Tube-Town Forum
Technik => Tube-Talk => Thema gestartet von: Leadman am 3.04.2020 12:03
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Grüße. Ich habe den TT 50VA Leistungstransformator für einen Pro Junior Fender Clone (2xel84 + xx12ax7) verwendet.
Die + b-Spannung betrug 338 Volt bei 62% Vorspannung. Der ursprüngliche Transformator liefert ungefähr 330 Volt bei 80% Vorspannung (330 V bei 67 mA DC). Das Verwandelte ist gebrochen.
Reicht dieser Transformator für dieses Projekt aus? Nach meinen Messungen war der Leistungstransformator ausreichend, es gab keinen "SAG". Was denkst du?
Vielen Dank für Ihre Hilfe und entschuldigen Sie mein Deutsch.
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It´s the TT 50Va toroidal transformer safe por a 2x12ax7 + 2xel84 push pull fixed biased amp? with a 15w output transformer 6940ohmm output impedance?
Thank you very much in advance.
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It´s the TT 50Va toroidal transformer safe por a 2x12ax7 + 2xel84 push pull fixed biased amp? with a 15w output transformer 6940ohmm output impedance?
Thank you very much in advance.
Hi,
although i don't have personal experience with this transformer, i would expect it to be sufficient. At least some 18W projects have been built with it - these would be even more demanding than a PJ with fixed bias and a bias current of approx 2x40mA on the EL84...
This is my personal impression...
regards
Jochen
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Thank you so much for your help. My maths says the same, maybe I have a bad apple with that singular unit. OTherwise I am going to order another one a put a fan in the combo for a better cooling.
Best Regards!
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Thank you so much for your help. My maths says the same, maybe I have a bad apple with that singular unit. OTherwise I am going to order another one a put a fan in the combo for a better cooling.
Best Regards!
I assume the translation of your first post as
"the new one (TT50VA) broke down"...
What ist the symptom?
Does it draw the primary fuse?
No HT present, but primary fuse intact
No Heater Voltage present?
regards
Jochen
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IT broke down in about three months of use at home. The HT secundary is shorted and now it puts only about 160Volts and get very hot.
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IT broke down in about three months of use at home. The HT secundary is shorted and now it puts only about 160Volts and get very hot.
you might es well consider the 80VA.....
just put a 2way rectifier in there B+ will be a bit lower, but i don't think that would hurt.
The 50VA might be on the edge
regards
Jochen
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2way is the same that full wave rectifier? I,think the +b will be higher than tt50va, and the 80va is heavier. The combo is ultra light now, only 7,3 kgs for 15watt (pro junior based).
If there are people that make 18watt clones with the TT50va transformer, it should survive with a pro junior layout.
Maybe in a small combo the heat is more dramatic in a toroidal transformer. I think that try with a pc fan a the 50va worth the pain.
Are there builder who have used the Tt50va for 2xel84 amps sucesfully?
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Ah, I have used the combo in one only gig against a MIA tweed pro junior (with the original eminence alnico blue) and my clone was superior and don't show signs of sagging or overheat, that should show that the tt50va have the specs for that design, when we struggle a power transformer the voltage comes down with the extra stress.
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Ah, I have used the combo in one only gig against a MIA tweed pro junior (with the original eminence alnico blue) and my clone was superior and don't show signs of sagging or overheat, that should show that the tt50va have the specs for that design, when we struggle a power transformer the voltage comes down with the extra stress.
the idea with the 80VA would only apply, if you don't trust the 50VA.
the math would says, that the 50VA should work
regards
Jochen
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Thanks for your friendly help Sr. Jochen :guitar:
Best regards!
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Hi Leadman,
I used the TT50VA toroid in several 18 Watt projects incl. a Pro Jr clone. It works fine, doesn't get hot, no sag. The output power of the tt50VA is much enough for two EL84 ans a couple of ECCs. In addition using a toroid you don't have to worry about the direction of installation.
