[Leadman]

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.

[Leadman]

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.

[cca88]

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

[Leadman]

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!

[cca88]

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

[Leadman]

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.

[cca88]

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

[Leadman]

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?

[Leadman]

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.

[cca88]

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

[Leadman]

Thanks for your friendly help Sr. Jochen 

Best regards!

[Striker52]

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

[Stubenrocker81]

Fixed Bias Class AB: 
Auto Bias/Class A: no-> hot Transformer! +- 60C°

Gruß Stephan

[Leadman]

Nice advises!
Thanks from Spain!

[cca88]

Nice advises!
Thanks from Spain!

SPAIN?

take care
stay safe

Jochen