I have some questions regarding output transformers:
I have been studying the Edcor push-pull audio output transformers with some interest due to their screen taps at 40%. I recently did a build using the Amp Supply 8025-H output transformer using a pair of 5881's which worked out very well. I was contemplating trying the Edcor CXPP50-5K and was curious if the 40% screen taps were desirable with the pair of 5881's? I have seen very few guitar amplifier ouput transformers with these screen taps, is there a benefit to be gained? If so, would I use screen dropping resistors as normal or would the screen drops use/values be affected by the taps? I have studied the ultra-linear in Hi-Fi that uses this technique but usually there are no dropping resistors. The Edcor is interleave wound and strikes me as a quality item. Being that it has only an 8 ohm secondary with no other taps, will taking my negative feedback for "presence" circuit off of the same tap as speaker be of any concern?
Thanks all!
P-P OT with Screen Taps
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Stevem
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Re: P-P OT with Screen Taps
A 5881 is not recommended for usage with a Ul output, at least if your looking to get more then 16 watts out of a pair, in general the screen voltage needs to 80 to 100 volts lees then what the plate is powered up with.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
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Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: P-P OT with Screen Taps
I did not know that. Tung Sol doesn't seem to agree with you.
I get 33.6W at 450V just by eyeballing the Tung Sol graph on the screen. Giuseppe gets 39.65W.
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Re: P-P OT with Screen Taps
I think any of the 6L6 types should be fine in UL. I can’t see why that shouldn’t be the case. But also, why 5881 in preference to 6L6GC? All 6L6 have the same nominal characteristics, so may as well use the variant with the best chance of having the longest life.
Screen grid resistors perhaps don’t tend to be used as much in hifi because heavy overdrive isn’t expected. Whereas with guitar amps, it is.
But even with hifi, I think g1 and g2 should have grid stoppers, even if low value.
As per the DrZ Route 66, I think a UL guitar amp may be best without a global NFB loop.
Screen grid resistors perhaps don’t tend to be used as much in hifi because heavy overdrive isn’t expected. Whereas with guitar amps, it is.
But even with hifi, I think g1 and g2 should have grid stoppers, even if low value.
As per the DrZ Route 66, I think a UL guitar amp may be best without a global NFB loop.
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FUCHSAUDIO
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Re: P-P OT with Screen Taps
You can use UL. I think Dumble did some power amps with Dyna iron and used the taps. You can also make them switchable from UL to screen supply or triode.
A couple of big toggles and off you go. You can safely add a screen resistor on each tube if you like. It'll make life easier on the tubes, especially modern ones.
A couple of big toggles and off you go. You can safely add a screen resistor on each tube if you like. It'll make life easier on the tubes, especially modern ones.
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Re: P-P OT with Screen Taps
Since the early ages of distributed load, 5881 family of tubes has been introduced in the suggested list of tubes that can benefit from UL as a pentode-like power with triode-like linearity, in the range of 40%. UL curves have been published too since early times and can be found in datasheets as well.
With 460V B+ 40%UL and 6k6 Raa, you can reach 40Wrms "clean" in AB1, just a bit more if you push it in AB2.
With 460V B+ 40%UL and 6k6 Raa, you can reach 40Wrms "clean" in AB1, just a bit more if you push it in AB2.
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Stevem
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Re: P-P OT with Screen Taps
I was just reporting back on then info listed by Duncan amps for that tube since I was commenting from work and was not home to dig in my RCA or GE book.
His site has listings in tube info if they can be used in UL and this time that info was not there so I ran with it.
His site has listings in tube info if they can be used in UL and this time that info was not there so I ran with it.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: P-P OT with Screen Taps
Thank you all for the nice replies and info-
I have been researching UL more and have found a number of guitar amp designs using it. Some are using grid stoppers. Of interest to me was some discussion of OT screen tap "percentages" of which the 40% region appears most often used. Some users of UL say the 20% region taps are best for guitar. I noticed Edcor offers some OT's with screen taps at 22% and some at 40%. Very interesting to me and I enjoy studying and learning more.
I am using the 5881 because I have some of the NOS TungSol 6l6WGB/5881 military surplus stock produced in 1956. I built an amp using a pair of these 5881's into a Heyboer APD-8025H OT with a clone of the Fender HRD ML212 preamp (3 triode stages) with bright/boost circuitry removed. Used the old Fender tube reverb circuit instead of solid state as in ML212. The amp was built for my son in law Chris Cameron who gigs in the Arkansas area, whom wanted a very clean amp to serve as a pedal platform. I am preparing for a couple more builds and want to try out some different ideas.
I have been researching UL more and have found a number of guitar amp designs using it. Some are using grid stoppers. Of interest to me was some discussion of OT screen tap "percentages" of which the 40% region appears most often used. Some users of UL say the 20% region taps are best for guitar. I noticed Edcor offers some OT's with screen taps at 22% and some at 40%. Very interesting to me and I enjoy studying and learning more.
I am using the 5881 because I have some of the NOS TungSol 6l6WGB/5881 military surplus stock produced in 1956. I built an amp using a pair of these 5881's into a Heyboer APD-8025H OT with a clone of the Fender HRD ML212 preamp (3 triode stages) with bright/boost circuitry removed. Used the old Fender tube reverb circuit instead of solid state as in ML212. The amp was built for my son in law Chris Cameron who gigs in the Arkansas area, whom wanted a very clean amp to serve as a pedal platform. I am preparing for a couple more builds and want to try out some different ideas.
Re: P-P OT with Screen Taps
The UL depends on the tone you are looking for, the tube, the loadline and the B+.
I like the sound of UL toghether with other feedbacks, not alone.
Some guitar UL designs have been introduced to save a choke and a supply cap, take this in mind too.
I like the sound of UL toghether with other feedbacks, not alone.
Some guitar UL designs have been introduced to save a choke and a supply cap, take this in mind too.