Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on July 04, 2012, 05:05:01 pm

Title: 5E3 Power tansformer
Post by: Leevi on July 04, 2012, 05:05:01 pm

I got a 5E3 wired and wonder the specs of the recommended 5E3 PT
where the secondary is on level 330-0-330. I think the optimal B+ is about 380V that many
have reached by using the recommend transformer?
I met last time problems with too high B+ and that's why I selected this time a PT with 275-0-275
secondary. The B+ is now 370V with Sovtek 5Y3GT rectifier.

What could be the reason that big difference?
- 230V/50Hz vs. 117V/60Hz
- better transformers

/Leevi

Title: Re: 5E3 Power tansformer
Post by: Tyrannocaster on July 04, 2012, 08:36:22 pm

I don't think it's the transformer.

The Sovtek 5Y3 isn't really a 5Y3, from what I have read. If you have another brand (an old NOS would be nice) try that instead - your voltage should be a lot lower. I tried using a Sovtek 5Y3 in one of my amps and the B+ was considerably higher with it than with an old real 5Y3, but that was several years ago and I don't remember exactly how much too high it was; as I recall, it was about the same as a 5AR4. I thought that by now they would have started making them to spec but it sounds like they haven't.

Rautalanka kaiku!  :icon_biggrin:

Title: Re: 5E3 Power tansformer
Post by: Tiny_Daddy on July 04, 2012, 08:49:51 pm

I agree, the Sovtek 5Y3 has a lower than expected voltage drop for a 5Y3. Seems more like they used 5AR4/GZ34 guts?

Title: Re: 5E3 Power tansformer
Post by: Leevi on July 05, 2012, 12:52:21 am

Quote

The Sovtek 5Y3 isn't really a 5Y3, from what I have read.

The rectifier tube can affect on this but doesn't clarify everything. I guess the
second reason is the transformer which doesn't drop the voltage with higher load.

Link to my previous topic of this item:
http://www.el34world.com/Forum/index.php?topic=11378.0 (http://www.el34world.com/Forum/index.php?topic=11378.0)

Another question is the the cathode resistor of the power tubes.
I increased it from 250 Ohm to 560 Ohm in order to get the cathode current (per tube) to
an acceptable level i.e. to 23mA.

/Leevi

Title: Re: 5E3 Power tansformer
Post by: John on July 05, 2012, 06:23:39 am

Raising the cathode R value will usually increase the B+ as well.

If your PT is robust in the current capacity department, maybe that is why the voltage isn't dropping as much under load? I dunno, just a thought. Anyway, if your PT is 275-0-275 then 385  B+ is about right (before rect. tube). Those new "5Y3s" only drop about 30 volts, just depending.

Title: Re: 5E3 Power tansformer
Post by: Leevi on July 05, 2012, 08:46:00 am

Quote

Raising the cathode R value will usually increase the B+ as well.

Yes, that's true and I checked this with several resistor values. The variation was
max 10V on the lowest and highest resistor value I tested.
/Leevi