Phase and NFB confusion

[Enzo]

g-1, my "grounded grid" notion is pretty much describing how a differential amplifier works, at least in my mind. Same stuff goes through my head when I look at the diffy pair input of a solid state power amp. LT mentioned the differential, and I would trust his technical analysis of it over mine. I am just looking for ways to conceptualize for the service tech. I think they are all ways of talking about the same thing.

[JoeM]

It's all marketing. It's so easy to do CCS. A NPN with resistor divider for the base to set the current is the best and easiest way. No power supply needed to power opamp. BUT then you cannot claim it's all tubes.

Tubes have a lot of short comings that you can overcome by mixing in transistors etc. But then you cheapen the amp!!! Musicman drive the power stage with cascode configuration that pretty much constant current source that you don't need to worry about matching tubes.

But there is no rhyme or reason, people just want all tubes amps. People here are a lot more technical oriented, they have more of an open mind. But if you go to a players' type of forum, they talk about all tubes all the time.

I don't know about marketing. It seemed more like "Lets see what I can do with this" Better balance was the possible goal, but that would be more for Hi-Fi IMO. Personally, I couldn't care less if an amp is tube, SS, modeling or whatever as long as it gets a sound I like.

[Alan0354]

I don't know about marketing. It seemed more like "Lets see what I can do with this" Better balance was the possibly the goal, but that would be more for Hi-Fi IMO. Personally, I couldn't care less if an amp is tube, SS, modeling or whatever as long as it gets a sound I like.

I agree, I don't care if it's all tubes or not, but players do care( even thought it's perception only). They are the ones that buy amps, not us!!!! Customers are always right!!!.

[loudthud]

I agree, I don't care if it's all tubes or not, but players do care( even thought it's perception only). They are the ones that buy amps, not us!!!! Customers are always right!!!.

In an effort to change their minds I built a solid state amp on a 5E8 tweed twin chassis that has tubes sticking down that light up. The Standby switch even cuts off the speaker so you don't hear the turn-on thump.

[Alan0354]

In an effort to change their minds I built a solid state amp on a 5E8 tweed twin chassis that has tubes sticking down that light up. The Standby switch even cuts off the speaker so you don't hear the turn-on thump.

You mean you designed a total SS amp and just put a few tubes and light up the filaments?

Ha, you make me thinking about doing a SS amp. I personally don't think SS is inferior.....and more important, I am not really trying to sell amp, just pretend to build as if I am. Maybe I should consider designing one and really compare. I am hundred times more comfortable with transistors, opamps than tubes. Also, buying a SS combo for a platform is a whole lot cheaper than tubes.

You know of any particular SS combo that is good price with strong chassis in used market? It does not have to sound good, I just rip out everything including the speaker. Just need a good thick chassis. I can even brace up a weaker cabinet.

Edit:

I just went on ebay, I saw some Fender Stage 185 1X12 for really cheap. the cabinet even look quite like the old SF amps.

[J M Fahey]

In an effort to change their minds I built a solid state amp on a 5E8 tweed twin chassis that has tubes sticking down that light up. The Standby switch even cuts off the speaker so you don't hear the turn-on thump.

I did the same
In my case, a Plexi 50W clone.
It was during one of our recurrent economic crisis and no tubes were available, period.
I had a couple 12AX7 left but a pair 6L6 or EL34 cost more than I had charged for the entire head and were doubtful quality so I made the real preamp and PI, put a PPIMV after it and drove a 100W SS power amp with it, current limited so it would only put out 50W into 4 ohms.
So one of the main tube amp advantages, that they still put high power into speakers when they have high impedance (at resonance and above 1 KHz) was met.
I put 2 old dead 6L6 there, with the filaments in series driving a speaker relay, so amp self turned on (without a click or pop) after a proper thermal delay, and if you pulled a 6L6 the amp went mute.
Best thing is that sound was *killer* , go figure.
3 months later, when tubes were available again, I called my customer, to finish the amp the way he wanted.
He did not want to, he liked this one more than an all tube one he had bought a year earlier.

[Dave H]

I just went on ebay, I saw some Fender Stage 185 1X12 for really cheap. the cabinet even look quite like the old SF amps.

I used to play bass in a band where the guitarist used a Stage 160. It sounded fine when he was playing it but when I tried playing it it just didn't 'feel' right if you know what I mean.

