" - thanks, that's the sort of info I was looking for, I'll search for EL86 schematics. I'm not looking for heaps of watts, 15-20 would be ok, so perhaps EL34s would do.
Power Trannies - actually, there are two, the one mentioned above was in the extension cab, another rated at 180va with massive wire to power all the 12ax7 heaters was in the organ itself. (& both actually have dual primaries wired in series for NZ 230v)
DCG & Chris - I definitely wasn't a Hammond organ, and there were on 2x 12" drivers and amps with one 6L6 pair each, one in the organ and in and extension cab - no fancy Rotating Loudspeaker Doofers (although that doesn't mean that the parts weren't the same as used in a fancier version of the organ). There is also what appears to be a very low impedance winding on the OPTs (for feedback?), or perhaps a screen. I'm going to take the covers off and investigate further this weekend.
Perhaps it's possible to split the secondary & parallel the windings, or is this not a good idea?
Thanks for the responses.
(P.S. my bass playing days are long over, I'l be happy never to see another road case again....)
Power Trannies - actually, there are two, the one mentioned above was in the extension cab, another rated at 180va with massive wire to power all the 12ax7 heaters was in the organ itself. (& both actually have dual primaries wired in series for NZ 230v)
DCG & Chris - I definitely wasn't a Hammond organ, and there were on 2x 12" drivers and amps with one 6L6 pair each, one in the organ and in and extension cab - no fancy Rotating Loudspeaker Doofers (although that doesn't mean that the parts weren't the same as used in a fancier version of the organ). There is also what appears to be a very low impedance winding on the OPTs (for feedback?), or perhaps a screen. I'm going to take the covers off and investigate further this weekend.
Perhaps it's possible to split the secondary & parallel the windings, or is this not a good idea?
Thanks for the responses.
(P.S. my bass playing days are long over, I'l be happy never to see another road case again....)
That was one reason I sugested the OP learn to play bass guitar. He likely has some premium bass OPTs. The low E on a four string bass is 41Hz. and there is not much about 4KHz
The thing about musical instrument amps is that they do not "reproduce" music, they "produce" music so by definition they are perfect.
I think the tube amps could easy go up to 20KHz but the "high frequency" speakers were 10" paper cones that I doubt had any response above 8K.
The amps however look real good and typcally use tons of NFB from a special winding on the OPT. I have to admit to dismantalling Hammond equipment because it was broken, I like to buy them for scrape prices just for the parts.
It would be fun to measure the THD of a 60 year old Organ amp but like I said above by definition the amp is dead-on perfect because a Hammond B3 sounds EXACTLY like a Hammond B3.
Hi Chris -- I agree completely with your last post, and the fact that production equipment and reproduction equipment have two entirely different goals. It also sounds like you and I dearly love the sound of a B3 -- it defines so much of what the old rock n' roll was and became. From a practical standpoint, the closest I can get to one in my humble abode is an early production M3 and a 147 Leslie. It's not a B, but lord, it'll do! But to keep this thread on some sort of track, my 147's amp does have a measured frequency response to about 25 kHz (within +/- 1 db) at 1 watt, but only has an effective power response to about 12 kHz. As you say though, who cares? It IS the sound of a B3! And, borrowing from it's Hammond heritage, it also uses push-pull feedback from a center tapped OT secondary back to the output tube cathodes. Thankfully, some things never change!
Dave
Dave
the plot sickens... I pulled the covers off, tinned the leads, & measured BOTH transformers again... what i thought was the secondary is probably the feedback winding - it can't be split into two halves, & anyway one of the halves on one transformer is open circuit. (these windings have a resistance of ~ 11 ohms/side, the primary is 285 ohms)
However, the good news -- what I thought was a screen winding is probably REALLY the secondary - it has a resistance of ~.5 ohm, comparable to another transformer I had nearby, & puts out .546 Volts for 15.7 into the primary - this works out to 6600 ohms primary for 8 ohms on the secondary - looks like I'm in business
So. two questions - is the .5 ohm resistance a good indication that that winding is the secondary?
and is 6600 ohms close enough for a Red Light District (EL84/6bq5) or should I go with 6L6's? (I have a few old 6aq5, 6M5 & 6bq5 at hand)
However, the good news -- what I thought was a screen winding is probably REALLY the secondary - it has a resistance of ~.5 ohm, comparable to another transformer I had nearby, & puts out .546 Volts for 15.7 into the primary - this works out to 6600 ohms primary for 8 ohms on the secondary - looks like I'm in business
So. two questions - is the .5 ohm resistance a good indication that that winding is the secondary?
and is 6600 ohms close enough for a Red Light District (EL84/6bq5) or should I go with 6L6's? (I have a few old 6aq5, 6M5 & 6bq5 at hand)
.5 ohms is OK, lower is better. Resistances that low are hard to measure with a typical meter since the lead/probe resistance is often .1 to.5 ohms, and the contact resistance is substantial and not repeatable.
