Direct driving of GM70 by one ECL86 ???

[noyan]

Hi all,
I attached a simple two tubed amplifier shematic. One ECL86 tube is directly driving (without coupling transformer) an 845 triode. Anyone has any idea if i put a GM-70 triode instead of 845 triode then this circuit will work or not?
Regards

 

[noyan]

Ecl86 as driver of GM70

Another thing which i wonder, how is the sound quality of ECL86? I mean, is it a very good sounding tube to drive a Hi-end power tube(845 or GM70)

 

[John Fader]

Noyen,

That's really a 3 tube circuit. There are two "tubes" in that first envelope. I can't speak about the sound of that mumber, as I've never heard one, though it appears to be TV vertucal osc/output tube (I could easily be wrong here) and I've heard a number of those, though not with a pentode seconc stage,finding them to be quite good.

Anyhow, the 845 and similar tubes need a lot of drive, buth voltage and current. That appears to be a published schematic, so one would expect that it is tried and tested (no guarantee unless you know the designer) so I expct that it would be reliable.

One other thing, I'd be leery of building it if the matching pPSU schamtic were not with it, or unless you have a firend who is familiar wit designing PSUs for transmitting tube qudio amplifiers. Not having enough voltage, or too much, can usually be easily Worked around with am audio triode, but not with a transmitting triode.

Charge on, McNulty 🙂

Cheers/Fader

 

[Yvesm]

Hi !

The ECL86 (6GW8) may be seen as an half 12AX7 and a (somewhat) derated 6BQ5 in the same envelope.

This schemo is from a French magazine, the writter being serious enough to publish only working designs.

For me, it looks reasonnable and simple, but I never heard it anyway !

Yves.

 

[Brett]

The ECL86 (6GW8) may be seen as an half 12AX7

That's a good enough reason for me not to use it.

 

[Sch3mat1c]

Well, a 5k with 10W through it (assuming they used a resistor rated double, as is proper) would be running around 44mA and 223V. Unlikely given +310V though.

What I'm suprised about, aside from the excessively rated parts, is they use the pentode in pentode mode, with no NFB.

And BTW, it's not direct coupled -- it has three coupling caps, one for each stage.

Tim

 

[Brett]

What I'm suprised about, aside from the excessively rated parts, is they use the pentode in pentode mode, with no NFB.

I've used 12HG7, 12HL7, C3g, C3m, D3a, EL84 as drivers of power tubes in pentode mode, no NFB, and they were superb, easily bettering the two stage triode designs I've used before, both measured and audibly.

The 20W rated resitor on the ECL86 pentode anode is a bulk foil TO220 cased item, and that's just the rating they come in. I'm guessing the Meggitt on the 845 cathode is one too, as it mentions different ratings with and without a heatsink and RS as a source. These are available here and are decently priced.

 

[planet10]

though it appears to be TV vertucal osc/output tube

The 6BM8/ECL82 was a dual purpose TV/Audio tube, the ECL86 is the next gen audio specific version (they built another tube aimed at TV). They be makes a decent amp* (one for instance in a recent audioXpress), oddly enuff the 6BM8 gets more cred thou.

*(not thou as slick as an EL84 with triode strapped EF86 thou)

dave

 

[Sch3mat1c]

As I recall, the GM has less Pd than the BM. Hence more people like BMs 🙂D).

Tim

 

[Yvesm]

Well, a 5k with 10W through it (assuming they used a resistor rated double, as is proper) would be running around 44mA and 223V. Unlikely given +310V though.

And probably the screen voltage is higher than plate one ...

What I'm suprised about, aside from the excessively rated parts, is they use the pentode in pentode mode, with no NFB.

And BTW, it's not direct coupled -- it has three coupling caps, one for each stage.

And three cathode bypasses too

With such hi voltage available, sure more than one link cap could be removed !

Yves.