6GB5 Cognates

http://www.diyaudio.com/forums/tubes-valves/265545-27gb5-pl504-same.html

According to the RCA tube manual there's a 27GB5/PL500. The PL504 is supposed to be a "sensibly equivalent" replacement for the PL500.

The EL500 XL500 and PL500 (6GB5, 13GB5 and 27GB5) all carry a published plate dissipation rating of 12 watts (Philips data). 

The EL504 and PL504 (there is no XL504) have a published plate dissipation rating of 16 watts (Philips data).

Most of the US data books show the EL/XL/PL500's with a plate dissipation rating of 17 watts. These tubes were used in some small color TV's in the US. The '504 was not given a US (JEDEC) type number. 

I have some Samsung XL500 and their internal structure resembles the older Philips EL500. I have 100+ XL500/13GB5 tubes with various US brands on them , and a few that are Mullard or Amperex branded. ALL of them are Mullard "made in Great Brittan tubes. These tubes have a larger internal structure than the Samsung tubes, that appears identical to the Philips PL504's that I have.

I suspect that at some point the tubes for the US market, and perhaps all of the '500 tubes got '504 guts to improve reliability. This was common with US made sweep (line output) tubes like the 6AV5. The 6FW5 was the higher spec version, but eventually all GE sourced 6AV5's had 6FW5 guts in them.

I know you want to use them at low voltage in my stereo tube amplifier for dummies 

PL 504 Vplate min = 50Vdc @ Vg1 = 0V
PL 500 Vplate min = 75Vdc @ Vg1 = 0V

PL 504 works a little better at low anode voltage than PL 500

Everything else is about the same.

pl500.pdf

pl504.pdf

I tested PL 504 starting from 24 Vdc anode voltage (it works with a very little audible distortion), it works quite well starting from 36 Vdc, instead PL 500 needs a minimum of 50 Vdc.

the big pentode EL5xx ( only pentode ) is EL 502 or EL 511 .
 
EL 500 ( PL ) = 12 W

EL 502 ( PL ) and EL 511 ( PL ) ( heater is 6.3 V~ 1.7 A or 1.3 A ) = 20 W

EL 504 ( PL ) = 16 W

the EL 502 is +/- EL 34 and socket is Magnoval , the mode " Triode " is very good 

RCA Tube Manual, RC-30, 1975, page 281