tube diode quest

[J Rindt]

If i replace a suspect 6X4 with Solid State Diodes...how do i figure the tube resistance.?

The RCA Book says:
Effective plate supply impedance = 525 Ohms.

Does that mean i can use a (aprox) 500 Ohm resistor, in series with the PT secondary center-tap, or the cathode, to simulate the effect of the tube.?

Or is the tube impedance a different spec.?
Thank You

[fossilshark]

I beleive impedance is not the same as DC resistance. I think someone more qualified can clarify though

[Paul1453]

Here is a rectifier tube cheat sheet.

The 6X5 you asked about will rectify your AC source at 1.1x and then will drop 22VDC from that.
SS rectification will give you 1.4x your AC input will no voltage drop.

You will get a significant boost of your B+ with SS rectification.  ;^)

[J Rindt]

Thanks for the replys, but.....i am asking about the 6X4...not 5...and not V Drop, but if there is a spec for approximate resistance.?
Thank You

[Paul1453]

OK, 6X4 is listed too.
Basically the same as 6X5 except for socket and heater current.

I don't understand your focus on resistance?
The tubes resistance will be what causes its voltage drop, hence none for SS.

Both of these tubes are likely used in small SE Class A designs, 70mA max current.
In Class A you are not going to get much if any sag/compression from PS resistance.

You can get a pretty big boost of voltage for your B+ if that is what you are seeking.
If increased B+ voltage is not your goal, I'm not sure why you want to change to SS.   

[J Rindt]

So use the aprox  mA  of 2x AX7 and 1x.....is it a 7199, similar to an EL84 in size...and listed V Drop to estimate series resistance.?
Maybe i did not state it well in my OP.....trying to simulate the Tube Diodes with SS Diodes.....get close to the same numbers listed on the schem B+.
Thanks Again

[Paul1453]

I guess you could calculate your current used, and the new voltage provided by the SS diodes.

Then calculate the proper value resistor for that current draw to drop your voltage back down to the normal B+.

It will take significant calculations and probably a few different high wattage resistors in install test and adjust mode to get it right.

If you think the 6X4 is causing a problem, why not get a known good one and just swap it out?
6X4s aren't really expensive like a vintage GZ34.   

[J Rindt]

I appreciate your restrained politeness. 
IF this were my amp, i would have ordered a new, 12 dollar, 6x4 yesterday.
LONG Story.....Friend of a Friend situation...we will just leave it at that.
Thank You Again.....Really Do Appreciate It

[PRR]

> Effective plate supply impedance = 525 Ohms.

That's in (or added to) the transformer. Not the tube.

If you are putting Silicon in place of vacuum, try 100 Ohms 10W and see if it comes near the expected voltage. There's no fixed value. The tube internal "resistance" is non-linear, lower at higher current. Fool around until you find a solution which works for your project.

[J Rindt]

Ah.....OK, that is what the spec means. Thank You.
I did know the tube presents a nonlinear resistance, but i was wondering on a general value to try.
50-150 Ohms does seem to be a common arena as i look at what others have done on The Internet.....with 25-35 Wattt resistors on the bigger amps.
Thanks Again