[J M Fahey]

The Fender Stage are very good.
The only problem is that the speaker is way too heavy (large voice coil, thick wire, thick cone cardboard, lots of adhesive, etc.) to survive all that power and is dull, slow, closed.
Very similar to the ones fitted in the 160W Super Twin, and for the same reasons.
But you plug the head section into a good 4x12" cabinet (or at least a 2 x 12") and wow !!!
Of course, it's equalized for headbangers and metalheads, not exactly subtle sounding

[Alan0354]

Ha ha, That's the reason I like this forum. You guys are very technical and have an open mind. Maybe I should forget the Marshall build and go for the SS. So far, I build my first circuit into the bassman with optimized layout as a starter. Every single thing that I improved can be retrofit into the KMD build. In another word, I am not breaking any grounds on the Marshall!!! Maybe it's time to consider a SS instead and leave the Marshall JCM900 alone until I have new idea.

I almost bought a Stage 112 in 1998. Only thing that stop me was I found out the chassis was only a 3 sided chassis vs the Fender/Marshall tube amps that are 5 sided chassis. But it looks like the chassis of the stage is quite thick. Does Marshall SS amp has a 5 sided chassis that is strong?

[Alan0354]

BTW, how do you guys get the lower voltages with higher current inside the tube amps to power the transistors?

[loudthud]

Low voltage toroids are available in a wide variety of voltages and VA. X mount EI transformers can be found, Hammond makes quite a few. Juan probably winds his own.

[Alan0354]

Where do you buy those transformers cheap? I looked on ebay, Amazon, Digikey etc. It is much harder to find LV transformer than 30 years ago. I remember I could go to any electronics stores including Radio Shack to get a transformer. Now a days, it seems a lot harder and lot more expensive. I remember back in 78, I bought many of those 110V to 36V tiny transformers and strings them together to power the tube preamp stages of the twin, 6.3V transformer for filament and put the PT on variac for power scaling. Those were cheap like dirt. Those tiny little thing were less than 1"X1"X1" in size. I just paid over $20 for a 18V transformer for breaking in the new speaker!!!

Well, I don't wind transformers, so that's out. Those LV transformers seems to be much more expensive now.

[J M Fahey]

Yes, i wind my own, but now I'd like to comment on an annoying trend I've been detecting for years.

At the beginning, the "new guy in the block", today China but earlier Japan, Korea, Hong Kong, Taiwan, you name it, starts selling very cheap, at impossible prices, and for a few years, so the earlier established suppliers die a slow or fast death and dissappear.

Or only the higher quality, expensive survive.

And then, after 5 or 6 years, the "new kid" starts raising prices, slow and steady ... until it's as expensive as the one he replaced.

In this case, I can't find those cheap as dirt small transformers any more, and I'm 8000 miles away, in an entirely different Economic area, so it must be happening Worldwide, not just in USA.

Same with other stuff.

Those Ceriatone Malaysian? made Marshall/Fender/Soldano/Dumble clone kits are CRAZY expensive for what they really are, have the same "Factory" price as the originals !!!

U$1100 for an Asian made Marshall (clone) 50W head?

I am quite certain that a real Marshall 50W head crosses Marshall Factory doors for less than that.

Of course they will never sell direct to us at that price, but to, say, an USA representative, who has Regional Sales offices, who sells to Distributors (or acts like one) who then sell to retail shops, and everybody along that chain adds markups, ... but you buy those Asian clones direct !!!!

No Distributors, no Service network, no backup, not even full page colour advertisements (what Marshall does pay), no big artists endorsements, no Dr Tube, no History, nothing.

"Globalized" Economy is crazy and sick.

So back to your small transformer problem: unfortunately it's the way it is.

[Leo_Gnardo]

Those Ceriatone Malaysian?

edit: apologies for the disinformation, I thought Ceria was in Indonesia. Even I get confused with SE Asia geography. If I'd ever done business with Ceria, I'd have remembered. As long as we don't insult the Sultan of Brunei, no worries. Thanks jazbo for setting me straight!

- - - - - - - - -

Ceriatone is in Indonesia (edit: to self - NO, DUMMY!), a couple hundred islands spread across 1000 miles of ocean. Malaysia, smaller but similar, right next door so to speak and includes part of the same peninsula that includes Singapore. Don't worry I get 'em confused all the time too. As long as you don't buy a ticket to Surinam when you want to go to Sarawak, or vice versa, it's all good.

[jazbo8]

Sorry, but Ceriatone is in KL, the capital of Malaysia. Good food there ;-)