Hi Fabio
Check out the "Z on Tube Rectifiers" thread pinned at the top of the
Tubes topic.
Lots of good info there.
Here's the first post from Lefty (from 2006) :
<< OK I have used 5U4GB's in RT 66's and I really liked the bloom and almost tweed like characteristic it gave the amp.
Lowered power and headroom but increased sustain.
Now time for a little rectifier primer by DR.Z.
A 5U4 is the toughest rectifier on the amps Power Transformer.
The filaments of a 5U4 are 5 Volts AC @ 3 AMP. Most designers cheapen out on this section of the PT and use a lower rating for say a 5AR4 and save copper ( i.e. CASH ) .
ALL the PT I designed and use in my amps have 3 AMP Rectifier Filament taps from the 5001 in the Ghia to 9001 in the Delta 88.
So a 5U4 can be safely used in any Z-Amp.
Just remember it will lower plate voltage so on FIXED biased Z-Amps Bias will need to be re-adjusted.
The 5U4GB sounds best in a 6L6/KT 66 amp IMHO, not so good in a EL-34/EL-84 based amp, but YMMV.
Hint the new EVAN DR.Z 6L6 amp has a 5U4GB in it right now and do like what I'm hearing, this may change in the final release or not.
I like 5V4's as they are in between the dynamic and higher powered 5AR4 and the spongy 5U4.
I would use them more but they are hard to find these day's and no one makes a GOOD replacement.
I like 5V4's in EL-84/EL34 amps especially for smooth BLUES tones.
OK 5Y3's they supply the least amount of Voltage and Currant.
A 5AR4 SHOULD supply 250 mA a 5Y3 supplies 125mA.
The draw of 4 EL-84's is typically 120 mA at idle so NO room is left
for any other tubes in the amp.
In a 2 EL-84 or two 6V6 amp a 5Y3 is fine just be careful ,too much sag and too much heat. A 5Y3 tube heats up a lot as it's internal voltage drop and dissipates that drop as HEAT.
As you can see all my amps are tube rectified, even the plug in SS amps Delta 88, KT 45 and 6545 are wired for and can except a tube rectifier as a plug in. I find that changing the rectifier type can make the biggest difference in an amps tone for the smallest amount of money. Just remember all changes in TONE are not for the best in all applications.
Happy New Year
DR.Z
>>