Strange tube

[pilovis]

I found this strange "three tubes" on a Grundig Stereo Radio.

ECLL 800E, Tube ECLL800E; Röhre ECLL 800E ID31029, Triode+Do

It is not a fake, it was a commercial "tube".

[smoking-amp]

Looks like a DIY compactron or some scheme to get around a tax per tube in radios. Maybe a repair workaround for a discontinued production tube for some radios. Any tube #'s on the tubes themselves? ELL80?

[pilovis]

Originally Posted by smoking-amp

Looks like a DIY compactron. Any tube #'s on the tubes themselves?

No.

I think this is the direct replacement of ECLL800, same thing but in one tube (triode + two pentodes):

ECLL 800, Tube ECLL800; Röhre ECLL 800 ID3449, Triode+Double

[kevinkr]

I've seen this in at least one stereo Grundig table radio and it appeared to have been in the radio since it was new. Very 0dd.. Must have been a work around for a tube that was designed in and was not available at some point in the product life cycle.

[smoking-amp]

According to Oldeurope in a 2008 thread:
pse help, unity µ triode as a phase inverter

The triode section in that ECLL800E (and presumeably the original ECLL800) had a Mu of just 1 for making a unity gain inverter stage. It would be very interesting to know what tube they used in the ECLL800E "E"mulation (picture with two tubes side by side, the right side one being the smaller triode apparently) for the triode function. Oldeurope would certainly be interested in knowing, since that was what he was searching for then. It's hard to imagine how one would even make a Mu=1 triode. Maybe the ECLL800E "E"mulation part used a higher Mu triode with some attenuation.

Ouch!, according to that radiomuseum link, 221 different radios used the original ECLL800 part.

[revintage]

The "real" ECLL800 in one envelope. The one shown is a substitute.

I have experimented with substitutes for the very expensive ECLL800´s that are to be found in the vintage Hagstrom guitaramps.

The best way today is to make a fake one by using two ECL82´s where one triode is left unused. No problem to go this route as the triode is for PI in paraphase.

[smoking-amp]

Looks like maybe a 1984 date code on that ECLL800E sticker.

[kevinkr]

Originally Posted by smoking-amp

Looks like maybe a 1984 date code on that ECLL800E sticker.

I took that to be a serial number.. The fabric tape and socket design makes me think it is much older than early 1980s..

[planet10]

Does that sub have 2 or 3 tubes... looks like 3 nipples in the 1st picture. Certainly not as elegant as ecll800 ... maybe i should put my stash up for sale? I have at least a couple.

dave

[riccoryder]

That looks pretty wild, almost as crazy as the 6550 replacement I wanted to make with a 6CB6 current mirrored to preserve curves and feeding a big transistor... I had my eyes out for a ECLL800 thinking it'd be fun to see how good of quality an amp could be made with one tube, but on looking closer I realized it would be so challenging. It has extra limitations with so many things tied together to get down to 9 pins. With only one cathode connection there'd be no hooking up feedback from the Com and 16 Ohm output taps with the 4 Ohm tap grounded. Even the inverter triode has the same cathode in common with the pentodes, the control grid tied to one also. The datasheet says mu=1.2 for the triode, which means that unity gain inverter uses no divider or external feedback beyond the influence of the plate signal on current. it looks like all three sections get -9V bias from a single 180 resistor. I suppose a Zener would be a minor upgrade to keep the triode from seeing variation. If biased a little hotter to get more gain, maybe the triode plate resistor could be trimmed for AC balance, maybe vary the bias on the second pentode some too? Maybe a 1N5302 current-source triode plate load then trim the following grid resistor for gain balance? Run the global feedback resistor with a lead compensation capacitor from the speaker to the input grid and and use a series input resistor for inverting mode? A series RLC across the transformer primary to kill the resonant peaking? Fire up those PC spectrum analyzers!