Hi everybody!
I wonder if a 70V Line Matching Transformer like this would do a good output transformer substitute for these small 35W4/50C5/12A?7 single ended tube amps.
I own several of these amps and today I was curious to see the turn ratio on each output transformers (Some of my amps are true old pepco/pine, and some are homemade built from old tube radio parts), so almost all of the OT were in the good range, I mean.. a 4 or 8 ohms speaker can be hooked while remaining in the 2K5 load impedance suggested for the 50C5 tube.
However, 2 amps in the lot were out of range. The first "out of range" OT is calling for a 1.8 ohms speaker, I'm actually not at my workbench, but if I remember I got 0.272 Vac at secondary while injecting 10.12 Vac at primary, and the second OT is calling for a 11.8 ohms speaker, those 2 amps sound quite good, but I wonder what is the effect of the impedance mismatch, if for example I hook the closest speaker available, so let say a 4 ohms speaker for the first one, and a 8 ohms speaker for the second amp, is it correct? I must say that I'm a bit confused since these 2 amps are all original, with the original OT/speakers...
So that's why I ask about the line transformers. They are rated at 10W but I heard something about an air gap that OT "must" have, the amps are only 2 watts... I don't know, maybe I'm better to find some old AA5 radios in the classified ads..
Anybody ever used one of these line transformer as a substitute for the OT in tube amp?
I wonder if a 70V Line Matching Transformer like this would do a good output transformer substitute for these small 35W4/50C5/12A?7 single ended tube amps.
I own several of these amps and today I was curious to see the turn ratio on each output transformers (Some of my amps are true old pepco/pine, and some are homemade built from old tube radio parts), so almost all of the OT were in the good range, I mean.. a 4 or 8 ohms speaker can be hooked while remaining in the 2K5 load impedance suggested for the 50C5 tube.
However, 2 amps in the lot were out of range. The first "out of range" OT is calling for a 1.8 ohms speaker, I'm actually not at my workbench, but if I remember I got 0.272 Vac at secondary while injecting 10.12 Vac at primary, and the second OT is calling for a 11.8 ohms speaker, those 2 amps sound quite good, but I wonder what is the effect of the impedance mismatch, if for example I hook the closest speaker available, so let say a 4 ohms speaker for the first one, and a 8 ohms speaker for the second amp, is it correct? I must say that I'm a bit confused since these 2 amps are all original, with the original OT/speakers...
So that's why I ask about the line transformers. They are rated at 10W but I heard something about an air gap that OT "must" have, the amps are only 2 watts... I don't know, maybe I'm better to find some old AA5 radios in the classified ads..
Anybody ever used one of these line transformer as a substitute for the OT in tube amp?
25V or 70V line transformers.
This has been discussed here before.
SE: can't take the DC
PP: can't get two similar windings for primary
Not really a viable solution.
AC power transformers: if you have a 110/220 primary and the right combination of V /I output rating of a toroid type then it has been done for PP...not SE
EI cores for AC power transformers are designed for 50/60Hz operation and the cores have significant losses at audio frequencies.
Hope that helps.
This has been discussed here before.
SE: can't take the DC
PP: can't get two similar windings for primary
Not really a viable solution.
AC power transformers: if you have a 110/220 primary and the right combination of V /I output rating of a toroid type then it has been done for PP...not SE
EI cores for AC power transformers are designed for 50/60Hz operation and the cores have significant losses at audio frequencies.
Hope that helps.
Okay so I'm better to check out for some old radios. But I still wonder how it can hurts the power tube (50C5) having a mismatched OT, these tubes become more pricey and harder to find.
I knew that it was not "the best" substitute and not an option at all with PP, but since I've read about a succes stoty using a 120/6.3 heater transformer (it was in a radio) I was curious to know if anyone has had success using this line transformer in a small 2W guitar amp, I thought that maybe because of the small wattage it would handle this DC saturation, but if you tell me about frequencies lost, I will definitely not play with this!
Sorry if this topic has been treated before I hadn't found it, I will try to have better eyes in the future.
Thanks so much for sharing your experience! 🙂
I knew that it was not "the best" substitute and not an option at all with PP, but since I've read about a succes stoty using a 120/6.3 heater transformer (it was in a radio) I was curious to know if anyone has had success using this line transformer in a small 2W guitar amp, I thought that maybe because of the small wattage it would handle this DC saturation, but if you tell me about frequencies lost, I will definitely not play with this!
Sorry if this topic has been treated before I hadn't found it, I will try to have better eyes in the future.
Thanks so much for sharing your experience! 🙂
I have built many guitar amps 5 watts and under for experimentation, teaching,home practice and recording - all using these trafos for the OPT.
They work well as instrument amps (not hifi)
They also work in SE amps if the current thro them is not more than about 20mA. This is more than enough if you live and practise in an apartment. (Using tubes such as EF86, ECF80, 6U8 etc as output tubes thro a 10 or 12" guitar speaker - surprisingly loud)
Self split topography for the PA is another option.
Not stadium amps but great for trying your design ideas and with a high WAF.
For something bigger a 20w line trafo will handle EL84's or 6V6's in pp.
Several of the designs in the 100 buck amp challenge thread in the stickies above used line trafos.
They work well as instrument amps (not hifi)
They also work in SE amps if the current thro them is not more than about 20mA. This is more than enough if you live and practise in an apartment. (Using tubes such as EF86, ECF80, 6U8 etc as output tubes thro a 10 or 12" guitar speaker - surprisingly loud)
Self split topography for the PA is another option.
