Debate on Eddie's Plexi

[YMI5150?]

can anyone explain/theorize why mustards would be replaced with chicklets, as seen in Ed's amp on V1 cathode, and both V1 bypass caps? what would the tonal differences between the two construction types be, if any? same with mica replacing the ceramic discs.

DF, I think you mentioned the recent overhall replaced all these with mustards, correct?

[Tone Slinger]

Even same material type caps can sound different ('dipped' mustards vs. chiclets, etc) The size and exact type of material (even variences in the grade of polyester used,etc) can sound different.

Old Mustards are expensive and vary quite a bit. Mallory (I think they make the 'SOZO' caps as well) seem to be tops in signal caps these days.

I know that alot of guy's will use different type caps (even same 'type' material wise) in different parts of the amp. Xicon, Sprague, etc.

Overall, the Mallory/Sozo brand seem to be best , overall, when talking NEW caps. Real mustards are expensive, inconsistant and hard to find, regarding specific values, though many consider them the Holy Grail. I wish I had experience with them (mustards) .

[jp0971]

The chicklets were most likely original to his amp. A few other amps I've seen from around that time have them as well

http://www.amparchives.com/album/Marsha ... 20022.html" onclick="window.open(this.href);return false;

[Marshall SL12301]

this thread is great and should be a sticky

[YMI5150?]

completed DF spec upgrades last night including Drake OT. Too late to evaluate but partway through it was awesome. still have a 32uf PI can. need to bump that up. moving soon so getting a recording setup is tough. will contribute to the cause when i can.
build has original fat bottles and variac. opted for the .68 mustard over the chicklet. think it'll be fine.

plexi guts small.jpg (168.11 KiB) Viewed 2603 times

setup small.jpg (188.3 KiB) Viewed 2603 times

[YMI5150?]

Played for about 10 mins. tone is there for sure. oversaturated in a static sort of way, all the way down to 4 on volume. i can see a bit of this as the sizzle on VH1. can be tamed when variac brought down to 75 volts.

could it be the low PI filter or the fat cap (currently 330uf)? its very close.

[Strat78]

Awesome! What PT tubes are you using? Wow, you can turn that ohmite variac down to 75v without the tone farting out? I can't get mine below 100v with out a negitive effect to the tone. Where do you have the bias tap?

[YMI5150?]

it is very cool but i have a bug to work out. probably belongs in its own thread. i swapped the OT to the Drake, changed NFB to 100k 4 ohm, and swapped a few Sozos for Mustards and the tone is there for sure, sizzle and all. but there is this undesireable inconsistent ringing that I cant describe well. it seems to be early in the preamp chain because its there at most volumes. it could be something in the OT feedback loop.

per DF i need to bump the PI can to 100uf. is the lower filtering a potential cause?

Strat - power tubes are vintage Sylvania fat bottle 6CA7s. I had the bias cranked on the amp and dialed the voltage down to 90v. the sizzle was really hot. at 90v, the bias v was -23 vdc. i backed that off to about -28 vdc and its better.

i think based on this, the difference between the first and second record is pure bias. crank bias - massive tube melting sizzle. the amp doesnt clean up for crap but the tone we're all looking for is definitely there.

http://www.youtube.com/watch?v=A6v6JfyKkm0" onclick="window.open(this.href);return false;

thoughts?

[Ralle]

What tubes did you say you have? Try it with out the variac, bias the amp as it should be, and see if the miss sound goes away...

[YMI5150?]

Sylvania 6CA7 fat bottles. will try but had those in with the Dagnall and it sounded pretty sweet. hoping its not the Marstrans Drake. hate distracting from the thread.

dispite this issue, the DF specs are very close to the real deal. lots of ways to skin the cat and this is definitely one of them.

cheers!

[Vegard]

Why do you have .68 and a 330uf in parallell in V2? : )

[Star*Guitar]

Just for the heck of it...see if the ringing is a microphonic preamp tube.

[YMI5150?]

thx guys. if i can't figure it out from here i'll start a different thread. ran straight to the wall and still there so variac's not it. i was thinking about the preamp tubes. something's unstable. hope i don't have to take the Drake out to trouble shoot...

notice how the sustain gets dampened after a second or so? it starts off fine, sweet tone with some sort of harmonic shadow behind it, then the signal appears to dampen out and the harmonic shadow diverges. weird. it's like squelch on a CB.

i'll mess with the preamp tubes and the NFB loop this weekend. oh, i also have the ohm selector on 8 ohms for a 16 ohm cab. worked well before but might need to change that. thoughts? measuring 483 B+ voltage with 120 wall supply - good?

anyway, the spec's Dave has shared are money. the fat cap adds a richness down low that is awesome. i would like to shake some of the gain. i get good CVH tone with volume at 6 or so so the amp really doesnt want to clean up. signal is always clipped. which component is adding that extra gain? v1a 250uf electrolytic?

[Ralle]

thx guys. if i can't figure it out from here i'll start a different thread. ran straight to the wall and still there so variac's not it. i was thinking about the preamp tubes. something's unstable. hope i don't have to take the Drake out to trouble shoot...

notice how the sustain gets dampened after a second or so? it starts off fine, sweet tone with some sort of harmonic shadow behind it, then the signal appears to dampen out and the harmonic shadow diverges. weird. it's like squelch on a CB.

i'll mess with the preamp tubes and the NFB loop this weekend. oh, i also have the ohm selector on 8 ohms for a 16 ohm cab. worked well before but might need to change that. thoughts? measuring 483 B+ voltage with 120 wall supply - good?

anyway, the spec's Dave has shared are money. the fat cap adds a richness down low that is awesome. i would like to shake some of the gain. i get good CVH tone with volume at 6 or so so the amp really doesnt want to clean up. signal is always clipped. which component is adding that extra gain? v1a 250uf electrolytic?

The b+ is fine... but I wouldn't have the ohmselector at 8 with a 16 ohm cab... I know people say that it's ok, but the fact is that the strain increases on the OT, and there's no info on how much voltage the OT can handle... I mean, we're talking missmatch... If you would have 16 ohm to an 8 ohm cab, there would be a current rush through the OT wich is more dangerous... but here we have a higher voltage, wich could mean a shortout between the wirings in the OT...Have you tried matching impedance? Thinking of it, it sounds as if it could be the reason it "crackes" like that...

Edit; I listened to it again, and I'm pretty sure that it's the OT being abused in some way...
If there's something else that's wrong, I'm sorry if I scared you like this... but I think it sounds as if the OT is being abused...

[YMI5150?]

You're making me want to bail from work early...