6V6 ?

[zaphod_phil]

There's a few folks that own a 4001 Studio 15 and say they love them - apparently, you just have to tweak the tone controls to the "right spot". However, I think the majority view is that it's a fairly mediocre amp. Personally, I never understood why the best that Marshall could come up with for a 6V6 amp was the Studio 15, and not something like a 6V6-based Plexi. Any 4001 owners out there, please don't kill me!

[lovedat800]

Yep....theres a reason the studio 15 never became a holy grail or even close. I've heard a lot of guys say it's not particularly good, and if it were i assure you they'd be far more sought after than they are. Sure would make a great chassis to build on tho !!!

[mickc]

I suspect the Bass issue is due to either the 6V6 (or the conversion of an EL84 design to 6V6's), and/or the cascading. I think the ENTIRE circuit must be revised for 6V6's... instead of trying to make a square peg fit in a round hole.

That was what made me think about it

Wow, looking at Marshall's 6V6 powered 4001 is a bit strange...

What's up with that Bass control?

Exactly what I was looking at

Personally, I never understood why the best that Marshall could come up with for a 6V6 amp was the Studio 15, and not something like a 6V6-based Plexi. Any 4001 owners out there, please don't kill me!

But that is the very reason I mentioned it, (and we'll never know) was it the best they could come up with ? were they finding problems sticking their tried and true pre-amps on different power amps? or "what the f*** that'll do ship em out lad's"

Yep....theres a reason the studio 15 never became a holy grail or even close. I've heard a lot of guys say it's not particularly good, and if it were i assure you they'd be far more sought after than they are. Sure would make a great chassis to build on tho !!!

I know what your saying, but my question is has anyone built a 4001 ? 18watter's have become a breed of their own thanks in part to this very forum and the people like yourself tweaking there builds and sharing the results good and bad, as a result there are lot's of variations and flavours. That's why I was asking the question has anyone ever played around with the 4001 circuit ? especially that tone stack ?

Mick

[zaphod_phil]

I've often thought about how to turn the 4001 into a decent amp, even discussed how you might do it with folks who were interested. Being PCB-based does make that difficult though....

[lovedat800]

Am i reading that schematic wrong or do those 6V6's have 100k grid stoppers? Isn't that kinda unusual? then i'm looking at some 6V6 fenders and they aren't using any grid stoppers at all. Can someon give me a quick tut on power tube grid stoppes? theres so much variance i'd like to know why. Are they just for the same 2 things as with pre tubes, ocsilation and high attenuation?

[zaphod_phil]

Yep

[JohnnyCrash]

The 4001 has some things that pop out as to why it's not a "great" 6V6 amp.

The preamp is one of them. Was it just me, or at first glance was there diodes in the PI? I'll have little time to look at the schem again - a lot of college assignments this week, plus a Dodger game and I'm going to see Tom Petty and Mudcrutch this week too...

That said, it can still be very usefull for a fresh perspective on a more modern take on a 6V6 power section.

I'll have to mess with my 6V6 TMB Cascade's PI and power section nxt week...

[zaphod_phil]

IIRC the 4001's power section uses both cathode bias and grid bias at the same time. Weird little amp...

[Alexo]

IIRC the 4001's power section uses both cathode bias and grid bias at the same time. Weird little amp...

I have an old organ amp like that, why do people do that? Parts count was just too low?

[lovedat800]

One wonders why, but then again there can be reasons even for the oddest things that you might not see unless you had designed it. The PV classic 30 is another one. I see lots of odd things in that one, but it's a pretty popular little amp. I've put some odd little things in mine from time to time that have made you guys go "wtf?". But the worked at the time.

[tubetek]

"IIRC the 4001's power section uses both cathode bias and grid bias at the same time. Weird little amp..."

Maybe this is one of the reasons this amp isn't considered to sound that good;
see the early silverface Fenders for example...They used a combination cathode and fixed bias scheme and users hated it! Fender abandoned that idea after a short while but the damage (to their reputation) was done...
tubetek

[rjgtr]

RE: Cathode resistor in 4001 ...

It might be to limit the output.

I worked on a fixed bias Sundown amp that included an 'RMS' control, which wqas simply a 5watt 25k pot between the cathodes and ground. As you elevated the amp from ground with the RMS control, you put out less power. Unfortunately, the estimate was too high for the guy to have his amp fixed, so I never got to hear it. I've thought about putting one in an amp to see how well it worked.

[MS15X2]

"IIRC the 4001's power section uses both cathode bias and grid bias at the same time. Weird little amp..."

Maybe this is one of the reasons this amp isn't considered to sound that good;
tubetek

Don't know who's doing the considering - certainly NOT Martin Barre who did three Tull albums with one or Clapton using it to record ' Behind The Sun ". The knock on the amp was the original list price which was roughly the same as the 50 watt head. If you didn't replace the original junky Ruskie tubes I can " hear " where you might not be floored but try NOS Mazdas or JAN RCA 6v6;Raytheon, Brimar, RFT 12ax7 and the amp just sings. GREAT versatility. If you're making a definitive tonal judgement strictly by looking at the schematic, the only thing I can tell you is that more often than not, ask a former owner of the amp and the first thing they'll tell you is that they regret having sold it . Playing is believing.