Regards Axel
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Fixed Bias Class AB: :topjob:
Auto Bias/Class A: no-> hot Transformer! +- 60C°
Gruß Stephan
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Nice advises!
Thanks from Spain!
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Nice advises!
Thanks from Spain!
SPAIN?
take care
stay safe
Jochen
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Hallo,
the calculation might look good on the paper but did you measure the real power and the current the amp draws from the transformer ? This is a MUST to make sure that there is no problem with the circuit or the layout and that the amp does not more current than exacted.
Best regards, Dirk
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I measured all voltages and bias current, all measures were in the correct range that the original schematic shows (+-5%).
I don't have a oscilloscopic and I can't measure the real clean power before clipping of the amp.
The transformer never get very hot, only when the short happened it get very toasty.
The output tubes are in good condition and nothing else in the circuit looks damage or wrong.
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SPAIN?
take care
stay safe
Jochen
We are throught a big drama, thanks for the support.
I think I report your comment by error when I was trying to quote your reply, sorry.
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I measured all voltages and bias current, all measures were in the correct range that the original schematic shows (+-5%).
I don't have a oscilloscopic and I can't measure the real clean power before clipping of the amp.
So you do not know if there was any kind of oscillation or the real power consume of the transformer.
Such issues happen from time to time but in most cases the user/customers refuses to take a critical look to his work. Of course a transformer can fail but if it breaks after it has been in use for a while then the eye-catching. The probability of incorrect use is greater the longer the transformer was in use. This is my experience.
Best regards, Dirk
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Thanks Kirk,
I thought that the conjuntive filter of the desing filter out all the high frequency and non audible oscillation in that particular circuit, that together with all corrects voltages, no power losses, sag or overheating, ... All this made me think All was running fine. I didn´t can measure any sub-bass oscillation, I don´t feel any lacks in perfomance in this department, but maybe it was the problem.
The transformer only gets hot when it lose power and shorted showing a low output voltage.
Best Regards!
PD. This forums is exciting, a lot of useful info but I am fighting with german google translator extension, hehehe.
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My Name is Dirk. I have nothing to do with Star Track :devil:
Please keep in mind that non audible oscillation must NOT be present all the time !
Best regards, Dirk
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Oh, Sorry Dirk for the error. Strak Trek rules, hehehe.
The new TT50Va is different of the old one, the diameter are 74mm in the new one (80mm in the old one) and the height is 34mm (40mm in the old one)
The green wax cover fully the hole in the new one Vs the old one only cover half of the height.
Maybe this changes could get the transformer more sensitive to the stress?
Do your think the new TT50VA conventional transformer is more robust?
Regards, Daniel.
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And a few pics of the clone:
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Here:
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Maybe this changes could get the transformer more sensitive to the stress?
No, it is just a different manufacturer. You should stop chasing cars.
Best regards, Dirk
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Hehehe, ok, the seclusion at home give a lot of time to turn thing around.
Best Regards, Daniel.
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Hehehe, ok, the seclusion at home give a lot of time to turn thing around.
Best Regards, Daniel.
Hi Daniel,
you might check your Leaddress - your amp might oscillate.
If you can gain access to an oscilloscope - i would recommend to use it...
You might also get a simple "Energy Monitor" which can measure effective power consumption... These are cheap. If the amp draws excessive power from the mains - you will see it there...
regards
Jochen
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It´s difficult now get any electronic equipment, only online shopping.
What part of the circuit do you think could oscillate?
Best Regards,
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It´s difficult now get any electronic equipment, only online shopping.
What part of the circuit do you think could oscillate?
Best Regards,
at least here - you won't find such an energy monitor plug in local shopping...
Online - they are are available for >20€
HHmmh - where to look at?
At first glance - sorry - please don't consider me rude - everywehre...
regards
Jochen
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The truth is never harsh, hehehe. I am going to find a monitor or a oscilloscopic and check de layout.
Thanks!
Regards!