'68 Plexi vs. '69 Plexi

[AK1]

There are slight differences on the circuit boards. Anybody knows how that translates into sonics ?
I'm looking at two 50w Plexis right now, trying to decide which one to get...
thanks for the help fellow vintage snobs.

[Playloudd308]

One tip PLAY THEM FIRST... the late 60's plexi's were really inconsistant and one sounds WAY different from one another. Get which ever one sounds better because they all sound a bit different

[AK1]

I know what you mean, I live in Hawai'i though, no can try bra...
but I've had a '68 before, so I've got some point of reference.
And you're right, no same model, same day of production point to point amp will sound the same. Even new production, like the Komets, I've tried
a couple...

[Playloudd308]

yes, in general they are amazing amps but there are some bad lemmons out there. But if you live in hawaii and theres no way around it, you could always sell if you didnt like it. And if you decide to get it... Congrats!

[sws1]

68 varied wildly. BY 69, they were starting to get more standardized. In general, the 69 is most likely a bit brighter. But not necessarily. Sometime in 68, they reached the circuit that was used in 69. So it all depends on when your 68 was built, and what stuff was lying around.

[riverastoasters]

There are slight differences on the circuit boards. Anybody knows how that translates into sonics ?
I'm looking at two 50w Plexis right now, trying to decide which one to get...
thanks for the help fellow vintage snobs.

They can sound like night and day. Play 'em. It's the only true way to know.

[riverastoasters]

I know what you mean, I live in Hawai'i though, no can try bra...
but I've had a '68 before, so I've got some point of reference.

If you can't try them, can you get someone you know close to them to try them?

[908SSP]

If your looking at all original condition and price is right just buy it you wont ever loose anything on it. It has ever been modded and the price is right then you can make it sound just like you want with very little changes. I played my early 68 tonight for a couple of hours and it sounds wonderful. Very warm and rich deep bass, nice crunch, alto leads loads of sustain just a joy. Is the 69 your looking at a Plexi or a metal panel? Same goes for it either way. If you have done your research and gotten lots of pictures and the price is right the only thing you have to worry about is shipping.

[Roe]

I believe amps from 68 often have more filtering than amps from 69.

[Fretmaster]

buy both....try em....keep which ever one is best to your ear and sell the other. chances of losing $$ on either of those amps is slim.

[AK1]

[QUOTE=Fretmaster]buy both....try em....

indeed, that would be the ideal scenario...
however, Plexi prices these days prevent that from turning into reality.
Thanks for all your input.

[smilefan]

Another thing to consider. Since you cant try them,
is it possible to find out,
as specifically as possible what tubes are in them?
There is a wealth of tube knowledge on this board,
the Weber VST board, Mike from KCA (Bluestrat),
that could round out your picture of what to expect
from the amps.

I once sat down with my old tech and A/B'ed a
variety of NOS tubes into a SF Bassman that he
"blueprinted" for me. All the tubes were American
NOS. RCA, GE, Sylvania, etc. Each set of tubes changed
the tone and response of the amp to the point where I wouldn't
have known it was the same amp.

Also, if one has a set of NOS Mullards, and the other
has a set of new JJ's, that would certainly help you
make your decision.

[bjm007]

I believe amps from 68 often have more filtering than amps from 69.

Not sure about the 50's but the 100 watters are just the opposite of that...

In '68 for example they had 100uF caps on the mains and 32uF on the screens, and all the caps were inside except for one.

In '69 they upped the screen filtering to 100uF (just like the mains) and put the caps up on top.

'68 was also a transitional year for the shared vs split cathode. Early '68's were most likely shared while later in the year they started doing more split. The'69's are split.

In general, the earlier in '68 you go, it's gonna be a little looser on the low end because the screen filtering is less. Also the shared cathode design has a slightly different gain structure. (Somewhat less...)

By the time you get to '69, you had more screen filtering so (in theory) it's going to be tighter and the shared cathode is going to change the gain structure somewhat.

The V1/V2 Lead Channel coupling cap also changed in '69 to a .0022uF (from a .022uF in '68) which is going to strip off more lows, giving the tone a little more of a treble character.

They also changed the bright cap in '69 from a 100pF to like a 4,700pF. That makes the '69's sound really ice picky when you back off the volume, but it's easy to change if you wanna swap it back to 100pF......

As the other guy said, since you're in Hawaii (like me) just buy it and try it out for a while. You can always sell it if you don't like it... They tend to hold their value pretty well...

[AK1]

that's great info, mahalo braddah.

[that_brianm_guy]

The V1/V2 Lead Channel coupling cap also changed in '69 to a .0022uF (from a .022uF in '68) which is going to strip off more lows, giving the tone a little more of a treble character.

They also changed the bright cap in '69 from a 100pF to like a 4,700pF. That makes the '69's sound really ice picky when you back off the volume, but it's easy to change if you wanna swap it back to 100pF......


I've owned a marshall RI and a clone.. I prefer the sound of .022 to the .0022, and I remove the bright cap altogether.

