The Playmaster 102 with 6BE6 Penta-Grid Vibrato

[jazbo8]

Original title: What Happened to ozvalveamp.org?

I think it has gone offline... does anyone know what happened to it? Anyway, I am looking for the article on Playmaster 102, if anyone has a copy, please send me/upload a copy.


TIA,
jaz

[Ritchie200]

Will this work?

http://web.archive.org/web/20150729001351/http://www.ozvalveamps.org/playmaster.htm

Jim

[Ritchie200]

Aww crap, can't get to the scanned article as it was not archived.  Sorry!

Jim

[jazbo8]

I know, so much for archiving...

[kagliostro]

Our friend Roly has some health problems

some time ago at AGGH (www.guitargear.net.au) someone was offering to continue his effort on www.ozvalveamps.org

but I don't know the actual situation

---

About the Playmaster 102 don't worry

Radio Television and Hobbies - October 1962 - Vol 24 - No. 7
http://www.mediafire.com/view/niw38zigdgtc23r/Playmaster_102.pdf

Schematic


Franco

[jazbo8]

Great! I knew someone must have download it at one point, too bad about ozvalveamp though, it had a lot of interesting information on Aussie amps.

[kagliostro]

To which part of the 102 are you interested ?


Franco

[jazbo8]

To which part of the 102 are you interested ?

Mainly the use of unusual tube such as the 6BE6 and the screen-grid-modulation of the vibrato circuit - you don't see those everyday...

[TIMBO]

Hi guys, Not sure what is happening with the site 
Jaz, Here is another Aussie amp that has a similar circuit.
http://el34world.com/Forum/index.php?topic=19585.0

[kagliostro]

Ciao TIMBO

Yes, also that is an interesting schematic 

the ef86 tube is used in a similar way




Franco

[jazbo8]

In the above Maxim schematic, the pentode drivers (6SK7's) appear to be drawn incorrectly - the suppressor and screen grids are reversed.

[PRR]

> 6BE6 and the screen-grid-modulation

That's not "screen" in a penta-grid.

G1 is oscillator grid, linear. G2 is osc plate. G3 is Signal Grid, remote-cutoff. G4 is amplifier "G2", accelerator screen. G2 and G4 are tied together to like +100V. G5 is suppressor,  masks the tetrode kink.

It seems logical to feed guitar to G3 because it does gain control. But the guitar would change its own gain, second harmonic distortion. That is acceptable in AM radio reception because the modulation is both-sides and is recovered in each narrow-tuned filter circuit. These techniques fail for baseband audio.

Here the guitar goes to G1, G3 only does wobble. This gives gain control without (as much) distortion.

In any case, the final plate current changes a LOT, which means the DC level at the plate changes a LOT, at a slightly sub-audio rate. This would gob-smack the next amplifier stages. So there's heavy R-C filtering to reduce sub-audio signal.

[jazbo8]

> 6BE6 and the screen-grid-modulation
That's not "screen" in a penta-grid.

My bad, I didn't even see that the 6BE6 was not a regular pentode, nor bothered to look up the datasheet... sigh...

[kagliostro]

Here the guitar goes to G1, G3 only does wobble. This gives gain control without (as much) distortion.

PRR is this to say that it is an interesting way to have a vibrato on the signal ?

Thanks

Franco


p.s.: Jazbo8, may be that if you correct the title of the thread (Playmaster 102 and the 6BE6 vibrato) a larger number of forumer is enticed to read it

[trobbins]

You probably found this article in your travels? It was on retrovox at one stage.
http://dalmura.com.au/projects/6BE6audi.pdf

[jazbo8]

You probably found this article in your travels? It was on retrovox at one stage.
http://dalmura.com.au/projects/6BE6audi.pdf

No I must have missed it, thanks for sharing it.