Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Woodrow F Call on December 27, 2024, 09:24:11 am
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Hey, I have some old transformers sitting around and want to build something with them. Both are Hammonds...
270EX
Power Rating (VA) 118
Primary VAC 115
Primary Frequency 60
A.C. High Voltage Secondary RMS 550V C.T. @ 144ma.
Filament # 1 VAC 5V @ 3A
Filament # 2 VAC 6.3V @ 4A
125E
15 Audio Watts
I was wanting to build a 5E3, but the voltages on the PT seem lower than most replacement transformers. I've also seen where people said they would work fine. I'd like some ideas of what I can do with these transformers since they are sitting around here. I'd also like to understand why these would work for a 5E3 or why not before I build.
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For 5E3 Deluxe one one would want a 290BX Pt and 1750H Ot So that 270EX is 110vdc low not bad really. 125E would work I guess but a pair of 6V6 in push pull can easily put out 18-20 watts, so the 125E is a little under spec.
The 270EX has a 115VAC input winding so if your wall voltage is like mine, up to 124-5VAC, the secondary would be higher and into the 300vdc + range.
Does the 270EX mount in a 5E3 chassis?
Someone else that is more familiar with 5E3s will certainly chime in.
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For 5E3 Deluxe one one would want a 290BX Pt and 1750H Ot So that 270EX is 110vdc low not bad really. 125E would work I guess but a pair of 6V6 in push pull can easily put out 18-20 watts, so the 125E is a little under spec.
Someone else that is more familiar with 5E3s will certainly chime in.
I came to the same conclusion on the 270EX, but saw where some said it would be a good choice. I didn't understand why. For the 125E, it's supposed to be good for 15 watts, where that's what a 5E3 is rated for, not sure if more room is needed.
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5E3 is rated at 20W ( and I corrected this below, its 15W my bad) IMO that 125E would probably start distorting earlier than a 20W Ot.
6V6 tubes work well at lower plate v's, they are pretty versatile that way and sound good. Thats why some say they would be fine and as I stated above you could use the 115v winding and you can probably use a 5AR4 instead of the 5Y3.
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Well I'm going to say that that 125E would also work just fine. I found this at AES and is rated at 15W so I would say you are good to go for building a 5E3 with that iron. The Hammond recommended OT for a Deluxe/Deluxe Reverb is what I was going by in saying 20W but I see the 5E3 is rated at 15W out sorry for the confusion.
https://www.tubesandmore.com/products/transformer-output-15w-8k-ct-primary-fender-deluxe-5e3 (https://www.tubesandmore.com/products/transformer-output-15w-8k-ct-primary-fender-deluxe-5e3)
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I have not used these transformers, but it looks like they could work for 2 x el84, plus either ez81 or 5y3 and 3 or so 12ax7.
Supposedly, an ez81 can ran off 6.3v along with the other tubes.
Ez81 1A
2 x el84 1.5A
12ax7 300ma per tube.
PP el84 should work well with 300dc plate voltage.
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I have not used these transformers, but it looks like they could work for 2 x el84, plus either ez81 or 5y3 and 3 or so 12ax7.
Supposedly, an ez81 can ran off 6.3v along with the other tubes.
Ez81 1A
2 x el84 1.5A
12ax7 300ma per tube.
PP el84 should work well with 300dc plate voltage.
Originally, that's what I was doing with them.... 18 watt clone. Maybe I should go back with that.
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To me, that transformer set would be perfect. I have never played an original 5E3. The clone I made was too loud and clean in my setting :dontknow:
I am much happier with B+ of 350 volts or less. My favorite cathode biased 6V6GT push-pull amp has B+ of 301 volts!
So it comes down to what you want your new build to be like. How much clean power is needed to get you to the sweet spot?
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To me, that transformer set would be perfect. I have never played an original 5E3. The clone I made was too loud and clean in my setting :dontknow:
I am much happier with B+ of 350 volts or less. My favorite cathode biased 6V6GT push-pull amp has B+ of 301 volts!
So it comes down to what you want your new build to be like. How much clean power is needed to get you to the sweet spot?
How would I guesstimate the B+?
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On a previous build, I used a Weber W025130 power transformer. 540 volt CT @ 150 ma. Pretty close match to yours. I used the 125 Volt primary taps to get the heaters at 6.3 Volts.
It ran two 6V6GT push-pull cathode biased power tubes. Three 12AX7 preamp tubes. I tried several rectifier tubes to get the B+ right for me:
5AR4 357 volts
5V4 346 Volts
5R4GYB 326 Volts
5Y3GT 308 Volts (Tungsol nos)
If you want to try math, some use the Duncan Power Supply Calculator. I have never used it but it might be helpful.
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On a previous build, I used a Weber W025130 power transformer. 540 volt CT @ 150 ma. Pretty close match to yours. I used the 125 Volt primary taps to get the heaters at 6.3 Volts.
It ran two 6V6GT push-pull cathode biased power tubes. Three 12AX7 preamp tubes. I tried several rectifier tubes to get the B+ right for me:
5AR4 357 volts
5V4 346 Volts
5R4GYB 326 Volts
5Y3GT 308 Volts (Tungsol nos)
If you want to try math, some use the Duncan Power Supply Calculator. I have never used it but it might be helpful.
Awesome! Thanks for the information. I guess I'll go back to figuring out a 5E3 build.