I also change the presence cap to a .068.

That removes the icepikiness, and smooths the presence quite nicely....

If you want to talk Marshall circuits, check out http://www.metroamp.com/forum/ - that's the place to be...

[Gordon]

The only thing that I haven't seen mentioned yet is the difference in tone circuits. The '68 used a much more bass oriented tone circuit, ie. a 56K slope resistor and a 250pf treble cap. The '69 used a more guitar oriented tone circuit, ie. 33k slope rx and 500pf treble cap. What does all that mean to the sound? The '68 will generally have a smoother, more musical sound (that's my personal way of describing it), the 69 more aggressive and mean sounding for lack a better term. The 68 will require you to throw away a buch of bass in order not to be too muddy. I mean like turning the bass knob down below 2. It will also have a low-end emphasis and will not get louder as you play higher notes. The 69 has a greater emphasis on the high notes and can sound weak on the low notes untill you really crank it. It will sing better on the high notes though. It's a matter of how and what you play as to which will be the perfect fit.

Good luck and have fun, they're both great amps.

Gordon

[awangotango]

that last post was a cool way of describing the differneces. The 68 has more of an early billy gibbons feel which is loose and fat and brown. The 69 will have more of a 'harder' tone with a faster response. It's only a couple components change from each other though. So no worries, a soldering iron can remove the bright cap and maybe change a filter cap or two, connect the pins on V1 or disonnect (split/shared) and it's the same amp. That's the great thing about the pre 73 amps, any guitar player can dick around inside and dial it in to his preference. 68-73 amps can all be made to sound like one end of the sepctrum or the other in about 15 mins. soldering time.

[bjm007]

....any guitar player can dick around inside and dial it in to his preference. 68-73 amps can all be made to sound like one end of the sepctrum or the other in about 15 mins. soldering time....

Ain't that the truth... :AOK

It's nice to be able to actually work on something as complicated as an amplifier and be able to dial it in YOURSELF... That's cooll... I haven't had this much fun working on my amps in years... :dude

[AK1]

damn, I'm gonna print this shit out for my reference.Thanks for the education.
I might even dust of my soldering iron.
Looks like I'm going for the '68, just because it's priced more realisticly.

[awangotango]

if you really want an education. head on over to the 'plexipalace' forum and search old posts. That's where one can really learn 'what is what'. There's really no mystical magic going on inside old marshall's. Depending on the style of music you play, there is a stock marshall circuit that will fit like a glove and there's also plenty of gain as well, without mods. I personally am into rev. billy G, nuge, angus, EVH, etc and find the 68 circuit to be real cool. I replace the bright cap with a 470k resistor, use a .68uf cap bypassing V2a for more raunch (stock at various times 67-72) and a .68uf presence cap (beefs up mid with cool presence) and can get all the tones mentioned above depending on how i set the vol. and tone, all at a reasonable volume, (because of the 470k resistor -parkhead mod, over at plexi palace). The new 'heritage' celestion G12M 20 watters, and a vanzandt trubucker pickup help me get "there" as well. That's all it takes, no pedals, fancy mods, expensive les paul's, vintage greenbacks, mystical PAF's etc.

[shakti]

Just a few things:

- although people usually talk about '67/'68/'69 Plexis and sometimes by that refer to a specific circuit, it's a really confusing field with lots of overlap. I think this is part of the reason why people say that Plexis sound wildly different, and you'll hardly find two that sound alike. Sure they do sound different if you put an early '67 with Drake 2" OT next to a '69 with tight filtering, split V1 cathode, V2a bypass cap, lots less negative feedback, different tone stack, different value coupling caps etc... But if you know a little about the circuits, which player used which amp etc, you can pinpoint much more closely which amp to look for. Definitely check out www.plexipalace.com and www.metroamp.com.

[Roe]

here is what greg germino writes about his 68 and 69 model 100watters:

"The Headroom 100 series consists of two models. ...1st version is late 67 early 68 specs with high initial power supply filtering of 110uf. Remaining stages of screen supply, phase inverter, tone section and preamp are all 32uf. respectively. Circuit available voiced as Lead amp with split cathode preamp, 33K/500pf. tone control values and .022uf. output stage coupling caps, or with Bass voicing/flat frequency response consisting of shared cathode preamp, 56K/250pf. tone control values and .1uf. output stage coupling caps.
2nd version is mid 68 to early 69 specs with lower initial power supply filtering of 32uf. and 32uf. of filtering each for the remaining stages. This version is voiced as a Lead amp only, split cathode, 33K/500pf. tone control values and .022uf. output stage coupling caps.
Both versions use a transformer set based on teardowns of an original Dagnall T-2562 power transformer, C 1998 output transformer and C 1999 choke. This iron is correct for the years late 1967 through mid 1969.
The two models are intended to give the user a choice between the two circuits and the two different power supply layouts available during these early periods of production with the Dagnall transformer sets. Both amps are very loud with the 1st version and its larger power supply being extremely percussive in its attack. Plate voltage is around 490vdc."