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Wanted: Lundahl OPT Pair http://www.dcaudiodiy.com/phpBB3/viewtopic.php?f=7&t=2075 |
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Author: | FerdinandII [ September 29th, 2021, 12:54 am ] |
Post subject: | Wanted: Lundahl OPT Pair |
Hi all, I'm looking for a pair of Lundahl output transformers and wondered if anyone in the group is willing to part with a set that are surplus to requirements. I'm building a tube power amp and I need a split primary, which almost all Lundahls have. I'm open to a variety of power and impedance combinations for this project, so I'm kinda fishing with a magnet at this point.... Thanks, Bruce |
Author: | Grover Gardner [ September 29th, 2021, 10:47 pm ] |
Post subject: | Re: Wanted: Lundahl OPT Pair |
FerdinandII wrote: Hi all, I'm looking for a pair of Lundahl output transformers and wondered if anyone in the group is willing to part with a set that are surplus to requirements. I'm building a tube power amp and I need a split primary, which almost all Lundahls have. I'm open to a variety of power and impedance combinations for this project, so I'm kinda fishing with a magnet at this point.... Thanks, Bruce What are you looking to build? I have quite a few OPTs with split primaries. What plate impedance are you looking for? |
Author: | FerdinandII [ September 30th, 2021, 2:20 am ] |
Post subject: | Re: Wanted: Lundahl OPT Pair |
I'm planning to use triodes in push-pull, so anything 5k Plate-to-Plate and above would work. 4 and 8 ohm taps on the secondary would be ideal. |
Author: | Grover Gardner [ September 30th, 2021, 7:01 am ] |
Post subject: | Re: Wanted: Lundahl OPT Pair |
FerdinandII wrote: I'm planning to use triodes in push-pull, so anything 5k Plate-to-Plate and above would work. 4 and 8 ohm taps on the secondary would be ideal. Do you plan to use true triodes or triode-strapped pentodes/beam power tubes? Feedback or no feedback? Is there a schematic you have in mind, or are you going to try something from scratch? I ask because I have a number of options here I won't get around to using, but it depends on what you plan to build. I've got a pair of Eico HF-22/35 OPTs, 7500 ohms p-p with 43% UL taps, with 4, 8 and 16 ohm outputs. They can do 25 watts. They'd probably afford the best bandwidth for a no-feedback amp. They're big, they're potted, they need repainting and the leads will need to be extended, but they're in good condition (or were the last time I checked). I've got a pair of Heathkit W4 OPTs, 10K p-p with 4, 8 and 16 ohms taps, good for 20 watts. These are small and potted, very nice little trannies, but I've never measured them without feedback. They'd probably do okay without it. I have an accompanying schematic for a swell 10wpc triode-strapped EL34 amp that is very zippy. You can see the project here: https://audiokarma.org/forums/index.php ... ld.795322/ And then I've got a pair of Sophia Electric OPTs from a Sophia stereo p-p EL34 amp that someone trashed with extensive (and unreversible) modifications. I rebuilt it as a PP stereo 300B amp but it wasn't impressive enough to dwell on, and I'm not interested in buying 300Bs anymore. If they're what I think they are, they're 5.5K p-p with 4 and 8 ohm taps, and Sophia still sells them for $700/pair. No split primary, and plate taps only. They're potted. These might actually be the best thing for your project if you plan to use true triodes and no feedback. I could throw them on my "hacker" amps and see what the bandwidth looks like with no feedback. You're welcome to these, I have no use for them, they're just sitting here. |
Author: | Grover Gardner [ September 30th, 2021, 10:39 am ] |
Post subject: | Re: Wanted: Lundahl OPT Pair |
Oh, and I also have a pair of James OPTs, 5K p-p with 16, 8 and 4 ohm outputs. Those aren't bad. |
Author: | FerdinandII [ September 30th, 2021, 5:05 pm ] |
Post subject: | Re: Wanted: Lundahl OPT Pair |
Hi Grover, I'm going to try adapting this output stage from a preamp. As you can see, the two separate windings in the primary provide a good place to insert the DC blocking capacitor. I suppose the cap could be inserted at either end of the primary winding, but I like the symmetry of the arrangement with the cap in series at the 'inner junction' of the two windings. Maybe I should try that arrangement with some of the OPTs I already have, before I add any more OPTs to my stockpile. Attachment: Did I use the right term when I said I was looking for a "Split Primary"? Some of the ones you mentioned don't look like they have two separate primary windings. |
Author: | Grover Gardner [ September 30th, 2021, 5:22 pm ] |
Post subject: | Re: Wanted: Lundahl OPT Pair |
Oh, I see. No, I knew what you meant. The Eico HF-22 OPTs and the Heathkit W4's have separate primaries, as do the Acro TO-300's I have. If you decide you want to try any of them I'm happy to send them out. It's only $20-40 shipping via priority mail. |
Author: | FerdinandII [ September 30th, 2021, 5:50 pm ] |
Post subject: | Re: Wanted: Lundahl OPT Pair |
Thanks Grover..... The Heathkit W4's would be a great starting point, I think. What are your preferred payment options to cover the shipping costs? Shipping address is: Bruce Normann 1126 Park St. NE Washington DC 20002 |
Author: | Grover Gardner [ September 30th, 2021, 9:09 pm ] |
Post subject: | Re: Wanted: Lundahl OPT Pair |
Oh, great! I'll pack them up Saturday and send them off. You can send me $20 via PayPal. grovergardner at charter dot net. |
Author: | FerdinandII [ September 30th, 2021, 9:45 pm ] |
Post subject: | Re: Wanted: Lundahl OPT Pair |
Done... I included a small tip. |
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