6V6 line preamp

[Salas]

Originally Posted by buzzforb

I have found that creating da best universal tube and its golden bias point leads to a need for a universal cure of sorts. I was just trying to keep everyone informed, I can quit anytime.

We want you to show us the varnished PSU box and write the sonic impressions of tube rectification VS SS diode bridge before you fulfill the destiny hourglass and eventually quit your noble mission though.

[buzzforb]

I said i could quit, not that i will. 26 or 45 or 6p15ev is next

[buzzforb]

Salas,
I have my 5U4G wired like this exactly
http://www.vt52.com/info/vt52/schema..._schema_6b.gif
THe only difference is that I am using my 6.3V secondary to power it. I am taking the suggestion of putting a cl60 thermistor and .15R resistor in series with the filament to reduce it to 5V. Without tube installed, I get 6VAC on across filament pins and 310 across both diode pins and ground. Checked all connections and have good continuity. PLug the 5u4g in and nothing. I am using toroid, so neutral of dual secondaries are tied together to ground with each hot tied to tube diode.

[Salas]

Why you did it like that? Having a center tap in the 6.3V secondary also? Is your 5U4G a used and tested before sample? Me I had wired like that File:VacRect2E.png - Wikipedia, the free encyclopedia

[buzzforb]

I realized after posting link that it would be misleading. I got it figured out. Works great and the thermistor idea is nice, although i donr know about its affect on sound.

[buzzforb]

The jury is still out, but i think i like SS rectification better than the tube. It seems that the smoothness, drive , and grunt i gained with this pre, especially with the RCA blackplates, is lost when using the tube rectifier. I have added motorun caps and choke, so i cant say for sure, but i know more later. Going to add the SS and switch, so i can go back and forth. Just wanted to get the tube rectifier up and running. HAven't tried SIlver in oil yet. Will do that after getting psu sorted.

[Salas]

What exact type of SS diodes you use?

[buzzforb]

Simple sf4007, although i think i have some fancy stealth diodes around here somewhere. I am going to really clean up the layout(AC hum from rectifier tube), and add SS rectifer and switch before pronouncing judgement. Ill give pics of components and layout, along with opinion for clarity sake.

[triode_al]

Originally Posted by buzzforb

- - I am going to really clean up the layout(AC hum from rectifier tube), and add SS rectifer and switch before pronouncing judgement. Ill give pics of components and layout, along with opinion for clarity sake.

a very important issue is the amount of capacitance the rectifier tube sees, and the resistance of the transformer plus the feeder resistor or choke to the next section. If wrongly dimensioned (too much) the tube will start to arc or oscillate maybe.
Trick is to get the sweet spot.

Example: WE274B text
The peak current increases in value as the capacitance of the capacitor is increased and may be much larger than the average rectified output current, though its duration in such cases is only a short fraction of a cycle. Since for good tube performance, the anode current must be considerably less at every part of the cycle than the total emission current from the filament, the maximum permissible output current must be limited to such a value that this condition is satisfied. The permissible output current may be larger, therefore, for a choke-input filter, in which the peak anode current is only slightly larger than the output current. The choke-input filter also gives much better regulation than the capacitor-input circuit. The choke-input filter, therefore, should always be selected in preference to the capacitor-input filter wherever possible.
With a capacitor-input filter, the capacitance of the input capacitor should preferably not exceed 4 microfarads.

The same value goes for the 5R4W and similars.

[buzzforb]

I have 100R then 4.7uF, then 68R, then 40uF, then hammond 193Q 10H 500mA choke, then 40uF, then supply umbilical into main case, then 1uF local decoupling.