Author Topic: Differences Between EL34 and 6550... (Read 37688 times)

the_bleeding · « **Reply #60 on:** January 30, 2008, 05:48:55 PM »

Quote from: jpfamps

The pin out of 6550s and KT88s is the same.

uhh, nope.

In a kt88, pin 8 is linked to the cathode and the screen, and pin 1 connects to nothing

in a 6550, pin 8 is exclusively linked to the cathode, and pin 1 to the screen.

pin 8 being linked to screen and cathode in kt88's would DEFINATELY have something to do with the ultralinear purpose because it would keep the screen and cathode the same :P

but, all this being said, i'm glad the winged "c" factory is making the kt88's and 6550's as different tubes instead of the same tubes with different packages.

jpfamps · « **Reply #61 on:** January 30, 2008, 06:44:42 PM »

All the manufacturer's data sheets I have seen for KT88s and 6550s have the same pin out indicated ie the cathode and beam forming plates are tied together internally and to pin 8 (see http://tdsl.duncanamps.com/ for valve data or Svetlana web-site), as have all the examples I have seen of these valves.

Beam tetrodes, unlike pentodes, don't have a suppressor grid but the distance between the screen grid and the plate is proportioned to reduce the effects of secondary emission, and this is enhanced by beam forming plates which are tied to the cathode.

The pentode EL34 has the suppressor grid — pin 1— and cathode —pin 8— tied to separate pins. This makes it possible to tie the suppressor grid to a voltage other than that of the cathode, perhaps the raw bias supply as used in some Traynor amps.

I'm not sure if tying the beam forming plates of a beam tetrode to a voltage other than the cathode would be useful, and indeed it might disrupt how the valves functions. However there may well be some versions of the 6550 that have this pin out option, although my suspicion might be that these are in fact pentodes and not beam tetrodes. Pentodes are generally cheaper to manufacture.

This pin out option has NOTHING to do with ultralinear operation; it is the screen grid (pin 4) which is tied to the UL taps on the output transformer.

HTH AMPS · « **Reply #62 on:** January 30, 2008, 09:38:37 PM »

here's a GEC datasheet showing the KT88 pinout... http://www.triodeel.com/kt8856p1.gif

AdamB · « **Reply #63 on:** January 30, 2008, 10:45:18 PM »

So what are the tonal differences between the 6L6 and 5881?

I've narrowed it down to these two for my new head (Egnater mod50) and style (hardcore), my 5150 II uses 6L6's and although i like them, i would like a little more mids in them, would 5881 sort this?

What's a good brand to get?

i know tung sols are but they're £65!!!! each on watford valves

the_bleeding · « **Reply #64 on:** January 31, 2008, 12:42:41 AM »

thanks for the informative post JPF :)

you probably just saved me alot of hassle later in life.

and the difference between 5881s and 6l6's i've found is that 5881s are a more sterile version, less bass, less highs. A very boring tube for me where i like extended bass. Mind you im running mesa/sovtek ones, which arent good tubes in the first place.