6550 ... self-split ... fender iron

[Andy Le Blanc]

Work is finally beginning to ease up for the season, so I have more time for the bench...

I've been digging around looking at self split PP circuits.
The ones that pop up are the firefly and similar 12au7 based low-watt rigs that are incredibly simple.

There are also old tech references that explore mathematically a notion
that has been superseded in a very practical sense by the phase inverter...

I figured why not try it with what I got.

I dressed a 50w tester for self split, that is one side of a push pull pair has
the grid to ground, the driven side is what you would expect a cap and grid return, like a SE amp.
the PP pair shares a common un-bypassed cathode resistor for bias and inversion.

I used 6550 and drove the thing with what was left of what ever I was
working on the last time I was in the rig.
happened to be a 1/2 6sl7 to a fender style TB tone/vol, to a 6sj7 driving the self split PP pair.

You know the damn thing works good, it's very definitely a "colored" tone.
Not clean, but for blues or a harp amp... jeeez

[Phil_S]

I'll bet it's a real honker!!!

[Andy Le Blanc]

screwing around with topology...

seems to be best with a old school 6sj7 and vol/ tone to 1/2 of a 6sn7

I've moved over to KT88, keeping the bias around 1/2 the PT rated current

simple rig, but damn, screams, it does that unstable paraphase inverter
thing like multiple vibratos, real colorful...

So... it works

KT88
I've set the bias again for the PS, around 1/2 the ma rating , cathode bias
the screens 2.5v are about negative relative to the plate, with a bleeder after
a 470r screen grid resistor

The OPT is a 18343 equivalent
The PT is a 22798 equivalent
the bias resistor could range from 300r to 500r, but needs to be substantial wattage, 25w

one hell of a blues rig

I need a octal single triode, a 6sn7 equivalent

[Cliff Schecht]

6j5 is a single 6sn7 in a octal format. Is that what you are looking for?

[Reeltarded]

screwing around with topology...

simple rig, but damn, screams, it does that unstable paraphase inverter
thing like multiple vibratos, real colorful...

Umm... is that the splatty attack of like a tiny 50s amp that blooms into more what they intended the note to sound like at 5 instead of DIME?

I am such a green amp nerd.

[Andy Le Blanc]

yes 6j5, thank you

Its big and loud, great crunch without the high gain and no pedal
nice harmonic content, blues leads are in the pocket, its a surprise.

but it only cleans up so far, nice color but its always there.

I like the simple amps, you peg them and hang on...

[Reeltarded]

Ummm.. record this (little) beast! I want to hear it!

[andrew]

Neat! Would you share a schematic please?

[rdjones]

[img:760:525]http://diyaudioprojects.com/Technical/P ... ematic.png[/img]

http://diyaudioprojects.com/Technical/P ... ematic.png

[Andy Le Blanc]

pretty close a little different pre etc. KT88, which was a surprize to me.
you see small tubes, you see more complicated approaches that try to "fix"
exactly what makes the circuit great as a musical instrument.
so the assumption is that it wont work... it does

I think I can come up with a Mp3 file, but what to do with it?, post, PM?

it is a colored tone, but if you have a big clean amp you end up running
effects any way, more than any thing else than to color the tone....

[Reeltarded]

Your description sounds like something I would like to add to the pile.

I don't want you to go to special trouble just for me, thanks for just putting it out there. Neat stuff that isn't like anything I have..

Yet!

[Andy Le Blanc]

I found a 6j5 in the bone pile, can't abuse a good 6sn7

great to go all primitive like, get that perfect beat old amp thing going on

the KT88 are a surprise too in this application, but I bias to a constant point
based on the PT, so it just doesn't matter what the tube type is, with in the
max plate dissipation, good chance to explore OPT and loading...

don't mind trying out a Mp3 file but where should I send it?

I was thinking too. I could hard pan a large diaphragm condenser @1M
on one side and a close mic on the speaker on the other.

still a little tinkering first...

[Andy Le Blanc]

redressed for the 6j5, more microphonic than the 6sn7but still a good sounding tube.

loud amp, colors up quick and then gets thicker as you turn up the wick.
Might have chance to gig it Sunday...