Not another cute, charming newbie!!

[titanicslim]

Gary

Thanks for the info. One of my favorite amps was a Laney with 4X 6V6s. We used it for blues, although it's supposed to be a "metal" amp, I guess.

And JJs are no problem for me, as I seem to have at least one of them in every amp I've got, and never had a ... well, I don't want to jinx myself

So, I guess it's time to start drawing it out and ordering parts. What do you think, the Bassman hybrid schematic? I need to make something that I can get a sound out of, and then experiment etc.

My understanding (having begun this avocation lately) of these circuits is very sketchy, to say the least. I've seen scemos that indicate the PT is supposed to have a 40% "screen tap", or something of that nature, but I've yet to see any kind of explanation of that concept and my trannies lost their factory packing somewhere, thus have no diagrams etc.. Can you point me in the general direction or do I need to worry about that?

Thanking you for the reduction of my confusion,
Dave

[ODwan]

Hello, titanicslim!
I just used the same trannies u have (1645 & 50W Marshall) for a dumbuild and it works/sounds fine with 6L6s. I also got a great sounding Express with a 1645 and a 272JX. The Hammond OTs are good for up to double the rated power at slightly reduced bandwidth, they're really overwound!
I build the Dumble with a 1k/11W power resistor instead of the choke.
The 40% screen taps are on the OT & for Ultralinear operation. Not really an option on either Dumble or Trainwreck. Just ditch them!

Timo

[titanicslim]

Hi Timo!

I have heard these things about the Hammond OTs before. I put a 1645 in a friend's Marshall JCM 800 and it seems just as loud as the original, and I believe it is rated at only 30watts(?)

I think the blue color of the PT tap confused me for a while. I need to stare at the shematics a while longer. Or maybe the "mystique" of the Dumble flummoxed me.

I like the idea of a big resistor instead of a more expensive choke, but it makes me wonder- why do the factories even bother with them? I mean, I am a cheap bastard, but nothing like the big MI factories. They sometimes do the most ridiculous things to save a penny.

You are from the Hannover area? That is a lovely place. It was always nice (I've lived in Bavaria) to drive out of the hills and see Hannover lying all spread out on the plains before me. It truly is the "Memphis of Europe"

[llemtt]

I like the idea of a big resistor instead of a more expensive choke, but it makes me wonder- why do the factories even bother with them? I mean, I am a cheap bastard, but nothing like the big MI factories. They sometimes do the most ridiculous things to save a penny.

A big resistor has almost the same effects as larger screen resistors because while the screens draw more current their voltage sags more than using a choke, and beeing connected to the screen supply node all the preamp voltages sag a little more. MesaBoogie has at least one amp where they use this to their advantage (obviuosly patented!).

Besides that screen voltages at idle are a little lower with a big resistor and this means less available power which is usually unacceptale for mktg departments!!

teo

[ODwan]

Hi Timo!

I like the idea of a big resistor instead of a more expensive choke, but it makes me wonder- why do the factories even bother with them? I mean, I am a cheap bastard, but nothing like the big MI factories. They sometimes do the most ridiculous things to save a penny.

You are from the Hannover area? That is a lovely place. It was always nice (I've lived in Bavaria) to drive out of the hills and see Hannover lying all spread out on the plains before me. It truly is the "Memphis of Europe"

The choke is mostly used for better ripple rejektion and max output. Though if you make the screen capacity a bit bigger it will compensate. My DumbClone only has almost nondiscernible hum at full distortion. It has a more rectotubelike feel, though, which I like.
Yes, I live just on the edge of those hills in a small village near Hildesheim. I'm sad to say that musicwise Hannover is definately not the "Memphis of Europe". We have (had) the Scorpions but thats about all worth mentioning (been in their old rehearsalroom once to jam with a local band and it still has their old stagebanner from the 70's on the wall ...the musky smell of rock history! )

Timo

[titanicslim]

Wow, I've got a little more to think about now. And I really do appreciate all this good info. the little bit of electronics knowledge I had was nothing much to do with tube amps, although I made my living with them for years. Now I've learned more in the past few months than I'd learned in several years proviously. Many thanks to all!

And Timo, I can really appreciate that smell. The place where I live positively REEKS

(I'll be in touch soon, after I start soldering. Right now I'm going to bed, where I'll probably trace and re-trace until I fall asleep.)

D