5879 voltages

[phsyconoodler]

What should the plates of the 5879 tube be getting? I have one in an 18 watt and I get 99v on one plate and 40v on the other.It has very low volume and I'm thinking this has something to do with it.
  Not having used the 5879 before,this is frustrating.Any help would be appreciated!

And trying to compare the 5879 amp schematic and layout,they are indeed different.In the schematic it shows the tone control assembly connected directly to pin 8 and in the layout it goes through the voltage divider 22k/1meg first.

[Geezer]

http://www.el34world.com/Forum/index.php?action=dlattach;topic=6176.0;attach=7791

On my HoSo amp the supply node is ~219v, plate is ~141v, & screen is ~56v.

G

[phsyconoodler]

I have 245v feeding the plate and screen and it drops to 90v and 40v respectively.Interesting.
  Can't really see why at this point.What about bias?I'm using 1.5k. Some amps I've seen use as low as 470 ohm for the 5879.
Something is sucking down that voltage. ??
 

[phsyconoodler]

Ok,maybe I'm not understanding how a 5879 works.Should I be able to sub it into an EF86 position,with rewire of course,and expect it to work similarly?Or does it need to be coupled to a 12AX7 for gain? I'm at a loss here.The data sheets say it should work or I'm missing something here???

[Geezer]

5879 is not a direct sub for EF86 (even with the rewire for different pinout), as the 5879 mu is much lower.....I believe another gain stage is in order.

If you look at the schematic linked above, I have a 5879, then a 12AX7 triode and a cathode follower feeding a TMB stack....plenty of gain & power there.

G

[phsyconoodler]

Yes indeed.Doesn't do it.No gain available with the 5879,I'm switching to EF86.If I jumper the channels it works but the tone is nothing to get excited about.Really kind of ordinary for me anyway.

That was disappointing,I was hoping the 5879 could do it on it'd own.

[SoundmasterG]

The 5879 sounds really nice with a parallel 12AX7 before it. It does seem to like a higher voltage than the EF86. Both a higher supply voltage and a higher plate voltage in relation to the screen.....I think it was like a .5 - .6v times plate relationship in mine whereas the EF86 was closer to a .6 - .7v times plate relationship.

Greg