Not stadium amps but great for trying your design ideas and with a high WAF.
For something bigger a 20w line trafo will handle EL84's or 6V6's in pp.
Several of the designs in the 100 buck amp challenge thread in the stickies above used line trafos.
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they work ok in lowpower (2 watt) amps with roll off in higher freq's
use the 1.25 watt and common tap for a 4k primary
use the 1.25 watt and common tap for a 4k primary
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Learn something every day.
Could you two provide some design details?
There are lots of people that might like to build something with 25V / 70V line transformers...even if not "HIFI" at least to experiment with.
Could you two provide some design details?
There are lots of people that might like to build something with 25V / 70V line transformers...even if not "HIFI" at least to experiment with.
This is very good to know, I will give a try in my future experimentation for sure but I dont think about using this line transfo as a substitute in my amps because of the roll off in the highs, but maybe it could be compensated in the circuit..
Now I'm pretty confused, some people say that tube amplifiers will tolerate a 2:1 mismatch speaker impedance, EITHER up or down, other say that an upper mismatch WILL kill the amp overtime, some say the same about a down mismatch... my god where is the thruth! 😕
The original OT in my little Garnet amp is taking my head, because if I rely on the maths, a 1.8 ohms speaker should be used in this amp. The original speaker is a 4 ohms (3.6 ohms), I wonder if this 2:1 upper speaker mismatch was intentional, Garnet are well known to have done things like no other..
In another amp (Trend from Pine Electronic), there's a down mismatch (all the parts are also original), the OT is calling for a 11,8 ohms speaker, though the speaker is a 7.8 ohms.
From my ears, the Garnet sounds better, a little louder and less harsh but this could be because of the different OT/speaker, however, once I have hooked the Trend to the Garnet (4 ohms) speaker, and vice versa, the Garnet to the Trend speaker... in all of this the Garnet was always the winner.
Now my big questions, is a perfect speaker impedance match (within tolerance) is the best in tube amp? What's the effect on the power tube, the sound.. by having an upper versus down mismatch?
The guy at geofex say that we don't have to worry about any mismatch, even a shorted secondary won't hurt, that the only thing to worry about is not to leave the OT without any load (no speaker/dummy connected), but it's another thread and I knew this.. my concern is the speaker mismatch 😀. Some other people say that a down mismatch will tire out the power tube... But for sure a mismatch will have an effect on the sound!
I would be very happy to hear your comments 🙂
Now I'm pretty confused, some people say that tube amplifiers will tolerate a 2:1 mismatch speaker impedance, EITHER up or down, other say that an upper mismatch WILL kill the amp overtime, some say the same about a down mismatch... my god where is the thruth! 😕
The original OT in my little Garnet amp is taking my head, because if I rely on the maths, a 1.8 ohms speaker should be used in this amp. The original speaker is a 4 ohms (3.6 ohms), I wonder if this 2:1 upper speaker mismatch was intentional, Garnet are well known to have done things like no other..
In another amp (Trend from Pine Electronic), there's a down mismatch (all the parts are also original), the OT is calling for a 11,8 ohms speaker, though the speaker is a 7.8 ohms.
From my ears, the Garnet sounds better, a little louder and less harsh but this could be because of the different OT/speaker, however, once I have hooked the Trend to the Garnet (4 ohms) speaker, and vice versa, the Garnet to the Trend speaker... in all of this the Garnet was always the winner.
Now my big questions, is a perfect speaker impedance match (within tolerance) is the best in tube amp? What's the effect on the power tube, the sound.. by having an upper versus down mismatch?
The guy at geofex say that we don't have to worry about any mismatch, even a shorted secondary won't hurt, that the only thing to worry about is not to leave the OT without any load (no speaker/dummy connected), but it's another thread and I knew this.. my concern is the speaker mismatch 😀. Some other people say that a down mismatch will tire out the power tube... But for sure a mismatch will have an effect on the sound!
I would be very happy to hear your comments 🙂
1241, 1321
Hi DUG,
Re 100-buck amp challenge stickie thread
For instance see (amongst others) my posts 1241 & 1321 for a SE design I have since used a number of times.
Check out page 8 for a pp design.
Current project is a pp amp using same trafo with EL91 tubes.
OPT used is 5 watt 100v line.
Hi DUG,
Re 100-buck amp challenge stickie thread
For instance see (amongst others) my posts 1241 & 1321 for a SE design I have since used a number of times.
Check out page 8 for a pp design.
Current project is a pp amp using same trafo with EL91 tubes.
OPT used is 5 watt 100v line.
Neat.
Post 1241 ( http://www.diyaudio.com/forums/instruments-amps/190738-hundred-buck-amp-challenge-125.html )
When depth pot is at 0...how is signal passed through?
It doesn't. I stuffed up that bit. But the trem oscillator works and the amp works. Just an example of using a small pentode in a power stage, and a non-gapped trafo in SE mode. One of my very early diy experiments out of the parts bin.
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ozvalveamps.org have a section on using line transformers in valve amps ( in their Articles section under the 'Particular Issues' subheading).
Since we are in a thread called " 70V Line Matching Transformer - Good OT substitute " I just want to be clear that we are talking about 70V audio line matching transformers and not AC power line transformers.
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