713A/1626 Darling

[hembrook]

Howdy.

I was looking over this schematic:

http://www.roehrentechnik.de/html/darling.html

(http://translate.google.com/translate?u ... n&ie=UTF-8 in english)

I think 713A (same as 717A except pinout) mushroom would be fun for a driver stage for the 1626/VT-136 outputs for a Darling. I am not interested in the mini chassis that he made, too hard for me.

Relooking at the schematic, it appears that the designer uses the -45 V to bias the grid for the 1626. Looking at it earlier, I missed the fact that he draws schematics with dots for connections and skips the dits for no connection, even if lines cross.

I bought a couple 7.5k ohm outputs and a power tranny from British Audio Supply on Ebay. The power tranny has a lot of heater (3-4 amps each on 12.6V and 6.3V) so heaters are easy. The secondary HT appears to be 0-260V. Not center tapped. Anyone want to walk down the path of power supply design with me to develop the B+ I need for a 1626? Either tube rectifed or solid state.

Thanks in advance!

[kheper]

hembrook wrote:
The power tranny has a lot of heater (3-4 amps each on 12.6V and 6.3V) so heaters are easy. The secondary HT appears to be 0-260V. Not center tapped. Anyone want to walk down the path of power supply design with me to develop the B+ I need for a 1626? Either tube rectifed or solid state.

What is the current capacity in ma of the power transformer?

A 0-260V non-center tapped supply has
260V across the windings. It was meant
to be used with a full-wave bridge rectifier.

I would go solid state. Although a hybrid
SS/tube rectifier would be cool, no need
to worry about delaying the B+. With a
SS full-wave and a tube full-wave, you can
easily fab a full-wave bridge rectifier.

http://homepages.ihug.co.nz/~rwillis/al ... ifier.html

So, let's see. For a SS full-wave bridge with
a capacitor input -

hypothetical B+ = 260 / .71 = +366V

Assuming a %10 drop for full loading brings
it down to +330V. Depending on the choke,
the B+ could be 30V lower.

The schematic calls for a 265V B+. You
could further drop the B+ with divider
resistors or find another schematic for a
different output tube.

[sorenj07]

or just keep dropping the first capacitor after the diode bridge to have it operate closer to choke-input. no need for a wasteful voltage divider!

tell me the current loads and i'll pop them into PSUDII. the current capacity of the 260V winding and its DC resistance would be useful as well...

[hembrook]

I don't know the exact current capacity of the power supply. its not marked. The heater secondaries are fused, but the HT is not, so I can't hazard a guess.

Here is what the advertisement in Ebay said:

--------------------------------------------------------------------------------
Tube amp power transformer perfect for a small Class A single ended amplifier.

Primary

Black (0v) White (100v) Yellow (115v) Blue (230v) Brown (240v)

Secondary

Blue (12v) Black (0v) Blue (12v) 3A

Orange (6.3v) Orange (0v) 4A

Red (260v) Red (0v)

Unfortunately, I do not have current (A) ratings for the HT tap, but it was used in a 1 x EL84 and 2 x 12AX7, Class A, single ended amplifier design. The weight is 3 lbs, 11 oz.

--------------------------------------------------------------------------------

So, I get to play with it. Given the large physical size, and the heater ratings, I guess it has decent current capacity. Others who bought it have estimated it at 80-100mA current. DCR of the HT secondary is 60.5 Ohms.

713A: Typical operating conditions for the 713A are 120V plate and screen, plate current of 7.5mA, screen current of 2.5mA

1626: Typical operating conditions for the 1626 are 250V Plate at 25mA , grid voltage of -32V

I have some 10H chokes (Noguchi from Japan) as well as 1.5H Hammonds left over from my GetSetGo, so that may help with the design.

How do I plug this all into the PSD][? I played with it a couple days ago, but I obviously have to get to know it better. i was putting in assumed values, so I know the results were way off.

Thanks!

[hembrook]

No posting in a couple days. Did I miss something?

[Slartibartfast]

No posting in a couple days. Did I miss something?

Ed is busy. He is trying to sell his house. Yellow_Light_Colorz_PDT_03

[hembrook]

I just thought maybe I led people astray, posting in several threads at once. I really want to learn the PSD stuff because it is one thing to copy someone else's work, its really another to design stuff yourself.

[Slartibartfast]

I just thought maybe I led people astray, posting in several threads at once. I really want to learn the PSD stuff because it is one thing to copy someone else's work, its really another to design stuff yourself.

But plagiarism is the sincerest form of flattery. Yellow_Light_Colorz_PDT_04

[hembrook]

Flattery will get you everywhere.

But I want to learn, oddly enough.