It's for an ultralinear 813/FU-13 SE with 850 Vdc plate and 100 ma primary current. The test OPT is an original series and flawed 5K:8 Hammond 1628SE using the 4 ohm tap to reflect a higher plate load. Does anyone have a recommendation for a proper high impedance SE OPT with UL taps that can take power? Softone's 9K OPT is close but doesn't have the current rating. Hammond has a 6.5K opt that just squeaks in but the tube really shines with 10k, breaking 35 watts into 8 ohms with very low 1 watt distortion. Worst case a newer 1628SEA run be off the 4 ohm tap but the preference is for a proper 8 ohm OPT ratio. Thoughts? Preferably something that doesn't cost like a used car.
Thanks.
Thanks.
Definitely not an off the shelf item! Most common brands use 600 volt wire for their windings which is why you have to talk to them about what you need. Now that Transcendar and Electa-print are gone you have less choices in the custom transformer area. Hammond might do it but I’ve never been thrilled by their stuff. I’ve had great luck with Hayboer and they are relatively quick. Edcore might do it but they take a long time to deliver. Don’t skimp on these outputs for many reasons like sound quality and safety at high voltages. You also have to find 1000 volt wire, I use silver plated with a Teflon jacket. Check with ApexJr to see what he has and you can get it by the foot! Are you going to series two caps for your power supply? It’s the most economical way to get the high voltages you need. Lots to consider doing this build!
The wire enamel breakdown voltage should not be the leading criteria. Primary to secondary dielectric layer is. Any seriously made OPT should have interlayer insulation. The most critical layers are the nearest to the anode, where a high voltage swing occurs, this is where the dielectric gets more stressed from AC. It is wise keeping the anode layer far away from secondary layers. Getting closer to the B+ output, AC swing becomes less and we're heading towards DC.
Last edited:
Thanks. Considered that but this amp is capable of ~150% of that model's power rating.
On the list, thanks. Coming from Hammond experience this is interesting. B+ is 900 volts.
Saw your note about caps. Digikey carries suitable polypropylene caps at very reasonable prices. 100uF 1100 Vdc Epcos for $20 CDN. Currently I'm using a pile of 660 VAC, 30 uF poly motor run caps salvaged from a ferroresonant UPS that held up an entire radio station the entire 90's. Well broken in.
Also added to the list, thanks! A 1638SEA with UL tap and a bit higher current capability would be spot on.
Thanks everyone.
That’s a great deal in those Epcos caps! It solves a lot of issues by being 1100v. I’m sure you know this but make sure your life insurance is paid up! Anything over 600 volts can stop your heart without even being a high current shock! I’d use a string of bleeder resistors to drain the caps at power off.
10K OPT with UL tap, rated 35W @30Hz with 100 mA DC, good bandwidth and proper insulation for 1KV+ anode voltage is really an uncommon bunch of specs. Normally 10K OPTs for the 211 are gapped for lower current and don't need to be 35W.
The 25W Edcor is ok if the 25W power rating is at 30Hz. That would mean 35W at 36Hz. Not a big a deal. Considering the cost, I would ask them before doing anything else.
The 25W Edcor is ok if the 25W power rating is at 30Hz. That would mean 35W at 36Hz. Not a big a deal. Considering the cost, I would ask them before doing anything else.
Nice stuff but also no clear UL tap? $1300 CDN a pair for the LL1691B excluding shipping and import duties. $2K wouldn't surprise all in.
Maybe Toroidy has or can make OPT that would fit your design?
https://sklep.toroidy.pl/en_US/p/-TTG-GM70SE-Tube-output-transformer-7kOhm-GM70-SE/613
https://sklep.toroidy.pl/en_US/p/-TTG-GM70SE-Tube-output-transformer-7kOhm-GM70-SE/613