Help Me with my Tube Amp Journey

[johngovan]

I want to build the power amp section of HoSo EL84 PP by the good people Tubenit and Geezer. I will post my progress the time i started the project. But as of now. I want to start with the PT and OT. Please correct me.

1.  PT:

a. So i need a PT that is rated 270-0-270v.
b. For 2 EL84's are 65mA x 2 = 130mA.
c. 12ax7 PI current needs around 1mA? I'm not sure.
d. For heaters of 2 EL84, i need .76 x 2 = 1.52 plus 300mA for 12ax7 1.82, So 3A @ 6.3v will do the job?

2. OT:

What is the ideal primary impedance of PP EL84?

5k or 8k?

[PRR]

I started figuring the PI current and realized that is dumb. ALL the current in the whole amp flows either in the 150r resistor or the 10k resistor. The no-signal voltages are noted. Do math. Then look-up the maker's suggested conditions and see if EL84 current rises at full signal (it does).

6V6 and EL84 load well in 8k. This is also the value on the plan you posted.

[johngovan]

Thank you PRR. So a PT with 150mA B+ voltage will suffice this poweramp?  I hope tubenit and geezer will chime in too. I'm still a learner. I really need some advices and also corrections. :)

[tubenit]

I would want a PT with at least 120ma for 6V6 0r EL84.   However, you could get by with 100ma probably. 

I'd want either 275-0-275 & use 5Y3GT(302V ON PLATES) or 5V4 rectifier (329V ON PLATES).   The plate voltages are approximate guesstimates.

OR 300-0-300 & use 5Y3GT for EL84's (330v on plates). ..... OR .... 5Y3GT or 5V4 (360v on plates) for 6V6's.

IF you are going to use EL84's (my personal least favorite tube), AND you have to use a solid state rectifier ………
then I'd shoot for a PT with 250-0-250.   250 x 1.4 solid state rectifier = 350v on plates.

The HoSo56 is primarily DaGeezer's design, I just happen to be building one as he was sharing information.

With respect, Tubenit

[johngovan]

I'm using el84 as my power tube and solid state rectifier since it is my first push pull build. I will use a 270-0-270v 150mA Transformer. I will post update this thread for the progress. :) I plan to make the poweramp section only. Maybe using plain steel sheet since aluminum is not widely available in our country.

[tubenit]

I would encourage you to look at some tube data sheets on the EL84 and maximum plate voltages:

http://tdsl.duncanamps.com/show.php?des=EL84

While it is a loose guesstimate,  270 x 1.4 (solid state rectifier) = 378v on the plates.  I would check the EL84 data sheets and see if a potential 378v is within the maximum limits.   As an FYI, I've had EL84's redplate at 350 before.

With respect, Tubenit

[johngovan]

Can i use dropping Resistor to make the voltage around 250 or 260 for the EL84 from 378.
The limiting value of my el84 is 300v. Or should i use a 220-0-220v x 1.4 = 308?
200-0-200 x 1.4 = 280v? 

[johngovan]

Tubenit. Do you have Voltage readings for the poweramp section? Or should i use spice to test it without building it first?