I have a bunch of 6600 ohm transformers, so I use them on most of my P-P builds including several 6BQ5/EL84 amps. They work fine. If you wand to build a RLD you should stick with a tube that doesn't need much bias voltage, or run at a high current. Otherwise you are going to need a lot of LED's. Read the research on NLD's and OLD's at the end of the thread. These circuits are adaptable to any tube and should offer better performance than LED's. I will resume my experiments when I get back home (about 10 days).
Eli, the 7591s look great, but unfortunately a bit expensive & hard to find here ;
Tubelab, yeah, i really need a good low ohms meter. I think I'll breadboard an amp using my old 6BQ5's, but I'll need to do some freq response testing of the OPTs first, they're not interleaved, so may be only good for guitar. In which case I may go for something along the lines of a low watt version of a Fender bassman. (I have a few dozen Philips 12ax7s from that same organ...)
I'll read the NLD & OLD posts more closely too...
Thanks for your help
Tubelab, yeah, i really need a good low ohms meter. I think I'll breadboard an amp using my old 6BQ5's, but I'll need to do some freq response testing of the OPTs first, they're not interleaved, so may be only good for guitar. In which case I may go for something along the lines of a low watt version of a Fender bassman. (I have a few dozen Philips 12ax7s from that same organ...)
I'll read the NLD & OLD posts more closely too...
Thanks for your help
Don't rule them out without testing. The 6600 ohm OPT's that I have were designed for guitar amps and specced for "80VA" from 80 Hz to 4KHz. There is zero interleaving and the cores look like power transformer iron. They however do 20 Hz to 60 KHz in a Simple P-P (EL84) amp at 15WPC. They sound good with everything from 6L6's to 300B's.
Pete,
The price tag on NOS 7591s is INSANE. OTOH, current production EH 7591s don't cause much in the way of "sticker shock" and they work very well. Jim McShane charges 79.50 USD for a quad. IMO, Jim's culling and matching are as good as it gets and he ships world wide. Perhaps a reliable EH dealer can be found closer to home.
The price tag on NOS 7591s is INSANE. OTOH, current production EH 7591s don't cause much in the way of "sticker shock" and they work very well. Jim McShane charges 79.50 USD for a quad. IMO, Jim's culling and matching are as good as it gets and he ships world wide. Perhaps a reliable EH dealer can be found closer to home.
I'd like to add in here, that excepting the tone cabs I have quite a pile of Hammond Organ PTs. (Also an M3 and a 147) For some reason organ power transformers are quite soft. The AO-29 PT for instance is about the same size as a Showman Pt but will barely drive a pair of 6BQ5 with a choke input filter. Given the conversation so far I'm thinking that the original tubes were plane jane metal 6L6 or maybe 6L6G. They were definitely NOT 6L6GC. Having said all that 6600 I think is too low for EL-84 personally. I would probably cathode bias AB1 with a pair of Valve Art KT-66 with lots of capacitance or even a choke entry filter. AES has some decent chokes for higher currents that will work spiffy here. But don't expect more than about 18 watts out the pipe unless you find another PT.
re:'Don't rule them out without testing' - good news, I won't
re:'a reliable EH dealer can be found closer to home' - ~$AUD50 each here
re:'maybe 6L6G' - definitely, unfortunately they got lost sometime in the last few decades
re:'Hammond Organ PTs' - just to clarify, these aren't Hammond ORGAN transformers, they're Hammond Guelph Ontario trannies - from some other brand organ.
I'll have a look at the KT66 data too...
re:'a reliable EH dealer can be found closer to home' - ~$AUD50 each here
re:'maybe 6L6G' - definitely, unfortunately they got lost sometime in the last few decades
re:'Hammond Organ PTs' - just to clarify, these aren't Hammond ORGAN transformers, they're Hammond Guelph Ontario trannies - from some other brand organ.
I'll have a look at the KT66 data too...
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